The blood vessels are hollow tubes that form a circuit. They begin and end in the heart. The red and blue in the figure correspond to oxygenated and unoxygenated blood. The circulatory system resembles a bakery delivery route. The bakery truck leaves the bakery, delivers the bread to the store, and returns empty to the bakery. Similarly, the heart pumps the blood from the heart to the rest of the body, delivering oxygen to the tissues and returning unoxygenated blood to the heart.
The slide illustrates the anatomical classification of blood vessels. Arteries carry blood away from the heart, and veins return blood to the heart. Blood flows from the large arteries, to the small arteries called arterioles to the capillaries to the venules, and to large veins back to the right atrium of the heart.
Blood vessels, except the capillaries, have three layers, or tunicas. The thickness and composition of the layers vary according to the function of the blood vessel. The large arteries are thick and strong to sustain high blood pressures. The arterioles contain a lot of smooth muscle. Veins are thinner than arteries because they don’t need to carry blood at high pressure. Veins have valves that are placed frequently along their length. They keep the blood moving forward toward the heart and prevent pooling of blood in dependent parts of the body like the legs. What are varicose veins? These veins are twisted and distended because of poor drainage of blood in the lower extremities, usually caused by defective valves.
The large arteries function like pipes or conductance vessels to carry blood at high pressure. The arterioles can contract and relax to control the radius of the vessel, hence their name, resistance vessels. The smaller the radius of the vessel, the greater the resistance. Capillaries’ single layers allow for exchange of nutrients and waste at the cellular level, hence their name, exchange vessels. Venules and veins temporarily “store” much blood and return it to the heart, hence their name, capacitance or storage vessels.
All arteries branch off the aorta, directly or indirectly.
The first branches off the ascending aorta, the left and right coronary arteries, nourish the heart, especially the myocardium. The aortic arch gives rise to the brachiocephalic artery, which branches into arteries that nourish the head, shoulders, and arms. The aortic arch also gives rise to the left common carotid, whereas the right common carotid branches off the brachiocephalic. The left and right subclavian arteries supply blood to the shoulders and upper extremities. The left subclavian arises directly from the aortic arch and the right subclavian arises from the brachiocephalic.
The subclavian arteries deliver blood to the shoulder and upper extremities. The subclavian arteries branch into the axillary arteries, which give rise to the brachial arteries. These vessels then branch into arteries that nourish the forearm and hand.
The descending aorta sends branches to the thoracic wall and organs. Intercostal arteries nourish the area between the ribs. Arising from the abdominal aorta, the celiac truck branches into the gastric, hepatic, and splenic arteries. Along with the mesenteric arteries, these nourish the organs of digestion and the spleen. The renal arteries nourish the kidneys. Other branching arteries nourish the pelvis and pelvic organs. The abdominal aorta splits into the common iliac arteries, primarily to nourish the lower extremities.
The vessels in the lower extremities are arranged in a branching system similar to that of the vessels in the upper extremities. The common iliac branches into internal and external iliac arteries. The internal iliac supplies the walls and viscera of the pelvis and the external iliac supplies the lower extremities. In the lower extremities, the external iliac gives rise to the femoral, popliteal, anterior and posterior tibial, and dorsalis pedis arteries.
Venous blood from all parts of the body eventually drains into the venae cavae and eventually into the right atrium of the heart. Unlike the arteries, which are a diverging system (constantly branching into smaller and smaller vessels), the veins are a converging system. They gather up blood from the capillaries, move it into larger and larger veins and return it to the heart.
One important venous pathway is the ulnar vein draining into the basilic vein, into the axillary vein, into the subclavian vein, and into the brachiocephalic vein, which empties into the SVC. The jugular veins drain blood from the head and brain into the subclavian veins. Why is jugular vein distention (JVD) observed in right heart failure? Because it is so close to the heart, the jugular vein distends to accommodate any backed-up blood.
The IVC receives blood from the lower part of the body. The first group of vessels on the slide drain the lower extremities. The renal veins drain the kidneys and the hepatic veins drain the liver. Why does hepatic congestion occur in right heart failure? Because of the liver’s rich supply of vessels and its close proximity to the heart, the liver distends to accommodate backed-up blood.
Typically, an organ is nourished with blood delivered by a large artery and drained by a large vein that empties into the vena cava. However, some organs have a different arrangement of blood vessels. These are called special circulations.
The brain is nourished by the carotid and vertebral arteries. The internal carotids ascend anterolaterally to the base of the brain. The vertebral arteries ascend posterolaterally to the base of the brain, where they merge to form the basilar artery. An artery that commonly suffers from occlusion (atherosclerotic plaque) is the common carotid. What is the primary clinical concern regarding this occlusion? Occlusion of the carotid artery causes inadequate circulation to the brain and impaired cognitive function. Depending on the cause, treatment includes surgery, stenting, and thrombolytics. The circle of Willis is described on the next slide.
The basilar artery and the internal carotids form the circle of Willis at the base of the brain. Branches of the circle of Willis penetrate the brain. The brain is drained primarily by the internal jugular veins. What happens if a vessel in this area is occluded or ruptures? Such an event would cause brain damage, the nature of which depends on the location of the accident.
The internal jugular vein provides the primary drainage for the brain and the external jugular veins drain the head and face. These veins eventually empty into the SVC.
The liver receives two blood supplies from the portal vein and the hepatic artery. The portal vein drains the organs of digestion. Rather than oxygen, it delivers blood rich in the end products of digestion to the liver. The liver uses the products of digestion and detoxifies the blood. The hepatic artery supplies oxygen to the liver. The portal vein is formed by the union of the superior mesenteric vein and splenic vein. The hepatic vein drains the liver. In cirrhosis of the liver, blood cannot enter the organ and backs up into the portal venous system, elevating portal pressure. Consequences are ascites and ruptured esophageal varices.
The fetus is submerged in amniotic fluid and therefore does not use lungs for breathing. The fetal and maternal blood supplies meet in the placenta where breathing, exchange of nutrients, and exchange of wastes occur. The heart modifications bypass the fetal lungs. Occasionally, the ductus arteriosis does not close at birth. What clinical consequences ensue? The blood continues to shunt from the baby’s descending aorta into the pulmonary artery, overworking the right ventricle and lungs. Usually, this is successfully treated with drugs or surgery to close the ductus arteriosus.
The umbilical vein, carrying oxygenated blood, comes from the placenta and partially bypasses the liver by the ductus venosus. This blood trains into the fetal IVC. Note the purple coloration of the umbilical vein on the slide. Blood returns to the placenta by two umbilical arteries that emerge from the fetal common iliac artery. What happens if the umbilical cord becomes compressed during labor from pressing against the cervix? The arterial blood supply to the fetus is cut off, depriving the fetal brain of oxygen. The fetal heart monitor will identify cord compression.
The pulse can be felt in any large artery lying close to the body, but the pulse is taken most often at the radial artery. Why might you be asked to take the pulse of a diabetic at the dorsalis pedis? A weak or absent pulse at this site indicates inadequate circulation to the feet.
Transcript of "Chapter 018"
The Human Body in Health and
Illness, 4th edition
Anatomy of the Blood Vessels