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Gas Exchange

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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 (mm Hg)

y axis- % saturation of Hb with O2
graph goes up and curves off at the end like an (S) shape fig 42.31

2. pH sensitivity: Bohr effect
-pH affects O2 affinity of Hb
lower ph decreases Hb O2 affinity

Significance of pH sensitivity
* RBC pH decreases in capillaries supplying body tissues
* co2 +h2o = H2CO3 = HCO23- + H+
* H+ binds to Hb, changing its shape so 02 is relased and diffuses * in lungs O2 diffuses into RBC
* High O2 displaces H+ from Hb
CO2 diffuses out of RBC and into alveoli
CH.44- Osmoregulation
– controlling solute conc and water gain/loss from body fluids A. Purpose
– Cell fxn requries specific, stable solute conc.
B. Osmolarity
– moles solute/L
– units: mOs m/L
C. Osmotic challenges

1. Conformers & regulators
x axis= external mOsm/L
y axis = internal mOsm/L
2. Marine animals
– body fluid (salt) < seawater
– body fluid osmolarity = 1000 mOsm
– high (urea) and (trimethylamine oxide)
– no water loss

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