Omar Bennett
The venous system is a complex network of vessels that transport deoxygenated blood back to the heart. The systemic venous system is responsible for transporting deoxygenated blood from the tissues to the right atrium of the heart. The major vessel in this system is the inferior vena cava, which receives venous drainage from structures below the diaphragm, including the kidneys, liver, and lower limbs. The portal venous system, on the other hand, is responsible for the venous drainage of organs like the spleen, pancreas, and gastrointestinal tract. This system converges at the portal vein, which ultimately drains into the liver. Understanding the venous drainage of different parts of the body, such as the abdomen, pelvis, lower extremities, and head and neck, is crucial for clinical applications and treating various conditions.
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What You'll Learn
Inferior vena cava
The inferior vena cava (IVC) is the largest vein in the human body. It is responsible for transporting deoxygenated blood from the lower half of the body to the right atrium of the heart. The IVC is formed by the confluence of the right and left common iliac veins, which occurs at the L5 vertebral level. It ascends the posterior abdominal wall, passing through the central tendon of the diaphragm at the T8 vertebral level.
The IVC has a large drainage area, which includes the abdomen, pelvis, and lower limbs. It receives venous blood from the abdominal wall through the lumbar veins and from the lower limbs through the common iliac veins. The hepatic veins, which carry blood from the abdominal viscera, also empty into the IVC. The IVC is located on the right side of the body, which affects the length of the vessels entering it from the left side, such as the left renal vein.
The function of the IVC is critical for returning venous blood from the lower half of the body to the heart. During diaphragmatic contraction, a negative pressure gradient is created in the chest, pulling venous blood from the abdominal IVC into the thoracic IVC and subsequently into the right atrium of the heart. This process ensures the forward flow of blood back toward the heart, as the IVC itself does not contain one-way valves to direct blood flow.
The IVC plays a crucial role in the systemic venous system, which transports deoxygenated blood to the right atrium. In the event of an obstruction in the IVC, collateral vessels to the superior vena cava open to maintain blood flow. Health issues associated with the IVC often arise from external compression, with potential sources including an enlarged aorta, aortocaval compression syndrome, and abdominal malignancies.
The embryologic development of the IVC involves the formation of three major pairs of veins: the vitelline veins, the umbilical veins, and the cardinal veins. In adults, only the vitelline veins and cardinal veins contribute to the formation of the IVC, with the vitelline veins forming a plexus around the primitive duodenum and the cardinal veins providing the hepatocardiac portion of the IVC.
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Deep and superficial systems
The venous drainage of the lower extremities is divided into the superficial and deep systems. The superficial veins are found in the subcutaneous tissue, and they eventually drain into the deep veins. The deep venous system is located beneath the deep fascia of the lower limb. The main venous structure of the foot is the dorsal venous arch, which mostly drains into the superficial veins. Some veins from the arch penetrate deep into the leg, forming the anterior tibial vein. The deep venous system courses alongside the arterial system and includes the anterior tibial, posterior tibial, and the peroneal veins, which ultimately form the popliteal vein. It is joined by the lesser saphenous vein from the superficial system, ascends, and forms the common femoral vein. The common femoral vein is joined by the greater saphenous vein, which usually receives the external pudendal vein, the superficial epigastric vein, and the superficial circumflex iliac vein.
The venous system of the upper limb drains deoxygenated blood from the arm, forearm, and hand. It can be subdivided into the superficial system and the deep system. The major superficial veins of the upper limb are the cephalic and basilic veins, located within the subcutaneous tissue of the upper limb. The basilic vein originates from the dorsal venous network of the hand and ascends the medial aspect of the upper limb. At the border of the teres major, the vein moves deep into the arm, where it combines with the brachial veins from the deep venous system to form the axillary vein. The deep venous system of the upper limb is situated underneath the deep fascia and is formed by paired veins, which accompany and lie on either side of an artery. The brachial veins are the largest in the upper extremity and are situated on either side of the brachial artery.
The primitive telencephalic, diencephalic, and mesencephalic veins drain into the tentorial sinus during early stages of embryonic life. The basal vein comprises three segments corresponding to the transverse veins of the telencephalon, diencephalon, and mesencephalon. The distal portion of the BVR indicates variable drainage patterns: to the vein of Galen or the internal cerebral vein (ICV), to the straight sinus (SS), to the transverse sinus (TS), and to the superior petrosal sinus. Tributaries of the first segment of the BVR drain into the BVR and VOG. The ICV receives venous return from the basal ganglia and white matter, merges with the venous return from the choroidal plexus, and drains into the VOG. Unlike the BVR, most veins that flow into the ICV are deep veins, and they receive veins from the ventricular wall, deep white matter, choroid plexus, striatum, thalamus, and corpus callosum.
