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Vein

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In the circulatory system
Circulatory system
The circulatory system is an organ system that passes nutrients , gases, hormones, blood cells, etc...

, veins (from the Latin vena) are blood vessels that carry blood
Blood
Blood is a specialized bodily fluid in animals that delivers necessary substances such as nutrients and oxygen to the cells and transports metabolic waste products away from those same cells....

 towards the heart
Heart
The heart is a myogenic muscular organ found in all animals with a circulatory system , that is responsible for pumping blood throughout the blood vessels by repeated, rhythmic contractions...

. Most veins carry deoxygenated blood from the tissues back to the heart; exceptions are the pulmonary
Pulmonary vein
The pulmonary veins are large blood vessels that carry blood from the lungs to the left atrium of the heart. In humans there are four pulmonary veins, two from each lung...

 and umbilical vein
Umbilical vein
The umbilical vein is a vein present during fetal development that carries oxygenated blood from the placenta to the growing fetus.The blood pressure inside the umbilical vein is approximately 20 mmHg.-Development:...

s, both of which carry oxygenated blood to the heart. Veins differ from arteries
Artery
Arteries are blood vessels that carry blood away from the heart. This blood is normally oxygenated, exceptions made for the pulmonary and umbilical arteries....

 in structure and function; for example, arteries are more muscular than veins, veins are often closer to the skin and contain valves to help keep blood flowing toward the heart, while arteries carry blood away from the heart.

Anatomy



In general, veins function to return deoxygenated blood to the heart
Heart
The heart is a myogenic muscular organ found in all animals with a circulatory system , that is responsible for pumping blood throughout the blood vessels by repeated, rhythmic contractions...

, and are essentially tubes that collapse when their lumens
Lumen (anatomy)
A lumen in biology is the inside space of a tubular structure, such as an artery or intestine...

 are not filled with blood. The thick outermost layer of a vein is made of connective tissue
Connective tissue
"Connective tissue" is a fibrous tissue. It is one of the four traditional classes of tissues . Connective Tissue is found throughout the body.In fact the whole framework of the skeleton and the different specialized connective tissues from the crown of the head to the toes determine the form of...

, called tunica adventitia or tunica externa. Deeper are bands of smooth muscle
Smooth muscle
Smooth muscle is an involuntary non-striated muscle. It is divided into two sub-groups; the single-unit and multiunit smooth muscle. Within single-unit smooth muscle tissues, the autonomic nervous system innervates a single cell within a sheet or bundle and the action potential is propagated by...

 called tunica media, which are, in general, thin, as veins do not function primarily in a contractile manner. The interior is lined with endothelial cells
Endothelium
The endothelium is the thin layer of cells that lines the interior surface of blood vessels, forming an interface between circulating blood in the lumen and the rest of the vessel wall. These cells are called endothelial cells. Endothelial cells line the entire circulatory system, from the heart...

 called tunica intima. . These are infoldings of the tunica intima. The precise location of veins is much more variable from person to person than that of arteries
Artery
Arteries are blood vessels that carry blood away from the heart. This blood is normally oxygenated, exceptions made for the pulmonary and umbilical arteries....

. Veins often display a lot of anatomical variation compared with arteries within a species and between species.

Notable veins and vein systems


The greater saphenous vein is the most important superficial vein of the lower limb. First described by the Persian physician Avicenna
Avicenna
Abū ʿAlī al-Ḥusayn ibn ʿAbd Allāh ibn Sīnā , commonly known as Ibn Sīnā or by his Latinized name Avicenna, was a Persian polymath, who wrote almost 450 treatises on a wide range of subjects, of which around 240 have survived...

, this vein derives its name from the word safina, meaning "hidden". This vein is "hidden" in its own fascial compartment
Fascial compartment
On the human body, the limbs can be divided into segments, such as the arm and the forearm of the upper limb, and the thigh and the leg of the lower limb.If these segments are cut transversely, it is apparent that they are divided into multiple sections...

 in the thigh and exits the fascia only near the knee. Incompetence of this vein is an important cause of varicose veins
Varicose veins
Varicose veins are veins that have become enlarged and tortuous. The term commonly refers to the veins on the leg, although varicose veins can occur elsewhere. Veins have leaflet valves to prevent blood from flowing backwards . Leg muscles pump the veins to return blood to the heart, against the...

 of lower limbs.

