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The blood vessels are the components of the
circulatory system The circulatory system, also called the cardiovascular system or the vascular system, is an organ system An organ system is a biological system A biological system is a complex biological network, network which connects several biologically ...
that transport
blood Blood is a body fluid Body fluids, bodily fluids, or biofluids are liquid A liquid is a nearly incompressible In fluid mechanics or more generally continuum mechanics, incompressible flow (isochoric process, isochoric flow) refers t ...

blood
throughout the
human body The human body is the structure of a human being Humans (''Homo sapiens'') are the most abundant and widespread species In biology, a species is the basic unit of biological classification, classification and a taxonomic rank of ...

human body
. These vessels transport blood cells, nutrients, and oxygen to the tissues of the body. They also take waste and carbon dioxide away from the tissues. Blood vessels are needed to sustain life, because all of the body's tissues rely on their functionality. There are five types of blood vessels: the
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 arteries, pulmonary ...

arteries
, which carry the blood away from the
heart The heart is a cardiac muscle, muscular Organ (biology), 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 ...

heart
; the
arteriole An arteriole is a small-diameter blood vessel The blood vessels are the components of the circulatory system The circulatory system, also called the cardiovascular system or the vascular system, is an organ system that permits blood to c ...

arteriole
s; the
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 microvessel ...

capillaries
, where the exchange of water and chemicals between the blood and the tissues occurs; the
venule A venule is a very small 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 a ...
s; and the
vein Veins are blood vessels The blood vessels are the components of the circulatory system The circulatory system, also called the cardiovascular system or the vascular system, is an Biological system, organ system that permits blood to circu ...

vein
s, which carry blood from the capillaries back towards the heart. The word ''vascular'', meaning relating to the blood vessels, is derived from the Latin ''vas'', meaning vessel. Some structures – such as
cartilage Cartilage (cartilaginous tissue) is a resilient and smooth elastic tissue Elastic fibers (or yellow fibers) are an essential component of the extracellular matrix In biology Biology is the natural science that studies life and living org ...

cartilage
, the
epithelium Epithelium is one of the four basic types of animal Animals (also called Metazoa) are multicellular eukaryotic organisms that form the Kingdom (biology), biological kingdom Animalia. With few exceptions, animals Heterotroph, consume ...
, and the
lens A lens is a transmissive optical Optics is the branch of physics Physics is the natural science that studies matter, its Elementary particle, fundamental constituents, its Motion (physics), motion and behavior through Spacetime, s ...
and
cornea The cornea is the transparent Transparency, transparence or transparent most often refer to transparency and translucency, the physical property of allowing the transmission of light through a material. They may also refer to: Literal uses * ...

cornea
of the eye – do not contain blood vessels and are labeled ''avascular''.


Structure

The arteries and veins have three layers. The middle layer is thicker in the arteries than it is in the veins: * The inner layer, ''
tunica intima The tunica intima (New Latin New Latin (also called Neo-Latin or modern Latin) is the revival of Latin Latin (, or , ) is a classical language belonging to the Italic branch of the Indo-European languages. Latin was originally spok ...
'', is the thinnest layer. It is a single layer of flat cells (
simple squamous epithelium A simple squamous epithelium, also known as pavement epithelium, and tessellated epithelium is a single layer of flattened, polygonal cells in contact with the basal lamina The basal lamina is a layer of extracellular matrix In biology Bi ...

