Chapter 42 - Circulation & Gas Exchange

Chapter 42 - Circulation & Gas Exchange - 42.1 Circulatory...

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42.1 Circulatory systems reflect phylogeny - diffusion is inefficient over distances > few millimeters time it takes for a substance to diffuse = proportional to square of the distance - circulatory system connects aqueous environment of body cells to the organs that exchange gases, absorb nutrients, & dispose of wastes by rapidly transporting fluid in bulk Invertebrate Circulation - Invertebrate body size diversity in circulatory systems - Invertebrate form - Environmental forms evolutionary modifications Gastrovascular Cavities - Hydras & other cnidarians - Do not require a true circulatory system - Body wall (2 cells thick) encloses a central gastrovascular cavity serves in digestion & distribution of substances - fluid inside cavity is continuous w/water outside through a single opening inner & outer tissue layers are bathed by fluid - thin branches of gastrovascular cavity extend into animal’s tentacles - digestion begins in the cavity only cells of inner layer have direct access to nutrients nutrients have to diffuse only a short distance to reach cells of the outer layer - planarians & most other flatworms - gastrovascular cavities that exchange materials w/ environment through a single opening - ensure cells are bathed by a suitable medium & diffusion distances are short - Open & Closed Circulatory Systems - Basic components of both systems: 1. Circulatory fluid (blood) 2. Set of tubes through which the blood moves through the body (blood vessels) 3. Muscular pump (heart) - Heart powers circulation by using metabolic energy to elevate the hydrostatic pressure of blood blood pressure = hydrostatic pressure force blood exerts against the wall of a vessel - Open Circulatory System - In insects, arthropods, mollusks 1. Hemolymph bathes tissues & organs directly - 2. Heart(s) pumps hemolymph into interconnected system of sinuses spaces surrounding organs - chemical exchange occurs btwn hemolymph & body cells - insects & arthropods: heart is an elongated tube located dorsally - movements: A. Heart contracts – pumps hemolymph through vessels out into sinuses B. Heart relaxes – draws hemolymph into circulatory system through pores called ostia - Closed Circulatory System - In earthworms, squids, octopuses, and all vertebrates - 1. Blood is confined to vessels & is distinct from the interstitial fluid
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- 2. Heart(s) pumps blood into large vessels that branch into smaller ones coursing through the organs - materials are exchanged by diffusion btwn blood & interstitial fluid bathing the cells - Advantages of Open Circulatory Systems - - - 1. Less energy expenditure - lower hydrostatic pressures less costly - 2. Lack extensive system of blood vessels require less energy to build & maintain - 3. Serve a variety of other functions - ie: mollusks & aquatic arthropods --? Functions as a hydrostatic skeleton in
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This note was uploaded on 04/17/2009 for the course BISC 220 taught by Professor Mcclure during the Spring '09 term at USC.

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Chapter 42 - Circulation & Gas Exchange - 42.1 Circulatory...

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