Gas Exchange

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Gas Exchange- Ch.42 Sections 42.5-42.7

A.Physical constraints on gas exchange: partial pressure of gassses - pressure exerted by a particular gas in a mix of gases
21% O2 P02=760mm Hg*.21 = 159.6 mm Hg

B. Respiratory medium
1. air : 21% 02, low density, low viscosity, easy to move over a surface and thru vessels 2. water: 4-8ml 02/L, 02 solubility decreased by higher temp and higher salt conc., water dense, viscous, more work to move over surface

C. Diffusion rates
- all 02 and C02 exchange occurs by diffusion
- Fick's law of diffusion
Qs= DA C2-C1/x *t
Qs= quantity of substance
d= diffusion constant, A= area of surface, C2-C1 conc gradient , x=thickness of surface, t = time Characteristics of respiratory membranes
- large surface area (A)
- large concentration difference (c2-c1)
-thin(small x)

II. Respiratory surfaces
A. Body surface
- amphibians, earthworms
B. Specialized surface
-must be ventilated : respiratory medium moved across surface - maintains high C2-C1
I. Aquatic animals
- gills-projections of body surface
Counter current flow in fish gills
- fig 42.23, blood flow thru and water flow over gill filament is counter current, maximized o2 exchange 2.Terrestrial animals
a.insects- branching system of air tubules, all body cells w/i diffusion distance tracheole end b. mammals,birds,reptiles
lungs: branching system of air tubules, ends in alveoli=air sacs of surrounded by capillaries -alveoli are site of gas exchange
III. Respiratory pigments
A. Structure: metalloproteins that increase solubility of O2 in blood, hemocyanin: metal = Cu, arthropods hemoglobin - metal = Fe, vertebrates, most invertebrates Hemoglobin
- 4 subunits, proteins with quaternary structure, each contains Fe and bins (1) O2 B.Properties
1. Cooperativity - (1) O2 binds, Hb molecule changes shape, easier for 2nd,3rd,4th,02 molecs to bind % saturation of Hb with 02- 25% saturation=25% of 02 binding sites in a hemoglobin solution are occupied x axis- P02...
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