simple squamous epithelium
) glued by a
polysaccharide Polysaccharides (), or polycarbohydrates, are the most abundant found in . They are long chain carbohydrates composed of units bound together by . This carbohydrate can react with water () using as catalyst, which produces constituent sugars ...
intercellular matrix, surrounded by a thin layer of subendothelial
connective tissue Connective tissue is one of the many basic types of animal Animals (also called Metazoa) are multicellular eukaryotic organisms that form the Kingdom (biology), biological kingdom Animalia. With few exceptions, animals Heterotroph, consum ...
interlaced with a number of circularly arranged elastic bands called the ''
internal elastic lamina Micrograph showing the internal elastic lamina (thin pink wavy line - image edge mid-left to image edge bottom-centre-left). H&E stain. The internal elastic lamina or internal elastic lamella is a layer of elastic tissue that forms the outermost pa ...
''. A thin membrane of elastic fibers in the tunica intima run parallel to the vessel. * The middle layer ''
tunica media The tunica media (New Latin "middle coat"), or media for short, is the middle tunica (biology), tunica (layer) of an artery or vein. It lies between the tunica intima on the inside and the tunica externa on the outside. Artery Tunica media is made ...
'' is the thickest layer in arteries. It consists of circularly arranged elastic fiber, connective tissue, polysaccharide substances, the second and third layer are separated by another thick elastic band called external elastic lamina. The tunica media may (especially in arteries) be rich in
vascular smooth muscle Vascular smooth muscle is the type of smooth muscle that makes up most of the walls of blood vessels. Structure Vascular smooth muscle refers to the particular type of smooth muscle found within, and composing the majority of the wall of blood ...
, which controls the caliber of the vessel. Veins don't have the external elastic lamina, but only an internal one. The tunica media is thicker in the arteries rather than the veins. * The outer layer is the ''
tunica adventitia The tunica externa (New Latin New Latin (also called Neo-Latin or Modern Latin) is the revival of Latin Latin (, or , ) is a classical language belonging to the Italic languages, Italic branch of the Indo-European languages. Latin was orig ...
'' and the thickest layer in veins. It is entirely made of connective tissue. It also contains
nerve A nerve is an enclosed, cable-like bundle of fibers (called axon An axon (from Greek ἄξων ''áxōn'', axis), or nerve fiber (or nerve fibre: see American and British English spelling differences#-re, -er, spelling differences), is a long, ...

nerve
s that supply the vessel as well as nutrient capillaries (
vasa vasorum Vasa may refer to: Places * Vaşa, Azerbaijan * Vasa County, a historic county in modern-day Finland * Vaasa or Vasa, Finland * Vasa, Rajasthan, a village in Sirohi District, Rajasthan, India * Vasa, Palghar, a village in Maharashtra, India * Väs ...

vasa vasorum
) in the larger blood vessels.
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 microvessel ...

Capillaries
consist of a single layer of
endothelial cell Endothelium is a single layer of squamous Epithelium () is one of the four basic types of animal Animals (also called Metazoa) are multicellular eukaryotic organisms that form the Kingdom (biology), biological kingdom Animalia. With ...
s with a supporting subendothelium consisting of a
basement membrane The basement membrane is a thin, pliable sheet-like type of extracellular matrix In biology Biology is the natural science that studies life and living organisms, including their anatomy, physical structure, Biochemistry, chemical processes ...
and
connective tissue Connective tissue is one of the many basic types of animal Animals (also called Metazoa) are multicellular eukaryotic organisms that form the Kingdom (biology), biological kingdom Animalia. With few exceptions, animals Heterotroph, consum ...
. When blood vessels connect to form a region of diffuse vascular supply it is called an
anastomosis An anastomosis (plural anastomoses) is a connection or opening between two things (especially cavities or passages) that are normally diverging or branching, such as between blood vessel The blood vessels are the components of the circulator ...
. Anastomoses provide critical alternative routes for blood to flow in case of blockages. Leg veins have valves which prevent backflow of the blood being pumped against gravity by the surrounding muscles.


Types

There are various kinds of blood vessels: *
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 arteries, pulmonary ...

Arteries
* Elastic arteries *
Distributing arteriesA muscular artery (or distributing artery) is a medium-sized artery that draws blood from an elastic artery and branches into "resistance vessels" including small arteries and arterioles. Their walls contain larger number of smooth muscles, allowing ...
*
Arteriole An arteriole is a small-diameter blood vessel The blood vessels are the components of the circulatory system The circulatory system, also called the cardiovascular system or the vascular system, is an organ system that permits blood to c ...

Arteriole
s *
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 microvessel ...

Capillaries
(smallest blood vessels) *
Venule A venule is a very small 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 a ...
s *
Vein Veins are blood vessels The blood vessels are the components of the circulatory system The circulatory system, also called the cardiovascular system or the vascular system, is an Biological system, organ system that permits blood to circu ...

Vein
s ** Large collecting vessels, such as the
subclavian vein The subclavian vein is a paired large vein Veins are blood vessels The blood vessels are the components of the circulatory system The circulatory system, also called the cardiovascular system or the vascular system, is an Biological sys ...
, the
jugular vein The jugular veins are 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 vein, pulmonary and umbilical veins, both of which carry ...
, the
renal vein The renal veins are veins that drain the kidney. They connect the kidney to the inferior vena cava. They carry the Human Blood, blood filtered by the kidney. Structure There is one vein per kidney, that divides into 4 divisions upon entering the k ...
and the iliac vein. **
Venae cavae The venae cavae (; from the Latin Latin (, or , ) is a classical language belonging to the Italic languages, Italic branch of the Indo-European languages. Latin was originally spoken in the area around Rome, known as Latium. Through the power ...
(the two largest veins, carry blood into the heart). * Sinusoids ** Extremely small vessels located within bone marrow, the spleen, and the liver. They are roughly grouped as "arterial" and "venous", determined by whether the blood in it is flowing ''away from'' (arterial) or ''toward'' (venous) the
heart The heart is a cardiac muscle, muscular Organ (biology), 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 ...

