Chapter 19 - Learning Objectives
Describe the three layers that typically form the wall of a blood vessel and state the function of each.
1) Tunica Intima: endothelium lines the lumen of all vessels; continuos with all endocardial lining; flat cells fit closely together to form a slick surface that minimizes friction as blood moves through the lumen
2) Tunica Media: smooth muscle (thinner in veins) and sheets of elastin; sympathetic vasomotor nerve fibers control vasoconstriction and vasodilatation of vessels; regulates circulatory dynamics.
3) Tunica Externa: collagen fibers protect, reinforce, and anchor vessels; innervated; infiltrated with lymphatic vessels (elastin in larger vessels); "vaso vasorum: --> vessel to the vessel
Define vasoconstriction and vasodilatation
Vasoconstriction: reduction in the lumen diameter as the smooth muscle contracts
Vasodilation: increase in the lumen diameter as the smooth muscle contracts
Compare and contract the structure and function of the three types of arteries
1) elastic (conducting) arteries: thick walled arteries near the heart (the aorta and it's major branches). They are the largest in diameter and the most elastic. They contain more elastin than other vessel types. They are pressure reservoirs (expand and recoil as blood in ejected from the heart)
2) muscular (distributing) arteries: deliver blood to specific body organs and account for most of the named arteries. They have the thickest tunica media of all vessels (more active in vasoconstriction and less distensible
3) arterioles: smallest of the arteries. Larger arterioles have all three tunics and smaller arterioles are little more than a single layer of smooth muscle cels spiraling around the endothelial lining
Describe the structure and function of a capillary bed.
Interweaving networks of capillaries. In most body regions, a capillary bes consists of 2 types of vessels (1) a vascular shunt and (2) true capillaries
Describe the structure and function of veins and explain how they differ from arteries.