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Chapter 44

BIOL 1107 Chapter Notes - Chapter 44: Gastrovascular Cavity, Extracellular Fluid, Hemolymph

Course Code
BIOL 1107
Thomas Abbot

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44.1 Animal Circulatory System: An Introduction
โž”Least complex animals (sponges, cnidarians, flatworms) have no distinct circulatory system
โ—†Aquatic or are surrounded by body fluids of a host animal
โ—†Bodies are structured as thin sheets of cells that lie close to the fluids of surrounding external
โ—†Substances diffuse between cells and environment through animalโ€™s external surface or through
surfaces of internal channels and cavities that are open to environment
โž”Sponges- water carrying nutrients and oxygen is pumped by surface cells with beating flagella through
pores in body wall surrounding central cavity
โ—†Passes through cavity and leaves through large exit pore (carrying CO๎€2๎€ and wastes)
โž”Gastrovascular cavity: saclike body cavity with single opening, mouth, which serves both digestive and
circulatory functions
โ—†Hydras, jellyfish, sea anemones, cnidarians
โž”Large, complex animals- most cells lie in cell layers too deep within body to exchange substances
directly with external environment by diffusion
โ—†Circulatory system conducts O๎€2๎€, CO๎€2๎€, nutrients, wastes between cells and specialized regions of
animal where substances are exchanged with external environment
โž”Animal circulatory systems have 3 basic components
โ—†Fluid- specialized fluid medium carries O๎€2๎€, CO๎€2๎€, nutrients, wastes, cells; plays major role in
โ—†Heart- muscular heart pumps fluid through circulatory system
โ—†Vessels- tubular vessels serve as conduits to distribute fluid pumped by heart
โ—Artery: vessel that conducts blood away from the heart at relatively high pressure
โ—Vein: vessel that carries blood back to the heart
โž”Open circulatory system: arrangement of circulatory system in some invertebrates in which, when heart
contracts, arteries leaving heart release hemolymph (bloodlike fluid) directly into body spaces called
sinuses that surround organs
โ—†There is no distinction between hemolymph and interstitial fluid, fluid immediately surrounding
body cells
โ—†After flowing through sinuses, hemolymph reenters the heart when heart relaxes
โ—Either hemolymph enters veins and moves into heart through valves in heart wall or
enters heart directly through ostia (pores)
โ—‹Valves prevent hemolymph exiting heart into veins through pores when heart
โ—†Arthropods and most mollusks
โ—One or more muscular hearts
โž”Closed circulatory system: circulatory system in which fluid, blood, is confined in blood vessels and is
distinct from interstitial fluid
โ—†Substances are exchanged between blood and the interstitial fluid and then between interstitial
fluid and cells
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