VPB 121: Veterinary Physiology - II (2+1)

RESPIRATORY MEMBRANE

• The respiratory membrane is where O₂ and CO₂ diffuse across the alveolar and capillary walls. It is a very thin membrane about 0.5 µm thick and consists of four layers. Exchange between alveoli and capillaries.

 

• Gas moving from alveolus to blood must pass through: 
• Thin layer of pulmonary surfactant
• Alveolar epithelium : A layer of type I and type II alveolar cells, and alveolar macrophages.
• The epithelial basement membrane.
• The capillary basement membrane.
• Capillary endothelium
• Plasma
• Red blood cell membrane
• Red blood cell to reach hemoglobin
• The pulmonary artery carries deoxygenated blood, while oxygenated blood returns to the left atrium via the pulmonary veins. The darker purple color of venous blood becomes bright red arterial blood during the saturation of hemoglobin with oxygen that has freshly diffused from the alveoli. 
• During exercise, cardiac output can increase by as much as eightfold. During this time, blood flow to the lungs must increase. Pulmonary blood vessels dilate. In the horse, pulmonary arterial pressure can be so high as to cause erythrocytes to leak from pulmonary capillaries, a condition called as exercise-induced pulmonary hemorrhage, in athletic horses.
• Pulmonary ventilation
  • Respiration, the process of gaseous exchange, occurs in three steps:
    • Pulmonary ventilation, or breathing, is the mechanical movement of air into (inspiration) and out (expiration) of the lungs.
    • External respiration is the exchange of gases between the lungs and the pulmonary capillaries, which occurs across the respiratory membrane. The blood gains O₂ and loses CO₂.
    • Internal respiration is the exchange of gases between systemic capillaries and tissue. The blood gains CO₂ and loses O₂.