Chapter 42 Circulatory System

Biology, 7th Edition (Book & CD-ROM)

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Chapter 42 Circulation and Gas Exchange I. Circulatory Systems Reflect Phylogeny A. General information 1. Diffusion is inefficient over long distances, so circulatory system solves this problem. 2. Circulatory system connects the aqueous environment of the body cells to the organs that exchange gases, absorb nutrients, and dispose wastes 3. Bulk flow movement is powered by the heart B. Invertebrate Circulation 1. Gastrovascular Cavities a. Because of a simple body plan, cnidarians do not need a true circulatory systems b. They have a gastrovascular cavity around their few cells and it serves in digestion and distribution of substances c. Fluid inside is continuous with the water outside through one opening d. Digestion begins in cavity i Only cells of the inner layer have direct access to nutrients e. Flatworms have gastrovascular cavities with one opening to the environment which is to exchange gasses C. Open and Closed Circulatory System 1. Both have: a. Circulatory fluid (blood) b. Set of tubes (blood vessel) c. Muscular pump (heart) d. Also: blood pressure- heart pumps blood, creates pressure, blood flows down a pressure gradient through its circuit back to the heart 2. Open Circulatory System a. There is no distinction between blood and interstitial fluid i Blood + interstitial fluid = hemolymph b. Hemolymph is pumped into sinuses (spaces surrounding the organs) i Chemical exchange occurs between hemolymph and cells c. Heart tends to be elongated dorsally. i When it contracts it pumps hemolymph through vessels ii When it relaxes it draws hemolymph in through pores d. Present in arthropods, insects, and molluscs 3. Closed Circulatory System: 4. Advantages a. Open Circulatory i Low hydrostatic pressure; less costly in terms of energy expenditure Don’t have to create any pressure for blood to flow with
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ii Also functions as a hydrostatic skeleton in supporting body b. Closed Circulatory i More effective at transporting circulatory fluids to meet the demands of cells and tissues and their need for blood ii Most highly developed vertebrates D. Survey of Vertebrate Circulation
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