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Blood is a
body fluid Body fluids, bodily fluids, or biofluids are liquids within the human body. In lean healthy adult men, the total body water is about 60% (60–67%) of the total body weight; it is usually slightly lower in women. The exact percentage of fluid rela ...
in humans and other animals that delivers necessary substances such as
nutrient A nutrient is a substance used by an organism to survive, grow, and reproduce. The requirement for dietary nutrient intake applies to animals, plants, fungi, and protists. Nutrients can be incorporated into cells for metabolic purposes or excreted ...
s and
oxygen Oxygen is the chemical element with the symbol O and atomic number 8. It is a member of the chalcogen group in the periodic table, a highly reactive nonmetal, and an oxidizing agent that readily forms oxides with most elements as well a ...
to the
cells Cell most often refers to: * Cell (biology), the functional basic unit of life Cell may also refer to: Closed spaces * Monastic cell, a small room, hut, or cave in which a monk or religious recluse lives * Prison cell, a room used to hold peopl ...
and transports
metabolic waste Metabolic wastes or excrements are substances left over from metabolic processes (such as cellular respiration) which cannot be used by the organism (they are surplus or toxic), and must therefore be excreted. This includes nitrogen compounds, wate ...
products away from those same cells. In
vertebrate Vertebrates () comprise all species of animals within the subphylum Vertebrata () (chordates with backbones). Vertebrates represent the overwhelming majority of the phylum Chordata, with currently about 69,963 species described. Vertebrates inclu ...
s, it is composed of
blood cell A blood cell, also called a hematopoietic cell, hemocyte, or hematocyte, is a cell produced through hematopoiesis and found mainly in the blood. Major types of blood cells include red blood cells (erythrocytes), white blood cells (leukocytes), ...
s suspended in
blood plasma Blood plasma is a yellowish liquid component of blood that holds the blood cells of whole blood in suspension. It is the liquid part of the blood that carries cells and proteins throughout the body. It makes up about 55% of the body's total blo ...
. Plasma, which constitutes 55% of blood fluid, is mostly water (92% by volume), and contains
protein Proteins are large biomolecules or macromolecules that are comprised of one or more long chains of amino acid residues. Proteins perform a vast array of functions within organisms, including catalysing metabolic reactions, DNA replication, respo ...
s,
glucose Glucose is a simple sugar with the molecular formula . Glucose is the most abundant monosaccharide, a subcategory of carbohydrates. Glucose is mainly made by plants and most algae during photosynthesis from water and carbon dioxide, using energy fr ...
, mineral
ion An ion () is a particle, atom or molecule with a net electrical charge. The charge of the electron is considered negative by convention. The negative charge of an ion is equal and opposite to charged proton(s) considered positive by convent ...
s,
hormone A hormone (from the Greek participle , "setting in motion") is any member of a class of signaling molecules in multicellular organisms, that are transported to distant organs to regulate physiology and / or behavior. Hormones are required for the ...
s, carbon dioxide (plasma being the main medium for excretory product transportation), and blood cells themselves.
Albumin Albumin is a family of globular proteins, the most common of which are the serum albumins. All the proteins of the albumin family are water-soluble, moderately soluble in concentrated salt solutions, and experience heat denaturation. Albumins ar ...
is the main protein in plasma, and it functions to regulate the
colloid A colloid is a mixture in which one substance of microscopically dispersed insoluble particles are suspended throughout another substance. However, some definitions specify that the particles must be dispersed in a liquid, and others extend the d ...
al
osmotic pressure#REDIRECT Osmotic pressure#REDIRECT Osmotic pressure {{R from other capitalisation ...
{{R from other capitalisation ...
of blood. The blood cells are mainly
red blood cell Red blood cells (RBCs), also referred to as red cells, red blood corpuscles (in humans or other animals not having nucleus in red blood cells), haematids, erythroid cells or erythrocytes (from Greek ''erythros'' for "red" and ''kytos'' for "hollo ...
s (also called RBCs or erythrocytes),
white blood cell White blood cells (WBCs), also called leukocytes or leucocytes, are the cells of the immune system that are involved in protecting the body against both infectious disease and foreign invaders. All white blood cells are produced and derived from ...
s (also called WBCs or leukocytes) and
platelet Platelets, also called thrombocytes (from Greek θρόμβος, "clot" and κύτος, "cell"), are a component of blood whose function (along with the coagulation factors) is to react to bleeding from blood vessel injury by clumping, thereby initi ...
s (also called thrombocytes). The most abundant cells in vertebrate blood are red blood cells. These contain
hemoglobin Hemoglobin, or haemoglobin (spelling differences) (Greek αἷμα (haîma, “blood”) + -in) + -o- + globulin (from Latin globus (“ball, sphere”) + -in) (), abbreviated Hb or Hgb, is the iron-containing oxygen-transport metalloprotein in th ...
, an iron-containing protein, which facilitates oxygen transport by reversibly binding to this
respiratory The respiratory system (also respiratory apparatus, ventilatory system) is a biological system consisting of specific organs and structures used for gas exchange in animals and plants. The anatomy and physiology that make this happen varies grea ...
gas and greatly increasing its solubility in blood. In contrast, carbon dioxide is mostly transported extracellularly as
bicarbonate In inorganic chemistry, bicarbonate (IUPAC-recommended nomenclature: hydrogen carbonate) is an intermediate form in the deprotonation of carbonic acid. It is a polyatomic anion with the chemical formula . Bicarbonate serves a crucial biochemical ...
ion transported in plasma. Vertebrate blood is bright red when its hemoglobin is oxygenated and dark red when it is deoxygenated. Some animals, such as
crustacean Crustaceans (Crustacea ) form a large, diverse arthropod taxon which includes such animals as crabs, lobsters, crayfish, shrimps, prawns, krill, woodlice, and barnacles. The crustacean group can be treated as a subphylum under the clade Mandibulat ...
s and
mollusk Mollusca is the second-largest phylum of invertebrate animals after the Arthropoda. The members are known as molluscs or mollusks (). Around 85,000 extant species of molluscs are recognized. The number of fossil species is estimated betwee ...
s, use
hemocyanin Hemocyanins (also spelled haemocyanins and abbreviated Hc) are proteins that transport oxygen throughout the bodies of some invertebrate animals. These metalloproteins contain two copper atoms that reversibly bind a single oxygen molecule (O2). ...
to carry oxygen, instead of hemoglobin. Insects and some mollusks use a fluid called
hemolymph Hemolymph, or haemolymph, is a fluid, analogous to the blood in vertebrates, that circulates in the interior of the arthropod (invertebrate) body remaining in direct contact with the animal's tissues. It is composed of a fluid plasma in which he ...
instead of blood, the difference being that hemolymph is not contained in a closed
circulatory system The circulatory system, also called the cardiovascular system or the vascular system, is an organ system that permits blood to circulate and transport nutrients (such as amino acids and electrolytes), oxygen, carbon dioxide, hormones, and blood ...
. In most insects, this "blood" does not contain oxygen-carrying molecules such as hemoglobin because their bodies are small enough for their tracheal system to suffice for supplying oxygen. Jawed vertebrates have an
adaptive immune system The adaptive immune system, also referred as the acquired immune system, is a subsystem of the immune system that is composed of specialized, systemic cells and processes that eliminate pathogens or prevent their growth. The acquired immune system ...
, based largely on white blood cells. White blood cells help to resist infections and parasites. Platelets are important in the
clotting Coagulation, also known as clotting, is the process by which blood changes from a liquid to a gel, forming a blood clot. It potentially results in hemostasis, the cessation of blood loss from a damaged vessel, followed by repair. The mechanism o ...
of blood.
Arthropod An arthropod (, (gen. ποδός)) is an invertebrate animal having an exoskeleton, a segmented body, and paired jointed appendages. Arthropods form the phylum Euarthropoda,Reference showing that Euarthropoda is a phylum: which includes insects, ...
s, using hemolymph, have
hemocyte A blood cell, also called a hematopoietic cell, hemocyte, or hematocyte, is a cell produced through hematopoiesis and found mainly in the blood. Major types of blood cells include red blood cells (erythrocytes), white blood cells (leukocytes), ...
s as part of their
immune system The immune system is a network of biological processes that protects an organism from diseases. It detects and responds to a wide variety of pathogens, from viruses to parasitic worms, as well as cancer cells and objects such as wood splinters, d ...
. Blood is circulated around the body through
blood vessel The blood vessels are the components of the circulatory system that transport blood throughout the human body. These vessels transport blood cells, nutrients, and oxygen to the tissues of the body. They also take waste and carbon dioxide away fr ...
s by the pumping action of the
heart The heart is a muscular organ in most animals, which pumps blood through the blood vessels of the circulatory system. The pumped blood carries oxygen and nutrients to the body, while carrying metabolic waste such as carbon dioxide to the lun ...
. In animals with
lung The lungs are the primary organs of the respiratory system in humans and many other animals including a few fish and some snails. In mammals and most other vertebrates, two lungs are located near the backbone on either side of the heart. Their ...
s,
arterial An artery (plural arteries) () is a blood vessel that takes blood away from the heart to one or more parts of the body (tissues, lungs, brain etc.). Most arteries carry oxygenated blood; the two exceptions are the pulmonary and the umbilical ar ...

arterial
blood carries oxygen from inhaled air to the tissues of the body, and
venous Veins are blood vessels that carry blood towards the heart. Most veins carry deoxygenated blood from the tissues back to the heart; exceptions are the pulmonary and umbilical veins, both of which carry oxygenated blood to the heart. In contrast to ...
blood carries carbon dioxide, a waste product of
metabolism Metabolism (, from el, μεταβολή ''metabolē'', "change") is the set of life-sustaining chemical reactions in organisms. The three main purposes of metabolism are: the conversion of food to energy to run cellular processes; the conve ...

metabolism
produced by cells, from the tissues to the lungs to be exhaled. Medical terms related to blood often begin with hemo- or hemato- ( also spelled haemo- and haemato-) from the Greek word (''haima'') for "blood". In terms of
anatomy Anatomy (Greek ''anatomē'', 'dissection') is the branch of biology concerned with the study of the structure of organisms and their parts. Anatomy is a branch of natural science which deals with the structural organization of living things. It ...
and
histology Histology, also known as microscopic anatomy or microanatomy, is the branch of biology which studies the microscopic anatomy of biological tissues. Histology is the microscopic counterpart to gross anatomy, which looks at larger structures visibl ...
, blood is considered a specialized form of
connective tissue Connective tissue is one of the four basic types of animal tissue, along with epithelial tissue, muscle tissue, and nervous tissue. It develops from the mesoderm. Connective tissue is found in between other tissues everywhere in the body, includin ...
, given its origin in the bones and the presence of potential molecular fibers in the form of
fibrinogen Fibrinogen (factor I) is a glycoprotein complex, made in the liver, that circulates in the blood of all vertebrates. During tissue and vascular injury, it is converted enzymatically by thrombin to fibrin and then to a fibrin-based blood clot. Fib ...
.


