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AP Biology Lab #10 Physiology of the Circulatory System Blood pressure is a measurement of the force applied to the walls of the arteries as the heart pumps blood throughout the body. Blood pressure is determined by the strength of contraction, amount of blood pumped into the arteries, the viscosity of the blood, and the size and flexibility of the arteries. fluids exert force against surfaces they come in contact with hydrostatic pressure fluids flow from high pressure to areas of low pressure fluids flow faster in narrower pipes… than wider pipes BUT -even though capillaries are than arteries; we have more capillaries smaller Therefore: greater crosssectional area of capillaries Therefore, fluids flow faster in arteries than capillaries This is a good thing, b/c gas exchange can take place in the capillaries Blood exerts a pressure against the wall of the vessel in which it is flowing. Tissue cell Capillary Red blood cell Net fluid movement out Net fluid movement in 15 m At the arterial end of a capillary, blood pressure is greater than osmotic pressure, and fluid flows out of the capillary into the interstitial fluid. At the venule end of a capillary, blood pressure is less than osmotic pressure, and fluid flows from the interstitial fluid into the capillary. Direction of blood flow Blood pressure Osmotic pressure Pressure Capillary INTERSTITIAL FLUID Inward flow Outward flow Arterial end of capillary Figure 42.14 Venule end • One type of cardiovascular disease, atherosclerosis – Is caused by the buildup of cholesterol within arteries Connective tissue Smooth muscle Plaque Endothelium (a) Normal artery 50 µm (b) Partly clogged artery Figure 42.18a, b 250 µm 140 or below is a normal systolic reading 90 or below is a normal diastolic reading Cuff is wrapped around the upper arm & inflated until the pressure closes the brachial artery *No blood can flow the cuff, now past Pressure from cuff is higher than pressure in the artery Stethoscope used to listen for the sound of blood flowing below the cuff If artery is closed, no blood flowing… no sound. Cuff is loosened until the blood can flow freely through the artery You will hear the sound of blood pulsing into the artery Pressure from blood is now greater than the pressure from the cuff Cuff is loosened until the blood can flow freely through the artery Sound below the cuff will disappear, pressure remaining in the artery when heart is relaxed. Range depends on heredity, gender, environment Range depends on heredity, gender, environment •All blood vessels •Arteries have thicker walls –To accommod ate the high pressure of blood pumped from the heart –Are built of similar tissues –Have three similar layers Artery Vein Basement membrane Endothelium 100 µm Valve Endothelium Smooth muscle Connective tissue Endothelium Smooth muscle Capillary Connective tissue Artery Vein Venule Figure 42.9 Arteriole • In the thinner-walled veins – Blood flows back to the heart mainly as a result of muscle action Direction of blood flow in vein (toward heart) Valve (open) Skeletal muscle Valve (closed) Figure 42.10