The pulmonary vein
Pulmonary vein
The pulmonary veins are large blood vessels that carry blood from the lungs to the left atrium of the heart. In humans there are four pulmonary veins, two from each lung...

s carry relatively oxygenated blood from the lungs to the heart. The superior
Superior vena cava
The superior vena cava is truly superior, a large diameter, yet short, vein that carries deoxygenated blood from the upper half of the body to the heart's right atrium...

 and inferior venae cavae
Inferior vena cava
The inferior vena cava , also known as the posterior vena cava, is the large vein that carries de-oxygenated blood from the lower half of the body into the right atrium of the heart....

 carry relatively deoxygenated blood from the upper and lower systemic circulations, respectively.

A portal venous system
Portal venous system
In human anatomy, the hepatic portal system is the system of veins comprising the hepatic portal vein and its tributaries. It is also called the portal venous system, although it is not the only example of a portal venous system, and splanchnic veins, which is not synonymous with hepatic portal...

 is a series of veins or venules that directly connect two capillary beds. Examples of such systems include the hepatic portal vein
Hepatic portal vein
The hepatic portal vein is not a true vein, because it does not conduct blood directly to the heart. It is a vessel in the abdominal cavity that drains blood from the gastrointestinal tract and spleen to capillary beds in the liver...

 and hypophyseal portal system
Hypophyseal portal system
The hypophyseal portal system is the system of blood vessels that link the hypothalamus and the anterior pituitary in the brain.It allows endocrine communication between the two structures. It is part of the hypothalamic-pituitary-adrenal axis. The anterior pituitary receives releasing and...



The Thebesian veins within the myocardium of the heart are valveless veins that drain directly into the chambers of the heart. The coronary veins all empty into the coronary sinus
Coronary sinus
The coronary sinus is a collection of veins joined together to form a large vessel that collects blood from the myocardium of the heart. It is present in all mammals, including humans...

 which empties into the right atrium.

The Dural sinuses within the dura mater surrounding the brain receive blood from the brain and also are a point of entry of cerebrospinal fluid from arachnoid villi absorption. Blood eventually enters the internal jugular vein.

Color


Vein color is determined in large part by the color of venous blood
Venous blood
Venous blood is deoxygenated blood in the circulatory system. It runs in the systemic veins from the organs to the heart. Deoxygenated blood is then pumped by the heart to lungs via the pulmonary arteries, one of the few arteries in the body that carries deoxygenated blood .Venous blood is...

, which is usually dark red (and not blue as is commonly believed) as a result of its low oxygen content. Veins appear blue because the subcutaneous fat absorbs low-frequency light, permitting only the highly energetic blue wavelengths to penetrate through to the dark vein and reflect off.
A recent study found the color of blood vessels is determined by the following factors: the scattering and absorption characteristics of skin at different wavelengths, the oxygenation state of blood, which affects its absorption properties, the diameter and the depth of the vessels, and the visual perception process.

Function


Veins serve to return blood from organs to the heart. Veins are also called "capacitance vessels" because most of the blood volume (60%) is contained within veins. In systemic circulation
Systemic circulation
Systemic circulation is the part of the cardiovascular system which carries oxygenated blood away from the heart to the body, and returns deoxygenated blood back to the heart. This physiologic theory of circulation was first described by William Harvey...

 oxygenated blood is pumped by the left ventricle
Left ventricle
The left ventricle is one of four chambers in the human heart. It receives oxygenated blood from the left atrium via the mitral valve, and pumps it into the aorta via the aortic valve.-Shape:...

 through the arteries
Artery
Arteries are blood vessels that carry blood away from the heart. This blood is normally oxygenated, exceptions made for the pulmonary and umbilical arteries....

 to the muscles and organs of the body, where its nutrients and gases are exchanged at capillaries
Capillary
Capillaries are the smallest of a body's blood vessels and are parts of the microcirculation. They are only 1 cell thick. These microvessels, measuring 5-10 μm in diameter, connect arterioles and venules, and enable the exchange of water, oxygen, carbon dioxide, and many other nutrient and waste...

, the blood then enter veinules, then veins filled with cellular waste and carbon dioxide
Carbon dioxide
Carbon dioxide is a naturally occurring chemical compound composed of two oxygen atoms covalently bonded to a single carbon atom...