heart
. The term "arterial blood" is nevertheless used to indicate blood high in
oxygen Oxygen is the chemical element Image:Simple Periodic Table Chart-blocks.svg, 400px, Periodic table, The periodic table of the chemical elements In chemistry, an element is a pure substance consisting only of atoms that all have the same ...

oxygen
, although the
pulmonary artery A pulmonary artery is an artery 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 t ...

pulmonary artery
carries "venous blood" and blood flowing in the
pulmonary vein The pulmonary veins are the 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 vein, pulmonary a ...
is rich in oxygen. This is because they are carrying the blood to and from the lungs, respectively, to be oxygenated.


Function

Blood vessels function to transport
blood Blood is a body fluid Body fluids, bodily fluids, or biofluids are liquid A liquid is a nearly incompressible In fluid mechanics or more generally continuum mechanics, incompressible flow (isochoric process, isochoric flow) refers t ...

blood
. In general, arteries and arterioles transport oxygenated blood from the lungs to the body and its
organs An organ is a group of tissues with similar functions. Plant life and animal life rely on many organs that co-exist in organ systems. A given organ's tissues can be broadly categorized as parenchyma Parenchyma () is the bulk of functional ...
, and veins and venules transport deoxygenated blood from the body to the lungs. Blood vessels also circulate blood throughout the
circulatory system The circulatory system, also called the cardiovascular system or the vascular system, is an organ system An organ system is a biological system A biological system is a complex biological network, network which connects several biologically ...
Oxygen Oxygen is the chemical element Image:Simple Periodic Table Chart-blocks.svg, 400px, Periodic table, The periodic table of the chemical elements In chemistry, an element is a pure substance consisting only of atoms that all have the same ...

Oxygen
(bound to
hemoglobin Hemoglobin or haemoglobin (spelling differences Despite the various English dialects Dialect The term dialect (from Latin , , from the Ancient Greek word , , "discourse", from , , "through" and , , "I speak") is used in two distinct wa ...

hemoglobin
in
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 language, Greek ''erythros'' for "red" and ''k ...

red blood cell
s) is the most critical nutrient carried by the blood. In all arteries apart from the pulmonary artery, hemoglobin is highly saturated (95–100%) with oxygen. In all veins apart from the
pulmonary vein The pulmonary veins are the 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 vein, pulmonary a ...
, the saturation of
hemoglobin Hemoglobin or haemoglobin (spelling differences Despite the various English dialects Dialect The term dialect (from Latin , , from the Ancient Greek word , , "discourse", from , , "through" and , , "I speak") is used in two distinct wa ...

hemoglobin
is about 75%. (The values are reversed in the
pulmonary The lungs are the primary organs of 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 animal ...
circulation.) In addition to carrying oxygen, blood also carries
hormone A hormone (from the Greek#REDIRECT Greek Greek may refer to: Greece Anything of, from, or related to Greece Greece ( el, Ελλάδα, , ), officially the Hellenic Republic, is a country located in Southeast Europe. Its population is appr ...

hormone
s, waste products and nutrients for cells of the body. Blood vessels do not actively engage in the transport of blood (they have no appreciable
peristalsis Peristalsis is a contraction and relaxation of s that propagates in a down a tube, in an direction. Peristalsis is progression of coordinated contraction of involuntary circular muscles, which is preceded by a simultaneous contraction of the ...

peristalsis
). Blood is propelled through arteries and arterioles through pressure generated by the
heartbeat Heartbeat or heartbeats may refer to: Physiology *Cardiac cycle, of the heart *Contraction of the cardiac muscle, muscles of the heart, or a perceived effect of it, such as: **Heart sounds, the noises generated by the beating heart and the resulta ...
. Blood vessels also transport red blood cells which contain the oxygen necessary for daily activities. The amount of red blood cells present in your vessels has an effect on your health. Hematocrit tests can be performed to calculate the proportion of red blood cells in your blood. Higher proportions result in conditions such as dehydration or heart disease while lower proportions could lead to anemia and long-term blood loss. Permeability of the endothelium is pivotal in the release of nutrients to the tissue. It is also increased in
inflammation Inflammation (from la, inflammatio) is part of the complex biological response of body tissues to harmful stimuli, such as pathogen In biology Biology is the natural science that studies life and living organisms, including their anato ...
in response to
histamine Histamine is an organic nitrogen Nitrogen is the chemical element with the Symbol (chemistry), symbol N and atomic number 7. It was first discovered and isolated by Scottish physician Daniel Rutherford in 1772. Although Carl Wilhelm Scheele a ...

