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17 BLOOD VESSELS Blood Vessels (dynamic structures that pulsate, as well as constrict and relax) 1. Main types of Vessels Arteries – vessels through which blood is pumped away from the heart. Arteries branch into arterioles and finally into capillary beds that feed the tissues From the capillary beds, blood is pumped into venules that empty into large veins (which take blood back to the heart through the great veins). Gas and nutrient exchange occurs only through the capillary walls 60,000 miles of vessels in a human 2. All vessels except capillaries have 3 layers or tunics a) Tunica Interna or Tunica Intima -(inner most layer) continuous with lining of heart; reduce friction of blood through lumen (the inside of the vessels) b) Tunica Media – Composed of smooth muscles and sheets of elastin – allows muscles to stretch and maintains blood pressure and continuous blood circulation i. Vasoconstriction – tighten (decreases diameter of lumen) triggered by low Oxygen in Systemic Circuit and cold temperatures 18 Vasodilation – open, loosen (increases diameter of lumen) triggered by excess or adequate Oxygen in Systemic Circuit and warm temperatures c) Tunica Externa – Composed of collagen fibers i. Protect and reinforce vessel ii. Anchor to surrounding structures iii. Contains nerve fibers and lymphatic vessels ii. 3. Capillaries – only vessels to directly serve cells in tissues; give cells oxygen (also hormones and nutrients) and remove carbon dioxide (and other wastes) a) Thin wall of just inner layer = Tunica Interna b) 3 types of Capillaries i. Continuous capillaries– abundant in the skin and muscles Uninterrupted lining Intercellular clefts allow fluids and small solutes through ii. Fenestrated capillaries – (fenestra = windows) abundant in small intestine, kidneys, endocrine glands – allows slightly larger things to pass through Endothelial cells (lining) have oval pores called fenestra 19 iii. Sinusoids capillaries – leaky capillaries abundant in the liver, bone marrow, lymphoid tissues and some endocrine Also have Fenestrations – larger holes Large intercellular clefts – leaky; lymphoid tissues and large lumens c) Capillary beds – capillaries function as networks, not independently i. Microcirculation – blood flow from arterioles capillary bed venules ii. Precapillary sphincter – contracted = closed = blood will bypass tissue when blood is not needed there (e.g., muscles tissue does not need a lot of blood when at rest) 20 LYMPHATIC SYSTEM Lymphatic System – pumpless system of vessels, lymph nodes, and other lymphoidal organs that aides the cardiovascular system in its function 21 Lymphatic Vessels – function to pick up the excess tissue fluid (lymph – primarily water and some dissolved proteins) that has leaked from the blood and return it to the bloodstream Although the lymphatic system is a low pressure pumpless system, the transport of lymph is actually conducted by smooth muscles in the lymphatic vessel walls. Small valves keep the lymph toward the heart during these contractions. Edema – accumulation of fluid in the body tissues Right Lymphatic Duct – drains the lymph from the right arm right side of the head and thorax and empties into the Subclavian Vein Thoracic Duct – drains lymph from the rest of the body and empties into the Subclavian Vein 22 Lymph Nodes – closely related to the immune system the lymph nodes are responsible for removing foreign material (bacteria and tumor cells) from the lymphatic system by producing lymphocytes. Particularly large clusters of lymph nodes are found in the inguinal, axillary, and cervical regions. Macrophages – cells of lymph nodes that engulf/destroy bacteria, viruses, & foreign substances Lymphocytes – a type of White Blood Cell (which arise from Red Bone Marrow) also found in the lymph nodes respond to foreign bodies as well Other Lymphoidal Organs include the spleen, thymus gland, tonsils, and Peyer’s Patches of the intestine as well as bits of lymphatic tissue scattered in the epithelial and connective tissues. Spleen – blood rich organ that filters & cleanses blood (rather than lymph as lymph nodes do) Functions of the Spleen: Destroys worn-out RBCs and returns some of their breakdown products to the liver Synthesizes lymphocytes Stores Platelets Blood Reservoir Thymus Gland – a lymphatic mass found low in the throat overlying the heart that produces hormones that function in programming of lymphocytes to carry out certain functions in the body 23 Tonsils – small masses of lymphatic tissue found in the throat that trap and remove bacteria or other foreign pathogens Peyer’s Patches – small masses of lymphatic tissue in the wall