Blood Vessels

A. Arteries - blood vessels which carry blood away from the heart

1. Elastic arteries - the largest of the arteries, these contain abundant elastic fibers in their walls; their function is to stretch with the pressure of cardiac systole
2. Muscular arteries - these are the distribution vessels; their walls consist predominantly of circular smooth muscle
3. Arterioles - the smallest of the arteries, they function to control blood pressure; they distribute and control blood flow to the capillary beds

B. Capillaries - the exchange vessels of the circulatory system, they consist of endothelium and a basal lamina

C. Veins

· conduct blood back to the heart

· they begin as venules and drain into increasingly larger-sized vessels

· they form anastomotic networks

· they are more numerous than arteries

· they tend to be paired or in multiples

· paired veins accompanying an artery in the extremities are termed venae comitantes

· approximately eighty percent of blood at any one time is in veins

· veins of the extremities contain valves, which allow flow of blood in only one direction

D. Lymphatics - vessels which conduct tissue fluid back into the blood vascular system

1. Lymph vessels - extremely thin-walled channels from the tissues, they collect in increasingly larger vessels, the largest of which are termed lymphatic ducts; they contain numerous valves and are afferent only, conducting lymph toward the heart

2. Lymph nodes - collections of lymphocyte producing tissues situated along lymph vessels at strategic sites; they filter lymph and dump lymphocytes into it to fight infection

Category: Anatomy Notes