Blood is a
body fluid
Body fluids, bodily fluids, or biofluids, sometimes body liquids, 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 (52-55% ...
in the
circulatory system
The blood circulatory system is a system of organs that includes the heart, blood vessels, and blood which is circulated throughout the entire body of a human or other vertebrate. It includes the cardiovascular system, or vascular system, tha ...
of
humans
Humans (''Homo sapiens'') are the most abundant and widespread species of primate, characterized by bipedalism and exceptional cognitive skills due to a large and complex brain. This has enabled the development of advanced tools, culture, ...
and other
vertebrate
Vertebrates () comprise all animal taxa within the subphylum Vertebrata () (chordates with backbones), including all mammals, birds, reptiles, amphibians, and fish. Vertebrates represent the overwhelming majority of the phylum Chordata, with c ...
s that delivers necessary substances such as
nutrients 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 ...
to the
cells, and transports
metabolic waste products away from those same cells. Blood in the circulatory system is also known as ''peripheral blood'', and the
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 it carries, ''peripheral blood cells''.
Blood is composed of blood cells suspended in
blood plasma
Blood plasma is a light amber-colored liquid component of blood in which blood cells are absent, but contains proteins and other constituents of whole blood in suspension. It makes up about 55% of the body's total blood volume. It is the intr ...
. Plasma, which constitutes 55% of blood fluid, is mostly water (92% by volume), and contains
protein
Proteins are large biomolecules and macromolecules that comprise one or more long chains of amino acid residues. Proteins perform a vast array of functions within organisms, including catalysing metabolic reactions, DNA replication, res ...
s,
glucose
Glucose is a simple sugar with the molecular formula . Glucose is overall the most abundant monosaccharide, a subcategory of carbohydrates. Glucose is mainly made by plants and most algae during photosynthesis from water and carbon dioxide, u ...
, mineral
ion
An ion () is an atom or molecule with a net electrical charge.
The charge of an electron is considered to be negative by convention and this charge is equal and opposite to the charge of a proton, which is considered to be positive by conve ...
s,
hormone
A hormone (from the Greek participle , "setting in motion") is a class of signaling molecules in multicellular organisms that are sent to distant organs by complex biological processes to regulate physiology and behavior. Hormones are require ...
s,
carbon dioxide
Carbon dioxide ( chemical formula ) is a chemical compound made up of molecules that each have one carbon atom covalently double bonded to two oxygen atoms. It is found in the gas state at room temperature. In the air, carbon dioxide is trans ...
(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 ...
is the main protein in plasma, and it functions to regulate the
colloidal
osmotic pressure 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 "holl ...
s (also called RBCs or erythrocytes),
white blood cells (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 i ...
s (also called thrombocytes). The most abundant cells in vertebrate blood are red blood cells. These contain
hemoglobin
Hemoglobin (haemoglobin BrE) (from the Greek word αἷμα, ''haîma'' 'blood' + Latin ''globus'' 'ball, sphere' + ''-in'') (), abbreviated Hb or Hgb, is the iron-containing oxygen-transport metalloprotein present in red blood cells (erythrocyt ...
, 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 gre ...
gas thereby increasing its solubility in blood. In contrast, carbon dioxide is mostly transported
extracellular
This glossary of biology terms is a list of definitions of fundamental terms and concepts used in biology, the study of life and of living organisms. It is intended as introductory material for novices; for more specific and technical definitions ...
ly as
bicarbonate
In inorganic chemistry, bicarbonate (IUPAC-recommended nomenclature: hydrogencarbonate) is an intermediate form in the deprotonation of carbonic acid. It is a polyatomic anion with the chemical formula .
Bicarbonate serves a crucial biochem ...
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 decapods, seed shrimp, branchiopods, fish lice, krill, remipedes, isopods, barnacles, copepods, amphipods and mantis shrimp. The crustacean group can ...
s and
mollusk
Mollusca is the second-largest phylum of invertebrate animals after the Arthropoda, the members of which are known as molluscs or mollusks (). Around 85,000 extant species of molluscs are recognized. The number of fossil species is e ...
