Gaseous Exchange

Gaseous Exchange

• Gaseous exchange is the movement of oxygen from the lungs into the blood and carbon dioxide from the blood to the lungs.
• This vital process occurs in the lungs between alveoli and capillaries.
• Capillaries line approximately 70% of the alveoli, creating a large surface area for gas diffusion.

The Alveoli

• The alveoli are the site of gaseous exchange.
• Alveoli are adapted for efficient gas exchange due to their small size (approximately 300 µm in diameter), resulting in a high surface area-to-volume ratio (around 70 square metres).
• Another crucial adaptation is the enormous number of alveoli (approximately 700 million, with 350 million in each lung).
• A short diffusion path—one cell thick walls, moistened with a thin fluid— further enhances gas exchange efficiency.

Structure of Alveoli

• The image shows blood from pulmonary arteries entering the delicate capillary network enveloping the alveoli. Air moves into and out of the alveoli.
• Blood leaves the alveoli as oxygenated blood through the pulmonary veins.
• The complex structure ensures rapid and efficient gas exchange.

How Gaseous Exchange Occurs

• Oxygen moves from the lungs to the blood, while carbon dioxide moves from the blood to the lungs, occurring in the alveoli and associated capillaries.
• The alveoli’s thin walls allow gases to pass between air and blood.
• Oxygen diffuses from the alveoli into the blood, attaching to red blood cells.
• Carbon dioxide diffuses from the blood into the alveoli to be exhaled.
• This process is essential for life as it provides the body with oxygen and removes waste carbon dioxide.