NSCI 1403 Lecture Notes - Lecture 14: Simple Squamous Epithelium, Arteriole, Collagen
27 Dec 2016
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Document Summary
Sponges, cnidarians and flatworms are groups of organisms with a thin body wall that makes a circulatory system unnecessary. Hydras have each cell exposed to water and can independently exchange gases and excrete wastes. Planaria have a trilobed gastrovascular cavity and a small, flat body where nutrients diffuse from cell to cell. Pseudocoelomates, such as nematodes, use the coelomic fluid of the body cavity to transport fluids. Echinoderms rely on movement of coelomic fluid as a circulatory system. In a circulatory system, a pumping heart moves one of two types of circulatory fluids. Blood is a circulatory fluid and is always contained within blood vessels. Hemolymph is a circulatory fluid which flows into the hemocoel of certain arthropods and molluscs; it is a mixture of blood and interstitial fluid. Certain arthropods and molluscs have an open circulatory system. Hemolymph is pumped by the heart into the body cavity or sac like sinuses.
