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Vasculature and Lymphatics Student Learning Objectives: • • • Identify the primary blood vessels of the body. Follow the blood through the path of the circulation. Identify the major structures of the lymphatic system. Structures to be studied: Vessels: Aorta Pulmonary artery Superior vena cava Inferior vena cava Pulmonary veins Brachiocephalic artery and vein Common carotid artery Internal carotid artery Eternal carotid artery Facial artery and vein Maxillary artery and vein Jugular veins Subclavian artery and vein Axillary artery and vein Brachial artery and vein Radial artery and vein Ulnar artery and vein Basilic vein Cephalic vein Accessory cephalic vein Median cubital vein Celiac artery (trunk) Superior mesenteric artery Renal artery and vein Gonadal artery and vein Inferior mesenteric artery Hepatic-portal vein Common iliac artery and vein Internal iliac artery and vein External iliac artery and vein Femoral artery and vein Popliteal artery and vein Anterior tibial artery and vein Posterior tibial artery and vein Great saphenous vein Lymphatic Structures: Lymphatic vessels Lymph nodes Tonsils Pharyngeal Palatine Lingual Spleen Thymus Introduction The vasculature consists of numerous blood vessels that provide the tubing through which the blood travels around the body. Arteries are the vessels that transport blood away from the heart. Such vessels typically transport highly oxygenated blood. The pulmonary arteries, however, carry blood with a low level of oxygen. Arterioles branch off of the arteries and help distribute the blood within an organ. Tiny capillaries serve as the exchange sites between blood and tissues. The venules connect the capillaries to the veins that transport blood back to the heart. Veins typically carry low oxygen blood (i.e. deoxygenated blood), again with the exception of the pulmonary veins. The arteries and arterioles have a very thick muscular wall. They help ensure that the blood will arrive at the tissues with enough energy to be able to return to the heart after they journey through the tissues. Capillaries have no muscle at all in the walls. Their very thin-walled design allows them to have efficient exchange with the tissue cells. The venules and veins have a thin muscular wall that helps them accommodate extra volumes of blood as the blood is being returned to the heart. In this exercise, you will be looking at the main arteries and veins of the body. The names of vessels in the body are often associated with terms that refer to a body region and the directional terms that you have learned earlier in the semester. In addition, we will examine the structure of the major lymphatic organs. The lymphatic system plays important roles in protecting the body from disease as well as helping to ensure that tissue fluids are recirculated back into the blood supply. Arteries of Upper Body In the last exercise, you became familiar with some of the major vessels associated with the heart. The pulmonary artery emerges from the right ventricle and transports blood to the lungs. This vessel carries deoxygenated blood (only artery in the body to do so) because the blood has just returned from the body organs and is on its way to the lungs to pick up oxygen. Most arteries of the body are branches off of the aorta, the artery associated with the left ventricle. The aorta emerges superiorly from the heart and after a short distance, makes a large Uturn and begins heading inferiorly towards the abdomen. The first part of the aorta is called the ascending aorta; the U-turn portion is known as the aortic arch; and the remainder is called the descending aorta. After passing through the diaphragm, the aorta enters the abdominal cavity and is often referred to as the abdominal aorta. The first branches off of the aorta provide blood to the myocardial cells of the heart. These vessels, coronary arteries, can be seen running over the outer surface of the heart. Three main vessels emerge from the aortic arch. The first major branch off of the aortic arch is the brachiocephalic artery. This very short artery quickly splits into two other vessels: the right common carotid artery and the right subclavian artery. The left subclavian and left common carotid arteries come off separately from the aortic arch as the next two main branches. The common carotid arteries travel superiorly through the neck region on either side of the airway (i.e. the trachea). The pulse can be taken in the neck by placing your fingers into the groove between the muscles just inferior to the mandible. At about the level of the ear, the common carotid arteries split into the internal and external carotid arteries. The internal carotid artery (which cannot be seen on the pictures) enters the skull and provides most of the nutrients to the tissues of the brain. The