Blood Vessels arteries carry blood away from ventricles

Blood Vessels • arteries • carry blood away from ventricles of heart • arterioles • receive blood from arteries • carry blood to capillaries • sites of exchange of substances between blood and body cells • venules • receive blood from capillaries • veins • carry blood toward ventricle of heart 15 -30

Arteries and Arterioles Artery • thick strong wall • endothelial lining • middle layer of smooth muscle and elastic tissue • outer layer of connective tissue • carries blood under relatively high pressure Arterioles • thinner wall than artery • endothelial lining • some smooth muscle tissue • small amount of connective tissue • helps control blood flow into a capillary 15 -31

Walls of Artery and Vein 15 -32

Arteriole • smallest arterioles only have a few smooth muscle fibers • capillaries lack muscle fibers 15 -33

Metarteriole connects arteriole directly to venule 15 -34

Capillaries • smallest diameter blood vessels • extensions of inner lining of arterioles • walls are endothelium only • semipermeable • sinusoids – leaky capillaries 15 -35

Capillary Network 15 -36

Regulation of Capillary Blood Flow Precapillary sphincters • may close a capillary • respond to needs of the cells • low oxygen and nutrients cause sphincter to relax 15 -37

Exchange in the Capillaries • water and other substances leave capillaries because of net outward pressure at the capillaries’s arteriolar ends • water enters capillaries’s venular ends because of a net inward pressure • substances move in and out along the length of the capillaries according to their respective concentration gradients 15 -38

Venules and Veins Venule • thinner wall than arteriole • less smooth muscle and elastic tissue than arteriole Vein • thinner wall than artery • three layers to wall but middle layer is poorly developed • some have flaplike valves • carries blood under relatively low pressure • serves as blood reservoir 15 -39

Venous Valves 15 -40

Blood Volumes in Vessels 15 -41

Arterial Blood Pressure – force the blood exerts against the inner walls of the blood vessels Arterial Blood Pressure • rises when ventricles contract • falls when ventricles relax • systolic pressure – maximum pressure • diastolic pressure – minimum pressure 15 -42

Pulse • alternate expanding and recoiling of the arterial wall that can be felt 15 -43

Factors That Influence Arterial Blood Pressure 15 -44

Control of Blood Pressure Controlling cardiac output and peripheral resistance regulates blood pressure 15 -45

Control of Blood Pressure If blood pressure rises, baroreceptors initiate the cardioinhibitory reflex, which lowers the blood pressure 15 -46

Control of Blood Pressure Dilating arterioles helps regulate blood pressure 15 -47

Venous Blood Flow • not a direct result of heart action • depends on skeletal muscle contraction • depends on breathing • depends on venoconstriction 15 -48