histamine
,
prostaglandin The prostaglandins (PG) are a group of physiologically active lipid In and , a lipid is a macro that is soluble in solvents. are typically s used to dissolve other naturally occurring hydrocarbon lipid s that do not (or do not easily) ...
s and
interleukin Interleukins (ILs) are a group of cytokines (secreted proteins and signal molecules) that were first seen to be expressed by white blood cell White blood cells (WBCs), also called leukocytes or leucocytes, are the cells of the immune system ...
s, which leads to most of the symptoms of inflammation (swelling, redness, warmth and pain).


Vessel size

Arteries—and veins to a degree—can regulate their inner diameter by contraction of the muscular layer. This changes the blood flow to downstream organs, and is determined by the
autonomic nervous system The autonomic nervous system (ANS), formerly the vegetative nervous system, is a division of the peripheral nervous system that supplies smooth muscle and glands, and thus influences the function of viscera, internal organs. The autonomic nervous ...

autonomic nervous system
. Vasodilation and vasoconstriction are also used antagonistically as methods of
thermoregulation Thermoregulation is the ability of an organism In biology, an organism () is any organic, life, living system that functions as an individual entity. All organisms are composed of cells (cell theory). Organisms are classified by taxo ...
. The size of blood vessels is different for each of them. It ranges from a diameter of about 25 millimeters for the aorta to only 8 micrometers in the capillaries. This comes out to about a 3000-fold range.
Vasoconstriction Vasoconstriction is the narrowing of the 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 th ...

Vasoconstriction
is the constriction of blood vessels (narrowing, becoming smaller in cross-sectional area) by contracting the
vascular smooth muscle Vascular smooth muscle is the type of smooth muscle that makes up most of the walls of blood vessels. Structure Vascular smooth muscle refers to the particular type of smooth muscle found within, and composing the majority of the wall of blood ...
in the vessel walls. It is regulated by
vasoconstrictor Vasoconstriction is the narrowing of the blood vessels resulting from contraction of the muscular wall of the vessels, in particular the large arteries and small arterioles. The process is the opposite of vasodilation, the widening of blood vessels ...
s (agents that cause vasoconstriction). These include
paracrineParacrine signaling is form of cell signaling or cell-to-cell communication in which a cell produces a signal to induce changes in nearby cells, altering the behaviour of those cells. Signaling molecules known as paracrine factors diffuse over a rel ...
factors (e.g.
prostaglandin The prostaglandins (PG) are a group of physiologically active lipid In and , a lipid is a macro that is soluble in solvents. are typically s used to dissolve other naturally occurring hydrocarbon lipid s that do not (or do not easily) ...
s), a number of
hormone A hormone (from the Greek#REDIRECT Greek Greek may refer to: Greece Anything of, from, or related to Greece Greece ( el, Ελλάδα, , ), officially the Hellenic Republic, is a country located in Southeast Europe. Its population is appr ...

hormone
s (e.g.
vasopressin Vasopressin, also called antidiuretic hormone (ADH), arginine vasopressin (AVP) or argipressin, is a hormone A hormone (from the Greek Greek may refer to: Greece Anything of, from, or related to Greece Greece ( el, Ελλάδα, , ...
and
angiotensin Angiotensin is a peptide hormonePeptide hormones or protein hormones are hormones whose molecules are peptides or proteins, respectively. The latter have longer amino acid chain lengths than the former. These hormones have an effect on the endocri ...
) and
neurotransmitter A neurotransmitter is a signaling molecule In biology, cell signaling (cell signalling in British English), or cell-cell communication, governs the basic activities of cells and coordinates multiple-cell actions. A signal is an entity that ...
s (e.g.
epinephrine Adrenaline, also known as epinephrine, is a hormone A hormone (from the Greek#REDIRECT Greek Greek may refer to: Greece Anything of, from, or related to Greece Greece ( el, Ελλάδα, , ), officially the Hellenic Republic, is a co ...

epinephrine
) from the nervous system.
Vasodilation Vasodilation is the widening of 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. ...

