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Biology 2601A/B
Brent Sinclair

Oct 1811 The systemic circuit Blood is delivering oxygen and nutrients and picking up waste products and delivering them to the kidneys Oxygenated blood goes to organs and muscles Linear flow rate or velocity is reduced when blood goes through the systemic circuit and the crosssectional area increases due to lots of capillaries There is also lower pressure because of this The blood slows because it has a greater crosssectional to pass through Also the capillaries are short so the blood must move slowly in order to have enough time to exchange with the tissues The venous part of the systemic circuit is a lowpressure lowresistance system Major arteries Composed of muscular elastic thick walls smooth muscle and elastin They have a pressure of 1020 kPa Their elastic property allows them to dampen pressure differences variations in arterial pressure over the cardiac cycle are reduced and store some elastic energy in the extension of arteries pressure is maintained in the arteries even when the heart is at rest between beats Some arteries are the aorta carotid artery and femoral artery The pressure in the arteries 16 kPa when the heart muscle is contracting and 10 kPa when the heart is relaxingTerminal arteries deliver blood to tissues and have a lower pressure 128 kPaArterioles have a pressure of 835 kPa and have the same structure as arteries Capillaries have a pressure of 253 kPa and are very thin Venules have a pressure of 132 kPa and are thin There is diffusive exchange of O2 and other materials between the blood and tissues and when blood goes through the capillary bed The blood flows from the capillary beds back to the heart through veins The right ventricle then increases the pressure to 19 kPa for passage through the lungs which are a network of arteries and veins The oxygenated blood is returned to the left side of the heart where it picks up pressure Veins have low pressure Their walls are thinner than arteries because they dont need to be capable of resisting high tensions because of the low pressure Veins have a system of oneway valves to ensure that blood only travels in the direction towards the heart
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