Chapter 50 - Chapter 50 Circulatory Systems Why Do Animals...

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Chapter 50: Circulatory Systems Why Do Animals Need a Circulatory System? Circulatory system consists of muscular pump (heart), blood, and series of conduits (blood vessels) Some animals do not have a circulatory system o Single celled and small aquatic organisms don’t have one, diffuse across skin Circulatory systems can be open or closed o Open- extracellular fluid is the same as the fluid in the circulatory system (called hemolymph) o Closed- contain blood in continuous system, with blood cells and large molecules staying within the system, but water and small molecules leaking out of the highly permeable capillaries Open circulatory systems move extracellular fluid o Heart pumps fluid through body, then hemolymph returns to heart through opening called ostia, which have valves to regulate direction Closed circulatory systems circulate blood through a system of blood vessels o Vessels allow separation from blood and interstitial fluid o Advantages over open: Fluid can flow quicker, and transport quicker; diameter and resistance change based on location, so can control flow and amount; specialized cells and molecules aid in transport of hormones/nutrients The way that open systems survive is because they don’t do gas exchange through their circulatory system, so it does not need to be as big How have vertebrate circulatory systems evolved?
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