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 ...
instead of blood, the difference being that hemolymph is not contained in a closed
circulatory system
The blood circulatory system is a system of organs that includes the heart, blood vessels, and blood which is circulated throughout the entire body of a human or other vertebrate. It includes the cardiovascular system, or vascular system, tha ...
. 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 known 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
Arthropods (, (gen. ποδός)) are invertebrate animals with an exoskeleton, a segmented body, and paired jointed appendages. Arthropods form the phylum Arthropoda. They are distinguished by their jointed limbs and cuticle made of chiti ...
s, using hemolymph, have
hemocytes 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 splint ...
.
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 ...
s by the pumping action of the
heart
The heart is a muscular organ in most animals. This organ 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 t ...
. In animals with
lungs,
arterial
An artery (plural arteries) () is a blood vessel in humans and most animals 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 pu ...
blood carries oxygen from inhaled air to the tissues of the body, and
venous
Veins are blood vessels in humans and most other animals 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 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 functions of metabolism are: the conversion of the energy in food to energy available to run c ...
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 () is the branch of biology concerned with the study of the structure of organisms and their parts. Anatomy is a branch of natural science that deals with the structural organization of living things. It is an old science, having 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 vi ...
, blood is considered a specialized form of
connective tissue,
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, produced 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 cl ...
.
Functions
![1GZX Haemoglobin](https://upload.wikimedia.org/wikipedia/commons/3/3d/1GZX_Haemoglobin.png)
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 ...
to tissues (bound to
hemoglobin
Hemoglobin (haemoglobin BrE) (from the Greek word αἷμα, ''haîma'' 'blood' + Latin ''globus'' 'ball, sphere' + ''-in'') (), abbreviated Hb or Hgb, is the iron-containing oxygen-transport metalloprotein present in red blood cells (erythrocyt ...
, which is carried in red cells)
* Supply of nutrients such as
glucose
Glucose is a simple sugar with the molecular formula . Glucose is overall the most abundant monosaccharide, a subcategory of carbohydrates. Glucose is mainly made by plants and most algae during photosynthesis from water and carbon dioxide, u ...
,
amino acid
Amino acids are organic compounds that contain both amino and carboxylic acid functional groups. Although hundreds of amino acids exist in nature, by far the most important are the alpha-amino acids, which comprise proteins. Only 22 alpha a ...
s, and
fatty acid
In chemistry, particularly in biochemistry, a fatty acid is a carboxylic acid with an aliphatic chain, which is either saturated or unsaturated. Most naturally occurring fatty acids have an unbranched chain of an even number of carbon atoms, ...
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 p ...
(e.g.,
blood lipid
Blood lipids (or blood fats) are lipids in the blood, either free or bound to other molecules. They are mostly transported in a protein capsule, and the density of the lipids and type of protein determines the fate of the particle and its influence ...
s))
* Removal of waste such as
carbon dioxide
Carbon dioxide ( chemical formula ) is a chemical compound made up of molecules that each have one carbon atom covalently double bonded to two oxygen atoms. It is found in the gas state at room temperature. In the air, carbon dioxide is trans ...
,
urea
Urea, also known as carbamide, is an organic compound with chemical formula . This amide has two amino groups (–) joined by a carbonyl functional group (–C(=O)–). It is thus the simplest amide of carbamic acid.
Urea serves an important ...
, and
lactic acid
Lactic acid is an organic acid. It has a molecular formula . 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 well as nat ...
* Immunological functions, including circulation of
white blood cells, and detection of foreign material by
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 mechanis ...
, 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 a class of signaling molecules in multicellular organisms that are sent to distant organs by complex biological processes to regulate physiology and behavior. Hormones are require ...
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 counte ...
functions
Constituents
In mammals
Blood accounts for 7% of the human body weight,
with an average density around 1060 kg/m
3, very close to pure water's density of 1000 kg/m
3. The average adult has a
blood volume 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 "holl ...
s, (erythrocytes) and
white blood cells (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 i ...
