Explain the structure and function of alveoli in the human respiratory system.

The alveoli are tiny, balloon-like structures found at the ends of the bronchial tubes in the lungs. They are a critical part of the human respiratory system and are involved in the exchange of gases—specifically oxygen and carbon dioxide—between the air and the bloodstream. Here’s a breakdown of their structure and function:

Structure of Alveoli:

  1. Size and Shape: Alveoli are microscopic, with each lung containing around 300 million alveoli. They are shaped like small sacs or clusters, resembling bunches of grapes, which increases the surface area for gas exchange.
  2. Thin Walls: The walls of the alveoli are extremely thin (only one cell layer thick), which allows gases to diffuse easily between the alveoli and the capillaries (tiny blood vessels that surround them).
  3. Surfactant: Alveolar cells secrete a substance called surfactant, which reduces surface tension and prevents the alveoli from collapsing after exhalation.
  4. Capillary Network: Each alveolus is surrounded by a dense network of capillaries. These capillaries carry deoxygenated blood from the heart to the lungs, where carbon dioxide is exchanged for oxygen.

Function of Alveoli:

The primary function of alveoli is gas exchange:

  • Oxygen Diffusion: When you inhale, air fills the alveoli, and oxygen from the air passes through the thin walls of the alveoli into the capillaries. The oxygen then binds to hemoglobin in red blood cells and is transported throughout the body to tissues and organs.
  • Carbon Dioxide Removal: At the same time, carbon dioxide, which is a waste product of metabolism, diffuses from the capillaries into the alveoli. When you exhale, this carbon dioxide is expelled from the lungs.

The efficiency of gas exchange is facilitated by the large surface area of the alveoli and their proximity to the blood supply. This allows for rapid and efficient transfer of gases between the lungs and the bloodstream.

In summary, the alveoli are essential for breathing, enabling the body to take in oxygen and remove carbon dioxide, both of which are critical for maintaining life.

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