. The de-oxygen
Oxygen
Oxygen is the element with atomic number 8 and represented by the symbol O. Its name derives from the Greek roots ὀξύς and -γενής , because at the time of naming, it was mistakenly thought that all acids required oxygen in their composition...

ated blood is taken by veins to the right atrium
Right atrium
The right atrium is one of four chambers in the hearts of mammals and archosaurs...

 of the heart, which transfers the blood to the right ventricle
Right ventricle
The right ventricle is one of four chambers in the human heart. It receives deoxygenated blood from the right atrium via the tricuspid valve, and pumps it into the pulmonary artery via the pulmonary valve and pulmonary trunk....

, where it is then pumped through the pulmonary arteries to the lung
Lung
The lung is the essential respiration organ in many air-breathing animals, including most tetrapods, a few fish and a few snails. In mammals and the more complex life forms, the two lungs are located near the backbone on either side of the heart...

s. In pulmonary circulation
Pulmonary circulation
Pulmonary circulation is the half portion of the cardiovascular system which carries Oxygen-depleted Blood away from the heart, to the Lungs, and returns oxygenated blood back to the heart. Encyclopedic description and discovery of the pulmonary circulation is widely attributed to Doctor Ibn...

 the pulmonary vein
Pulmonary vein
The pulmonary veins are large blood vessels that carry blood from the lungs to the left atrium of the heart. In humans there are four pulmonary veins, two from each lung...

s return oxygenated blood from the lungs to the left atrium
Left atrium
The left atrium is one of the four chambers in the human heart. It receives oxygenated blood from the pulmonary veins, and pumps it into the left ventricle, via the mitral valve.-Foramen ovale:...

, which empties into the left ventricle, completing the cycle of blood circulation.

The return of blood to the heart is assisted by the action of the skeletal-muscle pump
Skeletal-muscle pump
The skeletal-muscle pump is a collection of skeletal muscles that aid the heart in the circulation of blood. It is especially important in increasing venous return to the heart, but may also play a role in arterial blood flow.-Arterial blood pumping:...

, and by the thoracic pump action of breathing during respiration. Standing or sitting for a prolonged period of time can cause low venous return from venous pooling vascular shock. Fainting can occur but usually baroreceptors within the aortic sinues initiate a baroreflex
Baroreflex
The baroreflex or baroreceptor reflex is one of the body's homeostatic mechanisms for maintaining blood pressure. It provides a negative feedback loop in which an elevated blood pressure reflexively causes heart rate to decrease therefore causing blood pressure to decrease; likewise, decreased...

 such angiotensin II and norepinephrine stimulate vasoconstriction and heart rate increases to return blood flow. Neurogenic
Neurogenic shock
Neurogenic shock is a distributive type of shock resulting in hypotension, occasionally with bradycardia, that is attributed to the disruption of the autonomic pathways within the spinal cord. Hypotension occurs due to decreased systemic vascular resistance resulting in pooling of blood within the...

 and hypovolaemic shock can also cause fainting. In these cases, the smooth muscles surrounding the veins become slack and the veins fill with the majority of the blood in the body, keeping blood away from the brain and causing unconsciousness. Jet pilots wear pressurized suits to help maintain their venous return and blood pressure.

The arteries are perceived as carrying oxygenated blood to the tissues, while veins carry deoxygenated blood back to the heart. This is true of the systemic circulation, by far the larger of the two circuits of blood in the body, which transports oxygen from the heart to the tissues of the body. However, in pulmonary circulation, the arteries carry deoxygenated blood from the heart to the lungs, and veins return blood from the lungs to the heart. The difference between veins and arteries is their direction of flow (out of the heart by arteries, returning to the heart for veins), not their oxygen content. In addition, deoxygenated blood that is carried from the tissues back to the heart for reoxygenation in systemic circulation still carries some oxygen, though it is considerably less than that carried by the systemic arteries or pulmonary veins.

Although most veins take blood back to the heart, there is an exception. Portal veins carry blood between capillary beds. For example, the hepatic portal vein takes blood from the capillary beds in the digestive tract and transports it to the capillary beds in the liver. The blood is then drained in the gastrointestinal tract and spleen, where it is taken up by the hepatic veins, and blood is taken back into the heart. Since this is an important function in mammals, damage to the hepatic portal vein can be dangerous. Blood clotting in the hepatic portal vein can cause portal hypertension, which results in a decrease of blood fluid to the liver.

