Figure 20.35Major Systemic Veins of the Body The major systemic veins of the body are shown here in an anterior view.
The right atrium receives all of the systemic venous return. Most of the blood flows into either the superior vena cava or inferior vena cava. If you draw an imaginary line at the level of the diaphragm, systemic venous circulation from above that line will generally flow into the superior vena cava; this includes blood from the head, neck, chest, shoulders, and upper limbs. The exception to this is that most venous blood flow from the coronary veins flows directly into the coronary sinus and from there directly into the right atrium. Beneath the diaphragm, systemic venous flow enters the inferior vena cava, that is, blood from the abdominal and pelvic regions and the lower limbs.
The Superior Vena Cava:
The superior vena cava drains most of the body superior to the diaphragm (Figure 20.36). On both the left and right sides, the subclavian vein forms when the axillary vein passes through the body wall from the axillary region. It fuses with the external and internal jugular veins from the head and neck to form the brachiocephalic vein. Each vertebral vein also flows into the brachiocephalic vein close to this fusion. These veins arise from the base of the brain and the cervical region of the spinal cord, and flow largely through the intervertebral foramina in the cervical vertebrae. They are the counterparts of the vertebral arteries. Each internal thoracic vein, also known as an internal mammary vein, drains the anterior surface of the chest wall and flows into the brachiocephalic vein.
The remainder of the blood supply from the thorax drains into the azygos vein. Each intercostal vein drains muscles of the thoracic wall, each esophageal vein delivers blood from the inferior portions of the esophagus, each bronchial vein drains the systemic circulation from the lungs, and several smaller veins drain the mediastinal region. Bronchial veins carry approximately 13 percent of the blood that flows into the bronchial arteries; the remainder intermingles with the pulmonary circulation and returns to the heart via the pulmonary veins. These veins flow into the azygos vein, and with the smaller hemiazygos vein (hemi- = “half”) on the left of the vertebral column, drain blood from the thoracic region. The hemiazygos vein does not drain directly into the superior vena cava but enters the brachiocephalic vein via the superior intercostal vein.
The azygos vein passes through the diaphragm from the thoracic cavity on the right side of the vertebral column and begins in the lumbar region of the thoracic cavity. It flows into the superior vena cava at approximately the level of T2, making a significant contribution to the flow of blood. It combines with the two large left and right brachiocephalic veins to form the superior vena cava.
Table 20.11 summarizes the veins of the thoracic region that flow into the superior vena cava.
Figure 20.36 Veins of the Thoracic and Abdominal Regions Veins of the thoracic and abdominal regions drain blood from the area above the diaphragm, returning it to the right atrium via the superior vena cava.Veins of the Thoracic Region
| Vessel | Description |
|---|---|
| Superior vena cava | Large systemic vein; drains blood from most areas superior to the diaphragm; empties into the right atrium |
| Subclavian vein | Located deep in the thoracic cavity; formed by the axillary vein as it enters the thoracic cavity from the axillary region; drains the axillary and smaller local veins near the scapular region and leads to the brachiocephalic vein |
| Brachiocephalic veins | Pair of veins that form from a fusion of the external and internal jugular veins and the subclavian vein; subclavian, external and internal jugulars, vertebral, and internal thoracic veins flow into it; drain the upper thoracic region and lead to the superior vena cava |
| Vertebral vein | Arises from the base of the brain and the cervical region of the spinal cord; passes through the intervertebral foramina in the cervical vertebrae; drains smaller veins from the cranium, spinal cord, and vertebrae, and leads to the brachiocephalic vein; counterpart of the vertebral artery |
| Internal thoracic veins | Also called internal mammary veins; drain the anterior surface of the chest wall and lead to the brachiocephalic vein |
| Intercostal vein | Drains the muscles of the thoracic wall and leads to the azygos vein |
| Esophageal vein | Drains the inferior portions of the esophagus and leads to the azygos vein |
| Bronchial vein | Drains the systemic circulation from the lungs and leads to the azygos vein |
| Azygos vein | Originates in the lumbar region and passes through the diaphragm into the thoracic cavity on the right side of the vertebral column; drains blood from the intercostal veins, esophageal veins, bronchial veins, and other veins draining the mediastinal region, and leads to the superior vena cava |
| Hemiazygos vein | Smaller vein complementary to the azygos vein; drains the esophageal veins from the esophagus and the left intercostal veins, and leads to the brachiocephalic vein via the superior intercostal vein |
Table20.11
Veins of the Head and Neck:
