BIOA02H3 Lecture Notes - Lecture 7: Heart Valve, Extracellular Fluid, Blood Pressure
16 Aug 2016
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The muscular heart pumps specialized fluid such as blood through tubular vessels. Blood caries oxygen and nutrients to body tissues and carries away carbon dioxide and wastes. Some protostomes have no specialized circulatory system. Some invertebrates and all vertebrates have closed circulatory systems. Vertebrate circulatory systems have evolved from single to double blood circuits. Protosomes with no specialized circulatory systems include sponges, cnidarians, flatworms, echinodermata and nematodes; nearly all of them are aquatic. Their bodies are thin sheets of cells lying close to fluids of the surrounding environment. Products of digestion diffuse among cells via interstitial fluids; oxygen and carbon dioxide are exchanged with medium through the animal surface. Open circulatory system: no distinction between hemolymph and interstitial fluid. Interstitial fluid: fluid occupying spaces between cells in multicellular animals. In most invertebrates the heart pumps hemolymph into the vessels that empty into body spaces called sinuses before returning to the heart.
