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Human Body Study

Respiratory System

The body’s gas exchanger — it brings in oxygen and expels carbon dioxide.

The respiratory tract From the upper airway down through larynx, trachea and bronchial branching into the two lungs, with the diaphragm at the base. A separate inset shows alveoli — the microscopic gas-exchange sacs inside the lungs. Each label links to the article for that part. Alveoli Upper respiratory tract Larynx Trachea Bronchi Lungs Diaphragm The respiratory tract — schematic, not to scale.

Main parts

Section titled “Main parts”
  • Upper respiratory tract — the nose, sinuses, and pharynx; conditions incoming air.
  • Larynx — the voice box; also guards the airway.
  • Trachea — the windpipe carrying air toward the lungs.
  • Bronchi — the branching airways within the lungs.
  • Lungs — the paired organs that house gas exchange.
  • Alveoli — the tiny air sacs where gas exchange actually happens.
  • Diaphragm — the muscle that powers breathing.

What it does

Section titled “What it does”
  • Gas exchange — at the alveoli, oxygen passes into the blood and carbon dioxide passes out, across a barrier just one cell thick.
  • pH balance — by adjusting how much carbon dioxide is exhaled, breathing helps keep the blood from becoming too acidic.
  • Other roles — warms and filters incoming air, enables speech, and serves the sense of smell.

Key idea

Section titled “Key idea”

Breathing is mostly automatic, set by the brainstem according to the blood’s carbon dioxide level — yet it is also one of the few vital functions we can consciously override.