Biology Chapter 42 I

Biology Chapter 42 I - Chapter 42 Circulation and Gas...

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Chapter 42 Circulation and Gas Exchange Overview: Trading with the Environment Every organism must exchange materials and energy with its environment, and this exchange ultimately occurs at the cellular level. ° 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. Concept 42.1 Circulatory systems reflect phylogeny Diffusion alone is not adequate for transporting substances over long distances in animals 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. Most invertebrates have a gastrovascular cavity or a circulatory system for internal transport. ° A body wall only two cells thick encloses a central gastrovascular cavity that serves for both digestion and for diffusion of substances throughout the body. ° The products of digestion in the gastrovascular cavity are directly available to the cells of the inner layer, and it is only a short distance to diffuse to the cells of the outer layer. In more complex animals, two types of circulatory systems that overcome the limitations of diffusion have evolved: open circulatory systems and closed circulatory systems. ° 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 insects, other arthropods, and most molluscs, blood bathes organs directly in an open circulatory system. There is no distinction between blood and interstitial fluid, collectively called hemolymph. One or more hearts pump the hemolymph into interconnected sinuses surrounding the organs, allowing exchange between hemolymph and body cells. ° When the heart contracts, it pumps hemolymph through vessels out into sinuses. ° When the heart relaxes, it draws hemolymph into the circulatory system through pores called ostia. ° Body movements that squeeze the sinuses help circulate the hemolymph. 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 through organs. ° Materials are exchanged by diffusion between the blood and the interstitial fluid bathing the cells.
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