Physio Lec3 PDF - Basics Properties of Gases

9/18/2024 Basics Properties of Gases By Assist. Prof. Dr. Dler Gallaly PhD in Medical Physiology University of Kurdistan- Hewlêr 2024 / 2025 Mob.#: (+964) 750 461 87 58 Email: d...

9/18/2024 Basics Properties of Gases By Assist. Prof. Dr. Dler Gallaly PhD in Medical Physiology University of Kurdistan- Hewlêr 2024 / 2025 Mob.#: (+964) 750 461 87 58 Email: [email protected] Contents:  Boyle’s law for pressure and volume of gases.  Dalton’s law of partial pressures and Henry’s law.  Atmospheric and alveolar air differ in composition, and explain these differences.  Dalton’s and Henry’s laws to events of external and internal respiration. 1  9/18/2024 Objectives: By the end of this lecture, you will be able to:  Know how Boyle’s law gives the relationship between the pressure and volume of a gas.  State Dalton’s law of partial pressures and Henry’s law.  Describe how atmospheric and alveolar air differ in composition.  Relate respiratory laws to events of external and internal respiration. Introduction:  during external respiration O2 enters and CO2 leaves the blood in the lungs by diffusion.  At the body tissues, where the process is called internal respiration, the same gases move in opposite directions, also by diffusion. 2  9/18/2024 Gases in Liquids:  Factors that affect the amount of gas that will dissolve in a liquid depends on: The partial pressure of the gas in contact with the liquid. The solubility of the gas in the liquid. The temperature of the liquid. Boyle’s Law:  Boyle’s law gives the relationship between the pressure and volume of a gas.  At constant temperature, the pressure of a gas varies inversely with its volume. 3  9/18/2024 Boyle’s Law:  Gases always fill their container.  Consequently, in a large container, the molecules in a given amount of gas will be far apart and the pressure will be low.  But if the volume of the container is reduced, the gas molecules will be forced closer together and the pressure will rise. Boyle’s Law: Changes in thoracic volume and sequence of events during inspiration. 4  9/18/2024 Boyle’s Law: Changes in thoracic volume and sequence of events during expiration. Boyle’s Law: Nonrespiratory Air Movements:  Many processes other than breathing move air into or out of the lungs, altering the normal respiratory rhythm.  These nonrespiratory air movements occur whenever you cough, sneeze, cry, laugh, hiccup, or yawn. can be:  produced voluntarily.  reflexive (sneezing and hiccups). 5  9/18/2024 Dalton’s Law of Partial Pressures:  Dalton’s law of partial pressures states that: the total pressure exerted by a mixture of gases is the sum of the pressures exerted independently by each gas in the mixture. Further, the pressure exerted by each gas, its partial pressure, is directly proportional to the percentage of that gas in the gas mixture. Dalton’s Law of Partial Pressures:  Dalton’s law of partial pressures states that: Nitrogen (N2) makes up ~79% of air, and the partial pressure of nitrogen PN2 is 78.6% x 760 mm Hg, or 597 mm Hg. Oxygen (O2), accounts for ~ 21% of air, has a partial pressure PO2 of 159 mm Hg (20.9% x 760 mm Hg). Together N2 and O2 contribute ~99% of the total atmospheric pressure. 6  9/18/2024 Dalton’s Law of Partial Pressures:  Air also contains: o 0.04% CO2 o 0.5% water vapor o insignificant amounts of inert gases (argon and helium). Dalton’s Law of Partial Pressures:  At high altitudes, partial pressures decline in direct proportion to the decrease in atmospheric pressure. For example: At 3,000 m above sea level where the atmospheric pressure is 523 mm Hg, PO2 is 110 mm Hg. 7  9/18/2024 Dalton’s Law of Partial Pressures:  Moving in the opposite direction, atmospheric pressure increases by 1 atm (760 mm Hg) for each 10 m of descent (in water) below sea level.  At 30 m below sea level, the total pressure exerted on the body is equivalent to 4 atm (3040 mmHg) and the partial pressure exerted by each component gas is also quadrupled. Henry’s Law:  Henry’s law states that:  when a gas is in contact with a liquid, the gas will dissolve in the liquid in proportion to its partial pressure. Accordingly, the greater the concentration of a particular gas in the gas phase, the more and the faster that gas will go into solution in the liquid. 8  9/18/2024 Henry’s Law:  At equilibrium, the partial pressures in the gas and liquid phases are the same.  If, however, the partial pressure of the gas later becomes greater in the liquid than in the adjacent gas phase, some of the dissolved gas molecules will reenter the gaseous phase.  The direction and amount of movement of a gas are determined by its partial pressure in the two phases. Henry’s Law:  This flexible situation is exactly what occurs when gases are exchanged in the lungs and tissues. For example:  when PCO2 in the pulmonary capillaries is higher than in the lungs, CO2 diffuses out of the blood and enters the air in the alveoli. 9  9/18/2024 Henry’s Law:  How much of a gas will dissolve in a liquid, at any given partial pressure, also depends on the solubility of the gas in the liquid and the temperature of the liquid.  The gases in air have very different solubilities in water (and in blood plasma). CO2 is most soluble. O2 is only 1/20 as soluble as CO2, N2 is only half as soluble as O2 (no N2 goes into solution). Henry’s Law:  When a liquid’s temperature rises, gas solubility decreases.  Example:  Soda drinks, when we take off the soda bottle cap:  if we leave it in the fridge, the CO2 gas will slowly go flat.  if we leave it at room temp., it will very quickly go flat.  In both cases, you end up with plain water, all the CO2 gas has escaped from solution. 10  9/18/2024 Questions/Comments 11