Organismal Physiology Lecture No. 14: Gas Physiology II
Tuesday October 30 , 2012
Gases Dissolve In Liquids:
-Gases dissolve in liquids in much the same way that solutes dissolve in water in that they do not form
bubbles. Gas in liquid solution depends upon three main factors: temperature (the degree of molecular
interactions), salinity (biological implications) as well as other gases. It is also important to note that
gases that have reacted chemically do not contribute to partial pressure in solution (no longer act as a
gas when dissolved). According to Henry’s Law, the solubility of a gas in a liquid is directly proportional
to the pressure of that gas above the surface of the solution.
-As mentioned previously, Henry’s Law states that the partial pressure and the concentration of a gas in
solution are proportional to each other. The following equation describes this relationship: C = AP x x
where C ix the concentration of the gas in solution, A is the absorption coefficient (solubility of the gas
in the liquid), and P xs the partial pressure in the liquid (established by the partial pressure in the air
above the liquid).
Thomas Graham & The Solubility Of Various Gases:
-Looking at the different properties and behaviours of gases in liquid solution, Thomas Graham deduced
that each gas acts differently under standard temperature and pressure (negligible in gas solution, but a
concern in liquid solution). CO , for example, has a greater solubility than oxygen and an even greater
solubility in liquid than nitrogen.
The Diffusion Of Gases & Fick’s Equation:
-The following equation describes the diffusion of gases derived from Fick’s equation: J = K (P1– P 2 / x
where J is the rate of net movement of the gas (per unit area), K is the diffusion coefficient, (P -P ) 1s 2he
concentration gradient, and x is the distance to be diffused.
Improving Gas Exchange:
-In order to improve gas exchange, there are three ways to maximize the rate of diffusion: by increasing
or maximizing the concentration gradient, minimizing the diffusion distance (having a very thin
basement membrane), and maximizing the surface area.
Convection & Diffusion:
-Diffusion is process upon which one would want to minimize dependence on. Convection accomplishes
this by essentially pushing molecules away from high concentration to low concentration. In the body,
the distance that gases are moved by convection is immensely greater than the distance that molecules
are taken by diffusion. Essentially, convection moves oxygen to the sites of diffusion in the body and convection (bulk flow) and diffusion do in fact alternate in transporting O fr2m the atmosphere to the
mitochondria in a person. Through each section of the cardiovascular system affected, there is a
consistent drop in partial pressure. However the drop in partial pressure from the systemic capillary
blood to the mitochondria is critical as it involves the greatest release of oxygen as well as direct fueling
of cellular respiration. When mountaineers venture to dangerous altitudes (where the air is deadly thin),
this diffusion of oxygen to mitochondria is much less and can result in death.
Convection & Vertebrates:
Convective air movement, in terms of burrows, is highly important as without exposure to convection,
animals residing in these burrows will likely die due to build-up of CO . 2his is why animals like Prairie
dogs build at least one surface tunnel at a greater height than another one because underground
animals desperately require a mechanism for maintaining oxygen flow.
Convection & Invertebrates:
-When sprayed with freshwater, sponge choanocytes stop beating their flagella because the organism
utilizes the positive and negative pressure of the current (convective force) in order to move water
passively at a sufficient rate. This is because its regular transport of water would lead to internal
exhaustion and way too much energy being spent.
-Cnidarian jellyfish have a canal system from their gastrovascular cavity (extensive throughout the inner
and outer tissue of the animal) that allows for the movement of water (oxygenated) via cilial movement.
They can also use their swimming muscles to move the bulk flow of fluid, using convection to dispel
deoxygenated water. It accomplishes this by contracting its umbrella and using the jet stream of water
to dispel deoxygenated water.
-Some of the difficulties that native organisms share in attaining oxygen from water include the fact that
there is typically less oxygen in water than there is in air as well as the increased viscosity of water,
which means more energy is required to extract O . Hum2n beings have a tidal ventilating system that
inhales air, extracts oxygen and dispels the air as CO ,2but that is a quite inefficient method for breathing
underwater. That is why a unidirectional system is used, because it takes more energy to extract the
water from oxygen. It is also important to no