Functions

Blood performs many important functions within the body, including: * Supply of
oxygen Oxygen is the chemical element with the symbol O and atomic number 8. It is a member of the chalcogen group in the periodic table, a highly reactive nonmetal, and an oxidizing agent that readily forms oxides with most elements as well a ...
to tissues (bound to
hemoglobin Hemoglobin, or haemoglobin (spelling differences) (Greek αἷμα (haîma, “blood”) + -in) + -o- + globulin (from Latin globus (“ball, sphere”) + -in) (), abbreviated Hb or Hgb, is the iron-containing oxygen-transport metalloprotein in th ...
, which is carried in red cells) * Supply of nutrients such as
glucose Glucose is a simple sugar with the molecular formula . Glucose is the most abundant monosaccharide, a subcategory of carbohydrates. Glucose is mainly made by plants and most algae during photosynthesis from water and carbon dioxide, using energy fr ...
,
amino acid Amino acids are organic compounds that contain amino (–NH2) and carboxyl (–COOH) functional groups, along with a side chain (R group) specific to each amino acid. The key elements of an amino acid are carbon (C), hydrogen (H), oxygen (O), a ...
s, and
fatty acid fatty acids have perfectly straight chain structure. Unsaturated ones are typically bent, unless they have a trans configuration. In chemistry, particularly in biochemistry, a fatty acid is a carboxylic acid with a long aliphatic chain, which is ...
s (dissolved in the blood or bound to
plasma proteins Blood proteins, also termed plasma proteins, are proteins present in blood plasma. They serve many different functions, including transport of lipids, hormones, vitamins and minerals in activity and functioning of the immune system. Other blood pro ...
(e.g., blood lipids)) * Removal of waste such as
carbon dioxide Carbon dioxide (chemical formula ) is a colorless gas with a density about 53% higher than that of dry air. Carbon dioxide molecules consist of a carbon atom covalently double bonded to two oxygen atoms. It occurs naturally in Earth's atmospher ...

carbon dioxide
,
urea Urea, also known as carbamide, is an organic compound with chemical formula CO(NH2)2. This amide has two –NH2 groups joined by a carbonyl (C=O) functional group. Urea serves an important role in the metabolism of nitrogen-containing compounds ...
, and
lactic acid Lactic acid is an organic acid. It has a molecular formula CH3CH(OH)COOH. It is white in the solid state and it is miscible with water. When in the dissolved state, it forms a colorless solution. Production includes both artificial synthesis as w ...
* Immunological functions, including circulation of
white blood cell White blood cells (WBCs), also called leukocytes or leucocytes, are the cells of the immune system that are involved in protecting the body against both infectious disease and foreign invaders. All white blood cells are produced and derived from ...
s, and detection of foreign material by
antibodies An antibody (Ab), also known as an immunoglobulin (Ig), is a large, Y-shaped protein used by the immune system to identify and neutralize foreign objects such as pathogenic bacteria and viruses. The antibody recognizes a unique molecule of the p ...

antibodies
*
Coagulation Coagulation, also known as clotting, is the process by which blood changes from a liquid to a gel, forming a blood clot. It potentially results in hemostasis, the cessation of blood loss from a damaged vessel, followed by repair. The mechanism o ...
, the response to a broken blood vessel, the conversion of blood from a liquid to a semisolid gel to stop bleeding * Messenger functions, including the transport of
hormone A hormone (from the Greek participle , "setting in motion") is any member of a class of signaling molecules in multicellular organisms, that are transported to distant organs to regulate physiology and / or behavior. Hormones are required for the ...
s and the signaling of tissue damage * Regulation of core
body temperature Thermoregulation is the ability of an organism to keep its body temperature within certain boundaries, even when the surrounding temperature is very different. A thermoconforming organism, by contrast, simply adopts the surrounding temperature ...
*
Hydraulic Hydraulics (from Greek: Υδραυλική) is a technology and applied science using engineering, chemistry, and other sciences involving the mechanical properties and use of liquids. At a very basic level, hydraulics is the liquid counterp ...
functions


Constituents


In mammals

Blood accounts for 7% of the human body weight, with an average density around 1060 kg/m3, very close to pure water's density of 1000 kg/m3. The average adult has a
blood volumeBlood volume is the volume of blood (red blood cells and plasma) in the circulatory system of any individual. Humans A typical adult has a blood volume of approximately 5 liters, with females and males having approximately the same blood volume. Blo ...
of roughly or 1.3 gallons, which is composed of plasma and ''formed elements''. The formed elements are the two types of blood cell or ''corpuscle'' – the
red blood cell Red blood cells (RBCs), also referred to as red cells, red blood corpuscles (in humans or other animals not having nucleus in red blood cells), haematids, erythroid cells or erythrocytes (from Greek ''erythros'' for "red" and ''kytos'' for "hollo ...
s, (erythrocytes) and
white blood cell White blood cells (WBCs), also called leukocytes or leucocytes, are the cells of the immune system that are involved in protecting the body against both infectious disease and foreign invaders. All white blood cells are produced and derived from ...
s (leukocytes), and the cell fragments called
platelet Platelets, also called thrombocytes (from Greek θρόμβος, "clot" and κύτος, "cell"), are a component of blood whose function (along with the coagulation factors) is to react to bleeding from blood vessel injury by clumping, thereby initi ...
s that are involved in clotting. By volume, the red blood cells constitute about 45% of whole blood, the plasma about 54.3%, and white cells about 0.7%. Whole blood (plasma and cells) exhibits non-Newtonian
fluid dynamics In physics and engineering, fluid dynamics is a subdiscipline of fluid mechanics that describes the flow of fluids—liquids and gases. It has several subdisciplines, including aerodynamics (the study of air and other gases in motion) and hydro ...
. File:Krew Frakcjonowana.jpg, Human blood fractioned by centrifugation: Plasma (upper, yellow layer), buffy coat (middle, thin white layer) and erythrocyte layer (bottom, red layer) can be seen. File:Blutkreislauf.png, Blood circulation: Red = oxygenated, blue = deoxygenated File:Blausen 0425 Formed Elements.png, Illustration depicting formed elements of blood File:Blut-EDTA.jpg, Two tubes of
EDTA Ethylenediaminetetraacetic acid (EDTA) is an aminopolycarboxylic acid with the formula H2N(CH2CO2H)2sub>2. This white, water-soluble solid is widely used to bind to iron and calcium ions. It binds these ions as a hexadentate ("six-toothed") chelat ...

EDTA
-anticoagulated blood.
Left tube: after standing, the RBCs have settled at the bottom of the tube.
Right tube: Freshly drawn blood


Cells

(SEM) image of a normal
red blood cell Red blood cells (RBCs), also referred to as red cells, red blood corpuscles (in humans or other animals not having nucleus in red blood cells), haematids, erythroid cells or erythrocytes (from Greek ''erythros'' for "red" and ''kytos'' for "hollo ...
(left), a
platelet Platelets, also called thrombocytes (from Greek θρόμβος, "clot" and κύτος, "cell"), are a component of blood whose function (along with the coagulation factors) is to react to bleeding from blood vessel injury by clumping, thereby initi ...
(middle), and a
white blood cell White blood cells (WBCs), also called leukocytes or leucocytes, are the cells of the immune system that are involved in protecting the body against both infectious disease and foreign invaders. All white blood cells are produced and derived from ...
(right) One microliter of blood contains: * 4.7 to 6.1 million (male), 4.2 to 5.4 million (female)
erythrocyte Red blood cells (RBCs), also referred to as red cells, red blood corpuscles (in humans or other animals not having nucleus in red blood cells), haematids, erythroid cells or erythrocytes (from Greek ''erythros'' for "red" and ''kytos'' for "hollo ...
s: Red blood cells contain the blood's
hemoglobin Hemoglobin, or haemoglobin (spelling differences) (Greek αἷμα (haîma, “blood”) + -in) + -o- + globulin (from Latin globus (“ball, sphere”) + -in) (), abbreviated Hb or Hgb, is the iron-containing oxygen-transport metalloprotein in th ...
and distribute oxygen. Mature red blood cells lack a
nucleus ''Nucleus'' (plural nuclei) is a Latin word for the seed inside a fruit. It most often refers to: *Atomic nucleus, the very dense central region of an atom *Cell nucleus, a central organelle of a eukaryotic cell, containing most of the cell's DNA ...

nucleus
and
organelle In cell biology, an organelle is a specialized subunit, usually within a cell, that has a specific function. The name ''organelle'' comes from the idea that these structures are parts of cells, as organs are to the body, hence ''organelle,'' the su ...
s in mammals. The red blood cells (together with
endothelial Endothelium is a single layer of squamous endothelial cells that line the interior surface of blood vessels, and lymphatic vessels. The endothelium forms an interface between circulating blood or lymph in the lumen and the rest of the vessel wall ...
vessel cells and other cells) are also marked by
glycoprotein Glycoproteins are proteins which contain oligosaccharide chains (glycans) covalently attached to amino acid side-chains. The carbohydrate is attached to the protein in a cotranslational or posttranslational modification. This process is known as ...
s that define the different
blood types Blood is a body fluid in humans and other animals that delivers necessary substances such as nutrients and oxygen to the cells and transports metabolic waste products away from those same cells. In vertebrates, it is composed of blood cells su ...
. The proportion of blood occupied by red blood cells is referred to as the
hematocrit The hematocrit () (Ht or HCT), also known by several other names, is the volume percentage (vol%) of red blood cells (RBC) in blood, measured as part of a blood test. The measurement depends on the number and size of red blood cells. It is normally ...
, and is normally about 45%. The combined surface area of all red blood cells of the human body would be roughly 2,000 times as great as the body's exterior surface. * 4,000–11,000
leukocyte White blood cells (WBCs), also called leukocytes or leucocytes, are the cells of the immune system that are involved in protecting the body against both infectious disease and foreign invaders. All white blood cells are produced and derived from ...
s: White blood cells are part of the body's
immune system The immune system is a network of biological processes that protects an organism from diseases. It detects and responds to a wide variety of pathogens, from viruses to parasitic worms, as well as cancer cells and objects such as wood splinters, d ...
; they destroy and remove old or aberrant cells and cellular debris, as well as attack infectious agents (
pathogen In biology, a pathogen ( el, πάθος ''pathos'' "suffering", "passion" and -γενής ''-genēs'' "producer of") in the oldest and broadest sense, is any organism that can produce disease. A pathogen may also be referred to as an infectious age ...
s) and foreign substances. The cancer of leukocytes is called
leukemia Leukemia, also spelled leukaemia, is a group of blood cancers that usually begin in the bone marrow and result in high numbers of abnormal blood cells. These blood cells are not fully developed and are called ''blasts'' or ''leukemia cells''. Sy ...
. * 200,000–500,000
thrombocytes Platelets, also called thrombocytes (from Greek θρόμβος, "clot" and κύτος, "cell"), are a component of blood whose function (along with the coagulation factors) is to react to bleeding from blood vessel injury by clumping, thereby initi ...
: Also called
platelet Platelets, also called thrombocytes (from Greek θρόμβος, "clot" and κύτος, "cell"), are a component of blood whose function (along with the coagulation factors) is to react to bleeding from blood vessel injury by clumping, thereby initi ...
s, they take part in blood clotting (
coagulation Coagulation, also known as clotting, is the process by which blood changes from a liquid to a gel, forming a blood clot. It potentially results in hemostasis, the cessation of blood loss from a damaged vessel, followed by repair. The mechanism o ...
). Fibrin from the coagulation cascade creates a mesh over the
platelet plugThe platelet plug, also known as the hemostatic plug or platelet thrombus, is an aggregation of platelets formed during the earlier stage of hemostasis in response to blood vessel wall injury. After platelets are recruited and begin to accumulate aro ...
.