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
A non-Newtonian fluid is a fluid that does not follow Newton's law of viscosity, i.e., constant viscosity independent of stress. In non-Newtonian fluids, viscosity can change when under force to either more liquid or more solid. Ketchup, for exa ...
fluid dynamics.
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 (Fe2+/Fe3+) and calcium ions (Ca2+), forming water-soluble complexes ev ...
-anticoagulated blood.
Left tube: after standing, the RBCs have settled at the bottom of the tube.
Right tube: Freshly drawn blood
Cells
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 "holl ...
s: Red blood cells contain the blood's
hemoglobin
Hemoglobin (haemoglobin BrE) (from the Greek word αἷμα, ''haîma'' 'blood' + Latin ''globus'' 'ball, sphere' + ''-in'') (), abbreviated Hb or Hgb, is the iron-containing oxygen-transport metalloprotein present in red blood cells (erythrocyt ...
and distribute oxygen. Mature red blood cells lack a
nucleus
Nucleus ( : 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
Nucl ...
and
organelles in mammals. The red blood cells (together with
endothelial
The 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 ...
vessel cells and other cells) are also marked by
glycoproteins that define the different
blood types
Blood is a body fluid in the circulatory system of humans and other vertebrates that delivers necessary substances such as nutrients and oxygen to the cells, and transports metabolic waste products away from those same cells. Blood in the ...
. 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 (RBCs) in blood, measured as part of a blood test. The measurement depends on the number and size of red blood cells. It is norm ...
, 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
leukocytes:
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 splint ...
; they destroy and remove old or aberrant cells and cellular debris, as well as attack infectious agents (
pathogen
In biology, a pathogen ( el, πάθος, "suffering", "passion" and , "producer of") in the oldest and broadest sense, is any organism or agent that can produce disease. A pathogen may also be referred to as an infectious agent, or simply a germ ...
s) and foreign substances. The cancer of leukocytes is called
leukemia
Leukemia ( also spelled leukaemia and pronounced ) 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 ...
.
* 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 in ...
:
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 i ...
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 mechanis ...
). Fibrin from the coagulation cascade creates a mesh over the
platelet plug
The platelet plug, also known as the hemostatic plug or platelet thrombus, is an aggregation of platelets formed during early stages of hemostasis in response to one or more injuries to blood vessel walls. After platelets are recruited and begi ...
.
Plasma
About 55% of blood is
blood plasma
Blood plasma is a light amber-colored liquid component of blood in which blood cells are absent, but contains proteins and other constituents of whole blood in suspension. It makes up about 55% of the body's total blood volume. It is the intr ...
, 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 re ...
solution containing 92% water, 8% blood plasma
protein
Proteins are large biomolecules and macromolecules that comprise one or more long chains of amino acid residues. Proteins perform a vast array of functions within organisms, including catalysing metabolic reactions, DNA replication, res ...
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 overall the most abundant monosaccharide, a subcategory of carbohydrates. Glucose is mainly made by plants and most algae during photosynthesis from water and carbon dioxide, u ...
,
amino acid
Amino acids are organic compounds that contain both amino and carboxylic acid functional groups. Although hundreds of amino acids exist in nature, by far the most important are the alpha-amino acids, which comprise proteins. Only 22 alpha a ...
s, and
fatty acid
In chemistry, particularly in biochemistry, a fatty acid is a carboxylic acid with an aliphatic chain, which is either saturated or unsaturated. Most naturally occurring fatty acids have an unbranched chain of an even number of carbon atoms, ...
s (dissolved in the blood or bound to plasma proteins), and removes waste products, such as
carbon dioxide
Carbon dioxide ( chemical formula ) is a chemical compound made up of molecules that each have one carbon atom covalently double bonded to two oxygen atoms. It is found in the gas state at room temperature. In the air, carbon dioxide is trans ...
,
urea
Urea, also known as carbamide, is an organic compound with chemical formula . This amide has two amino groups (–) joined by a carbonyl functional group (–C(=O)–). It is thus the simplest amide of carbamic acid.
