The systemic circulation of the body begins at the origin of the aorta from the left ventricle. Follow the outlines in your Syllabus as you memorize the major branches of each part of the aorta. You should be able to trace the major arteries to each part of the body; and trace the veins back to the heart.
Arteries carry blood away from the heart. As arteries branch from one another, we refer to their origin. For example, the orign of the right coronary artery is the ascending aorta. The origin of the right subclavian artery is the brachiocephalic trunk. On the other hand, the origin of the left subclavian artery is the the arch of the aorta. (Oh no, a side-to-side difference that defies the rule of bilateral symmetry somewhat!)
Following the pattern of moving away from the heart, arteries have branches. The branches of the arch of the aorta are the brachiocephalic trunk and the left common carotid and left subclavian arteries. Arteries branch until they reach their terminal branches. When terminal branches arise, their origin marks the end of that artery. A good example is the abdominal aorta which has both paired and unpaired branches. However, inferiorly, the abdominal aorta ends by dividing into the right and left common iliac arteries. These arteries are the terminal branches of the abdominal aorta.
Arteries are named for the regions of the body they supply. That's why the origin of arteries can vary, but this topic is beyond the coverage required for a beginning Anatomy course. The axillary artery supplies the axilla. As soon as this artery moves into the arm (brachium), it becomes the brachial artery. Where is the facial artery located? What about the maxillary artery? Arteries may join together or anastomose to supply a region of the body. When arteries anastomose, that part of the body has alternate routes of supply if atherosclerosis should clog one of the major arteries in the region. Unfortunately, some regions of the body are supplied by end arteries or separate arteries and have no other supply in case of emergency.
Arteries always have vena communicantes, or accompanying veins, associated with them. Usually arteries are accompanied by veins of the same name. A good example is the femoral artery and femoral vein or brachial artery and brachial vein. However, we already discussed an exception in the coronary arteries and cardiac veins.
Since veins carry blood back to the heart, veins do not have branches. Rather, with veins, we begin our discussion at the tissues. Smaller veins unite to form larger and larger veins. Veins do not have origins like arteries; they are formed by the union of two or more smaller veins. A good example is the formation of the superior vena cava which is a very large vein that carries blood back to the heart from the head, neck, upper extremity, and part of the thorax. The superior vena cava is formed by the union of the right and left brachiocephalic veins. Another example: the right brachiocephalic vein is formed by the union of the right internal jugular vein and the right subclavian vein.
Veins do not have branches, but they may receive tributaries between their formation and the point at which they empty into, or participate in the formation of, a larger vein. After its formation from the brachiocephalic veins, the superior vena cava receives the azygos vein before the SVC empties into the right atrium. The azygos vein is my absolute favorite of any vein in the body. It's formation begins in the intercostal spaces of thorax. This vein is always pinned on the last lab practicum!!
And now for the last general fact. Arteries supply a region of the body; veins drain a region. The internal jugular vein drains the cranial cavity. The subclavian vein drains the upper extremity.
The typical pattern seen most often in the body is a pattern in which blood flows from the heart to arteries to arterioles into a capillary bed into venules to veins and back to the heart. Study the pictures of this pattern in your textbook. Note the position of the metarteriole with its precapillary sphincter of smooth muscle which controls flow into the capillary bed. Notice the large surface area of the capillary bed.
Such a large surface area is not practical for the skin. Remember that blood vessels extend well into the dermis, but not into the epidermis of the skin. These blood vessels bring blood very close to the surface of the body--close enough for heat exchange to take place. If a capillary bed existed in the skin, too much heat would be lost from the body. Therefore, there is no capillary bed in the skin. Blood moves from arterioles directly into venules.
On the other hand, when an extra capillary bed is present, a portal system is described. The best example of a portal system begins at the small intestine. In the process of absorbing nutrients from the food you eat, bacteria and toxic substances like alcohol may also move into the blood with the nutrients. Rather than send this blood directly back to the heart, the blood is diverted to the liver sinusoids which contain macrophages and other mechanisms (more in Physiology) to prepare the blood for its return to the heart.
This flow diagragm begins with the abdominal aorta which gives rise to the superior mesenteric artery. Arterioles carry oxygenated blood into the capillary bed of the villus. Here the blood picks up the products of absorption. This is the first capillary bed. The superior mesenteric vein unites with the splenic vein to form the hepatic portal vein which carries the deoxygenated blood from the gastrointestinal tract into the liver sinusoids. This is the second capillary system. The hepatic vein drains the liver sinusoids; it is a tributary of the IVC.
How does the liver receive oxygenated blood? Although not a part of the portal circulation story, this is still an important question. The hepatic artery, a branch of the celiac trunk, supplies the liver sinusoids with oxygenated blood. The celiac trunk is an unpaired branch of the abdominal aorta. It is called a trunk because it immediately divides into several branches just distal to its origin.
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