The veins of Trolard, the superficial middle cerebral vein (SMCV), and Labbé have sufficient anastomosis. The drainage pattern of the SMCV changes with the regression of the primitive tentorial sinus and forms the following: medial group, to the cavernous sinus (CS); intermediate group, to the laterocavernous sinus (LCS); lateral group, to the transverse sinus (TS) through the sphenobasal vein, and to the superior petrosal sinus (SPS) through the sphenopetrosal vein.
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The portal vein
In summary, the portal vein is a vital component of the body's venous system, primarily involved in draining venous blood from the gastrointestinal tract and associated organs, delivering it to the liver, and facilitating the processing of nutrients and toxins. Its structure, functions, and pathologies make it a critical area of study in anatomy and medicine.
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The systemic venous system
The inferior vena cava is formed by the union of the common iliac veins at the L5 vertebral level. It ascends through the abdomen on the right of the aorta, piercing the central tendon of the diaphragm at the T8 level (the caval hiatus). The common iliac veins are formed by the external and internal iliac veins, which drain the lower limbs and gluteal region. The internal iliac vein is also joined by the common femoral vein, which receives blood from the greater saphenous vein, the external pudendal vein, the superficial epigastric vein, and the superficial circumflex iliac vein.
The hepatic portal venous system includes the superior mesenteric vein, which drains blood from the small intestine, cecum, ascending colon, and transverse colon. The superior mesenteric vein joins the splenic vein, which drains the spleen, to form the portal vein. The portal vein then divides into right and left branches, which enter the liver separately. The portal vein also receives tributaries from the right and left gastric veins, which drain the stomach, and the cystic veins, which drain the gallbladder.
In the lower extremities, the deep system consists of the anterior and posterior tibial veins and the peroneal vein. These veins drain into the popliteal vein and eventually into the superficial femoral vein. The superficial femoral vein is joined by the greater and lesser saphenous veins, which provide drainage of blood from the lower extremity to the inferior vena cava through the iliac veins.
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Venous drainage of the brain and meninges
The brain is a highly perfused organ, receiving up to 20% of the resting cardiac output. The venous drainage of the brain is highly complex and specialised. The veins of the brain are divided into superficial cerebral veins and internal cerebral veins, depending on whether they drain the superficial or deep structures of the brain.
The internal cerebral veins run parallel to each other along the dorsomedial aspect of the thalamus. They merge to form the great cerebral vein, which drains into the straight sinus. The internal cerebral veins are the main vessels that drain the internal structures of the cerebral hemisphere. The internal cerebral veins are formed by the merger of the thalamostriate vein and the choroidal vein. The thalamostriate vein runs between the thalamus and the caudate nucleus, while the choroidal vein drains the choroid plexus of the lateral ventricle. The subependymal veins join the thalamostriate and choroidal veins, draining the choroid plexus and much of the deep grey nuclei. These veins then form the internal cerebral veins.
The cerebral veins drain the capillary network that supplies the brain, removing carbon dioxide and other metabolic waste products while allowing fresh blood to circulate. These veins collect blood from the entire brain, as well as from the eyes, meninges, and part of the face via the pterygoid plexus. The dural sinuses, particularly the superior sagittal sinus, drain cerebrospinal fluid (CSF) through the arachnoid granulations, returning it to the bloodstream. The cerebral venous system is particularly delicate, and even minor trauma or abrupt deceleration can rupture cortical bridging veins, resulting in a subdural hematoma (SDH).
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Frequently asked questions
Venous drainage refers to the veins that drain blood from various parts of the body, such as the brain, scalp, face, neck, abdomen, and pelvis.
The venous drainage of the brain and meninges is handled by the dural venous sinuses, which drain into the internal jugular vein.
The inferior vena cava is responsible for the venous drainage of structures below the diaphragm in the abdomen. It receives tributaries from various veins, including the common iliac, lumbar, and renal veins.
The superficial venous drainage of the lower extremities involves veins such as the greater and lesser saphenous veins, while the deep venous system includes veins like the anterior and posterior tibial veins, which eventually form the popliteal vein.
Obstruction or issues with venous drainage in the superior or inferior vena cava can cause a range of symptoms, including swelling in the upper or lower body, shortness of breath, leg pain, abdominal pain, weight changes, and tachycardia.
