01:119:116 Lecture Notes - Lecture 24: Body Cavity, Cardiac Cycle, Systolic Geometry
23 Apr 2016
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All animals need to exchange substances with their environment = nutrients, oxygen, and wastes (ex. Co2) ultimately occur by diffusion into and out of cells. Problem = diffusion is very slow over long distances. Some animals do not have a circulatory system don"t need it. Flatworm flat body efficient diffusion. Cnidarians gastrovascular cavity brings nutrients close to cells. Nematodes fluid in pseudocoelom helps circulate materials. Animals with many layer of cells (especially if terrestrial) need a circulatory system. Circulatory system connects interstitial fluid with the organs that. System can be open or closed vary in the number of circuits in the body. Hemolymph = circulatory fluid bathes the tissues directly. Heart contractions pump hemolymph through circulatory vessels into interconnected sinuses (spaces surrounding organs) relaxation draws hemolymph back into heart via pores. Low pressure relatively inefficient but less costly in e expenditure. Ex. arthropods and some molluscs (except cephalopods) Blood = circulatory fluid inside vessels distinct from interstitial fluid.