Plasma

About 55% of blood is
blood plasma Blood plasma is a yellowish liquid component of blood that holds the blood cells of whole blood in suspension. It is the liquid part of the blood that carries cells and proteins throughout the body. It makes up about 55% of the body's total blo ...
, a fluid that is the blood's liquid medium, which by itself is straw-yellow in color. The blood plasma volume totals of 2.7–3.0 liters (2.8–3.2 quarts) in an average human. It is essentially an
aqueous An aqueous solution is a solution in which the solvent is water. It is mostly shown in chemical equations by appending (aq) to the relevant chemical formula. For example, a solution of table salt, or sodium chloride (NaCl), in water would be repr ...
solution containing 92% water, 8% blood plasma
protein Proteins are large biomolecules or macromolecules that are comprised of one or more long chains of amino acid residues. Proteins perform a vast array of functions within organisms, including catalysing metabolic reactions, DNA replication, respo ...
s, and trace amounts of other materials. Plasma circulates dissolved nutrients, such as
glucose Glucose is a simple sugar with the molecular formula . Glucose is the most abundant monosaccharide, a subcategory of carbohydrates. Glucose is mainly made by plants and most algae during photosynthesis from water and carbon dioxide, using energy fr ...
,
amino acid Amino acids are organic compounds that contain amino (–NH2) and carboxyl (–COOH) functional groups, along with a side chain (R group) specific to each amino acid. The key elements of an amino acid are carbon (C), hydrogen (H), oxygen (O), a ...
s, and
fatty acid fatty acids have perfectly straight chain structure. Unsaturated ones are typically bent, unless they have a trans configuration. In chemistry, particularly in biochemistry, a fatty acid is a carboxylic acid with a long aliphatic chain, which is ...
s (dissolved in the blood or bound to plasma proteins), and removes waste products, such as
carbon dioxide Carbon dioxide (chemical formula ) is a colorless gas with a density about 53% higher than that of dry air. Carbon dioxide molecules consist of a carbon atom covalently double bonded to two oxygen atoms. It occurs naturally in Earth's atmospher ...

carbon dioxide
,
urea Urea, also known as carbamide, is an organic compound with chemical formula CO(NH2)2. This amide has two –NH2 groups joined by a carbonyl (C=O) functional group. Urea serves an important role in the metabolism of nitrogen-containing compounds ...
, and
lactic acid Lactic acid is an organic acid. It has a molecular formula CH3CH(OH)COOH. It is white in the solid state and it is miscible with water. When in the dissolved state, it forms a colorless solution. Production includes both artificial synthesis as w ...
. Other important
components Component may refer to: In engineering, science, and technology Generic systems *System components, an entity with discrete structure, such as an assembly or software module, within a system considered at a particular level of analysis *Lumped ele ...
include: *
Serum albumin#REDIRECT serum albumin#REDIRECT serum albumin {{R from other capitalisation ...
{{R from other capitalisation ...
* Blood-clotting factors (to facilitate
coagulation Coagulation, also known as clotting, is the process by which blood changes from a liquid to a gel, forming a blood clot. It potentially results in hemostasis, the cessation of blood loss from a damaged vessel, followed by repair. The mechanism o ...
) * Immunoglobulins (
antibodies An antibody (Ab), also known as an immunoglobulin (Ig), is a large, Y-shaped protein used by the immune system to identify and neutralize foreign objects such as pathogenic bacteria and viruses. The antibody recognizes a unique molecule of the p ...

antibodies
) *
lipoprotein 250px, Structure of a chylomicron. ApoA, ApoB, ApoC, ApoE are apolipoproteins; green particles are phospholipids; T is triacylglycerol; C is cholesterol ester. A lipoprotein is a biochemical assembly whose primary function is to transport ...
particles * Various other
protein Proteins are large biomolecules or macromolecules that are comprised of one or more long chains of amino acid residues. Proteins perform a vast array of functions within organisms, including catalysing metabolic reactions, DNA replication, respo ...
s * Various
electrolyte An electrolyte is a substance that produces an electrically conducting solution when dissolved in a polar solvent, such as water. The dissolved electrolyte separates into cations and anions, which disperse uniformly through the solvent. Electricall ...
s (mainly
sodium Sodium is a chemical element with the symbol Na (from Latin "natrium") and atomic number 11. It is a soft, silvery-white, highly reactive metal. Sodium is an alkali metal, being in group 1 of the periodic table. Its only stable isotop ...
and
chloride The chloride ion is the anion (negatively charged ion) Cl−. It is formed when the element chlorine (a halogen) gains an electron or when a compound such as hydrogen chloride is dissolved in water or other polar solvents. Chloride salts suc ...

chloride
) The term serum refers to plasma from which the clotting proteins have been removed. Most of the proteins remaining are albumin and
immunoglobulins An antibody (Ab), also known as an immunoglobulin (Ig), is a large, Y-shaped protein used by the immune system to identify and neutralize foreign objects such as pathogenic bacteria and viruses. The antibody recognizes a unique molecule of the p ...

immunoglobulins
.


pH values

Blood pH Blood is a body fluid in humans and other animals that delivers necessary substances such as nutrients and oxygen to the cells and transports metabolic waste products away from those same cells. In vertebrates, it is composed of blood cells su ...
is regulated to stay within the narrow range of 7.35 to 7.45, making it slightly
basic BASIC (Beginners' All-purpose Symbolic Instruction Code) is a family of general-purpose, high-level programming languages whose design philosophy emphasizes ease of use. The original version was designed by John G. Kemeny and Thomas E. Kurtz and ...
. Blood that has a pH below 7.35 is too
acid An acid is a molecule or ion capable of donating a proton (hydrogen ion H+) (a Brønsted–Lowry acid), or, alternatively, capable of forming a covalent bond with an electron pair (a Lewis acid). The first category of acids are the proton do ...
ic, whereas blood pH above 7.45 is too basic. Blood pH, partial pressure of oxygen (pO2), partial pressure of carbon dioxide (pCO2), and
bicarbonate In inorganic chemistry, bicarbonate (IUPAC-recommended nomenclature: hydrogen carbonate) is an intermediate form in the deprotonation of carbonic acid. It is a polyatomic anion with the chemical formula . Bicarbonate serves a crucial biochemical ...
(HCO3) are carefully regulated by a number of homeostatic mechanisms, which exert their influence principally through the
respiratory system The respiratory system (also respiratory apparatus, ventilatory system) is a biological system consisting of specific organs and structures used for gas exchange in animals and plants. The anatomy and physiology that make this happen varies grea ...

respiratory system
and the
urinary system The urinary system, also known as the renal system or urinary tract, consists of the kidneys, ureters, bladder, and the urethra. The purpose of the urinary system is to eliminate waste from the body, regulate blood volume and blood pressure, cont ...

urinary system
to control the
acid–base balance An acid dissociation constant, ''K''a, (also known as acidity constant, or acid-ionization constant) is a quantitative measure of the strength of an acid in solution. It is the equilibrium constant for a chemical reaction :HA A^- + H^+ known ...
and respiration. An
arterial blood gas test An arterial blood gas (ABG) test measures the amounts of arterial gases, such as oxygen and carbon dioxide. An ABG test requires that a small volume of blood be drawn from the radial artery with a syringe and a thin needle, but sometimes the femor ...
measures these. Plasma also circulates
hormone A hormone (from the Greek participle , "setting in motion") is any member of a class of signaling molecules in multicellular organisms, that are transported to distant organs to regulate physiology and / or behavior. Hormones are required for the ...
s transmitting their messages to various tissues. The list of normal reference ranges for various blood electrolytes is extensive.


In non-mammalian vertebrates

Human blood is typical of that of mammals, although the precise details concerning cell numbers, size,
protein structure Protein structure is the three-dimensional arrangement of atoms in an amino acid-chain molecule. Proteins are polymers specifically polypeptides formed from sequences of amino acids, the monomers of the polymer. A single amino acid monomer may a ...

protein structure
, and so on, vary somewhat between species. In non-mammalian vertebrates, however, there are some key differences: * Red blood cells of non-mammalian vertebrates are flattened and ovoid in form, and retain their cell nuclei. * There is considerable variation in the types and proportions of white blood cells; for example, acidophils are generally more common than in humans. * Platelets are unique to mammals; in other vertebrates, small nucleated, spindle cells called
thrombocytes Platelets, also called thrombocytes (from Greek θρόμβος, "clot" and κύτος, "cell"), are a component of blood whose function (along with the coagulation factors) is to react to bleeding from blood vessel injury by clumping, thereby initi ...
are responsible for blood clotting instead.


Physiology


Cardiovascular system

Blood is circulated around the body through
blood vessel The blood vessels are the components of the circulatory system that transport blood throughout the human body. These vessels transport blood cells, nutrients, and oxygen to the tissues of the body. They also take waste and carbon dioxide away fr ...
s by the pumping action of the
heart The heart is a muscular organ in most animals, which pumps blood through the blood vessels of the circulatory system. The pumped blood carries oxygen and nutrients to the body, while carrying metabolic waste such as carbon dioxide to the lun ...
. In humans, blood is pumped from the strong
left ventricle A ventricle is one of two large chambers toward the bottom of the heart that collect and expel blood received from an atrium towards the peripheral beds within the body and lungs. The atrium (an adjacent/upper heart chamber that is smaller than a v ...
of the heart through
arteries An artery (plural arteries) () is a blood vessel that takes blood away from the heart to one or more parts of the body (tissues, lungs, brain etc.). Most arteries carry oxygenated blood; the two exceptions are the pulmonary and the umbilical ar ...

arteries
to peripheral
tissues Tissue may refer to: Biology * Tissue (biology), an ensemble of similar cells that together carry out a specific function * ''Triphosa haesitata'', a species of geometer moth found in North America * ''Triphosa dubitata'', a species of geometer mot ...
and returns to the right atrium of the heart through
vein Veins are blood vessels that carry blood towards the heart. Most veins carry deoxygenated blood from the tissues back to the heart; exceptions are the pulmonary and umbilical veins, both of which carry oxygenated blood to the heart. In contrast to ...
s. It then enters the right ventricle and is pumped through the
pulmonary artery A pulmonary artery is an artery in the pulmonary circulation that carries deoxygenated blood from the right side of the heart to the lungs. The largest pulmonary artery is the ''main pulmonary artery'' or ''pulmonary trunk'' from the heart, and th ...
to the
lung The lungs are the primary organs of the respiratory system in humans and many other animals including a few fish and some snails. In mammals and most other vertebrates, two lungs are located near the backbone on either side of the heart. Their ...
s and returns to the left atrium through the
pulmonary vein The pulmonary veins are the veins that transfer oxygenated blood from the lungs to the heart. The largest pulmonary veins are the four ''main pulmonary veins'', two from each lung that drain into the left atrium of the heart. The pulmonary veins ...
s. Blood then enters the left ventricle to be circulated again. Arterial blood carries oxygen from inhaled air to all of the cells of the body, and
venous blood 200px, Concentrated blood after oxygenation Venous blood is deoxygenated blood which travels from the peripheral blood vessels, through the venous system into the right atrium of the heart. Deoxygenated blood is then pumped by the right ventricle t ...
carries carbon dioxide, a waste product of
metabolism Metabolism (, from el, μεταβολή ''metabolē'', "change") is the set of life-sustaining chemical reactions in organisms. The three main purposes of metabolism are: the conversion of food to energy to run cellular processes; the conve ...

metabolism
by
cells Cell most often refers to: * Cell (biology), the functional basic unit of life Cell may also refer to: Closed spaces * Monastic cell, a small room, hut, or cave in which a monk or religious recluse lives * Prison cell, a room used to hold peopl ...
, to the lungs to be exhaled. However, one exception includes pulmonary arteries, which contain the most deoxygenated blood in the body, while the pulmonary veins contain oxygenated blood. Additional return flow may be generated by the movement of
skeletal muscle Skeletal muscle (also called striated muscle - although cardiac muscle is also striated) is one of three major muscle types, the others being cardiac muscle and smooth muscle. It is a form of striated muscle tissue which is under the voluntary cont ...
s, which can compress veins and push blood through the valves in veins toward the
right atrium The atrium (Latin ātrium, “entry hall”) is the upper chamber through which blood enters the ventricles of the heart. There are two atria in the human heart – the left atrium receives blood from the pulmonary (lung) circulation, and the right ...
. The blood circulation was famously described by
William Harvey William Harvey (1 April 1578 – 3 June 1657) was an English physician who made influential contributions in anatomy and physiology. He was the first known physician to describe completely, and in detail, the systemic circulation and properti ...
in 1628.