Blood from the brain and the superficial facial vein flow into each internal jugular vein (Figure 20.37). Blood from the more superficial portions of the head, scalp, and cranial regions, including the temporal vein and maxillary vein, flow into each external jugular vein. Although the external and internal jugular veins are separate vessels, there are anastomoses between them close to the thoracic region. Blood from the external jugular vein empties into the subclavian vein. Table 20.12 summarizes the major veins of the head and neck.Major Veins of the Head and Neck
| Vessel | Description |
|---|---|
| Internal jugular vein | Parallel to the common carotid artery, which is more or less its counterpart, and passes through the jugular foramen and canal; primarily drains blood from the brain, receives the superficial facial vein, and empties into the subclavian vein |
| Temporal vein | Drains blood from the temporal region and flows into the external jugular vein |
| Maxillary vein | Drains blood from the maxillary region and flows into the external jugular vein |
| External jugular vein | Drains blood from the more superficial portions of the head, scalp, and cranial regions, and leads to the subclavian vein |
Table20.12
Venous Drainage of the Brain:
Circulation to the brain is both critical and complex (see Figure 20.37). Many smaller veins of the brain stem and the superficial veins of the cerebrum lead to larger vessels referred to as intracranial sinuses. These include the superior and inferior sagittal sinuses, straight sinus, cavernous sinuses, left and right sinuses, the petrosal sinuses, and the occipital sinuses. Ultimately, sinuses will lead back to either the inferior jugular vein or vertebral vein.
Most of the veins on the superior surface of the cerebrum flow into the largest of the sinuses, the superior sagittal sinus. It is located midsagittally between the meningeal and periosteal layers of the dura mater within the falx cerebri and, at first glance in images or models, can be mistaken for the subarachnoid space. Most reabsorption of cerebrospinal fluid occurs via the chorionic villi (arachnoid granulations) into the superior sagittal sinus. Blood from most of the smaller vessels originating from the inferior cerebral veins flows into the great cerebral vein and into the straight sinus. Other cerebral veins and those from the eye socket flow into the cavernous sinus, which flows into the petrosal sinus and then into the internal jugular vein. The occipital sinus, sagittal sinus, and straight sinuses all flow into the left and right transverse sinuses near the lambdoid suture. The transverse sinuses in turn flow into the sigmoid sinuses that pass through the jugular foramen and into the internal jugular vein. The internal jugular vein flows parallel to the common carotid artery and is more or less its counterpart. It empties into the brachiocephalic vein. The veins draining the cervical vertebrae and the posterior surface of the skull, including some blood from the occipital sinus, flow into the vertebral veins. These parallel the vertebral arteries and travel through the transverse foramina of the cervical vertebrae. The vertebral veins also flow into the brachiocephalic veins. Table 20.13 summarizes the major veins of the brain.
Figure 20.37Veins of the Head and Neck This left lateral view shows the veins of the head and neck, including the intercranial sinuses.Major Veins of the Brain
| Vessel | Description |
|---|---|
| Superior sagittal sinus | Enlarged vein located midsagittally between the meningeal and periosteal layers of the dura mater within the falx cerebri; receives most of the blood drained from the superior surface of the cerebrum and leads to the inferior jugular vein and the vertebral vein |
| Great cerebral vein | Receives most of the smaller vessels from the inferior cerebral veins and leads to the straight sinus |
| Straight sinus | Enlarged vein that drains blood from the brain; receives most of the blood from the great cerebral vein and leads to the left or right transverse sinus |
| Cavernous sinus | Enlarged vein that receives blood from most of the other cerebral veins and the eye socket, and leads to the petrosal sinus |
| Petrosal sinus | Enlarged vein that receives blood from the cavernous sinus and leads into the internal jugular veins |
| Occipital sinus | Enlarged vein that drains the occipital region near the falx cerebelli and leads to the left and right transverse sinuses, and also the vertebral veins |
| Transverse sinuses | Pair of enlarged veins near the lambdoid suture that drains the occipital, sagittal, and straight sinuses, and leads to the sigmoid sinuses |
| Sigmoid sinuses | Enlarged vein that receives blood from the transverse sinuses and leads through the jugular foramen to the internal jugular vein |
Table20.13
Veins Draining the Upper Limbs:
The digital veins in the fingers come together in the hand to form the palmar venous arches (Figure 20.38). From here, the veins come together to form the radial vein, the ulnar vein, and the median antebrachial vein. The radial vein and the ulnar vein parallel the bones of the forearm and join together at the antebrachium to form the brachial vein, a deep vein that flows into the axillary vein in the brachium.