Vasodilation
is a similar process mediated by antagonistically acting mediators. The most prominent vasodilator is
nitric oxide Nitric oxide (nitrogen oxide or nitrogen monoxide) is a colorless gas with the formula . It is one of the principal oxides of nitrogen. Nitric oxide is a free radical: it has an unpaired electron, which is sometimes denoted by a dot in its che ...

nitric oxide
(termed
endothelium-derived relaxing factorEndothelium-derived relaxing factor (EDRF) is a name for a substance Robert F. Furchgott discovered had the eponymous properties. Today, it is firmly established this substance is nitric oxide Nitric oxide ( nitrogen oxide or nitrogen monoxide) ...
for this reason).


Blood flow

The circulatory system uses the channel of blood vessels to deliver blood to all parts of the body. This is a result of the left and right side of the heart working together to allow blood to flow continuously to the lungs and other parts of the body. Oxygen-poor blood enters the right side of the heart through two large veins. Oxygen-rich blood from the lungs enters through the pulmonary veins on the left side of the heart into the aorta and then reaches the rest of the body. The capillaries are responsible for allowing the blood to receive oxygen through tiny air sacs in the lungs. This is also the site where carbon dioxide exits the blood. This all occurs in the lungs where blood is oxygenated. The blood pressure in blood vessels is traditionally expressed in millimetres of mercury (1 mmHg = 133 Pa). In the arterial system, this is usually around 120 mmHg
systolic to supply all body systems; 2) oxygen-depleted blood (blue arrow) in the right ventricle begins pulsing through the pulmonic (pulmonary) valve en route to the lungs for reoxygenation. depolarization is the start-point of the atrial stage of syst ...
(high pressure wave due to contraction of the heart) and 80 mmHg
diastolic Image:Heart diastole.png, upright=1.5, Heart performance during ventricular diastole: early diastole is a suction mechanism that draws blood 'down' from the left atrium (pink) and right atrium (blue) into each of the two ventricles. Then, in late ve ...
(low pressure wave). In contrast, pressures in the venous system are constant and rarely exceed 10 mmHg.
Vascular resistance Vascular resistance is the resistance that must be overcome to push blood through the circulatory system and create fluid dynamics, flow.The resistance offered by the systemic circulation is known as the systemic vascular resistance (SVR) or may so ...
occurs where the vessels away from the heart oppose the flow of blood. Resistance is an accumulation of three different factors: blood viscosity, blood vessel length, and vessel radius.Anatomy Physiology: The Unity of Form and Function, Saladin, McGraw Hill, 2012 Blood viscosity is the thickness of the blood and its resistance to flow as a result of the different components of the blood. Blood is 92% water by weight and the rest of blood is composed of protein, nutrients, electrolytes, wastes, and dissolved gases. Depending on the health of an individual, the blood viscosity can vary (i.e. anemia causing relatively lower concentrations of protein, high blood pressure an increase in dissolved salts or lipids, etc.). Vessel length is the total length of the vessel measured as the distance away from the heart. As the total length of the vessel increases, the total resistance as a result of friction will increase. Vessel radius also affects the total resistance as a result of contact with the vessel wall. As the radius of the wall gets smaller, the proportion of the blood making contact with the wall will increase. The greater amount of contact with the wall will increase the total resistance against the blood flow.


Disease

Blood vessels play a huge role in virtually every medical condition.
Cancer 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 tumor A benign tumor is a mass of cells Cell most often refers to: * Cell (biolo ...

Cancer
, for example, cannot progress unless the tumor causes
angiogenesis Angiogenesis is the physiological process through which new blood vessel The blood vessels are the components of the circulatory system The circulatory system, also called the cardiovascular system or the vascular system, is an organ sy ...

angiogenesis
(formation of new blood vessels) to supply the malignant cells' metabolic demand.
Atherosclerosis Atherosclerosis is a disease in which the wall of the artery An artery (plural arteries) () is a blood vessel The blood vessels are the components of the circulatory system that transport blood throughout the human body. These vessels tr ...

