Gas Laws in Respiration

GAS LAWS To understand the behavior of gases one should be able to explain 4 gas laws. 1. BOYLE’S GAS LAW 2. DALTON’S LAW OF PARTIAL PRESSURE 3. HENRY’S GAS LAW 4. GRAHAM’S LAW BOYLE’S GAS LAW

P1V1 = P2V2 The relationship between the pressure and volume of gases is given by Boyle’s law. It states that when the temperature is constant, the pressure of a gas varies inversely with its volume. As volume increases, pressure decreases. As volume decreases, pressure will increase. Boyle’s Law • Inhalation:

Diaphragm contracts/flattens, rib muscles contract raising the rib cage, creating low pressure in the chest cavity. The lungs respond by expanding, creating a low pressure in the lungs and the air rushes from high partial pressure to low partial pressure into the lungs. Exhalation: • Diaphragm relaxes into dome -shape, rib muscles relax lowering the rib cage, creating high

pressure in the chest cavity. The lungs respond by reducing in size, creating a high pressure in the lungs. The air rushes from high partial pressure to low partial pressure out the lungs. DALTON’S

LAW OF PARTIAL PRESSURE

The partial pressure of a gas in a gas mixture as the pressure that the gas would exert if it occupied the total volume of the mixture in the absence of the other components, it means Dalton's law follows directly from the Ideal Gas Law since it states that the pressure exerted by a gas is proportional to the number of moles of that g as. Thus,

Total pressure exerted by a mixture of gases is the sum of the pressures exerted independently by each gas in the mixture. Ptotal = P1 + P2+ P3…

Since, by definition, PB is the total to tal pressure of all gases in a mixture in contact with the atmospheric pressure. For instance, at sea level, barometric pressure is 760 mm Hg, and oxygen makes up 21% of dry air. Thus, the partial pressure of oxygen in dry air is 160 mm Hg.

PO2 =

0.21 × 760 mm Hg =

Henry’s Law

When a liquid is put in contact with a gas phase of partial pressure, Pgas, gas will dissolve in the liquid until equilibrium is reached between the two phases. The condition for equilibrium of a gas between a gas phase and a liquid phase is that the partial pressures of the gas are equal in the two phases, not the concentrations, as is the more familiar case for non-gaseous solutes. Thus, at equilibrium, Pliquid = Pgas rather than Cliquid = Cgas. This is an important principle in understanding gas exchange between the alveolar space (gas phase) and the pulmonary capillary blood (liquid phase). In general, gases diffuse between sites where there is a difference in partial pressure (e.g., red blood cell and plasma, ISF and cell cytoplasm), not in concentration. Thus, gas exchange takes place between the two phases as long as there is a partial pressure difference between them. Once equilibrium is reached, net gas exchange ceases. A mixture of gases is in contact with a liquid, each gas will dissolve in the liquid in to its partial pressure and its solubility coefficient. Graham’s Law Graham’s Law can be applied to the diffusion rate of gas ses in the alveoli. The relative rate of

diffusion of a gas is proportional to the solubility of that gas. When gases are dissolved in liquids, the relative rate of diffusion of a given gas is proportional to its solubility in the liquid and inversely proportional to the square root of its molecular mass. Important in the transport of respiration gases is the relative diffusion rate of oxygen and carbon dioxide in the plasma of the human body. Carbon dioxide has 22 times the solubility, but is more massive (44 amu compared to 32 for oxygen). According to Graham's law, the relative rate of diffusion is given by

Hyperphysics by Department of Physics and Astronomy in Georgia State University http://hyperphysics.phy-astr.gsu.edu/hbase/kinetic/henry.html Respiratory System How do your cells obtain oxygen and remove carbon dioxide? http://www.haspi.org/curriculum-library/Med-Chemlessons/05%20Standard%204%20Gases%20and%20Their%20Properties/Medical%20Applications %20and%20Resources/Med%20Chem%20Gas%20Laws%20and%20Respiration.pdf  Pittman RN. San Rafael (CA): Morgan & Claypool Life Sciences; 2011. C hapter 3 The Respiratory System and Oxygen Transport http://www.ncbi.nlm.nih.gov/books/NBK54114/ Muhammad Iqbal KMU, Integrated Sciences-II (Physics) http://www.kmu.edu.pk/ins/sites/kmu.edu.pk.ins/files/Lectures/Application%20of%20gas%20law s%20to%20resp%20system%20presentation.pdf