The median antebrachial vein parallels the ulnar vein, is more medial in location, and joins the basilic vein in the forearm. As the basilic vein reaches the antecubital region, it gives off a branch called the median cubital vein that crosses at an angle to join the cephalic vein. The median cubital vein is the most common site for drawing venous blood in humans. The basilic vein continues through the arm medially and superficially to the axillary vein.
The cephalic vein begins in the antebrachium and drains blood from the superficial surface of the arm into the axillary vein. It is extremely superficial and easily seen along the surface of the biceps brachii muscle in individuals with good muscle tone and in those without excessive subcutaneous adipose tissue in the arms.
The subscapular vein drains blood from the subscapular region and joins the cephalic vein to form the axillary vein. As it passes through the body wall and enters the thorax, the axillary vein becomes the subclavian vein.
Many of the larger veins of the thoracic and abdominal region and upper limb are further represented in the flow chart in Figure 20.39. Table 20.14 summarizes the veins of the upper limbs.
Figure 20.38Veins of the Upper Limb This anterior view shows the veins that drain the upper limb.
Figure 20.39Veins Flowing into the Superior Vena Cava The flow chart summarizes the distribution of the veins flowing into the superior vena cava.Veins of the Upper Limbs
| Vessel | Description |
|---|---|
| Digital veins | Drain the digits and lead to the palmar arches of the hand and dorsal venous arch of the foot |
| Palmar venous arches | Drain the hand and digits, and lead to the radial vein, ulnar veins, and the median antebrachial vein |
| Radial vein | Vein that parallels the radius and radial artery; arises from the palmar venous arches and leads to the brachial vein |
| Ulnar vein | Vein that parallels the ulna and ulnar artery; arises from the palmar venous arches and leads to the brachial vein |
| Brachial vein | Deeper vein of the arm that forms from the radial and ulnar veins in the lower arm; leads to the axillary vein |
| Median antebrachial vein | Vein that parallels the ulnar vein but is more medial in location; intertwines with the palmar venous arches; leads to the basilic vein |
| Basilic vein | Superficial vein of the arm that arises from the median antebrachial vein, intersects with the median cubital vein, parallels the ulnar vein, and continues into the upper arm; along with the brachial vein, it leads to the axillary vein |
| Median cubital vein | Superficial vessel located in the antecubital region that links the cephalic vein to the basilic vein in the form of a v; a frequent site from which to draw blood |
| Cephalic vein | Superficial vessel in the upper arm; leads to the axillary vein |
| Subscapular vein | Drains blood from the subscapular region and leads to the axillary vein |
| Axillary vein | The major vein in the axillary region; drains the upper limb and becomes the subclavian vein |
Table20.14
The Inferior Vena Cava:
Other than the small amount of blood drained by the azygos and hemiazygos veins, most of the blood inferior to the diaphragm drains into the inferior vena cava before it is returned to the heart (see Figure 20.36). Lying just beneath the parietal peritoneum in the abdominal cavity, the inferior vena cava parallels the abdominal aorta, where it can receive blood from abdominal veins. The lumbar portions of the abdominal wall and spinal cord are drained by a series of lumbar veins, usually four on each side. The ascending lumbar veins drain into either the azygos vein on the right or the hemiazygos vein on the left, and return to the superior vena cava. The remaining lumbar veins drain directly into the inferior vena cava.
Blood supply from the kidneys flows into each renal vein, normally the largest veins entering the inferior vena cava. A number of other, smaller veins empty into the left renal vein. Each adrenal vein drains the adrenal or suprarenal glands located immediately superior to the kidneys. The right adrenal vein enters the inferior vena cava directly, whereas the left adrenal vein enters the left renal vein.
From the male reproductive organs, each testicular vein flows from the scrotum, forming a portion of the spermatic cord. Each ovarian vein drains an ovary in females. Each of these veins is generically called a gonadal vein. The right gonadal vein empties directly into the inferior vena cava, and the left gonadal vein empties into the left renal vein.
