Surface exchange and breathing

• The alveoli are the site of gas exchange between the air and blood.
• Alveolar walls consist of type I pneumocytes, which have thin membranes that allow gases to diffuse easily into the capillaries.
• Type II pneumocytes produce surfactant, which reduces surface tension at the alveolus-capillary interface and prevents collapse during exhalation.
• Capillaries surround the alveoli and form a network called the pulmonary circulation system.
• Pulmonary veins carry oxygenated blood from the pulmonary circulation back to the left side of the heart.
• Capillaries surround the alveoli and contain red blood cells (RBC) with hemoglobin molecules.