Also transports proteins and other materials through out the body.

Classification


Veins are classified in a number of ways, including superficial vs. deep, pulmonary vs. systemic, and large vs. small.

Superficial veins
Superficial vein
Superficial vein
Superficial vein is a term used to describe a vein that is close to the surface of the body. It is used to differentiate veins that are close to the surface from veins that are far from the surface, known as deep veins....

s are those whose course is close to the surface of the body, and have no corresponding arteries.


Deep veins
Deep vein
Deep vein
Deep vein is a term used to describe a vein that is deep in the body. It is used to differentiate deep veins from veins which are close to the surface, also known as superficial veins....

s are deeper in the body and have corresponding arteries.


Pulmonary veins
The pulmonary vein
Pulmonary vein
The pulmonary veins are large blood vessels that carry blood from the lungs to the left atrium of the heart. In humans there are four pulmonary veins, two from each lung...

s are a set of veins that deliver oxygenated blood from the lung
Lung
The lung is the essential respiration organ in many air-breathing animals, including most tetrapods, a few fish and a few snails. In mammals and the more complex life forms, the two lungs are located near the backbone on either side of the heart...

s to the heart.


Systemic veins
Systemic veins drain the tissues of the body and deliver deoxygenated blood to the heart.

Clinical significance



Phlebology


Phlebology is the medical discipline that involves the diagnosis and treatment of disorders of venous origin. Diagnostic techniques used include the history and physical examination, venous imaging techniques and laboratory evaluation related to venous thromboembolism
Thrombosis
Thrombosis is the formation of a blood clot inside a blood vessel, obstructing the flow of blood through the circulatory system. When a blood vessel is injured, the body uses platelets and fibrin to form a blood clot to prevent blood loss...

. The American Medical Association has added phlebology to their list of self-designated practice specialties. A medical specialist in Phlebology is termed a Phlebologist
Phlebologist
A Phlebologist is a medical specialist in the diagnosis and treatment of disorders of venous origin. The specialty of Phlebology has developed to enable physicians sharing an interest in venous disease but with a variety of backgrounds such as dermatology, vascular surgery, haematology, or general...

. A related image is called a phlebography
Impedance phlebography
Impedance phlebography, or impedance plethysmography , is a non-invasive medical test that measures small changes in electrical resistance of the chest, calf or other regions of the body. These measurements reflect blood volume changes, and can indirectly indicate the presence or absence of venous...



The American College of Phlebology (ACP) is a professional organization of physicians and healthcare professionals from a variety of backgrounds. ACP meetings are conducted to facilitate learning and sharing of knowledge regarding venous disease. The equivalent body for countries in the Pacific is the Australasian College of Phlebology, active in Australia and New Zealand.

The American Venous Forum (AVF) is the leading academic international consortium of venous and lymphatic specialists dedicated to improving patient care. The highest-quality research in clinical and basic sciences is reported at the AVF annual meetings, along with the reports on new developments in diagnosis and treatment of venous diseases. The main body of the AVF consists of vascular surgeons and other physicians who specialized in management of not only simple varicose veins but the whole spectrum of venous and lymphatic diseases from congenital abnormalities to deep vein thrombosis to chronic venous diseases.

Venous insufficiency


Venous insufficiency is the most common disorder of the venous system, and is usually manifested as spider veins
Telangiectasia
Telangiectasias /tɛ.læn.dʒiː'ɛk.teɪ.ʃi:ə/ are small dilated blood vessels near the surface of the skin or mucous membranes, measuring between 0.5 and 1 millimeter in diameter. They can develop anywhere on the body but are commonly seen on the face around the nose, cheeks, and chin...

 or varicose veins
Varicose veins
Varicose veins are veins that have become enlarged and tortuous. The term commonly refers to the veins on the leg, although varicose veins can occur elsewhere. Veins have leaflet valves to prevent blood from flowing backwards . Leg muscles pump the veins to return blood to the heart, against the...

. Several varieties of treatments are used, depending on the patient's particular type and pattern of veins and on the physician's preferences. Treatment can include radiofrequency ablation
Somnoplasty
Somnoplasty is composed of the Latin root somnus meaning sleep, and the Greek word plastia meaning molding or formation. Somnoplasty is a medical treatment approved by the Food and Drug Administration to treat three conditions: habitual snoring, chronic nasal obstruction, and obstructive sleep...