vertebral and basilar arteries provide the remaining blood flow to the brain tissue. The external carotid artery supplies nutrients to the surface areas of the skull and face. The facial artery, supplying the skin and some muscles of the face, and the maxillary artery (this vessel is internal and cannot be seen on the picture), supplying deeper muscles and the oral cavity, are important branches of the external carotid artery. The facial artery is an important pressure point used to stop bleeding from the face. Pressure is applied to the vessel where it curves around the mandible. The subclavian arteries travel towards the arms. In the region of the armpit, the vessel receives a new name – not because of any branching, but merely due to the change of location. The vessel will now be known as the axillary artery. As the vessel moves into the upper arm, the name is once again changed – due to a new location – to the brachial artery. These names are similar to terms you learned for the body regions earlier in the semester associated with the armpit and upper arm areas. The brachial artery is an important pressure point for controlling bleeding from the hand or arm. Pressure is applied to the midbrachial region, in the crevice between the biceps and triceps muscles. In the area of the elbow, the vessel finally has its first major branches. The branch that runs down the medial aspect of the lower arm is the ulnar artery. The branch that runs laterally in the lower arm is the radial artery. These names refer to the bones that are located in the same area. The radial artery is the vessel used for taking the pulse in the wrist region. Arteries of Lower Body As the aorta enters the abdominal cavity, a number of additional major vessels emerge. The celiac artery (trunk) is the first abdominal branch off of the aorta. This very short vessel splits almost immediately into the gastric artery (supplying the stomach), the splenic artery (supplying the spleen), the hepatic artery (supplying the liver), and the pancreatic artery (supplying the pancreas). The superior mesenteric artery is the next branch to emerge from the abdominal aorta. This can only be seen as a small “stump” on the picture because the vessel travels out of the aorta and into the tissues that are associated with the small intestine. That tissue has been cut away on this model to allow you to visualize the vessels underneath. This normally fans out with many branches to the intestine. A short distance inferior to the superior mesenteric artery, the renal arteries emerge from the sides of the aorta. One renal artery supplies blood to each kidney. The gonadal arteries branch off of the aorta just below the renal arteries. These vessels supply the reproductive organs of the male and female. These vessels are usually called ovarian arteries in the female and the testicular arteries in the male. The inferior mesenteric artery is the last branch off of the abdominal aorta. This vessel supplies blood to the large intestine. The aorta ends by splitting into the two common iliac arteries which lead to the lower portion of the body. Like the common carotid arteries in the head/neck region, the common iliac arteries have internal and external branches. The internal iliac artery supplies the pelvic cavity organs. The external iliac artery transports blood to the leg. As soon as the external iliac artery exits the pelvic cavity, the name is changed to the femoral artery. This vessel supplies blood to the thigh region. Below the knee, the femoral artery splits into the anterior tibial artery and the posterior tibial artery which run down the front and back of the lower leg, respectively. Veins of Lower Body The return of blood to the heart from various body structures follows a path similar to the flow of blood out to the various body areas. You will find that many of the veins bear the same names as the arteries that travel to the same body region. Blood often has difficulty returning to the heart through the veins, however, due to the low blood pressures within the vessels so there will be a number of “alternative” routes through which the blood can make the journey. Blood is collected from the lower leg by the anterior tibial vein and posterior tibial vein. These run next to the arteries of the same name and cannot be seen on the picture. The tibial veins flow into the femoral vein which runs through the thigh region and feeds into the external iliac vein once inside the pelvic cavity. Blood from the leg can also be routed through the great saphenous vein, a long vessel that spans the area from the ankle to the groin. This vessel is often removed due to the development of varicose veins, a condition in which the vein valves become damaged. This vessel is also used for cardiac bypass surgeries, providing the “new” blood vessel segments that will be used to bridge