Each side of the diaphragm drains into a phrenic vein; the right phrenic vein empties directly into the inferior vena cava, whereas the left phrenic vein empties into the left renal vein. Blood supply from the liver drains into each hepatic vein and directly into the inferior vena cava. Since the inferior vena cava lies primarily to the right of the vertebral column and aorta, the left renal vein is longer, as are the left phrenic, adrenal, and gonadal veins. The longer length of the left renal vein makes the left kidney the primary target of surgeons removing this organ for donation. Figure 20.40 provides a flow chart of the veins flowing into the inferior vena cava. Table 20.15 summarizes the major veins of the abdominal region.
Figure 20.40Venous Flow into Inferior Vena Cava The flow chart summarizes veins that deliver blood to the inferior vena cava.Major Veins of the Abdominal Region
| Vessel | Description |
|---|---|
| Inferior vena cava | Large systemic vein that drains blood from areas largely inferior to the diaphragm; empties into the right atrium |
| Lumbar veins | Series of veins that drain the lumbar portion of the abdominal wall and spinal cord; the ascending lumbar veins drain into the azygos vein on the right or the hemiazygos vein on the left; the remaining lumbar veins drain directly into the inferior vena cava |
| Renal vein | Largest vein entering the inferior vena cava; drains the kidneys and flows into the inferior vena cava |
| Adrenal vein | Drains the adrenal or suprarenal; the right adrenal vein enters the inferior vena cava directly and the left adrenal vein enters the left renal vein |
| Testicular vein | Drains the testes and forms part of the spermatic cord; the right testicular vein empties directly into the inferior vena cava and the left testicular vein empties into the left renal vein |
| Ovarian vein | Drains the ovary; the right ovarian vein empties directly into the inferior vena cava and the left ovarian vein empties into the left renal vein |
| Gonadal vein | Generic term for a vein draining a reproductive organ; may be either an ovarian vein or a testicular vein, depending on the sex of the individual |
| Phrenic vein | Drains the diaphragm; the right phrenic vein flows into the inferior vena cava and the left phrenic vein empties into the left renal vein |
| Hepatic vein | Drains systemic blood from the liver and flows into the inferior vena cava |
Table20.15
Veins Draining the Lower Limbs:
The superior surface of the foot drains into the digital veins, and the inferior surface drains into the plantar veins, which flow into a complex series of anastomoses in the feet and ankles, including the dorsal venous arch and the plantar venous arch (Figure 20.41). From the dorsal venous arch, blood supply drains into the anterior and posterior tibial veins. The anterior tibial vein drains the area near the tibialis anterior muscle and combines with the posterior tibial vein and the fibular vein to form the popliteal vein. The posterior tibial vein drains the posterior surface of the tibia and joins the popliteal vein. The fibular vein drains the muscles and integument in proximity to the fibula and also joins the popliteal vein. The small saphenous vein located on the lateral surface of the leg drains blood from the superficial regions of the lower leg and foot, and flows into to the popliteal vein. As the popliteal vein passes behind the knee in the popliteal region, it becomes the femoral vein. It is palpable in patients without excessive adipose tissue.
Close to the body wall, the great saphenous vein, the deep femoral vein, and the femoral circumflex vein drain into the femoral vein. The great saphenous vein is a prominent surface vessel located on the medial surface of the leg and thigh that collects blood from the superficial portions of these areas. The deep femoral vein, as the name suggests, drains blood from the deeper portions of the thigh. The femoral circumflex vein forms a loop around the femur just inferior to the trochanters and drains blood from the areas in proximity to the head and neck of the femur.
As the femoral vein penetrates the body wall from the femoral portion of the upper limb, it becomes the external iliac vein, a large vein that drains blood from the leg to the common iliac vein. The pelvic organs and integument drain into the internal iliac vein, which forms from several smaller veins in the region, including the umbilical veins that run on either side of the bladder. The external and internal iliac veins combine near the inferior portion of the sacroiliac joint to form the common iliac vein. In addition to blood supply from the external and internal iliac veins, the middle sacral vein drains the sacral region into the common iliac vein. Similar to the common iliac arteries, the common iliac veins come together at the level of L5 to form the inferior vena cava.
Figure 20.42 is a flow chart of veins flowing into the lower limb. Table 20.16 summarizes the major veins of the lower limbs.
