Gas Exchange - Anatomy & Physiology

()Map CARDIORESPIRATORY SYSTEM (Map)

Introduction

The air in the alveoli is renewed regularly, thanks to the ventilation process. Gas Exchange in the lungstakes place between the blood in the capillary network surrounding the alveoli, and the air in the alveoli itself.

All of the blood from the Right Ventricle flows through the capillary network which surrounds the alveoli. Another set of pulmonary capillaries recieve small amounts of arterial blood from the Left Ventricle, via the Bronchial Arteries. These capillaries provide oxygen and nutrients to the [[Lungs - Anatomy & Physiology|lung] tissue.

Gas Exchange

• Gas exchange occurs between the air within the alveoli, and the pulmonary capillaries occurs by diffusion. The oxygen must first dissolve before passing through the respiratory epithelium.
• Gas moves from a region of high partial pressure to a region of low partial pressure, down a Partial Pressure Gradient.

Oxygen Exchange

• The PO2 is always lower in the alveoli due to the oxygen diffusing across the wall continuously, and the CO2 entering the alveoli which has the effect of 'diluting' the oxygen.
• Once through the alveolar and capillary walls, the Oxygen combines with Haemoglobin to form Oxyhaemoglobin and is transported within the bloodstream.

Carbon Dioxide Exchange

• Carbon Dioxide enters the red blood cell as a waste product from cells. In the red blood cell it reacts with water to form Carbonic Acid, CA.
• CA dissociates to Bicarbonate ions and Hydrogen ions.
• These diffuse into plasma, where H+ are buffered by haemoglobin.
  • Approx 5% of the total body CO2 dissolves in the plasma.
  • Approx 5% of the total body CO2 is carried as carboxyhaemoglobin on proteins.
  • Approx 90% is carried as bicarbonate ions in the plasma.