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100CCirculatorySystem - Circulatory System Internal...

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Circulatory System Internal Transport & Gas Exchange
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Types of Circulatory Systems Open Circulatory System —e.g insects, other arthropods, and most mollusks 1) body fluid composed of blood and lymph (clear fluid derived from interstitial fluid) = hemolymph 2) One or more hearts pump hemolymph through vessels into interconnected spaces ( sinuses ) surrounding the organs where chemical exchange occurs—direct contact of hemolymph with tissues, not separated by blood vessel walls. 3) the heart relaxes, and draws hemolymph into the circulatory system through ostia (pores). Body movement that compress sinuses circulate the hemolymph—lower pressure; lower rate of flow Closed Circulatory System —e.g. earthworms, octopuses, vertebrates 1) blood is confined to vessels; interstitial fluid is separate 2) blood is pumped by heart into large vessels, and then into progressively smaller ones where materials are exchanged by diffusion between blood and interstitial fluid. Vessels return blood to heart—higher pressure; higher rate of flow.
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Closed and Open Circulatory Systems Closed system: Blood never leaves vessels. Blood travels through closed blood vessels Tubular heart Single heart Lymph travels through closed lymph vessels Hemolymph (“blood-lymph”) flows throughout body cavity Open system: Hemolymph leaves vessels and comes into direct contact with tissues.
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Structure and Types of Blood Vessels Arteries carry blood away from the heart —thicker outer layer of connective tissue containing elastic fibers, thicker middle layer of smooth muscle, inner endothelium (layer of smooth cells that provide less resistance for blood flow)— rapid blood movement; high pressure Veins carry blood back to the heart —thinner outer connective tissue layer, thinner smooth muscle layer, inner endothelium—low blood velocity; low pressure—valves prevent backward blood flow Capillaries exchange of materials between blood and tissues —lack outer two layers; thin walls consist of endothelium and its basement membrane—form capillary beds = networks of capillaries that infiltrate every organ and tissue Arteriole —vessel that transports blood between an artery and capillary bed Venule —vessel that transports blood between a capillary bed and vein
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Figure 44-22 Red blood cells Nucleus Capillaries are small and extremely thin walled. Basement membrane Endothelial cells Capillary Fibrous tissue Muscle tissue Elastic tissue Endothelium Vein (Medium-sized) Artery (Medium-sized) Veins and arteries differ in structure.
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Capillaries possess only a thin endothelium and its basement layer. This facilitates the exchange of substances (gases, nutrient, wastes) between the blood and the interstitial fluid that bathes cells.
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