BIOL 1911 Chapter Notes - Chapter 42.1: Homeostasis, Arteriole, Pulmonary Circulation
29 Apr 2018
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42 – Circulation and Gas Exchange
• Transfer of substances between an animal and its surroundings occurs at the cellular level
o Required resources enter the cytoplasm by crossing into the plasma membrane
o Waste products exist by crossing out of the plasma membrane
• Direct exchange between every cell and the environment is not possible for most animals
o Use specialized respiratory systems for exchange with the environment
o Use specialized circulatory systems for transport of materials between sites of exchange and the rest of the
body
• Intimate association between gas exchange (respiratory system) and internal transport (circulatory system)
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• common elements between and remarkable variation in form and organization in
these two systems among a range of species
• roles of circulatory and respiratory systems in homeostasis
42.1 – Circulatory systems link exchange surfaces with cells
throughout the body
• every cell in the body is involved in the molecular trade
o gaining oxygen and nutrients while releasing carbon dioxide and other waste products
• diffusion is random thermal motion
o experienced by small molecules such as O2 and CO2
o results in net movement when there is a difference in concentration between a cell and its immediate
surroundings
o very slow movement: time it takes for a substance to diffuse is proportional to square of the distance needed to
travel -> NEED OTHER MECHANISMS FOR EFFECTIVE EXCHANGE
Two basic adaptations for efficient exchange
• simple body plan that places many or all cells in direct contact with environment
o each cell can exchange materials directly with environment
o present in certain invertebrates (cnidarians and flatworms)
• circulatory system
o ’
o exchange with environment and exchange with body tissues both occur very short distances
Gastrovascular Cavities
• in animals with a simple body plan and no distinct circulatory system
• Central gastrovascular cavity functions in distribution of substances throughout the body
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o in hydras, jellies and other cnidarians
o also functions in digestion
o opening at one connects cavity to surrounding water
o branching pattern
▪ , G.C. ’
▪ in jellies and other cnidarians, more elaborate branching patterns exist
• fluid bathes both inner and outer tissue layers of animals to facilitate exchange of gases and cellular waste
• only cells lining the cavity have direct access to nutrients released by digestion
o nutrients only need to diffuse a short distance the cells of the outer tissue layers because the body is a mere two
cells thick
• planarians and most other flatworms
o combination of G.C. and flat body well suited for exchange with environment
o flat body maximizes surface area for exchange and minimizes diffusion distances
Open and Closed Circulatory Systems
• three basic components of a circulatory system:
o circulatory system
o set of interconnecting vessels
o muscular pump AKA the heart
• function of the heart
o ’
o hydrostatic pressure = pressure that the fluid exerts on surrounding vessels
o fluid flows through vessels and back to the heart
• function of the circulatory system
o functionally connects aqueous environment of body cells to organs that exchange gases, absorb nutrients and
dispose of wastes
o ex in mammals: i
▪ inhaled O2 only diffuses across two layers of cells in the lungs before reaching the blood
▪ blood is then carried to all parts of the body
▪ blood passes through body tissues in tiny blood vessels
▪ O2 in blood diffuses only a short distance between entering the fluid that bathes the cells
Open circulatory systems
• Circulatory fluid = hemolymph = also interstitial fluid that bathes body cells
• In arthropods and some molluscs
• Contraction of heart pumps hemolymph through circulatory vessels into interconnected sinuses (spaces surrounding the
organs)
o Hemolymph and body cells exchange gases and other chemicals within the sinuses
• Relaxation of heart draws hemolymph back in through pores
o Pores have valves that close when the heart contracts
• Body movements periodically squeeze the sinuses, helping circulate the hemolymph
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