The human respiratory system

The respiratory system absorbs oxygen and removes carbon dioxide from the body.

Mouth or Nose:

• Air enters the body through the mouth or nose.

Trachea (Windpipe):

• A muscular tube lined with C-shaped rings of cartilage.

• Cartilage prevents the trachea from collapsing while allowing it to expand and contract.

Bronchi:

• The trachea splits into two smaller tubes called bronchi, each leading to a lung.

Bronchioles:

• The bronchi branch into smaller tubes called bronchioles.

Alveoli:

• Bronchioles end in tiny air sacs called alveoli.

• Each alveolus is surrounded by a capillary network for gas exchange.

• Alveoli walls are one cell thick to allow efficient diffusion.

Gas exchange

Oxygen:

• Diffuses from the air in the alveoli into the blood in the capillaries (high → low concentration).

Carbon Dioxide:

• Diffuses from the blood in the capillaries into the alveoli to be exhaled (high → low concentration).

Structure of the respiratory system

Adaptations of the lungs for gas exchange

Large Surface Area:

• Millions of alveoli provide a large area for gas exchange.

Thin Membrane:

• Alveoli walls are only one cell thick, providing a short diffusion path.

Efficient Blood Supply:

• Capillaries surrounding each alveolus maintain a steep concentration gradient.

Ventilation:

• Breathing ensures fresh air is constantly supplied, maintaining a high oxygen concentration in the lungs.