Production and degradation of blood cells

In vertebrates, the various cells of blood are made in the
bone marrow Bone marrow is a semi-solid tissue found within the spongy or cancellous portions of bones. In birds and mammals, bone marrow is the primary site of new blood cell production or haematopoiesis. It is composed of hematopoietic cells, marrow adipos ...
in a process called
hematopoiesis Haematopoiesis (, from Greek , 'blood' and 'to make'; also hematopoiesis in American English; sometimes also h(a)emopoiesis) is the formation of blood cellular components. All cellular blood components are derived from haematopoietic stem cells. ...
, which includes
erythropoiesis 400px, Haematopoiesis Erythropoiesis (from Greek 'erythro' meaning "red" and 'poiesis' meaning "to make") is the process which produces red blood cells (erythrocytes), which is the development from erythropoietic stem cell to mature red blood cell. ...
, the production of red blood cells; and
myelopoiesis In hematology, myelopoiesis in the broadest sense of the term is the production of bone marrow and of all cells that arise from it, namely, all blood cells. In a narrower sense, myelopoiesis also refers specifically to the regulated formation of my ...
, the production of white blood cells and platelets. During childhood, almost every human bone produces red blood cells; as adults, red blood cell production is limited to the larger bones: the bodies of the vertebrae, the breastbone (sternum), the ribcage, the pelvic bones, and the bones of the upper arms and legs. In addition, during childhood, the
thymus The thymus is a specialized primary lymphoid organ of the immune system. Within the thymus, thymus cell lymphocytes or ''T cells'' mature. T cells are critical to the adaptive immune system, where the body adapts specifically to foreign invaders ...
gland, found in the
mediastinum The mediastinum (from ) is the central compartment of the thoracic cavity surrounded by loose connective tissue, as an undelineated region that contains a group of structures within the thorax. The mediastinum contains the heart and its vessels, th ...

mediastinum
, is an important source of
T lymphocytes A T cell is a type of lymphocyte. T cells are one of the important white blood cells of the immune system, and play a central role in the adaptive immune response. T cells can be easily distinguished from other lymphocytes by the presence of a T- ...
. The proteinaceous component of blood (including clotting proteins) is produced predominantly by the
liver The liver is an organ only found in vertebrates which detoxifies various metabolites, synthesizes proteins and produces biochemicals necessary for digestion and growth. In humans, it is located in the right upper quadrant of the abdomen, below th ...

liver
, while hormones are produced by the
endocrine gland Endocrine glands are ductless glands of the endocrine system that secrete their products, hormones, directly into the blood. The major glands of the endocrine system include the pineal gland, pituitary gland, pancreas, ovaries, testes, thyroid glan ...
s and the watery fraction is regulated by the
hypothalamus The hypothalamus (from Ancient Greek ὑπό, "under", and θάλαμος, "chamber") is a portion of the brain that contains a number of small nuclei with a variety of functions. One of the most important functions of the hypothalamus is to link ...

hypothalamus
and maintained by the
kidney The kidneys are two reddish-brown bean-shaped organs found in vertebrates. They are located on the left and right in the retroperitoneal space, and in adult humans are about in length. They receive blood from the paired renal arteries; blood ex ...
. Healthy
erythrocytes Red blood cells (RBCs), also referred to as red cells, red blood corpuscles (in humans or other animals not having nucleus in red blood cells), haematids, erythroid cells or erythrocytes (from Greek ''erythros'' for "red" and ''kytos'' for "hollo ...
have a plasma life of about 120 days before they are degraded by the
spleen The spleen is an organ found in all vertebrates. Similar in structure to a large lymph node, it acts primarily as a blood filter. The word spleen comes .
, and the
Kupffer cell Kupffer cells, also known as stellate macrophages and Kupffer–Browicz cells, are specialized cells localized in liver within the lumen of the liver sinusoids and are adhesive to their endothelial cells which make up the blood vessel walls. Kupffer ...
s in the liver. The liver also clears some proteins, lipids, and amino acids. The kidney actively secretes waste products into the
urine Urine is a liquid by-product of metabolism in humans and in many other animals. Urine flows from the kidneys through the ureters to the urinary bladder. Urination results in urine being excreted from the body through the urethra. Cellular metab ...
.


Oxygen transport

About 98.5% of the
oxygen Oxygen is the chemical element with the symbol O and atomic number 8. It is a member of the chalcogen group in the periodic table, a highly reactive nonmetal, and an oxidizing agent that readily forms oxides with most elements as well a ...
in a sample of arterial blood in a healthy human breathing air at sea-level pressure is chemically combined with the
hemoglobin Hemoglobin, or haemoglobin (spelling differences) (Greek αἷμα (haîma, “blood”) + -in) + -o- + globulin (from Latin globus (“ball, sphere”) + -in) (), abbreviated Hb or Hgb, is the iron-containing oxygen-transport metalloprotein in th ...
. About 1.5% is physically dissolved in the other blood liquids and not connected to hemoglobin. The hemoglobin molecule is the primary transporter of oxygen in
mammal Mammals (from Latin , 'breast') are a group of vertebrate animals constituting the class Mammalia (), and characterized by the presence of mammary glands which in females produce milk for feeding (nursing) their young, a neocortex (a region ...
s and many other species (for exceptions, see below). Hemoglobin has an oxygen binding capacity between 1.36 and 1.40 ml O2 per gram hemoglobin, which increases the total
blood oxygen capacity Blood is a body fluid in humans and other animals that delivers necessary substances such as nutrients and oxygen to the cells and transports metabolic waste products away from those same cells. In vertebrates, it is composed of blood cells su ...
seventyfold, compared to if oxygen solely were carried by its solubility of 0.03 ml O2 per liter blood per mm Hg partial pressure of oxygen (about 100 mm Hg in arteries). With the exception of pulmonary and
umbilical arteries The umbilical artery is a paired artery (with one for each half of the body) that is found in the abdominal and pelvic regions. In the fetus, it extends into the umbilical cord. Structure Development The umbilical arteries supply deoxygenated blo ...
and their corresponding veins, arteries carry oxygenated blood away from the heart and deliver it to the body via
arteriole An arteriole is a small-diameter blood vessel in the microcirculation that extends and branches out from an artery and leads to capillaries. Arterioles have muscular walls (usually only one to two layers of smooth muscle) and are the primary site ...

arteriole
s and
capillaries A capillary is a small blood vessel from 5 to 10 micrometres (μm) in diameter, and having a wall one endothelial cell thick. They are the smallest blood vessels in the body: they convey blood between the arterioles and venules. These microvessels ...

capillaries
, where the oxygen is consumed; afterwards,
venule A venule is a very small blood vessel in the microcirculation that allows blood to return from the capillary beds to drain into the larger blood vessels, the veins. Venules range from 7μm to 1mm in diameter. Veins contain approximately 70% of to ...
s and veins carry deoxygenated blood back to the heart. Under normal conditions in adult humans at rest, hemoglobin in blood leaving the lungs is about 98–99% saturated with oxygen, achieving an oxygen delivery between 950 and 1150 ml/minEdwards Lifesciences LLC – Normal Hemodynamic Parameters – Adult
2009
to the body. In a healthy adult at rest, oxygen consumption is approximately 200–250 ml/min, and deoxygenated blood returning to the lungs is still roughly 75% (70 to 78%) saturated. Increased oxygen consumption during sustained exercise reduces the oxygen saturation of venous blood, which can reach less than 15% in a trained athlete; although breathing rate and blood flow increase to compensate, oxygen saturation in arterial blood can drop to 95% or less under these conditions. Oxygen saturation this low is considered dangerous in an individual at rest (for instance, during surgery under anesthesia). Sustained hypoxia (oxygenation less than 90%), is dangerous to health, and severe hypoxia (saturations less than 30%) may be rapidly fatal. A
fetus A fetus or foetus (; plural fetuses, feti, foetuses, or foeti) is the unborn offspring of an animal that develops from an embryo. Following embryonic development the fetal stage of development takes place. In human prenatal development, fetal de ...
, receiving oxygen via the
placenta The placenta is a temporary fetal organ that begins developing from the blastocyst shortly after implantation. It plays critical roles in facilitating nutrient, gas and waste exchange between the physically separate maternal and fetal circulations ...

placenta
, is exposed to much lower oxygen pressures (about 21% of the level found in an adult's lungs), so fetuses produce another form of hemoglobin with a much higher affinity for oxygen ( hemoglobin F) to function under these conditions.


Carbon dioxide transport

CO2 is carried in blood in three different ways. (The exact percentages vary depending whether it is arterial or venous blood). Most of it (about 70%) is converted to bicarbonate ions by the enzyme
carbonic anhydrase The carbonic anhydrases (or carbonate dehydratases) form a family of enzymes that catalyze the interconversion between carbon dioxide and water and the dissociated ions of carbonic acid (i.e. bicarbonate and hydrogen ions). The active site of m ...

carbonic anhydrase
in the red blood cells by the reaction CO2 + H2O → H2CO3 → H+ + ; about 7% is dissolved in the plasma; and about 23% is bound to hemoglobin as
carbamino Carbamino refers to a compound composed by the addition of carbon dioxide with a free amino group in an amino acid or a protein, such as hemoglobin forming carbaminohemoglobin. References Functional groups {{biochemistry-stub ...
compounds. Hemoglobin, the main oxygen-carrying molecule in red blood cells, carries both oxygen and carbon dioxide. However, the CO2 bound to hemoglobin does not bind to the same site as oxygen. Instead, it combines with the N-terminal groups on the four globin chains. However, because of
allosteric 300px, Allosteric regulation of an enzyme In biochemistry, allosteric regulation (or allosteric control) is the regulation of an enzyme by binding an effector molecule at a site other than the enzyme's active site. The site to which the effector ...

allosteric
effects on the hemoglobin molecule, the binding of CO2 decreases the amount of oxygen that is bound for a given partial pressure of oxygen. The decreased binding to carbon dioxide in the blood due to increased oxygen levels is known as the
Haldane effect#REDIRECT Haldane effect {{R from other capitalisation ...
, and is important in the transport of carbon dioxide from the tissues to the lungs. A rise in the partial pressure of CO2 or a lower pH will cause offloading of oxygen from hemoglobin, which is known as the
Bohr effect The Bohr effect is a phenomenon first described in 1904 by the Danish physiologist Christian Bohr. Hemoglobin's oxygen binding affinity (see oxygen–haemoglobin dissociation curve) is inversely related both to acidity and to the concentration of ...

Bohr effect
.


Transport of hydrogen ions

Some oxyhemoglobin loses oxygen and becomes deoxyhemoglobin. Deoxyhemoglobin binds most of the hydrogen ions as it has a much greater affinity for more hydrogen than does oxyhemoglobin.


Lymphatic system

In mammals, blood is in equilibrium with
lymph Lymph (from Latin, ''lympha'' meaning "water") is the fluid that flows through the lymphatic system, a system composed of lymph vessels (channels) and intervening lymph nodes whose function, like the venous system, is to return fluid from the tiss ...
, which is continuously formed in tissues from blood by capillary ultrafiltration. Lymph is collected by a system of small lymphatic vessels and directed to the
thoracic duct In human anatomy, the thoracic duct is the larger of the two lymph ducts of the lymphatic system. It is also known as the ''left lymphatic duct'', ''alimentary duct'', ''chyliferous duct'', and ''Van Hoorne's canal''. The other duct is the right lym ...
, which drains into the left
subclavian vein The subclavian vein is a paired large vein, one on either side of the body, that is responsible for draining blood from the upper extremities, allowing this blood to return to the heart. The left subclavian vein plays a key role in the absorption o ...
, where lymph rejoins the systemic blood circulation.


Thermoregulation

Blood circulation transports heat throughout the body, and adjustments to this flow are an important part of
thermoregulation Thermoregulation is the ability of an organism to keep its body temperature within certain boundaries, even when the surrounding temperature is very different. A thermoconforming organism, by contrast, simply adopts the surrounding temperature ...
. Increasing blood flow to the surface (e.g., during warm weather or strenuous exercise) causes warmer skin, resulting in faster heat loss. In contrast, when the external temperature is low, blood flow to the extremities and surface of the skin is reduced and to prevent heat loss and is circulated to the important organs of the body, preferentially.


Rate of blood flow

Rate of blood flow varies greatly between different organs. Liver has the most abundant blood supply with an approximate flow of 1350 ml/min. Kidney and brain are the second and the third most supplied organs, with 1100 ml/min and ~700 ml/min, respectively. Relative rates of blood flow per 100 g of tissue are different, with kidney, adrenal gland and thyroid being the first, second and third most supplied tissues, respectively.


