chap42studyguide - Chapter 42 Circulation and Gas Exchange...

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Chapter 42 Circulation and Gas Exchange Study Guide Overview: Trading with the Environment Every organism must exchange materials and energy with its environment, and this exchange ultimately occurs at the cellular level. ° Cells live in aqueous environments. ° The resources that they need, such as nutrients and oxygen, move across the plasma membrane to the cytoplasm. ° Metabolic wastes, such as carbon dioxide, move out of the cell. Most animals have organ systems specialized for exchanging materials with the environment, and many have an internal transport system that conveys fluid (blood or interstitial fluid) throughout the body. Concept 42.1 Circulatory systems reflect phylogeny Diffusion alone is not adequate for transporting substances over long distances in animals —for example, for moving glucose from the digestive tract and oxygen from the lungs to the brain of a mammal. Diffusion is insufficient over distances of more than a few millimeters, because the time it takes for a substance to diffuse from one place to another is proportional to the square of the distance. ° For example, if it takes 1 second for a given quantity of glucose to diffuse 100 microns, it will take 100 seconds for it to diffuse 1 mm and almost three hours to diffuse 1 cm. The circulatory system solves this problem by ensuring that no substance must diffuse very far to enter or leave a cell. The bulk transport of fluids throughout the body functionally connects the aqueous environment of the body cells to the organs that exchange gases, absorb nutrients, and dispose of wastes. ° For example, in the mammalian lung, oxygen from inhaled air diffuses across a thin epithelium and into the blood, while carbon dioxide diffuses out. ° Bulk fluid movement in the circulatory system, powered by the heart, quickly carries the oxygen-rich blood to all parts of the body. ° As the blood streams through the tissues within microscopic vessels called capillaries, chemicals are exchanged between blood and the interstitial fluid that bathes the cells. In more complex animals, two types of circulatory systems that overcome the limitations of diffusion have evolved: open circulatory systems and closed circulatory systems.
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° Both have a circulatory fluid (blood), a set of tubes (blood vessels), and a muscular pump (the heart ). The heart powers circulation by using metabolic power to elevate the hydrostatic pressure of the blood (blood pressure), which then flows down a pressure gradient through its circuit back to the heart. In a closed circulatory system, found in earthworms, squid, octopuses, and vertebrates, blood is confined to vessels and is distinct from interstitial fluid. ° One or more hearts pump blood into large vessels that branch into smaller ones coursing
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This note was uploaded on 04/07/2008 for the course BIO bsc2010 taught by Professor Trombley during the Spring '08 term at FSU.

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chap42studyguide - Chapter 42 Circulation and Gas Exchange...

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