Urea serves an important ...
, and
lactic acid
Lactic acid is an organic acid. It has a molecular formula . 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 well as nat ...
.
Other important
components include:
*
Serum albumin
Serum albumin, often referred to simply as blood albumin, is an albumin (a type of globular protein) found in vertebrate blood. Human serum albumin is encoded by the ''ALB'' gene. Other mammalian forms, such as bovine serum albumin, are chemica ...
* 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 mechanis ...
)
* Immunoglobulins (
antibodies)
*
lipoprotein
A lipoprotein is a biochemical assembly whose primary function is to transport hydrophobic lipid (also known as fat) molecules in water, as in blood plasma or other extracellular fluids. They consist of a triglyceride and cholesterol center, su ...
particles
* Various other
protein
Proteins are large biomolecules and macromolecules that comprise one or more long chains of amino acid residues. Proteins perform a vast array of functions within organisms, including catalysing metabolic reactions, DNA replication, res ...
s
* Various
electrolytes (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 ...
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 sa ...
)
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 ...
.
pH values
Blood pH
Blood is a body fluid in the circulatory system of humans and other vertebrates that delivers necessary substances such as nutrients and oxygen to the cells, and transports metabolic waste products away from those same cells. Blood in the ...
is regulated to stay within the narrow range of 7.35 to 7.45, making it slightly
basic (compensation).
Extra-cellular fluid in blood that has a pH below 7.35 is too
acidic, whereas blood pH above 7.45 is too basic.
A pH below 6.9 or above 7.8 is usually lethal.
Blood pH,
partial pressure of oxygen (pO2),
partial pressure of carbon dioxide (pCO2), and
bicarbonate
In inorganic chemistry, bicarbonate (IUPAC-recommended nomenclature: hydrogencarbonate) is an intermediate form in the deprotonation of carbonic acid. It is a polyatomic anion with the chemical formula .
Bicarbonate serves a crucial biochem ...
(HCO
3−) 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 ...
and the
urinary system
The urinary system, also known as the urinary tract or renal system, 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, c ...
to control the
acid–base balance and respiration, which is called compensation.
An
arterial blood gas test
An arterial blood gas (ABG) test, or arterial blood gas analysis (ABGA) 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 an ...
measures these. Plasma also circulates
hormone
A hormone (from the Greek participle , "setting in motion") is a class of signaling molecules in multicellular organisms that are sent to distant organs by complex biological processes to regulate physiology and behavior. Hormones are require ...
s transmitting their messages to various tissues. The list of normal
reference ranges
In medicine and health-related fields, a reference range or reference interval is the range or the interval of values that is deemed normal for a physiological measurement in healthy persons (for example, the amount of creatinine in the blood, o ...
for various blood electrolytes is extensive.
In non-mammalian vertebrates
![Newbloodm](https://upload.wikimedia.org/wikipedia/commons/e/ed/Newbloodm.jpg)
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 monom ...
, 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 in ...
are responsible for blood clotting instead.
Physiology
Circulatory system
![Diagram of the human heart (cropped)](https://upload.wikimedia.org/wikipedia/commons/e/e5/Diagram_of_the_human_heart_%28cropped%29.svg)
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 ...
s by the pumping action of the
heart
The heart is a muscular organ in most animals. This organ 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 t ...
. 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 towards the peripheral beds within the body and lungs. The blood pumped by a ventricle is supplied by an atrium, an adjacent chamber in the uppe ...
of the heart through
arteries
An artery (plural arteries) () is a blood vessel in humans and most animals 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 pu ...
to peripheral
tissues and returns to the right
atrium of the heart through
vein
Veins are blood vessels in humans and most other animals 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 oxygenat ...
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 ...
to the
lungs 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 vei ...
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
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 to the lungs via the pulmonary artery wh ...
