1 / 14

GAS EXCHANGE

GAS EXCHANGE. Goals • To apply gas law relationships - between partial pressure, solubility, and concentration - to gas exchange . • To explore the factors which affect external and internal respiration. Gas Exchange.

theta
Download Presentation

GAS EXCHANGE

An Image/Link below is provided (as is) to download presentation Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author. Content is provided to you AS IS for your information and personal use only. Download presentation by click this link. While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server. During download, if you can't get a presentation, the file might be deleted by the publisher.

E N D

Presentation Transcript

  1. GAS EXCHANGE Goals • To apply gas law relationships - between partial pressure, solubility, and concentration - to gas exchange. • To explore the factors which affect external and internal respiration

  2. Gas Exchange Oxygen and carbon dioxide diffuse between the alveoli and pulmonary capillaries in the lungs, and between the systemic capillaries and cells throughout the body. • The diffusion of these gases, moving in opposite directions, is called gas exchange. Gas exchange results in end capillary blood gases that are in equilibrium with the partial pressure of gases in the alveoli

  3. ATMOSPHERIC or BAROMETRIC PRESSURE [PB]and Daltons Law • Dry air is composed of a mixture of gases. • • Each gas exerts a partial pressure which is the pressure it would exert if it alone occupied a given • volume. • • Barometric pressure [PB] is the total pressure exerted by • this mixture of gases = 760 mmHg at sea level 760 20.9% 159 440 0.04% 0.3 78.6% 597 3.5 0.46% 0 This demonstrates Dalton's Law of Partial Pressures, which states that in a mixture of gases, the total pressure equals the sum of the partial pressures exerted by each gas.

  4. COMPOSITION OF GASES IN ATMOSPHERIC AIR Determining Their Partial Pressure Nitrogen 78.08 Oxygen 20.94 Argon 0.93 Carbon Dioxide 0.03 and trace amounts of-- Neon Methane Helium Krypton Hydrogen Xenon In dry air at sea level PO2 = 760 mmHg X 0.21= 160 mmHg During inspiration in the conducting airways PO2 = [760 – 47 mmHg) X 0.21 = 150 mmHg Inspired air is heated to 37ºC, humidified & saturated with water vapour PH2O = 47 mmHg

  5. THE PARITAL PRESSURE OF OXYGEN DECREASES AS INSPIRED AIR COURSES THROUGH THE AIRWAYS PO2 = 160 mmHg PCO2 = 0 DRY AIR AT SEA LEVEL PH2O = 0 PO2 = 150 CONDUCTING AIRWAYS PCO2 = 0 (HEATED & HUMIDIFIED) PH2O = 47 PO2 = 100 ALVEOLI PCO2 = 40 (MIXED IN A RESERVOIR OF AIR- FRC) PH2O = 47

  6. DETERMINE THE PARTIAL PRESSURE OF OXYGEN AT HIGH ALTITUDE At the summit of Mount Everest at 18,000 ft, barometric pressure is half of its value at sea level. What happens to the partial pressure of inspired oxygen? How about the PO2 at the level of carina? At the summit: PO2 = [760/2]X 0.21 = 380X0.21 = 80 mmHg In the carina: PIO2 = [380-47]X 0.21 = 333X0.21 = 70 mmHg In the Alveoli- very less due to ? High altitude pulmonary edema

  7. Henry's Law Within the lungs, oxygen and carbon dioxide diffuse between the air in the alveoli and the blood, that is between a gas and a liquid. • This movement is governed by Henry's Law, which states that the amount of gas which dissolves in aliquid is proportional to: 1. the partial pressure of the gas 2. the solubility of the gas In the container on left, the oxygen in the air is at equilibrium with the oxygen in the liquid. At equilibrium, the pressure of the oxygen in the air is the same as in the liquid, with the gas molecules diffusing at the same rate in both directions. If you increase the pressure in the container(right) more oxygen molecules dissolve in the liquid, moving from a region of high pressure to a region of low pressure. Diffusion continues until a new equilibrium is reached. This is what happens when oxygen moves from the alveoli into the blood. • carbon dioxide- much more soluble than oxygen

  8. Sites of gas exchange in the body: • External Respiration. • Blood that is low in oxygen is pumped from the right side of the heart, through the pulmonary arteries to the lungs. • External respiration occurs within the lungs, as carbon dioxide diffuses from the pulmonary capillaries into the alveoli, and oxygen diffuses from the alveoli into the pulmonary capillaries. • Oxygen-rich blood leaves the lungs and is transported through the pulmonary veins to the left side of the heart. • Internal Respiration. • From there it is pumped through the systemic circuit to tissues throughout the body. • Internal respiration occurs within tissues, as oxygen diffuses from the systemic capillaries into the cells, and carbon dioxide diffuses from the cells into the systemic capillaries.

  9. Factors Influencing External Respiration • Efficient external respiration depends on three main factors: The surface area and structure of the respiratory membrane. The partial pressure gradients between the alveoli and capillaries. 3. Efficient gas exchange requires matching alveolar airflow to pulmonary capillary blood flow. Branch of pulmonary vein Branch of pulmonary arterie capillaries

  10. 10 Diffusion Barrier This can be as short as 0.3 mm between air and blood plasma – thus representing very little barrier to diffusion! This is an amazing feat of engineering since within that space you have to fit - alveolar liquid, an epithelial cell, extracellular space and an endothelial cell, then some plasma, then the red cell membrane and cytoplasm before O2 is able to bind with hemoglobin (Hb)!!!! O2 O2 O2 PO2 O2 O2 O2 + Hb Type I cell Alveolar Fluid Interstitium Endothelial cell plasma RBC

  11. External Respiration: Partial Pressures • Let's see how partial pressure gradients affect gas exchange between the alveoli and the pulmonary capillaries. 159 100 40 47 0.3 3.5 The partial pressures in the alveoli differ from those in the atmosphere. This difference is caused by a combination of several factors: 1. Humidification of inhaled air 2. Gas exchange between the alveoli and pulmonary capillaries 3. Mixing of new and old air

  12. A Key Factor In The Amount Of Gas Exchange Is The Partial Pressure Difference Across The Gas Exchange Barrier a.k.a. the driving pressure Across pulmonary capillaries O2 partial pressure gradient from alveoli to blood = 60 mm Hg (100 –> 40) CO2 partial pressure gradient from blood to alveoli = 6 mm Hg (46 –> 40) Across tissue capillaries O2 partial pressure gradient from blood to tissue= 60 mm Hg (100 –> 40) CO2 partial pressure gradient from tissue cell to blood = 6 mm Hg (46 –> 40)

  13. GAS EXCHANGE ACROSS THE PULMONARY CAPILLARY Is Complete Within ¼ Second • at rest pulmonary transit time [¾ second] is more than that required to complete gas exchange [¼ second]. • during exercise, despite increased cardiac output, pulmonary transit time remains > ¼ second & gas exchange is complete. • in pulmonary fibrosis, reduced gas exchange is often seen in patients during exercise. At rest, the additional time spent in the capillary is sufficient to compensate for the thickened barrier

  14. Dalton's Law of Partial Pressures If we analyze percentage of each gas in the air. atmosphere is a mixture of gases. The combined pressure of these gases equals atmospheric pressure. oxygen, Carbon dioxide, nitrogen, water 20.9% 0.04% At sea level, atmospheric pressure is 760 mm Hg, 78.6% 0.46% Each gas within the atmosphere is responsible for part of that pressure in proportion to its percentage in the atmosphere.

More Related