Atherosclerosis
, the formation of
lipid In biology Biology is the natural science that studies life and living organisms, including their anatomy, physical structure, Biochemistry, chemical processes, Molecular biology, molecular interactions, Physiology, physiological mechanis ...
lumps (
atheroma An atheroma, or atheromatous plaque ("plaque"), is an abnormal accumulation of material in the inner layer of the wall of an artery An artery (plural arteries) () is a blood vessel that takes blood away from the heart to one or more parts of ...

atheroma
s) in the blood vessel wall, is the most common
cardiovascular disease Cardiovascular disease (CVD) is a class of diseases that involve the heart The heart is a cardiac muscle, muscular Organ (biology), organ in most animals, which pumps blood through the blood vessels of the circulatory system. The pumped ...
, the main cause of death in the Western world. Blood vessel permeability is increased in
inflammation Inflammation (from la, inflammatio) is part of the complex biological response of body tissues to harmful stimuli, such as pathogen In biology Biology is the natural science that studies life and living organisms, including their anato ...
. Damage, due to
trauma Trauma most often refers to: *Major trauma, in physical medicine, severe physical injury caused by an external source *Psychological trauma, a type of damage to the psyche that occurs as a result of a severely distressing event *Traumatic injur ...
or spontaneously, may lead to
hemorrhage Bleeding, also known as a hemorrhage, haemorrhage, or simply blood loss, is blood Blood is a body fluid in humans and other animals that delivers necessary substances such as nutrient A nutrient is a substance used by an organism to survi ...
due to mechanical damage to the vessel endothelium. In contrast, occlusion of the blood vessel by atherosclerotic plaque, by an embolised
blood clot A thrombus, colloquially called a blood clot, is the final product of the 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 ...

blood clot
or a foreign body leads to downstream
ischemia Ischemia or ischaemia is a restriction in blood Blood is a body fluid Body fluids, bodily fluids, or biofluids are liquid A liquid is a nearly incompressible fluid In physics, a fluid is a substance that continually Deformation ( ...
(insufficient blood supply) and possibly
necrosis Necrosis (from Ancient Greek Ancient Greek includes the forms of the Greek language used in ancient Greece and the classical antiquity, ancient world from around 1500 BC to 300 BC. It is often roughly divided into the following periods: ...
. Vessel occlusion tends to be a positive feedback system; an occluded vessel creates eddies in the normally
laminar flow In fluid dynamics In and , fluid dynamics is a subdiscipline of that describes the flow of s—s and es. It has several subdisciplines, including ' (the study of air and other gases in motion) and hydrodynamics (the study of liquids in mo ...

laminar flow
or
plug flowIn fluid mechanics Fluid mechanics is the branch of physics concerned with the mechanics Mechanics (Ancient Greek, Greek: ) is the area of physics concerned with the motions of physical objects, more specifically the relationships among force ...
blood currents. These eddies create abnormal fluid velocity gradients which push blood elements such as cholesterol or
chylomicron Chylomicrons (from the Greek χυλός, chylos, meaning ''juice'' (of plants or animals), and micron, meaning ''small particle''), also known as ultra low-density lipoproteins (ULDL), are lipoprotein, lipoprotein particles that consist of trigl ...

chylomicron
bodies to the endothelium. These deposit onto the arterial walls which are already partially occluded and build upon the blockage. The most common disease of the blood vessels is hypertension or high blood pressure. This is caused by an increase in the pressure of the blood flowing through the vessels. Hypertension can lead to more serious conditions such as heart failure and stroke. To prevent these diseases, the most common treatment option is medication as opposed to surgery. Aspirin helps prevent blood clots and can also help limit inflammation.
Vasculitis Vasculitis is a group of disorders that destroy blood vessel The blood vessels are the components of the circulatory system The circulatory system, also called the cardiovascular system or the vascular system, is an organ system that p ...
is
inflammation Inflammation (from la, inflammatio) is part of the complex biological response of body tissues to harmful stimuli, such as pathogen In biology Biology is the natural science that studies life and living organisms, including their anato ...
of the vessel wall, due to
autoimmune disease An autoimmune disease is a condition arising from an abnormal immune response An immune response is a reaction which occurs within an organism for the purpose of defending against foreign invaders. These invaders include a wide variety of differe ...

autoimmune disease
or
infection An infection is the invasion of an organism's body tissues by disease-causing agents, their multiplication, and the reaction of host A host is a person responsible for guests at an event or for providing hospitality during it. Host may ...

infection
.


See also

*
Circulatory system The circulatory system, also called the cardiovascular system or the vascular system, is an organ system An organ system is a biological system A biological system is a complex network Network and networking may refer to: Arts, entertai ...
* List of bones of the human skeleton *
List of skeletal muscles of the human body This is a table 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 t ...
* List of nerves of the human body


References

{{Authority control Angiology Soft tissue