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BIO202H5 Chapter Notes - Chapter all: Perfusion, Countercurrent Exchange, Intracellular Ph

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Sanja Hinic- Frlog

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Gaseous Exchange 09/20/2014
a hydrophobic surface that creates an airspace on the spiders body surface
allows diving arthropods to take dissolved oxygen from water, through the thin film of air that creates an
incompressible exchange surface, into their gaseous exchange system
hydrophobicity of a surface is enhanced by reducing surface energy through chemical modification of the
Gaseous exchange
Exchange of gases with the respiratory medium, transport of gases in the circulatory system of the animal,
and exchange at the tissues to supply mitochondria with oxygen and to remove carbon dioxide
Basic Principles of Gaseous Exchange
A Simple Diffusion
Fick’s law
The bulk or mass of an organism is generally proportional to its volume
Small volume = large relative surface area = small path length from environment to any internal cell
Bacteria – small volume – large surface area – allows simple diffusion to supply enough oxygen and
remove carbon dioxide
Larger volume relative to surface area requires specialized structures to acquire oxygen and excrete carbon
dioxide – larger path length
Influenced by metabolic rate which drives the need for gas exchange – and the nature of the animals’ outer
Fick’s Law
Ventilation – gas exchange with the environment
Perfusion – gas delivery within the body
Both ventilation and perfusion maximize diffusion
P1 – increased by ventilation as animals move air or water past the respiratory surface
P2 – lowered by perfusion as it moves body fluids on the other side of the surface
Animals use fick’s law to their advantage to maximize diffusion – concentration gradient maximizes
Animals must adjust ventilatory activity according to the internal concentration of carbon dioxide to ensure
that appropriate levels of water or air reach the respiratory surfaces
Sensors in brain connected to blood vessels to detect change in pH and CO2 concentration - causes
changes in ventilation to maintain appropriate levels

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In Helix species sensors control the size of the opening of the mantle cavity, the pneumostome
Changes in intracellular pH of specialized cell accurately reflect changes in ventilation
In the face of changes in extracellular pH, it is important that the mechanisms used by other cells to
regulate internal pH be inactive in chemosensory cells, so that the response to ventilatory cues does not
become weaker
Similarity of options among different species suggests an ancient lineage of sensors controlling ventilation
across respiratory surfaces
Values obtained by calculating simple rate of diffusion, the effects of surface are: volume ratios on diffusion
distance (L), or partial pressures and the resultant concentration gradients strongly influence life on earth
by affecting animals’ access to oxygen
Respiratory Water Loss
Water loss is proportional to gas exchange by a factor of 1
Surface temperature of the respiratory surface
Gas consumed
Steepness of concentration gradients for gas and vapor
Whether the mode of water transport is convective or diffusive
Sites for Gaseous Exchange
Fick’s law plays major role in determining the size and shape of the respiratory surfaces and their suitability
for gaseous exchange
Animal respiratory surfaces
Mantle cavities
Large respiratory surface increases A in Fick
Respiratory surface close to circulatory system in order to decrease diffusion distance (L) and creating a
close relationship between perfusion and ventilation
When oxygen is being extracted from water its uptake by blood is enhanced by countercurrent exchange
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