Hydraulic functions

The restriction of blood flow can also be used in specialized tissues to cause engorgement, resulting in an
erection An erection (clinically: penile erection or penile tumescence) is a physiological phenomenon in which the penis becomes firm, engorged, and enlarged. Penile erection is the result of a complex interaction of psychological, neural, vascular, ...
of that tissue; examples are the
erectile tissueErectile tissue is tissue in the body with numerous vascular spaces, or cavernous tissue, that may become engorged with blood. However, tissue that is devoid of or otherwise lacking erectile tissue (such as the labia minora, the vestibule/vagina and ...
in the
penis A penis (plural ''penises'' or ''penes'' ) is the primary sexual organ that male animals use to inseminate females (or hermaphrodites) during copulation. Such organs occur in many animals, both vertebrate and invertebrate, but males do not bea ...
and
clitoris The clitoris ( or ) is a female sex organ present in mammals, ostriches and a limited number of other animals. In humans, the visible portion – the glans – is at the front junction of the labia minora (inner lips), above the openin ...
. Another example of a hydraulic function is the
jumping spider Jumping spiders or the Salticidae are a family of spiders. As of 2019, it contained over 600 described genera and over 6000 described species, making it the largest family of spiders at 13% of all species. Jumping spiders have some of the best vi ...
, in which blood forced into the legs under pressure causes them to straighten for a powerful jump, without the need for bulky muscular legs.


Invertebrates

In insects, the blood (more properly called
hemolymph Hemolymph, or haemolymph, is a fluid, analogous to the blood in vertebrates, that circulates in the interior of the arthropod (invertebrate) body remaining in direct contact with the animal's tissues. It is composed of a fluid plasma in which he ...
) is not involved in the transport of oxygen. (Openings called tracheae allow oxygen from the air to diffuse directly to the tissues.) Insect blood moves nutrients to the tissues and removes waste products in an open system. Other invertebrates use respiratory proteins to increase the oxygen-carrying capacity. Hemoglobin is the most common respiratory protein found in nature.
Hemocyanin Hemocyanins (also spelled haemocyanins and abbreviated Hc) are proteins that transport oxygen throughout the bodies of some invertebrate animals. These metalloproteins contain two copper atoms that reversibly bind a single oxygen molecule (O2). ...
(blue) contains copper and is found in
crustacean Crustaceans (Crustacea ) form a large, diverse arthropod taxon which includes such animals as crabs, lobsters, crayfish, shrimps, prawns, krill, woodlice, and barnacles. The crustacean group can be treated as a subphylum under the clade Mandibulat ...
s and
mollusks Mollusca is the second-largest phylum of invertebrate animals after the Arthropoda. The members are known as molluscs or mollusks (). Around 85,000 extant species of molluscs are recognized. The number of fossil species is estimated betwee ...
. It is thought that
tunicate A tunicate is a marine invertebrate animal, a member of the subphylum Tunicata . It is part of the Chordata, a phylum which includes all animals with dorsal nerve cords and notochords (including vertebrates). The subphylum was at one time called ...
s (sea squirts) might use vanabins (proteins containing
vanadium Vanadium is a chemical element with the symbol V and atomic number 23. It is a hard, silvery-grey, malleable transition metal. The elemental metal is rarely found in nature, but once isolated artificially, the formation of an oxide layer (passiv ...
) for respiratory pigment (bright-green, blue, or orange). In many invertebrates, these oxygen-carrying proteins are freely soluble in the blood; in vertebrates they are contained in specialized red blood cells, allowing for a higher concentration of respiratory pigments without increasing
viscosity The viscosity of a fluid is a measure of its resistance to deformation at a given rate. For liquids, it corresponds to the informal concept of "thickness": for example, syrup has a higher viscosity than water. Viscosity can be conceptualized ...
or damaging blood filtering organs like the kidneys.
Giant tube worm ''Riftia pachyptila'', commonly known as the giant tube worm, is a marine invertebrate in the phylum Annelida (formerly `grouped in phylum Pogonophora and Vestimentifera) related to tube worms commonly found in the intertidal and pelagic zones. ...
s have unusual hemoglobins that allow them to live in extraordinary environments. These hemoglobins also carry sulfides normally fatal in other animals.


Color

The coloring matter of blood (hemochrome) is largely due to the protein in the blood responsible for oxygen transport. Different groups of organisms use different proteins.


Hemoglobin

Hemoglobin is the principal determinant of the color of blood in vertebrates. Each molecule has four heme groups, and their interaction with various molecules alters the exact color. In
vertebrate Vertebrates () comprise all species of animals within the subphylum Vertebrata () (chordates with backbones). Vertebrates represent the overwhelming majority of the phylum Chordata, with currently about 69,963 species described. Vertebrates inclu ...
s and other hemoglobin-using creatures, arterial blood and capillary blood are bright red, as oxygen imparts a strong red color to the heme group. Deoxygenated blood is a darker shade of red; this is present in veins, and can be seen during
blood donation A blood donation occurs when a person voluntarily has blood drawn and used for transfusions and/or made into biopharmaceutical medications by a process called fractionation (separation of whole blood components). Donation may be of whole blood, ...
and when venous blood samples are taken. This is because the spectrum of light absorbed by hemoglobin differs between the oxygenated and deoxygenated states. Blood in
carbon monoxide poisoning Carbon monoxide poisoning typically occurs from breathing in carbon monoxide (CO) at excessive levels. Symptoms are often described as "flu-like" and commonly include headache, dizziness, weakness, vomiting, chest pain, and confusion. Large expos ...
is bright red, because
carbon monoxide#REDIRECT Carbon monoxide#REDIRECT Carbon monoxide {{Redirect category shell, 1= {{R from other capitalisation ...
{{Redirect category shell, 1= {{R from other capitalisation ...
causes the formation of
carboxyhemoglobin Carboxyhemoglobin or carboxyhaemoglobin (symbol COHb or HbCO) is a stable complex of carbon monoxide and hemoglobin (Hb) that forms in red blood cells upon contact with carbon monoxide (CO). Carboxyhemoglobin is often mistaken for the compound form ...
. In
cyanide A cyanide is a chemical compound that contains the group C≡N. This group, known as the cyano group, consists of a carbon atom triple-bonded to a nitrogen atom. In inorganic cyanides, the cyanide group is present as the anion CN−. Soluble sa ...
poisoning, the body cannot utilize oxygen, so the venous blood remains oxygenated, increasing the redness. There are some conditions affecting the heme groups present in hemoglobin that can make the skin appear blue – a symptom called
cyanosis Cyanosis is the bluish or purplish discoloration of the skin or mucous membranes due to the tissues near the skin surface having low oxygen saturation. Based on Lundsgaard and Van Slyke's work, it is classically described as occurring if 5.0&nb ...
. If the heme is oxidized,
methemoglobinMethemoglobin (British: methaemoglobin) (pronounced "met-hemoglobin") is a hemoglobin ''in the form of metalloprotein'', in which the iron in the heme group is in the Fe3+ (ferric) state, not the Fe2+ (ferrous) of normal hemoglobin. Methemoglobin can ...
, which is more brownish and cannot transport oxygen, is formed. In the rare condition
sulfhemoglobinemia Sulfhemoglobinemia is a rare condition in which there is excess sulfhemoglobin (SulfHb) in the blood. The pigment is a greenish derivative of hemoglobin which cannot be converted back to normal, functional hemoglobin. It causes cyanosis even at lo ...
, arterial hemoglobin is partially oxygenated, and appears dark red with a bluish hue. Veins close to the surface of the skin appear blue for a variety of reasons. However, the factors that contribute to this alteration of
color perception#REDIRECT Color vision {{R from alternate spelling ...
are related to the light-scattering properties of the skin and the processing of visual input by the
visual cortex The visual cortex of the brain is the area of the cerebral cortex that processes visual information. It is located in the occipital lobe. Sensory input originating from the eyes travels through the lateral geniculate nucleus in the thalamus and the ...
, rather than the actual color of the venous blood.
Skink Skinks are lizards belonging to the family Scincidae, a family in the infraorder Scincomorpha. With more than 1,500 described species across 100 different taxonomic genuses, the family Scincidae is one of the most diverse families of lizards. Ski ...
s in the genus ''
Prasinohaema ''Prasinohaema'' (Greek: "green blood") is a genus of skinks characterized by having green blood. This condition is caused by an excess buildup of the bile pigment biliverdin. ''Prasinohaema'' species have plasma biliverdin concentrations appro ...
'' have green blood due to a buildup of the waste product
biliverdin Biliverdin is a green tetrapyrrolic bile pigment, and is a product of heme catabolism.Boron W, Boulpaep E. Medical Physiology: a cellular and molecular approach, 2005. 984-986. Elsevier Saunders, United States. It is the pigment responsible for a ...
.


Hemocyanin

The blood of most
mollusks Mollusca is the second-largest phylum of invertebrate animals after the Arthropoda. The members are known as molluscs or mollusks (). Around 85,000 extant species of molluscs are recognized. The number of fossil species is estimated betwee ...
– including
cephalopods A cephalopod is any member of the molluscan class Cephalopoda (Greek plural , ; "head-feet") such as a squid, octopus, cuttlefish, or nautilus. These exclusively marine animals are characterized by bilateral body symmetry, a prominent head, and ...
and
gastropods The gastropods (), commonly known as snails and slugs, belong to a large taxonomic class of invertebrates within the phylum Mollusca called Gastropoda . WoRMS (2020). Gastropoda. Accessed at: http://marinespecies.org/aphia.php?p=taxdetails&id=101 ...
– as well as some
arthropod An arthropod (, (gen. ποδός)) is an invertebrate animal having an exoskeleton, a segmented body, and paired jointed appendages. Arthropods form the phylum Euarthropoda,Reference showing that Euarthropoda is a phylum: which includes insects, ...
s, such as
horseshoe crab Horseshoe crabs are marine and brackish water arthropods of the family Limulidae, suborder Xiphosurida, and order Xiphosura. Their popular name is a misnomer, as they are not true crabs, nor even crustaceans, as crabs are, but a different order of ...

horseshoe crab
s, is blue, as it contains the copper-containing protein hemocyanin at concentrations of about 50 grams per liter. Hemocyanin is colorless when deoxygenated and dark blue when oxygenated. The blood in the circulation of these creatures, which generally live in cold environments with low oxygen tensions, is grey-white to pale yellow, and it turns dark blue when exposed to the oxygen in the air, as seen when they bleed. This is due to change in color of hemocyanin when it is oxidized. Hemocyanin carries oxygen in
extracellular fluid Extracellular fluid (ECF) denotes all body fluid outside the cells of any multicellular organism. Total body water in healthy adults is about 60% (range 45 to 75%) of total body weight; women and the obese typically have a lower percentage than lean ...
, which is in contrast to the intracellular oxygen transport in mammals by hemoglobin in RBCs.


Chlorocruorin

The blood of most
annelid The annelids (Annelida , from Latin ', "little ring"), also known as the ringed worms or segmented worms, are a large phylum, with over 22,000 extant species including ragworms, earthworms, and leeches. The species exist in and have adapted to ...
worms and some marine
polychaetes The Polychaeta , also known as the bristle worms or polychaetes, are a paraphyletic class of annelid worms, generally marine. Each body segment has a pair of fleshy protrusions called parapodia that bear many bristles, called chaetae, which are m ...
use chlorocruorin to transport oxygen. It is green in color in dilute solutions.Carnegie Library of Pittsburgh, ''The Handy Science Answer Book'', p. 465, Visible Ink Press, 2011 .


