Pulmonary Circulation and Respiratory Membrane Quiz

Pulmonary Circulation

• The pathway of pulmonary circulation: right ventricle → pulmonary artery → right and left pulmonary arteries → pulmonary capillaries → pulmonary veins → left atrium

Diffusion of Oxygen and Carbon Dioxide

• Diffusion is the movement of gas molecules between the alveolar air and the pulmonary blood through the respiratory membrane
• The respiratory unit is composed of a respiratory bronchiole, alveolar ducts, atria, and alveoli
• There are approximately 300 million alveoli in the two lungs
• Each alveolus has an average diameter of about 0.2 μm
• The total surface area of the respiratory membrane is about 70 m2 in the normal adult human male

Respiratory Membrane

• The total quantity of blood in the capillaries of the lungs is 60-140 ml
• The diameter of the pulmonary capillaries is only about 5 micrometers
• The respiratory membrane consists of six layers:
  • Thin fluid lining the alveolus and containing surfactant
  • The alveolar epithelium
  • A basement membrane
  • An interstitial space between the alveolar epithelium and the capillary membrane
  • A capillary basement membrane
  • The capillary endothelial membrane

Factors Affecting Gas Diffusion

• The rate of diffusion through the membrane is inversely proportional to its thickness
• Factors that increase the thickness of the respiratory membrane:
  • Edema fluid in the interstitial space of the membrane
  • Fibrosis of the lungs, which can increase the thickness of the respiratory membrane