of the small intestine that trap bacteria (always in high numbers in intestine) and keep them from penetrating the intestinal wall 24 25 Major Arteries in Systemic Circulation Arteries are typically located deep in well protected areas of the body. Aorta – largest artery in the body Major Regions and Branches of the Aorta: 1. Ascending aorta – first part of the aorta the ascends from the heart a. Right and Left Coronary Arteries that serve the heart 2. Aortic Arch – large bend in the aorta soon after is leaves the heart a. Brachiocephalic Artery – branches into the Right Common Carotid Artery and Right Subclavian Artery b. Left Common Carotid – branches into the Left Internal Carotid that serves the brain and the Left External Carotid that serves the skin and muscles of the head and neck c. Left Subclavian Artery – branches into the Vertebral Artery (which serves part if the brain) the Axillary Artery and the Brachial Artery. The Brachial Artery further divides into the Radial and Ulnar Arteries. 3. Thoracic Aorta – next section of the aorta contained within the thorax running on the anterior side of the spine a. Intercostal Arteries (ten pairs) – supply the muscles of the thoracic wall b. Bronchial Arteries – serve the lungs c. Esophageal Arteries and Phrenic Arteries serve the esophagus and diaphragm respectively 4. Abdominal Aorta – last section of the aorta located inferior to the diaphragm within the abdominal cavity a. Celiac Trunk – branches into the Left Gastric Artery (supplies the stomach), the Splenic Artery (serves the spleen), and the Common Hepatic Artery (supplies the liver). b. Superior Mesenteric Artery – supplies the small intestines and first ½ of the large intestine c. Renal Arteries – serve the kidneys d. Gonadal Arteries – serve the gonads (called the ovarian arteries in females and testicular arteries in males) e. Lumbar Arteries – several pairs of arteries serving the heavy muscles of the abdominal and trunk walls f. Inferior Mesenteric Artery – supplies second ½ of large intestine g. Common Iliac Arteries – divide into the Internal Iliac Artery (supplies the bladder and rectum) and the External Iliac Artery which enters the thigh and becomes the Femoral Artery. The Femoral Artery and its branch the Deep Femoral Artery which serve the thigh. At the knee the Femoral Artery Branches into the Popliteal Artery which again splits into the Anterior and Posterior Tibial Arteries. The Anterior Tibial Artery terminates into the Dorsalis Pedis Artery which supplies the dorsum of the foot. 26 27 Major Veins in Systemic Circulation Veins are typically located in more superficial areas of the body but some some follow the course of the major arteries. With a few exceptions the naming of these veins is identical to that of the companion arteries Superior Vena Cava – veins draining the head and arms Inferior Vena Cava – veins draining the lower body Major Veins that drain into the Superior Vena Cava: 1) Radial and Ulnar Veins drain the forearm and unite to form the Brachial Vein which in turn drains into the Axillary Vein 2) The Cephalic Vein which drains the lateral aspect of the arm also drains into the Axillary Vein and the Basilic Vein that drains the medial aspect of the arm drains into the Brachial Vein. The Cephalic and Basilic veins are joined at the anterior aspect of the elbow by the median cubital vein. 3) The Axillary Vein and the External Jugular Vein (which drains blood from the skin and muscles of the head) empty into the Subclavian Vein. 4) The Vertebral Vein drains the posterior part of the head as the Internal Jugular Vein drains the dural sinuses of the brain. 5) The Brachiocephalic Veins receive blood from the Subclavian Vein, Vertebral Vein, and Internal Jugular Veins before joining to form the Superior Vena Cava. 6) The Azygos Vein drains the thorax before leading into the Superior Vena Cava Major Veins the drain into the Inferior Vena Cava: 1) The Anterior and Posterior Tibial Veins and Peronal Vein drain the leg before ascending into the Popliteal Vein, then the Femoral Vein, and finally the External Iliac Vein. 2) The Great Saphenous Veins (the longest veins in the body) receive superficial drainage of the leg beginning at the Dorsal Venous Arch and emptying into the Femoral Vein in the thigh. 3) The Common Iliac Vein which is formed from the junction of the External Iliac Vein and the Internal Iliac Vein drains directly into the Inferior Vena Cava 4) The Gonadal Veins drain the gonads and the Renal Veins drain the kidneys. 5) The Hepatic Portal Vein drains the digestive tract organs and carries this blood through the liver before it enters the systemic circulation. The Hepatic Veins drain the liver. 28