Hemerythrin

Hemerythrin is used for oxygen transport in the marine invertebrates
sipunculid The Sipuncula or Sipunculida (common names sipunculid worms or peanut worms) is a group containing about 162 species of bilaterally symmetrical, unsegmented marine worms. The name ''Sipuncula'' is from the genus name ''Sipunculus'', and comes fr ...
s,
priapulid Priapulida (priapulid worms, from Gr. πριάπος, ''priāpos'' 'Priapus' + Lat. ''-ul-'', diminutive), sometimes referred to as penis worms, is a phylum of unsegmented marine worms. The name of the phylum relates to the Greek god of fertility, ...
s,
brachiopod Brachiopods (), phylum Brachiopoda, are a group of lophotrochozoan animals that have hard "valves" (shells) on the upper and lower surfaces, unlike the left and right arrangement in bivalve molluscs. Brachiopod valves are hinged at the rear end, ...
s, and the annelid worm, magelona. Hemerythrin is violet-pink when oxygenated.


Hemovanadin

The blood of some species of
ascidians Ascidiacea, commonly known as the ascidians, tunicates (in part), and sea squirts (in part), is a polyphyletic class in the subphylum Tunicata of sac-like marine invertebrate filter feeders. Ascidians are characterized by a tough outer "tunic" mad ...
and tunicates, also known as sea squirts, contains proteins called vanadins. These proteins are based on
vanadium Vanadium is a chemical element with the symbol V and atomic number 23. It is a hard, silvery-grey, malleable transition metal. The elemental metal is rarely found in nature, but once isolated artificially, the formation of an oxide layer (passiv ...
, and give the creatures a concentration of vanadium in their bodies 100 times higher than the surrounding seawater. Unlike hemocyanin and hemoglobin, hemovanadin is not an oxygen carrier. When exposed to oxygen, however, vanadins turn a mustard yellow.


Disorders


General medical

* Disorders of volume ** Injury can cause blood loss through bleeding. A healthy adult can lose almost 20% of blood volume (1 L) before the first symptom, restlessness, begins, and 40% of volume (2 L) before shock sets in.
Thrombocyte Platelets, also called thrombocytes (from Greek θρόμβος, "clot" and κύτος, "cell"), are a component of blood whose function (along with the coagulation factors) is to react to bleeding from blood vessel injury by clumping, thereby initi ...
s are important for blood
coagulation Coagulation, also known as clotting, is the process by which blood changes from a liquid to a gel, forming a blood clot. It potentially results in hemostasis, the cessation of blood loss from a damaged vessel, followed by repair. The mechanism o ...
and the formation of blood clots, which can stop bleeding. Trauma to the internal organs or bones can cause
internal bleeding Internal bleeding (also called internal hemorrhage) is a loss of blood from a blood vessel that collects inside the body. Internal bleeding is usually not visible from the outside. It is a serious medical emergency but the extent of severity depends ...
, which can sometimes be severe. **
Dehydration In physiology, dehydration is a lack of total body water, with an accompanying disruption of metabolic processes. It occurs when free water loss exceeds free water intake, usually due to exercise, disease, or high environmental temperature. Mild ...

Dehydration
can reduce the blood volume by reducing the water content of the blood. This would rarely result in shock (apart from the very severe cases) but may result in
orthostatic hypotension Orthostatic hypotension, also known as postural hypotension, is a medical condition wherein a person's blood pressure drops when standing up or sitting down. The drop in blood pressure may be sudden (vasovagal orthostatic hypotension), within 3 mi ...
and
fainting Syncope, also known as fainting, is a loss of consciousness and muscle strength characterized by a fast onset, short duration, and spontaneous recovery. It is caused by a decrease in blood flow to the brain, typically from low blood pressure. ...
. * Disorders of circulation ** Shock is the ineffective
perfusion Perfusion is the passage of fluid through the circulatory system or lymphatic system to an organ or a tissue, usually referring to the delivery of blood to a capillary bed in tissue. Perfusion is measured as the rate at which blood is delivered ...
of tissues, and can be caused by a variety of conditions including blood loss, infection, poor
cardiac output Cardiac output (CO), also known as heart output denoted by the symbols Q, or \dot Q_ , is a term used in cardiac physiology that describes the volume of blood being pumped by the heart, by the left and right ventricle, per unit time. Cardiac o ...
. **
Atherosclerosis Atherosclerosis is a disease in which the wall of the artery develops abnormalities, called lesions. These lesions may lead to narrowing due to the buildup of atheromatous plaque. Initially, there are generally no symptoms. When severe, it can re ...

Atherosclerosis
reduces the flow of blood through arteries, because atheroma lines arteries and narrows them. Atheroma tends to increase with age, and its progression can be compounded by many causes including smoking,
high blood pressure Hypertension (HTN or HT), also known as high blood pressure (HBP), is a long-term medical condition in which the blood pressure in the arteries is persistently elevated. High blood pressure typically does not cause symptoms. Long-term high blo ...
, excess circulating lipids (
hyperlipidemia Hyperlipidemia is abnormally elevated levels of any or all lipids or lipoproteins in the blood. citing: and Hyperlipidemia is an umbrella term that refers to acquired or genetic disorders that result in high levels of lipids (fats, cholesterol ...
), and
diabetes Diabetes mellitus (DM), commonly known as diabetes, is a group of metabolic disorders characterized by a high blood sugar level over a prolonged period of time. Symptoms often include frequent urination, increased thirst and increased appetite. I ...
mellitus. ** Coagulation can form a
thrombosis Thrombosis (from Ancient Greek "clotting”) is the formation of a blood clot inside a blood vessel, obstructing the flow of blood through the circulatory system. When a blood vessel (a vein or an artery) is injured, the body uses platelets (thr ...

thrombosis
, which can obstruct vessels. ** Problems with blood composition, the pumping action of the heart, or narrowing of blood vessels can have many consequences including hypoxia (lack of oxygen) of the tissues supplied. The term ''ischemia'' refers to tissue that is inadequately perfused with blood, and ''infarction'' refers to tissue death (
necrosis Necrosis (from Ancient Greek νέκρωσις, ''nékrōsis'', "death") is a form of cell injury which results in the premature death of cells in living tissue by autolysis. Necrosis is caused by factors external to the cell or tissue, such as i ...
), which can occur when the blood supply has been blocked (or is very inadequate).


Hematological

* Anemia ** Insufficient red cell mass (
anemia Anemia (also spelled anaemia) is a decrease in the total amount of red blood cells (RBCs) or hemoglobin in the blood, or a lowered ability of the blood to carry oxygen. When anemia comes on slowly, the symptoms are often vague and may include f ...

anemia
) can be the result of bleeding, blood disorders like
thalassemia Thalassemias are inherited blood disorders characterized by decreased hemoglobin production. Symptoms depend on the type and can vary from none to severe. Often there is mild to severe anemia (low red blood cells or hemoglobin). Anemia can result ...
, or
nutritional deficiencies Malnutrition is a condition that results from eating a diet which does not supply a healthy amount of one or more nutrients. This includes diets that have too little nutrients or so many that the diet causes health problems. The nutrients invol ...
, and may require one or more
blood transfusion Blood transfusion is the process of transferring blood products into one's circulation intravenously. Transfusions are used for various medical conditions to replace lost components of the blood. Early transfusions used whole blood, but modern med ...
s. Anemia can also be due to a
genetic disorder A genetic disorder is a health problem caused by one or more abnormalities in the genome. It can be caused by a mutation in a single gene (monogenic) or multiple genes (polygenic) or by a chromosomal abnormality. Although polygenic disorders are ...
in which the red blood cells simply do not function effectively. Anemia can be confirmed by a
blood test A blood test is a laboratory analysis performed on a blood sample that is usually extracted from a vein in the arm using a hypodermic needle, or via fingerprick. Multiple tests for specific blood components, such as a glucose test or a cholestero ...

blood test
if the hemoglobin value is less than 13.5 gm/dl in men or less than 12.0 gm/dl in women. Several countries have
blood bankA blood bank is a center where blood gathered as a result of blood donation is stored and preserved for later use in blood transfusion. The term "blood bank" typically refers to a division of a hospital where the storage of blood product occurs and w ...
s to fill the demand for transfusable blood. A person receiving a blood transfusion must have a
blood type A blood type (also known as a blood group) is a classification of blood, based on the presence and absence of antibodies and inherited antigenic substances on the surface of red blood cells (RBCs). These antigens may be proteins, carbohydrates, g ...
compatible with that of the donor. **
Sickle-cell anemia Sickle cell disease (SCD) is a group of blood disorders typically inherited from a person's parents. The most common type is known as sickle cell anaemia (SCA). It results in an abnormality in the oxygen-carrying protein haemoglobin found in red ...
* Disorders of cell proliferation **
Leukemia Leukemia, also spelled leukaemia, is a group of blood cancers that usually begin in the bone marrow and result in high numbers of abnormal blood cells. These blood cells are not fully developed and are called ''blasts'' or ''leukemia cells''. Sy ...
is a group of
cancers Cancer is a group of diseases involving abnormal cell growth with the potential to invade or spread to other parts of the body. These contrast with benign tumors, which do not spread. Possible signs and symptoms include a lump, abnormal bleedi ...
of the blood-forming tissues and cells. ** Non-cancerous overproduction of red cells (
polycythemia vera Polycythemia vera is an uncommon myeloproliferative neoplasm in which the bone marrow makes too many red blood cells. It may also result in the overproduction of white blood cells and platelets. Most of the health concerns associated with polycyt ...
) or platelets ( essential thrombocytosis) may be
premalignant A precancerous condition is a condition or lesion involving abnormal cells which are associated with an increased risk of developing into cancer. Clinically, precancerous conditions encompass a variety of conditions or lesions with an increased ris ...
. **
Myelodysplastic syndrome A myelodysplastic syndrome (MDS) is one of a group of cancers in which immature blood cells in the bone marrow do not mature, so do not become healthy blood cells. Early on, no symptoms typically are seen. Later, symptoms may include feeling tired ...
s involve ineffective production of one or more cell lines. * Disorders of coagulation **
Hemophilia Haemophilia (also spelled hemophilia) is a mostly inherited genetic disorder that impairs the body's ability to make blood clots, a process needed to stop bleeding. This results in people bleeding for a longer time after an injury, easy bruisin ...
is a genetic illness that causes dysfunction in one of the blood's clotting mechanisms. This can allow otherwise inconsequential wounds to be life-threatening, but more commonly results in
hemarthrosis Hemarthrosis is a bleeding into joint spaces. It is a common feature of hemophilia. Causes It usually follows injury but occurs mainly in patients with a predisposition to hemorrhage such as those being treated with warfarin (or other anticoagulant ...
, or bleeding into joint spaces, which can be crippling. ** Ineffective or insufficient platelets can also result in
coagulopathy Coagulopathy (also called a bleeding disorder) is a condition in which the blood's ability to coagulate (form clots) is impaired. This condition can cause a tendency toward prolonged or excessive bleeding (bleeding diathesis), which may occur spont ...
(bleeding disorders). ** Hypercoagulable state (
thrombophilia Thrombophilia (sometimes called hypercoagulability or a prothrombotic state) is an abnormality of blood coagulation that increases the risk of thrombosis (blood clots in blood vessels). Such abnormalities can be identified in 50% of people who h ...
) results from defects in regulation of platelet or clotting factor function, and can cause thrombosis. * Infectious disorders of blood ** Blood is an important vector of infection. HIV, the virus that causes AIDS, is transmitted through contact with blood, semen or other body secretions of an infected person.
Hepatitis B Hepatitis B is an infectious disease caused by the hepatitis B virus (HBV) that affects the liver; it is a type of viral hepatitis. It can cause both acute and chronic infection. Many people have no symptoms during the initial infection. In acute ...
and C are transmitted primarily through blood contact. Owing to blood-borne infections, bloodstained objects are treated as a
biohazard A biological hazard, or biohazard, is a biological substance that poses a threat to the health of living organisms, primarily humans. This could include a sample of a microorganism, virus or toxin that can adversely affect human health. A bioha ...
. ** Bacterial infection of the blood is
bacteremia Bloodstream infections (BSIs), which include bacteremias when the infections are bacterial and fungemias when the infections are fungal, are infections present in the blood. Blood is normally a sterile environment, so the detection of microbes in ...
or
sepsis Sepsis is a life-threatening condition that arises when the body's response to infection causes injury to its own tissues and organs. This initial stage is followed by suppression of the immune system. Common signs and symptoms include fever, in ...
. Viral Infection is viremia.
Malaria Malaria is a mosquito-borne infectious disease that affects humans and other animals. Malaria causes symptoms that typically include fever, tiredness, vomiting, and headaches. In severe cases, it can cause yellow skin, seizures, coma, or death. ...

