The human breathing system

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  • Created by: zoolouise
  • Created on: 04-05-16 16:55

The human breathing system

The lungs are enclosed in an airtight compartment called the thorax. Pleural membranes line the thorax and cover each lung. Fluid between the membranes prevents friction between the lungs and chest cavity.
The diaphragm is a dome-shaped sheet of muscle at the base of the thorax, it separates the thorax from the abdomen
Ribs surround the thorax and there's intercoastal muscles between the ribs. The trachea is a flexible airway to bring air to the lungs, it has semi-circles of cartilage. Two bronchi, then bronchioles and then air sacs called alveoli.

Ventilation of the lungs

Mammals ventilate their lungs by negative pressure breathing, i.e. air enters the lungs because the pressure inside the lungs is lower than the atmospheric pressure. The pressure wants to balance out and so air will flow from an area of high pressure to an area of low pressure.


Inspiration is an active process as the muscle contraction requires energy in the form of ATP.

  • 1) The external intercostal muscles contract and the internal intercostal muscles relax
  • 2) The ribs are pulled upwards and outwards
  • 3) The diaphragm muscles


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