, vein stripping
Vein stripping
Vein stripping is a surgical procedure done under general or local anaesthetic to remove varicose veins. The surgery involves making one or more incisions upon the desired area followed by insertion of a special wire into the vein. The wire is tied to and advanced through the vein to a desired...

, ambulatory phlebectomy
Ambulatory phlebectomy
Ambulatory phlebectomy is a treatment for superficial varicose veins. The procedure involves the removal of the varicose veins through small 2–3 mm incisions in the skin overlying the veins. The procedure may be performed in hospital or outpatient settings...

, foam sclerotherapy
Sclerotherapy
Sclerotherapy is a procedure used to treat blood vessels or blood vessel malformations and also those of the lymphatic system. A medicine is injected into the vessels, which makes them shrink. It is used for children and young adults with vascular or lymphatic malformations...

, laser
Laser
A laser is a device that emits light through a process of optical amplification based on the stimulated emission of photons. The term "laser" originated as an acronym for Light Amplification by Stimulated Emission of Radiation...

s, or compression.

Postphlebitic syndrome is venous insufficiency that develops following deep vein thrombosis
Deep vein thrombosis
Deep vein thrombosis is the formation of a blood clot in a deep vein. Deep vein thrombosis commonly affects the leg veins or the deep veins of the pelvis. Occasionally the veins of the arm are affected...

.

Deep vein thrombosis


Deep-vein thrombosis is a condition in which a blood clot
Thrombus
A thrombus , or blood clot, is the final product of the blood coagulation step in hemostasis. It is achieved via the aggregation of platelets that form a platelet plug, and the activation of the humoral coagulation system...

 forms in a deep vein, which can lead to pulmonary embolism
Pulmonary embolism
Pulmonary embolism is a blockage of the main artery of the lung or one of its branches by a substance that has travelled from elsewhere in the body through the bloodstream . Usually this is due to embolism of a thrombus from the deep veins in the legs, a process termed venous thromboembolism...

 and chronic venous insufficiency.

Thrombophlebitis


Thrombophlebitis is an inflammatory condition of the veins related to blood clots
Thrombus
A thrombus , or blood clot, is the final product of the blood coagulation step in hemostasis. It is achieved via the aggregation of platelets that form a platelet plug, and the activation of the humoral coagulation system...

.

See also

  • Artery
    Artery
    Arteries are blood vessels that carry blood away from the heart. This blood is normally oxygenated, exceptions made for the pulmonary and umbilical arteries....

  • Deep vein
    Deep vein
    Deep vein is a term used to describe a vein that is deep in the body. It is used to differentiate deep veins from veins which are close to the surface, also known as superficial veins....

  • Deep vein thrombosis
    Deep vein thrombosis
    Deep vein thrombosis is the formation of a blood clot in a deep vein. Deep vein thrombosis commonly affects the leg veins or the deep veins of the pelvis. Occasionally the veins of the arm are affected...

  • Peripheral vein
    Peripheral vein
    Peripheral Veins are the veins not in the chest or abdomen . These veins lead deoxygenated blood from the capillaries in the extremities back to the heart....

  • Phlebologist
    Phlebologist
    A Phlebologist is a medical specialist in the diagnosis and treatment of disorders of venous origin. The specialty of Phlebology has developed to enable physicians sharing an interest in venous disease but with a variety of backgrounds such as dermatology, vascular surgery, haematology, or general...

  • Pulmonary circulation
    Pulmonary circulation
    Pulmonary circulation is the half portion of the cardiovascular system which carries Oxygen-depleted Blood away from the heart, to the Lungs, and returns oxygenated blood back to the heart. Encyclopedic description and discovery of the pulmonary circulation is widely attributed to Doctor Ibn...

  • Superficial vein
    Superficial vein
    Superficial vein is a term used to describe a vein that is close to the surface of the body. It is used to differentiate veins that are close to the surface from veins that are far from the surface, known as deep veins....

  • Varicose veins
    Varicose veins
    Varicose veins are veins that have become enlarged and tortuous. The term commonly refers to the veins on the leg, although varicose veins can occur elsewhere. Veins have leaflet valves to prevent blood from flowing backwards . Leg muscles pump the veins to return blood to the heart, against the...


External links



Scientific publications