Malaria
and
trypanosomiasis Trypanosomiasis or trypanosomosis is the name of several diseases in vertebrates caused by parasitic protozoan trypanosomes of the genus ''Trypanosoma''. In humans this includes African trypanosomiasis and Chagas disease. A number of other diseases ...
are blood-borne parasitic infections.


Carbon monoxide poisoning

Substances other than oxygen can bind to hemoglobin; in some cases, this can cause irreversible damage to the body. Carbon monoxide, for example, is extremely dangerous when carried to the blood via the lungs by inhalation, because carbon monoxide irreversibly binds to hemoglobin to form carboxyhemoglobin, so that less hemoglobin is free to bind oxygen, and fewer oxygen molecules can be transported throughout the blood. This can cause suffocation insidiously. A fire burning in an enclosed room with poor ventilation presents a very dangerous hazard, since it can create a build-up of carbon monoxide in the air. Some carbon monoxide binds to hemoglobin when smoking tobacco.


Treatments


Blood products

Blood for transfusion is obtained from human donors by blood donation and stored in a
blood bankA blood bank is a center where blood gathered as a result of blood donation is stored and preserved for later use in blood transfusion. The term "blood bank" typically refers to a division of a hospital where the storage of blood product occurs and w ...
. There are many different
blood type A blood type (also known as a blood group) is a classification of blood, based on the presence and absence of antibodies and inherited antigenic substances on the surface of red blood cells (RBCs). These antigens may be proteins, carbohydrates, g ...
s in humans, the
ABO blood group system The ABO blood group system is used to denote the presence of one, both, or neither of the A and B antigens on erythrocytes. In human blood transfusions it is the most important of the 38 different blood type (or group) classification systems c ...
, and the
Rhesus blood group system The Rh blood group system is a human blood group system. It contains proteins on the surface of red blood cells. It is the second most important blood group system, after the ABO blood group system. The Rh blood group system consists of 49 defined ...
being the most important. Transfusion of blood of an incompatible blood group may cause severe, often fatal, complications, so
crossmatching Cross-matching or crossmatching is a test performed before a blood transfusion as part of blood compatibility testing. Normally, this involves adding the recipient's blood plasma to a sample of the donor's red blood cells. If the blood is incompa ...
is done to ensure that a compatible blood product is transfused. Other blood products administered
intravenous Intravenous therapy (abbreviated as IV therapy) is a medical technique that delivers fluids, medications and nutrition directly into a person's vein. The intravenous route of administration is commonly used for rehydration or to provide nutrition ...
ly are platelets, blood plasma, cryoprecipitate, and specific coagulation factor concentrates.


Intravenous administration

Many forms of medication (from
antibiotic An antibiotic is a type of antimicrobial substance active against bacteria. It is the most important type of antibacterial agent for fighting bacterial infections, and antibiotic medications are widely used in the treatment and prevention of su ...
s to
chemotherapy Chemotherapy (often abbreviated to chemo and sometimes CTX or CTx) is a type of cancer treatment that uses one or more anti-cancer drugs (chemotherapeutic agents) as part of a standardized chemotherapy regimen. Chemotherapy may be given with a ...
) are administered intravenously, as they are not readily or adequately absorbed by the digestive tract. After severe acute blood loss, liquid preparations, generically known as plasma expanders, can be given intravenously, either solutions of salts (NaCl, KCl, CaCl2 etc.) at physiological concentrations, or colloidal solutions, such as dextrans,
human serum albumin Human serum albumin is the serum albumin found in human blood. It is the most abundant protein in human blood plasma; it constitutes about half of serum protein. It is produced in the liver. It is soluble in water, and it is monomeric. Albumin tr ...
, or fresh frozen plasma. In these emergency situations, a plasma expander is a more effective life-saving procedure than a blood transfusion, because the metabolism of transfused red blood cells does not restart immediately after a transfusion.


Bloodletting

In modern
evidence-based medicine Evidence-based medicine (EBM) is "the conscientious, explicit and judicious use of current best evidence in making decisions about the care of individual patients." The aim of EBM is to integrate the experience of the clinician, the values of the ...
, bloodletting is used in management of a few rare diseases, including
hemochromatosis Iron overload or haemochromatosis (spelled ''hemochromatosis'' in American English) indicates accumulation of iron in the body from any cause. The most important causes are hereditary haemochromatosis (HHC), a genetic disorder, and transfusional i ...
and
polycythemia Polycythemia (also known as polycythaemia or polyglobulia) is a disease state in which the hematocrit (the volume percentage of red blood cells in the blood) and/or hemoglobin concentration are elevated in peripheral blood. It can be due to an inc ...
. However,
bloodletting Bloodletting (or blood-letting) is the withdrawal of blood from a patient to prevent or cure illness and disease. Bloodletting, whether by a physician or by leeches, was based on an ancient system of medicine in which blood and other bodily flui ...
and leeching were common unvalidated interventions used until the 19th century, as many diseases were incorrectly thought to be due to an excess of blood, according to
Hippocratic Hippocrates of Kos (; grc-gre, Ἱπποκράτης ὁ Κῷος, Hippokrátēs ho Kṓos; ), also known as Hippocrates II, was a Greek physician of the Age of Pericles (Classical Greece), who is considered one of the most outstanding figures in ...

Hippocratic
medicine.


Etymology

up Jan Janský is credited with the first classification of blood into four types (A, B, AB, and O) English ''blood'' (
Old English Old English (, ), or Anglo-Saxon, is the earliest recorded form of the English language, spoken in England and southern and eastern Scotland in the early Middle Ages. It was brought to Great Britain by Anglo-Saxon settlers in the mid-5th centur ...
''blod'') derives from and has cognates with a similar range of meanings in all other Germanic languages (e.g. German ''Blut'', Swedish ''blod'', Gothic ''blōþ''). There is no accepted
Indo-European The Indo-European languages are a language family native to western and southern Eurasia. It comprises most of the languages of Europe together with those of the northern Indian subcontinent and the Iranian Plateau. A few of these languages, su ...
etymology.


History


Classical Greek medicine

(a Swedish physician who devised the
erythrocyte sedimentation rate The erythrocyte sedimentation rate (ESR or sed rate) is the rate at which red blood cells in anticoagulated whole blood descend in a standardized tube over a period of one hour. It is a common hematology test, and is a non-specific measure of inflam ...
) suggested that the Ancient Greek system of
humorism Humourism, the humoural theory or humouralism, was a system of medicine detailing a supposed makeup and workings of the human body, adopted by Ancient Greek and Roman physicians and philosophers. Humourism began to fall out of favor in the 1850s ...

humorism
, wherein the body was thought to contain four distinct bodily fluids (associated with different temperaments), were based upon the observation of blood clotting in a transparent container. When blood is drawn in a glass container and left undisturbed for about an hour, four different layers can be seen. A dark clot forms at the bottom (the "black bile"). Above the clot is a layer of red blood cells (the "blood"). Above this is a whitish layer of white blood cells (the "phlegm"). The top layer is clear yellow serum (the "yellow bile").


Types

The ABO blood group system was discovered in the year 1900 by
Karl Landsteiner Karl Landsteiner (; 14 June 1868 – 26 June 1943) was an Austrian biologist, physician, and immunologist. He distinguished the main blood groups in 1900, having developed the modern system of classification of blood groups from his identificatio ...
.
Jan Janský Jan Janský on bronze Janského medal Prof. MUDr. Jan Janský () (3 April 1873 in Smíchov, now Prague – 8 September 1921 in Černošice, near Prague) was a Czech serologist, neurologist and psychiatrist. He is credited with the first classific ...
is credited with the first classification of blood into the four types (A, B, AB, and O) in 1907, which remains in use today. In 1907 the first
blood transfusion Blood transfusion is the process of transferring blood products into one's circulation intravenously. Transfusions are used for various medical conditions to replace lost components of the blood. Early transfusions used whole blood, but modern med ...
was performed that used the ABO system to predict compatibility. The first non-direct transfusion was performed on 27 March 1914. The Rhesus factor was discovered in 1937.


Culture and religion

Due to its importance to life, blood is associated with a large number of beliefs. One of the most basic is the use of blood as a symbol for family relationships through birth/parentage; to be "related by blood" is to be related by ancestry or descendence, rather than marriage. This bears closely to
bloodline Heredity, also called inheritance or biological inheritance, is the passing on of traits from parents to their offspring; either through asexual reproduction or sexual reproduction, the offspring cells or organisms acquire the genetic informat ...
s, and sayings such as "
blood is thicker than water Blood is thicker than water is a medieval proverb in English meaning that familial bonds will always be stronger than bonds of friendship or love. The oldest record of this saying can be traced back in the 12th century in German. History The equiva ...
" and " bad blood", as well as "
Blood brother Blood brother can refer to one of two things: a male related by birth, or two or more men not related by birth who have sworn loyalty to each other. This is in modern times usually done in a ceremony, known as a blood oath, where each person make ...
". Blood is given particular emphasis in the
Jewish Jews ( he, יְהוּדִים ISO 259-2 , Israeli pronunciation ) or Jewish people are members of an ethnoreligious group and a nation originating from the Israelites Israelite origins and kingdom: "The first act in the long drama of Jewish ...
and
Christian Christians () are people who follow or adhere to Christianity, a monotheistic Abrahamic religion based on the life and teachings of Jesus Christ. The words ''Christ'' and ''Christian'' derive from the Koine Greek title ''Christós'' (Χριστ ...
religions, because Leviticus 17:11 says "the life of a creature is in the blood." This phrase is part of the Levitical law forbidding the drinking of blood or eating meat with the blood still intact instead of being poured off. Mythic references to blood can sometimes be connected to the life-giving nature of blood, seen in such events as childbirth, as contrasted with the blood of injury or death.


Indigenous Australians

In many indigenous Australian Aboriginal peoples' traditions,
ochre Ochre ( ; from grc, ὤχρα, from , , pale), or ocher in American English, is a natural clay earth pigment which is a mixture of ferric oxide and varying amounts of clay and sand. It ranges in colour from yellow to deep orange or brown. It i ...
(particularly red) and blood, both high in iron content and considered
Maban Maban or Mabain is a material that is held to be magical in Australian Aboriginal mythology. It is the material from which the shamans and elders of indigenous Australia supposedly derive their magical powers. Notes Known as maparn among the Ngaa ...
, are applied to the bodies of dancers for ritual. As Lawlor states:
In many Aboriginal rituals and ceremonies, red ochre is rubbed all over the naked bodies of the dancers. In secret, sacred male ceremonies, blood extracted from the veins of the participant's arms is exchanged and rubbed on their bodies. Red ochre is used in similar ways in less-secret ceremonies. Blood is also used to fasten the feathers of birds onto people's bodies. Bird feathers contain a protein that is highly magnetically sensitive.
Lawlor comments that blood employed in this fashion is held by these peoples to attune the dancers to the invisible energetic realm of the Dreamtime. Lawlor then connects these invisible energetic realms and
magnetic field A magnetic field is a vector field that describes the magnetic influence on moving electric charges, electric currents, and magnetic materials. A moving charge in a magnetic field experiences a force perpendicular to its own velocity and to the ...
s, because iron is
magnetic Magnetism is a class of physical phenomena that are mediated by magnetic fields. Electric currents and the magnetic moments of elementary particles give rise to a magnetic field, which acts on other currents and magnetic moments. Magnetism is one ...

magnetic
.


