3.05.10 - Circulatory systems Movement of substances by...

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Circulatory systems Movement of substances by bulk flow (convection) is needed in large animals (> ~ 1 mm) to overcome the limitations of diffusion . Circulatory systems consist of: • a pump (heart) to provide power in the form of hydrostatic pressure (may be more than one pump) • a system of tubes (vessels) through which fluid circulates -- open or closed system • a circulatory fluid (blood) -- interstitial fluid or specialized tissue (as in vertebrates) Circulatory systems Architecture of the circulatory vessels Open circulations: blood contained in vessels for only part of its circuit (blood = interstitial fluid) Closed circulations: blood always remains in vessels (blood can be different from interstitial fluid); common in active animals Circulatory anatomy depends on animal size, how gases are exchanged, and metabolic rate • Usually, animals with high metabolism need rapid blood circulation Circulatory systems Architecture of the circulatory vessels Flow rate of blood in a vessel depends on blood pressure and resistance to flow : for high flow rates, need high pressure and low resistance Blood pressure depends largely on power of the heart resistance is largely an inverse function of vessel diameter large tubes are used to carry blood rapidly over long distances (less resistance to flow; less pumping power needed): in closed systems, narrow, thin walled capillaries are the sites of exchange (large surface area) -- impossible in large, thick vessels Same cross-section area low resistance high resistance Circulatory systems Architecture of the circulatory vessels Flow rate of blood in a vessel depends on blood pressure and resistance to flow : for high flow rates, need high pressure and low resistance Blood pressure depends largely on power of the heart resistance is largely an inverse function of vessel diameter large tubes are used to carry blood rapidly over long distances (less resistance to flow; less pumping power needed): in closed systems, narrow, thin walled capillaries are the sites of exchange (large surface area) -- impossible in large, thick vessels Same cross-section area low resistance high resistance When blood at high pressure in a large vessel is forced through a network of narrow-diameter capillaries, high flow resistance causes pressure to drop.
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3.05.10 - Circulatory systems Movement of substances by...

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