Figure 20.41Major Veins Serving the Lower Limbs Anterior and posterior views show the major veins that drain the lower limb into the inferior vena cava.
Figure 20.42Major Veins of the Lower Limb The flow chart summarizes venous flow from the lower limb.Veins of the Lower Limbs
| Vessel | Description |
|---|---|
| Plantar veins | Drain the foot and flow into the plantar venous arch |
| Dorsal venous arch | Drains blood from digital veins and vessels on the superior surface of the foot |
| Plantar venous arch | Formed from the plantar veins; flows into the anterior and posterior tibial veins through anastomoses |
| Anterior tibial vein | Formed from the dorsal venous arch; drains the area near the tibialis anterior muscle and flows into the popliteal vein |
| Posterior tibial vein | Formed from the dorsal venous arch; drains the area near the posterior surface of the tibia and flows into the popliteal vein |
| Fibular vein | Drains the muscles and integument near the fibula and flows into the popliteal vein |
| Small saphenous vein | Located on the lateral surface of the leg; drains blood from the superficial regions of the lower leg and foot, and flows into the popliteal vein |
| Popliteal vein | Drains the region behind the knee and forms from the fusion of the fibular, anterior, and posterior tibial veins; flows into the femoral vein |
| Great saphenous vein | Prominent surface vessel located on the medial surface of the leg and thigh; drains the superficial portions of these areas and flows into the femoral vein |
| Deep femoral vein | Drains blood from the deeper portions of the thigh and flows into the femoral vein |
| Femoral circumflex vein | Forms a loop around the femur just inferior to the trochanters; drains blood from the areas around the head and neck of the femur; flows into the femoral vein |
| Femoral vein | Drains the upper leg; receives blood from the great saphenous vein, the deep femoral vein, and the femoral circumflex vein; becomes the external iliac vein when it crosses the body wall |
| External iliac vein | Formed when the femoral vein passes into the body cavity; drains the legs and flows into the common iliac vein |
| Internal iliac vein | Drains the pelvic organs and integument; formed from several smaller veins in the region; flows into the common iliac vein |
| Middle sacral vein | Drains the sacral region and flows into the left common iliac vein |
| Common iliac vein | Flows into the inferior vena cava at the level of L5; the left common iliac vein drains the sacral region; formed from the union of the external and internal iliac veins near the inferior portion of the sacroiliac joint |
Table20.16
Hepatic Portal System:
The liver is a complex biochemical processing plant. It packages nutrients absorbed by the digestive system; produces plasma proteins, clotting factors, and bile; and disposes of worn-out cell components and waste products. Instead of entering the circulation directly, absorbed nutrients and certain wastes (for example, materials produced by the spleen) travel to the liver for processing. They do so via the hepatic portal system (Figure 20.43). Portal systems begin and end in capillaries. In this case, the initial capillaries from the stomach, small intestine, large intestine, and spleen lead to the hepatic portal vein and end in specialized capillaries within the liver, the hepatic sinusoids. You saw the only other portal system with the hypothalamic-hypophyseal portal vessel in the endocrine chapter.
The hepatic portal system consists of the hepatic portal vein and the veins that drain into it. The hepatic portal vein itself is relatively short, beginning at the level of L2 with the confluence of the superior mesenteric and splenic veins. It also receives branches from the inferior mesenteric vein, plus the splenic veins and all their tributaries. The superior mesenteric vein receives blood from the small intestine, two-thirds of the large intestine, and the stomach. The inferior mesenteric vein drains the distal third of the large intestine, including the descending colon, the sigmoid colon, and the rectum. The splenic vein is formed from branches from the spleen, pancreas, and portions of the stomach, and the inferior mesenteric vein. After its formation, the hepatic portal vein also receives branches from the gastric veins of the stomach and cystic veins from the gall bladder. The hepatic portal vein delivers materials from these digestive and circulatory organs directly to the liver for processing.
Because of the hepatic portal system, the liver receives its blood supply from two different sources: from normal systemic circulation via the hepatic artery and from the hepatic portal vein. The liver processes the blood from the portal system to remove certain wastes and excess nutrients, which are stored for later use. This processed blood, as well as the systemic blood that came from the hepatic artery, exits the liver via the right, left, and middle hepatic veins, and flows into the inferior vena cava. Overall systemic blood composition remains relatively stable, since the liver is able to metabolize the absorbed digestive components.