European paganism

Among the
Germanic tribes This list of ancient Germanic peoples is a list of groups and alliances of ancient Germanic peoples in ancient times. These reports begin in the 2nd century BC and extend into late antiquity. Beginning with the states of the Early Middle Ages, the ...
, blood was used during their sacrifices; the ''
Blót '', by August Malmström is the term for "blood sacrifice" in Norse paganism. A ' could be dedicated to any of the Norse gods, the spirits of the land, and to ancestors. The sacrifice involved aspects of a sacramental meal or feast. The cognat ...
s''. The blood was considered to have the power of its originator, and, after the butchering, the blood was sprinkled on the walls, on the statues of the gods, and on the participants themselves. This act of sprinkling blood was called ''blóedsian'' in
Old English Old English (, ), or Anglo-Saxon, is the earliest recorded form of the English language, spoken in England and southern and eastern Scotland in the early Middle Ages. It was brought to Great Britain by Anglo-Saxon settlers in the mid-5th centur ...
, and the terminology was borrowed by the
Roman Catholic Church The Catholic Church, often referred to as the Roman Catholic Church, is the largest Christian church, with approximately 1.3 billion baptised Catholics worldwide . As the world's oldest and largest continuously functioning international ...
becoming ''to bless'' and ''blessing''. The Hittite word for blood, ''ishar'' was a cognate to words for "oath" and "bond", see
Ishara Ishara (') is an ancient deity of unknown origin from northern modern Syria. She first appeared in Ebla and was incorporated into the Hurrian pantheon, from which she found her way to the Hittite pantheon. In Hurrian and Semitic traditions, Iš ...
. The
Ancient Greeks Ancient Greece ( el, Ἑλλάς, Hellás) was a civilization belonging to a period of Greek history from the Greek Dark Ages of the 12th–9th centuries BC to the end of antiquity ( AD 600). This era was immediately followed by the Early Middle ...
believed that the blood of the gods, ''
ichor In Greek mythology, ichor (; grc, ἰχώρ) is the ethereal fluid that is the blood of the gods and/or immortals. In classical myth Ichor originates in Greek mythology, where it is the ethereal fluid that is the Greek gods' blood, sometimes said ...
'', was a substance that was poisonous to mortals. As a relic of Germanic Law, the
cruentation Cruentation (Latin: "ius cruentationis" or "Ius feretri sine sandapilae") was one of the medieval methods of finding proof against a suspected murderer. The common belief was that the body of the victim would spontaneously bleed in the presence of ...
, an ordeal where the corpse of the victim was supposed to start bleeding in the presence of the murderer, was used until the early 17th century.


Christianity

In
Genesis Genesis may refer to: Literature and comics * Genesis (DC Comics), a 1997 DC Comics crossover * Genesis (Marvel Comics), a Marvel Comics villain * Genesis, a fictional character from the ''Preacher'' comic-book series * ''Genesis'', a 1951 story ...
9:4, God prohibited
Noah In the traditions of Abrahamic religions, Noah ''Nukh''; am, ኖህ, ''Noḥ''; ar, نُوح '; grc, Νῶε ''Nôe'' () features as the tenth and last of the pre-Flood patriarchs. His story appears in the Hebrew Bible (in the Book of Genesis, ...
and his sons from eating blood (see Noahide Law). This command continued to be observed by the
Eastern Orthodox Church The Eastern Orthodox Church, officially the Orthodox Catholic Church, is the second-largest Christian church, with approximately 220 million baptised members. It operates as a communion of autocephalous churches, each governed by its bishops ...
. It is also found in the Bible that when the Angel of Death came around to the Hebrew house that the first-born child would not die if the angel saw lamb's blood wiped across the doorway. At the
Council of Jerusalem The Council of Jerusalem or Apostolic Council was held in Jerusalem around AD 50. It is unique among the ancient pre-ecumenical councils in that it is considered by Catholics and Orthodox to be a prototype and forerunner of the later ecumenica ...
, the
apostles upright=1.35, Jesus and his Twelve Apostles, Chi-Rho symbol ☧, Chi_Rho">Chi-Rho_symbol_☧,_Catacombs_of_Domitilla,_Rome.html" style="text-decoration: none;"class="mw-redirect" title="Catacombs of Domitilla">Chi Rho">Chi-Rho symbol ☧, C ...

apostles
prohibited certain Christians from consuming blood – this is documented in Acts 15:20 and 29. This chapter specifies a reason (especially in verses 19–21): It was to avoid offending Jews who had become Christians, because the Mosaic Law Code prohibited the practice. Christ's blood is the means for the
atonement Atonement (also atoning, to atone) is the concept of a person taking action to correct previous wrongdoing on their part, either through direct action to undo the consequences of that act, equivalent action to do good for others, or some other exp ...
of sins. Also, ″... the blood of Jesus Christ his odSon cleanseth us from all sin." (1 John 1:7), “... Unto him odthat loved us, and washed us from our sins in his own blood." (Revelation 1:5), and "And they overcame him (Satan) by the blood of the Lamb esus the Christ and by the word of their testimony ...” (Revelation 12:11). Some Christian churches, including Roman Catholicism,
Eastern Orthodoxy The Eastern Orthodox Church, officially the Orthodox Catholic Church, is the second-largest Christian church, with approximately 220 million baptised members. It operates as a communion of autocephalous churches, each governed by its bishops ...
,
Oriental Orthodoxy The Oriental Orthodox Churches are a group of Eastern Christian churches adhering to Miaphysite Christology, with a total of approximately 60 million members worldwide. The Oriental Orthodox Churches are broadly part of the trinitarian Nic ...
, and the
Assyrian Church of the East The Assyrian Church of the East ( syc, ܥܕܬܐ ܕܡܕܢܚܐ ܕܐܬܘܖ̈ܝܐ, ʿĒḏtā ḏ-Maḏnḥā ḏ-ʾĀṯūrāyē, ar, كنيسة المشرق الآشورية), officially the Holy Apostolic Catholic Assyrian Church of the East ( syc, ܥ ...
teach that, when consecrated, the
Eucharist The Eucharist (; also known as Holy Communion and the Lord's Supper among other names) is a Christian rite considered a sacrament in most churches, an ordinance in others. According to the New Testament, the rite was instituted by Jesus Christ ...
ic wine actually becomes the
blood of Jesus Blood of Christ in Christian theology refers to (a) the physical blood actually shed by Jesus Christ primarily on the Cross, and the salvation which Christianity teaches was accomplished thereby; or (b) the sacramental blood present in the Euchari ...
for worshippers to drink. Thus in the consecrated wine, Jesus becomes spiritually and physically present. This teaching is rooted in
the Last Supper#REDIRECT Last Supper {{Redirect category shell, 1= {{R from other capitalisation ...

the Last Supper
, as written in the four gospels of the Bible, in which Jesus stated to his Twelve Apostles, disciples that the bread that they ate was his body, and the wine was his blood. ''"This cup is the new testament in my blood, which is shed for you." ()''. Most forms of Protestantism, especially those of a Methodist or Presbyterian lineage, teach that the wine is no more than a symbol of the blood of Christ, who is spiritually but not physically present. Lutheran theology teaches that the body and blood is consubstantiation, present together "in, with, and under" the bread and wine of the Eucharistic feast.


Judaism

In Judaism, animal blood may not be consumed even in the smallest quantity (Leviticus 3:17 and elsewhere); this is reflected in Jewish diet (nutrition), dietary laws (Kashrut). Blood is purged from meat by rinsing and soaking in water (to loosen clots), salting (food), salting and then rinsing with water again several times. Eggs must also be checked and any blood spots removed before consumption. Although blood from fish is biblically kosher, it is rabbinically forbidden to consume fish blood to avoid the appearance of breaking the Biblical prohibition. Another ritual involving blood involves the covering of the blood of fowl and Game (food), game after slaughtering (Leviticus 17:13); the reason given by the Torah is: "Because the life of the animal is [in] its blood" (ibid 17:14). In relation to human beings, Kabbalah expounds on this verse that the animal soul of a person is in the blood, and that physical desires stem from it. Likewise, the mystical reason for salting temple sacrifices and slaughtered meat is to remove the blood of animal-like passions from the person. By removing the animal's blood, the animal energies and life-force contained in the blood are removed, making the meat fit for human consumption.


Islam

Consumption of food containing blood is forbidden by Islamic dietary laws. This is derived from the statement in the Qur'an, sura Al-Ma'ida (5:3): "Forbidden to you (for food) are: dead meat, blood, the flesh of swine, and that on which has been invoked the name of other than Allah." Blood is considered unclean, hence there are specific methods to obtain physical and ritual status of cleanliness once bleeding has occurred. Specific rules and prohibitions apply to menstruation, postnatal bleeding and irregular vaginal bleeding. When an animal has been slaughtered, the animal's neck is cut in a way to ensure that the spine is not severed, hence the brain may send commands to the heart to pump blood to it for oxygen. In this way, blood is removed from the body, and the meat is generally now safe to cook and eat. In modern times, blood transfusions are generally not considered against the rules.


Jehovah's Witnesses

Based on their interpretation of scriptures such as Acts 15:28, 29 ("Keep abstaining...from blood."), many Jehovah's Witnesses neither consume blood nor accept transfusions of whole blood or its major components: red blood cells, white blood cells, platelets (thrombocytes), and plasma. Members may personally decide whether they will accept medical procedures that involve their own blood or substances that are further fractionated from the four major components.


East Asian culture

In East Asian cultural sphere, south East Asian popular culture, it is often said that if a man's nose produces a small flow of blood, he is experiencing sexual desire. This often appears in Chinese-language and Hong Kong films as well as in Culture of Japan, Japanese and Culture of Korea, Korean culture parodied in anime, manga, and Korean drama, drama. Characters, mostly males, will often be shown with a epistaxis, nosebleed if they have just seen someone nude or in little clothing, or if they have had an erotic thought or fantasy; this is based on the idea that a male's blood pressure will spike dramatically when aroused.


Vampire legends

Vampires are mythical creatures that drink blood directly for sustenance, usually with a preference for human blood. Cultures all over the world have myths of this kind; for example the 'Nosferatu' legend, a human who achieves damnation and immortality by drinking the blood of others, originates from Eastern European folklore. Ticks, leeches, female mosquitoes, vampire bats, and an assortment of other natural creatures do consume the blood of other animals, but only bats are associated with vampires. This has no relation to vampire bats, which are new world creatures discovered well after the origins of the European myths.


Applications


In the applied sciences

Blood residue can help forensic investigators identify weapons, reconstruct a criminal action, and link suspects to the crime. Through bloodstain pattern analysis, forensic information can also be gained from the spatial distribution of bloodstains. Blood residue analysis is also a technique used in archeology.


In art

Blood is one of the body fluids that has been used in art."Nostalgia"
Artwork in blood
In particular, the performances of Viennese Actionism, Viennese Actionist Hermann Nitsch, Istvan Kantor, Franko B, Lennie Lee, Ron Athey, Yang Zhichao, Justice Yeldham, Lucas Abela and Kira O'Reilly, along with the photography of Andres Serrano, have incorporated blood as a prominent visual element. Marc Quinn has made sculptures using frozen blood, including a cast of his own head made using his own blood.


In genealogy and family history

The term ''blood'' is used in Genealogy, genealogical circles to refer to one's Ancestor, ancestry, Human evolution, origins, and Ethnic group, ethnic background as in the word ''Heredity, bloodline''. Other terms where blood is used in a family history sense are ''Nobility#"Blue" blood, blue-blood'', ''Royal descent, royal blood'', ''mixed-blood'' and ''Kinship terminology, blood relative''.


See also

* Autotransfusion * Blood as food * Blood pressure * Blood substitutes ("artificial blood") * Blood test * Blood phobia, Hemophobia * Luminol, a visual test for blood left at crime scenes. * Oct-1-en-3-one ("Smell" of blood) * Taboo food and drink#Blood, Taboo food and drink: Blood


References


External links


Blood Groups and Red Cell Antigens.
Free online book at National Center for Biotechnology Information, NCBI Bookshelf ID: NBK2261 *
Blood Photomicrographs
{{Authority control Blood, Hematology Tissues (biology) Articles containing video clips