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Blood Vessels Types of Blood Vessels Artery – carries blood away from the heart Vein – A vessel that carries blood towards the heart Capillaries – microscopic vessels that carry blood from small arteries to small viens Artery The Pathway of Blood Arteriole Cappillary Venuole Vein Blood Vessel Structure Tunica Intima (endothelium) Tunica Media (smooth muscle; elastic connective tissue) Tunica Adventitia (fibrous type of vessel connective tissue) Arteries Tunica Intima – Smooth lining Tunica Media – Allows constriction and dilation of vessels; thicker than in veins; muscle innervated by autonomic fibers Tunica Adventitia – Provides flexible support that resists collapse or injury; thicker than in veins; thinner than tunica media Veins Tunica Intima – Smooth lining with semi-lunar valves to ensure one way blood flow Tunica Media – Allows constriction and dilation of vessels; thinner than in arteries; muscle innervated by autonomic fibers Tunica Adventitia – Provides flexible support that resists collapse or injury; thinner than in arteries; thicker than tunica media Cappillaries Tunica Intima – Makes up the entire wall of the capillary; thinness permits transport across vessel wall Tunica Media – Absent Tunica Adventitia – Absent Micrograph of Blood Vessel Structure This light micrograph of a cross section of tissue contains an artery (left) and a vein (right). Note the prominence of the smooth muscle (tunica media) in the artery compared to the vein Function of Capillaries Most important vessels functionally Very tiny (on average, only 1mm long) According to one estimate, 1 cubic cm of muscle tissue contains more than 100,000 capillaries Primary exchange vessels The small size and large number ensures slow blood flow Microcirculation Function of Arteries Arteries serve mainly as “distributors,” carrying blood to the arterioles, which then carry blood to the capillaries Arterioles are important in maintaining normal blood pressure and circulation (resistance vessels) Precapillary sphincters function as valves regulating blood flow into the capillaries Function of Veins Function both as collectors and reservoir vessels (ability to hold blood) Capacitance -- Great ability to strech, therefore, they can hold large amounts of blood with almost no change in blood pressure Valves maintain the one way flow of blood The reservoir function of veins Pooled blood is moved toward the heart as valves are forced open by pressure from volume of blood from below. Closure of valves prevents backflow. Circulatory Routes Systemic Circulation – blood is pumped from the left side of the heart to all the tissues of the body Pulmonary Circulation – blood is pumped from the right side of the heart to the gas exchange tissues of the lungs Blood Flow Through the Circulatory System Main Arteries of the Body The Aorta Arteries of the Head and Neck Arteries at the Base of the Brain Major Arteries of the Upper Extremity Major Arteries of the Loser Extremity General Principles About Veins Veins branch into vessels of increasing size Vessels vary considerable in size and location from person to person Veins found deep in the body are called deep veins and those found near the surface are called superficial veins Major Veins of the Body Major Veins of the Head and Neck Major Veins of the Upper Extremity Principal Veins of the Thorax Inferior Vena Cava and its Abdominopelvic Tributaries Disorders of the Cardiovascular System Mitral Valve Prolapse Coronary Bypass Partial Blockage of Artery in Atherosclerosis Balloon Angioplasty Varicose Veins