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 functions of metabolism are: the conversion of the energy in food to energy available to run c ...
by
cells, 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 muscles, which can compress veins and push blood through the valves in veins toward the
right atrium
The atrium ( la, ātrium, , entry hall) is one of two upper chambers in the heart that receives blood from the circulatory system. The blood in the atria is pumped into the heart ventricles through the atrioventricular valves.
There are two at ...
.
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 propert ...
in 1628.
Cell production and degradation
In vertebrates, the various cells of blood are made in the
bone marrow 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
Erythropoiesis (from Greek 'erythro' meaning "red" and 'poiesis' "to make") is the process which produces red blood cells (erythrocytes), which is the development from erythropoietic stem cell to mature red blood cell.
It is stimulated by decrea ...
, 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 to specific foreign invaders. ...
gland, found in the
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 distinguished from other lymphocytes by the presence of a T-cell rec ...
.
The proteinaceous component of blood (including clotting proteins) is produced predominantly by the
liver
The liver is a major organ only found in vertebrates which performs many essential biological functions such as detoxification of the organism, and the synthesis of proteins and biochemicals necessary for digestion and growth. In humans, it ...
, 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, ...
s and the watery fraction is regulated by the
hypothalamus
The hypothalamus () is a part of the brain that contains a number of small nuclei with a variety of functions. One of the most important functions is to link the nervous system to the endocrine system via the pituitary gland. The hypothalamu ...
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; blo ...
.
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 "holl ...
have a plasma life of about 120 days before they are degraded by the
spleen
The spleen is an organ found in almost 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 the liver within the lumen of the liver sinusoids and are adhesive to their endothelial cells which make up the blood vessel walls. Ku ...
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 ...
.
Oxygen transport
![Oxyhaemoglobin dissociation curve](https://upload.wikimedia.org/wikipedia/commons/8/8a/Oxyhaemoglobin_dissociation_curve.png)
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 ...
in a sample of arterial blood in a healthy human breathing air at sea-level pressure is chemically combined with the
hemoglobin
Hemoglobin (haemoglobin BrE) (from the Greek word αἷμα, ''haîma'' 'blood' + Latin ''globus'' 'ball, sphere' + ''-in'') (), abbreviated Hb or Hgb, is the iron-containing oxygen-transport metalloprotein present in red blood cells (erythrocyt ...
. 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
mammals and many other species (for exceptions, see below). Hemoglobin has an oxygen binding capacity between 1.36 and 1.40 ml O
2 per gram hemoglobin, which increases the total
blood oxygen capacity
Blood is a body fluid in the circulatory system of humans and other vertebrates that delivers necessary substances such as nutrients and oxygen to the cells, and transports metabolic waste products away from those same cells. Blood in the cir ...
seventyfold,
compared to if oxygen solely were carried by its solubility of 0.03 ml O
2 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 ...
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 cells) and are the primar ...
s and capillaries
A capillary is a small blood vessel from 5 to 10 micrometres (μm) in diameter. Capillaries are composed of only the tunica intima, consisting of a thin wall of simple squamous endothelial cells. They are the smallest blood vessels in the body: ...
, 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 t ...
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/min[Edwards 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 that develops from an animal embryo. Following embryonic development the fetal stage of development takes place. In human prenatal development, fetal dev ...
, receiving oxygen via the placenta
The placenta is a temporary embryonic and later 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 mate ...
, 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
Fetal hemoglobin, or foetal haemoglobin (also hemoglobin F, HbF, or α2γ2) is the main oxygen carrier protein in the human fetus. Hemoglobin F is found in fetal red blood cells, and is involved in transporting oxygen from the mother's bloodstream ...
) 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 in the red blood cells by the reaction ; about 7% is dissolved in the plasma; and about 23% is bound to hemoglobin as carbamino 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 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, 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.
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, , 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 tissues ...
, 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 righ ...
, which drains into the left subclavian vein, 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 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 of that tissue; examples are the erectile tissue Erectile 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 d ...
and clitoris.
Another example of a hydraulic function is the jumping spider
Jumping spiders are a group of spiders that constitute the family Salticidae. As of 2019, this family contained over 600 described genera and over 6,000 described species, making it the largest family of spiders at 13% of all species. Jumping spi ...