over the blocked areas of the coronary arteries in the heart. In the pelvis, the external iliac vein joins with the internal iliac vein returning blood from the pelvis, to form the common iliac vein. The short common iliac veins fuse forming the inferior vena cava. As the inferior vena cava makes its way through the abdomen, blood returning from the abdominal organs will be routed to this vessel. The renal veins return blood from the kidneys directly into the inferior vena cava. Blood from most of the other abdominal organs, however, will be making a detour prior to entering the vena cava. Blood collected from the stomach, small intestine, most of the large intestine, pancreas, and spleen travels through veins that join to form the hepatic-portal vein which makes a stop at the liver before traveling back to the heart. This unusual path allows the liver to modify the composition of the blood and remove harmful materials before the blood returns to the heart and circulates back around to the body organs. Blood leaving the liver enters the inferior vena cava via the hepatic veins. The inferior vena cava then enters the thoracic cavity and drains into the right atrium of the heart. Veins of Upper Body Blood returning from the arm travels through the radial vein and ulnar vein of the lower arm. These vessels run along side the arteries of the same name. These vessels cannot be seen on the pictures because the vessels were removed so that you could view the arteries. The radial and ulnar veins join to form the brachial vein which becomes the axillary vein when the vessel reaches the area of the armpit. In the area of the shoulder the name of the vessel changes to the subclavian vein. There are several “alternative” routes for the blood returning from the arms. The basilic vein runs medially up the arm from the wrist to the axilla where it joins with the brachial vein. The accessory cephalic vein and the cephalic vein run laterally up the forearm and upper arm, respectively. The cephalic vein joins the axillary vein in the shoulder. The median cubital vein cuts diagonally across the antebrachial region, connecting the cephalic and basilic veins. Blood returning from the head travels through the jugular veins. These vessels form from the joining of veins from areas that were served by the branches of the common carotid arteries. There are no carotid veins and there are no jugular arteries! The arteries in the head/neck are the carotids and the veins in the head/neck are the jugulars. The jugular veins from the head join with the subclavian veins from the arm to form the brachiocephalic veins. The left and right brachiocephalic veins fuse to from the superior vena cava which enters the right atrium of the heart. Lymphatic System The lymphatic system is structured somewhat like the vasculature of the circulation. Tiny lymphatic capillaries collect up excess tissue fluid and send it to the larger, vein-like lymphatic vessels. These lymphatic vessels travel to various parts of the body, often along side the circulatory vessels. The fluid, known as lymph, eventually is returned to the blood circulation when the largest lymphatic vessels (the right lymphatic duct and the thoracic duct) join into the subclavian veins. Before returning the lymph to the blood circulation, the fluid is filtered by lymph nodes. Lymph nodes are responsible for filtering the fluid that was retrieved from the local area near the lymph node. Lymph nodes are not evenly distributed over the entire body. They tend to congregate near portals of entry, the places where it is likely that environmental materials would enter the body. As a result, there are numerous lymph nodes in the head, neck, thorax, and abdomen, but few in the region of the arms and legs except where the limb attaches to the trunk of the body. Because there are so many surfaces that are exposed to the environment up in the head region, the tonsils have been placed into the throat region. This additional set of special lymph nodes provides a second filtering of the lymph before it returns to the blood supply. The pharyngeal tonsils lie posterior to the nasal area and are more commonly known as the adenoids. The palatine tonsils are found in the posterior oral cavity and are referred to as the tonsils. The lingual tonsils lie at the base of the tongue. The spleen is located in the upper left abdomen and filters blood much the same way that the lymph nodes filtered the lymph. Anything that was missed by the lymph nodes or that was placed directly into the blood could be captured by the spleen. The final organ, the thymus, is found in the thorax, just anterior to the large vessels associated with the heart. This organ is very large in children, but atrophies (i.e. shrinks) after puberty. The thymus is involved in the maturation of the T-lymphocytes that are important for immunity.