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Diffusion of gases through respiratory membrane
- 1. DIFFUSION OF GASES THROUGH RESPIRATORY MEMBRANE ZEYNAB ATTA (Physiotherapist to be)
- 2. INTRODUCTION • The purpose of the respiratory system is to perform gas exchange. • Pulmonary ventilation provides air to the alveoli for this gas exchange process. • At the respiratory membrane, where the alveolar and capillary walls meet, gases move across the membranes, with oxygen entering the bloodstream and carbon dioxide exiting. • It is through this mechanism that blood is oxygenated and carbon dioxide, the waste product of cellular respiration, is removed from the body.
- 3. RESPIRATORY UNIT: • is composed of a respiratory bronchiole, alveolar ducts, atria, and alveoli. • There are about 300 million alveoli in the two lungs, and each alveolus has an average diameter of about 0.2 millimeter. • Between the alveoli is a network of interconnecting capillaries.
- 6. Diffusion of Oxygen • The partial pressure of oxygen is low in the alveoli compared to the external environment. • This is due to continuous diffusion of oxygen across the alveolar membrane and the diluting effect of carbon dioxide entering the alveoli to leave the body.
- 7. Cont… • Despite this, the partial pressure is still higher in the alveoli than the capillaries, resulting in a net diffusion into the blood. • Once it has diffused across the alveolar and capillary membranes, it combines with haemoglobin. • This forms oxyhaemoglobin which transports the oxygen to respiring tissues via the bloodstream.
- 8. Cont… • During exercise, blood spends around half the normal time (1s at rest) in the pulmonary capillaries due to the increase in cardiac output. • However, diffusion of oxygen is complete within 0.5s of the blood cell arriving in the capillary, which means that exercise is not limited by gas exchange.
- 9. Diffusion of Carbon Dioxide • The partial pressure of carbon dioxide in the capillaries is much higher than that in the alveoli. • This means that net diffusion occurs into the alveoli from capillaries. The carbon dioxide can then be exhaled as the partial pressure in the alveoli is also higher than the partial pressure in the external environment.
- 10. Cont… • However it is important to note that these pressure differences are much smaller than those for oxygen, as carbon dioxide is able to diffuse more rapidly. • Carbon dioxide is transported in the blood in multiple ways; including dissolved, associated with proteins and as bicarbonate ions.
- 11. Factors That Affect the Rate of Gas Diffusion Through the Respiratory Membrane • the factors that determine how rapidly a gas will pass through the membrane are • (1) the thickness of the membrane, • (2) the surface area of the membrane, • (3) the diffusion coefficient of the gas in the substance of the membrane, and • (4) the partial pressure difference of the gas between the two sides of the membrane.