, 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 ...
) 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 decapods, seed shrimp, branchiopods, fish lice, krill, remipedes, isopods, barnacles, copepods, amphipods and mantis shrimp. The crustacean group can ...
s and mollusks. 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 ...
s (sea squirts) might use vanabins
Vanabins (also known as vanadium-associated proteins or vanadium chromagen) are a group of vanadium-binding proteins. metalloproteins. Vanabins are found almost exclusively in the blood cells, or vanadocytes, of some tunicates (sea squirts), inclu ...
(proteins containing vanadium) for respiratory pigment A respiratory pigment is a metalloprotein that serves a variety of important functions, its main being O2 transport. Other functions performed include O2 storage, CO2 transport, and transportation of substances other than respiratory gases. There ar ...
(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 quantifies the inte ...
or damaging blood filtering organs like the kidneys.
Giant tube worm
''Riftia pachyptila'', commonly known as the giant tube worm and less commonly known as the Giant beardworm, is a marine invertebrate in the phylum Annelida (formerly grouped in phylum Pogonophora and Vestimentifera) related to tube worm ...
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 animal taxa within the subphylum Vertebrata () (chordates with backbones), including all mammals, birds, reptiles, amphibians, and fish. Vertebrates represent the overwhelming majority of the phylum Chordata, with c ...
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 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 is bright red, because carbon monoxide causes the formation of carboxyhemoglobin. In cyanide poisoning, the body cannot use 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. If the heme is oxidized, methemoglobin, which is more brownish and cannot transport oxygen, is formed. In the rare condition sulfhemoglobinemia, 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 visual perception, color perception are related to the light-scattering properties of the skin and the processing of visual input by the visual cortex, rather than the actual color of the venous blood.
Skinks in the genus ''Prasinohaema'' have green blood due to a buildup of the waste product biliverdin.
Hemocyanin
The blood of most mollusks – including cephalopods and gastropods – as well as some arthropods, such as horseshoe crabs, 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, which is in contrast to the intracellular oxygen transport in mammals by hemoglobin in RBCs.
Chlorocruorin
The blood of most annelid worms and some marine polychaetes 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 sipunculids, priapulids, brachiopods, and the annelid worm, magelona. Hemerythrin is violet-pink when oxygenated.[
]
Hemovanadin
The blood of some species of Ascidiacea, ascidians and tunicates, also known as sea squirts, contains proteins called vanadins. These proteins are based on vanadium, 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 (circulatory), shock sets in. Thrombocytes 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 mechanis ...
and the formation of blood clots, which can stop bleeding. Trauma to the internal organs or bones can cause internal bleeding, which can sometimes be severe.
** Dehydration can reduce the blood volume by reducing the water content of the blood. This would rarely result in shock (circulatory), shock (apart from the very severe cases) but may result in orthostatic hypotension and fainting.
* Disorders of circulation
** Shock is the ineffective perfusion of tissues, and can be caused by a variety of conditions including blood loss, infection, poor cardiac output.
** 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, Hypertension, high blood pressure, excess circulating lipids (hyperlipidemia), and diabetes mellitus.
** Coagulation can form a 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), which can occur when the blood supply has been blocked (or is very inadequate).
Hematological
* Anemia
** Insufficient red cell mass (anemia) can be the result of bleeding, blood disorders like thalassemia, or Illnesses related to poor nutrition, nutritional deficiencies, and may require one or more blood transfusions. Anemia can also be due to a genetic disorder in which the red blood cells do not function effectively. Anemia can be confirmed by a 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 banks to fill the demand for transfusable blood. A person receiving a blood transfusion must have a blood type compatible with that of the donor.
** Sickle-cell anemia
* Disorders of cell proliferation
** Leukemia is a group of cancer (medicine), cancers of the blood-forming tissues and cells.
** Non-cancerous overproduction of red cells (polycythemia vera) or platelets (essential thrombocytosis) may be Premalignant condition, premalignant.
