Biology 2672a: Comparative Animal Physiology

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Biology 2672a: Comparative Animal Physiology. Gas Exchange I: Principles &amp; breathing in water. Gas Exchange. Getting O 2 out of the external medium and into the cells Often via the circulatory system Getting CO 2 out of the cells and into the external medium.

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### Biology 2672a: Comparative Animal Physiology

Gas Exchange I:

Principles & breathing in water

Gas Exchange
• Getting O2 out of the external medium and into the cells
• Often via the circulatory system
• Getting CO2 out of the cells and into the external medium

C6H12O6 + 6O2 6CO2 + 6H2O

+ 2820 kJ/mol

Where is the oxygen?

(Cold)(Sea) water: ~0.8% O2 in solution

Air: ~21% O2 as a gas

Partial pressure
• Each gas in a mix (either as a gas or in solution) exerts pressure
• Partial pressure is the amount of pressure that the gas of interest exerts
Partial pressure of gas x

Partial pressure

Px=FxPtot

Fractional concentration of the gas (moles or by volume)

Total pressure of the gas mixture

Eqn. 21.2

Partial pressure
• Air
• 20.95 % O2
• 78.09 % N2
• 0.93 % Ar
• 0.038 % CO2

Px=FxPtot

PO2 = 0.2095 × 101.3 kPa = 21.22 kPa

Partial pressure on Mt Everest

Px=FxPtot

• Air
• 20.95 % O2
• 78.09 % N2
• 0.93 % Ar
• 0.038 % CO2

PO2 = 0.2095

Gases dissolve in liquids
• Not the same as having air bubbles!
• Pliquid is proportional to Pair
• Amount of gas in solution depends on
• Temperature
• Salinity
• Gas
• Gases that have reacted chemically do not contribute to partial pressure in solution
Henry’s Law

Concentration in solution

C=AP

Partial pressure

Absorption coefficient

(solubility)

Eqn. 21.3

P1-P2

J=K

X

Diffusion of gases

Partial pressure

Rate of net movement of the gas

Diffusion coefficient

Distance to be diffused

Eqn. 21.4

Diffusion coefficient
• Depends on gas, temperature, medium
• Also depends on the permeability of any barriers, e.g. cell membranes, cuticle, epidermis

(m2/sec × 10-9)

Unidirectional flow (convection) in circulatory system

Tidal convection ventilates lungs

Diffusion from capillaries into tissues

Diffusion into bloodstream

Breathing water
• Getting rid of CO2 isn’t a problem
• High diffusivity & absorption
• Getting O2is
• Low absorption in water = low PO2
How to breathe water?
• Fast ventilation
• More water across respiratory surface = more O2 to absorb
• Efficient absorption
• Would predict countercurrent exchange
• Highly vascularised system with a large surface area
Ventilatory structures
• Gas exchange surfaces
• Usually highly vascularised
• Need to open to the ‘outside world’
• Are usually actively ventilated (convective flow of medium)
Ventilatory structures
• Skin
• Gills
• Evaginations (outpocketings)
• Lungs
• Invaginations (inpocketings)
• (or some combination of the above…)
Cutaneous respiration

Fig. 22.8 (top half)

Blood vessel terminology
• Afferent
• Entering the structure (Arriving)
• Efferent
• Leaving the structure (Exit)
Gill structure in fishes

Primary Lamellae

Buccal Cavity

(mouth)

Blood is oxygenated while flowing through 1° lamella

Operculum

Gill Arch

Fig. 22.10b

Gill structure in fishes

Afferent (deoxygenated)

Efferent (oxygenated)

2° Lamellae

Fig. 22.10b&c

Counter-current gas exchange

Fig. 22.10d

Fig 22.4b

Ventilating the gills

Buccal-opercular pumping

Ram Ventilation

Water in at mouth, pumped out of buccal cavity with positive pressure

Water pumped out of opercular cavity with positive pressure

Fig 22.11