HowOrganismsExchangeGasesSimpleDiffusion

1、1How Organisms Exchange Gases: Simple DiffusionGas is exchanged between respiratory medium and body fluids through diffusion across a respiratory surfaceTo effectively exchange gases, the surface must bethin1. wet2How Organisms Exchange Gases: Simple Diffusion Some animals have no specialized respir

2、atory organs or circulatory systems O2 obtained through simple diffusion O2 tension must be high enough at the surface for O2 to reach the center of the organism3How Organisms Exchange Gases: Simple Diffusion With radius, the greater O2 at the surface must be to supply oxygen to the core Example: ra

3、dius = 1 mm, VO2 = 0.001 ml/g*min PO2 needed= 0.15 atm Example: radius = 1 cm, VO2 = 0.001 ml/g*min PO2 needed = 15 atm Few animals thicker than 1 mm rely on simple diffusion for gas exchange4How Organisms Exchange Gases: Respiratory Organs Larger animals possess specialized respiratory surfaces reg

4、ions with large surface area/volume ratio branches, flattened areas, etc. - SA thin walls - diffusion distance allow easy passage of gas into a circulatory system Convection of respiratory medium over the respiratory surfaces (ventilation) typically required5Types of Respiratory Surfaces Integument

5、use skin for gas exchange requires thin, moist, permeable integument Evaginations (gills) specialized respiratory organ increases external surface area Invaginations (lungs) increase respiratory surface area protect respiratory surface6Respiratory Surface Ventilation Unidirectional Flow Medium flows

6、 over respiratory surfaces in one direction New medium continuously flows over surfaces Bidirectional (Tidal) Flow Medium flows into respiratory surfaces then out in the opposite direction Incoming medium mixed with “used” medium7Gas Exchange Between Body Fluids and the Environment Occurs through di

7、ffusion Dependent on difference in PO2 and PCO2 between the body fluids and respiratory medium The flow of body fluids relative to the flow of the respiratory medium influence pressure gradients for gas exchange8Patterns of Flow at Exchange Surfaces Concurrent Flow Body fluid and respiratory medium

8、flow in same direction Gradient reduced with distance Countercurrent Flow Body fluid and respiratory medium flow in opposite directions Gradients sustained over distance Crosscurrent Flow Body fluid and respiratory medium flow at nonparallel angles to each other Gradient slowly decreases with distan

9、ce9Respiration in Water: Integument Small Animals High SA/V ratio Large Animals Often elevated surface area Often used in conjunction with other respiratory systems Requires permeable integument Elevated water intake, ion loss, etc.10Respiration in Water: Lungs Not very practical Requires animal to

10、generate tidal flow of water Energetically expensive Low efficiency of O2 uptake Sea cucumber Respiratory tree derived from anal canal11Respiration in Water: Gills Evaginations of the respiratory surface large surface area thin cuticle Used primarily for respiration in water external exposure helps

11、increase circulation of medium across respiratory surface water supports weight of the gills without need for structural support12Respiration in Water: Gill Ventilation Flow of water over gills is necessary for supplying oxygen Move gill through the water (practical only for small animals) Move wate

12、r over the gill: ciliary action (bivalves) pumping devices (teleost fish and arthropods) ram ventilation (sharks, tuna)13Teleost Fish Gills: Structure Gills positioned on either side of buccal cavity underneath the operculum Four brachial arches, each carrying two rows of gill filaments Each filamen

13、t carries rows of parallel lamellae Capillary circulation is countercurrent to water14Teleost Fish Gills: Ventilation Water flows into mouth, over the gills, and out the gill slits Water is driven across the gills by two pumps: Buccal pressure pump forces water from mouth over the gills Opercular su

14、ction pump sucks water from the mouth over the gills15Buccal Pump FunctionMouth opens, buccal cavity floor depressedWater drawn into buccal cavityMouth closes, floor raisesdrives water over gills into opercular cavitiestissue flaps prevent backflow of water back out mouthExpansion of opercula draws

15、water into opercular cavity from oral cavityflaps prevent water from being pulled in through gill slitsCompression of opercula forces water out through the gill slitsSynchronization of the two pumps allows flow over the gills through most of the respiratory cycle16Respiration in Air Higher oxygen co

16、ntent Higher gas diffusion rates can get O2 from less volume Lower density and viscosity easier to move Loss of water problematic17Respiration in Air: Integument Use skin for gas exchange Limited surface area Must keep surface moist Often used in conjunction with other respiratory organs18Respiratio

17、n in Air: Integument Integumental exchange often supplements that of other respiratory organs Relative contribution of different surfaces to overall gas exchange varies among species and among conditions19Respiration in Air: Integument Anurans Use both lungs and skin for gas exchange Usage of each d

18、epends on gas and on metabolic demands and developmental stage20Respiration in Air: Gills Uncommon poorly suited for gas exchange in air Thin, branched structures require support if too thin, collapse under own weight and stick together due to water surface tension if too thick, lose effectiveness a

19、s respiratory surface External exposure increases evaporative water loss Covering reduces passive ventilation21Respiration in Air: GillsTerrestrial Crabs and Isopods Smaller gills w/ fewer, shorter branches than aquatic spp. Thicker cuticles on branches (more rigid) Chambers are larger and more high

20、ly vascularized more lung-like22Modified Gill Structures of Air-Breathing Fish Hundreds of fish species can breathe air Various structures Vascularized buccal and opercular cavities Suprabranchial chambers Modified swim bladders Modified digestive tract Possible adaptation to low PO2 water23Respirat

21、ion in Air: Tracheae Network of air-filled tubes (tracheae) extending throughout body of the animal Connected to exterior by spiracles (gated) Gas transport independent of circulatory system Work by passive ventilation or by active ventilationInsects, Arachnids, Isopods24Respiration in Air: Tracheae

22、 Spiracles regulate gas exchange and water loss Discontinuous gas exchange CO2 released in bursts accompanied by H2O loss Reduce H2O loss Avoid oxygen toxicity25Respiration in Air: Lungs Invaginations of the respiratory surface increase surface area Used primarily for air breathing supports and prot

23、ects respiratory surface isolates volumes of air from the atmosphere reduces evaporative water loss requires pumping action for circulation of medium26Examples of Lungs Gastropods - simple cavity in mantle highly vascularized epithelium single opening (pneumostome) passive or active ventilation27Exa

24、mples of Lungs Arachnids: Book Lung multiple lamellar folds typically passive air exchange28Examples of Lungs Alveolar Lungs Most terrestrial vertebrates formation of numerous partitions or sacs (alveoli) within the lungs walls of sacs very thin and highly vascularized Tidally ventilated29Examples o

25、f Lungs Parabronchial Lungs (Birds) lungs connected to a series of air sacs allows continuous, unidirectional flow of air through the lungs30How is Air Circulated in Lungs?Two methods in vertebrates: Positive Pressure Pump push air out of oral cavity into the lungs Negative Pressure Pump pull air in

26、to lungs from oral cavity31Positive Pressure Lungs1Glottis closed, buccal cavity expanded, air drawn in through nares2Glottis opens, air in lung passes out through nares2Nares close, oral cavity compresses, driving fresh air into lungsLungfish, Amphibians, Some Reptiles32Negative Pressure Lungs Expansion of thoracic cavity pulls air into lungs from oral/nasal cavities Relaxation of muscles compresses thoracic cavity, pushing air outReptiles, Mammals, Birds33Air Flow in Parabronchial Lungs Avian lungs are linked to several air sacs cranial group caudal group Sacs not d