** Myelodysplastic syndromes involve ineffective production of one or more cell lines.
* Disorders of coagulation
** Hemophilia is a Genetic disorder, genetic illness that causes dysfunction in one of the blood's coagulation, clotting mechanisms. This can allow otherwise inconsequential wounds to be life-threatening, but more commonly results in hemarthrosis, or bleeding into joint spaces, which can be crippling.
** Ineffective or insufficient platelets can also result in coagulopathy (bleeding disorders).
** Hypercoagulable state (thrombophilia) 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 and Hepatitis C, C are transmitted primarily through blood contact. Owing to blood-borne infections, bloodstained objects are treated as a Biological hazard, biohazard.
** Bacterial infection of the blood is bacteremia or sepsis. Viral Infection is viremia. Malaria and trypanosomiasis 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
Transfusion
Blood for transfusion is obtained from human donors by blood donation and stored in a blood bank. There are many different blood types in humans, the ABO blood group system, and the Rhesus blood group system being the most important. Transfusion of blood of an incompatible blood group may cause severe, often fatal, complications, so crossmatching is done to ensure that a compatible blood product is transfused.
Other blood products administered intravenously are platelets, blood plasma, cryoprecipitate, and specific coagulation factor concentrates.
Intravenous administration
Many forms of medication (from antibiotics to chemotherapy) 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, 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.
Letting
In modern evidence-based medicine, bloodletting is used in management of a few rare diseases, including hemochromatosis and polycythemia. However, bloodletting and Hirudotherapy, 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 Hippocrates, Hippocratic medicine.
Etymology
English ''blood'' (Old English ''blod'') derives from Germanic languages, Germanic 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 Proto-Indo-European language, Indo-European etymology.
History
Classical Greek medicine
Robin Fåhræus (a Swedish physician who devised the erythrocyte sedimentation rate) suggested that the Ancient Greek system of 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. Jan Janský 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 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 bloodlines, and sayings such as "blood is thicker than water" and "wikt:bad blood, bad blood", as well as "Blood brother".
Blood is given particular emphasis in the Judaism, Jewish and Christianity, Christian 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 Australians, indigenous Australian Aboriginal peoples' traditions, ochre (particularly red) and blood, both high in iron content and considered Maban, are applied to the bodies of dancers for ritual. As Lawlor states: 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 fields, because iron is magnetism, magnetic.
European paganism
Among the Germanic peoples, Germanic tribes, blood was used during their sacrifices; the ''Blóts''. 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 language, Old English, and the terminology was borrowed by the Roman Catholic Church becoming ''to bless'' and ''blessing''. The Hittite language, Hittite word for blood, ''ishar'' was a cognate to words for "oath" and "bond", see Ishara.
The Ancient Greece, Ancient Greeks believed that the blood of the gods, ''ichor'', was a substance that was poisonous to mortals.
As a relic of Germanic Law, the cruentation, 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 Book of Genesis, Genesis 9:4, God prohibited Noah and his sons from eating blood (see Noahide Law). This command continued to be observed by the Eastern Orthodox Church.
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 Apostles in the New Testament, 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 in Christianity, atonement of sins. Also, "... the blood of Jesus Christ his [God] Son cleanseth us from all sin." (1 John 1:7), "... Unto him [God] that 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 [Jesus the Christ], and by the word of their testimony ..." (Revelation 12:11).
Some Christian churches, including Roman Catholicism, Eastern Orthodox Church, Eastern Orthodoxy, Oriental Orthodoxy, and the Assyrian Church of the East teach that, when consecrated, the Eucharistic wine transubstantiation, actually becomes the Blood of Christ, blood of Jesus for worshippers to drink. Thus in the consecrated wine, Jesus becomes spiritually and physically present. This teaching is rooted in 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.
Vampirism
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.
Other uses
Forensic and archaeological
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.
Artistic
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.
Genealogical
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
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Blood Photomicrographs
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Blood,
Hematology
Tissues (biology)
Articles containing video clips