Human respiratory system. Image credit

Human respiratory system. Image credit

ZIMSEC O Level Combined Science Notes: The respiratory system and gaseous exchange

  • The respiratory system is responsible for gaseous exchange and breathing so that oxygen is taken into the body and carbon dioxide is released from the body.
  • Mammals including humans need oxygen in order to live.
  • The oxygen is taken into cells and combined with glucose resulting in the production of energy in a process called respiration.
  • The human respiratory system is made up of the lungs and other organs found in the head and chest.
  • The system is responsible of getting air in and out of the lungs.
  • During inhaling the intercostal muscles contract thus lifting the ribs.
  • The volume of the chest cavity increases thus resulting in reduced pressure inside the cavity.
  • Atmospheric pressure forces air into the lungs.
  • During exhaling the intercostal muscles muscles relax allowing the ribs to fall back into place.
  • The volume within the chest cavity decreases resulting in increased pressure.
  • As pressure will be now higher inside the cavity air is forced out of the lungs.
  • When air is breathed in, it enters through the nasal passages.
  • It is warmed, moisturized by the mucus and filtered by tiny hairs.
  • It then moves down into the larynx also known as the voice box (the organ that makes the sound when humans speak).
  • The air passes down through the trachea/wind pipe which branches into 2 smaller tubes called bronchi.
  • All the tubes are lined with tiny hairs and a fluid (mucus) to trap germs and other foreign particles in the air.
  • he bronchi later branches into smaller and smaller tubes called bronchioles until the tubes end at microscopic air sacs.
  • These microscopic air sacs are known as alveoli.
  • There are millions of alveoli in each lung which make up large surface area so that oxygen can easily be absorbed.
  • Around each alveolus are many microscopic capillaries (blood vessels).
  • While the air is in the lungs its compositions changes as gaseous exchange takes place.
  • Gaseous exchange takes place in the alveoli.
  • Gaseous exchange-as exchange is the delivery of oxygen from the lungs to the bloodstream, and the elimination of carbon dioxide from the bloodstream to the lungs.
  • It occurs in the lungs between the alveoli and a network of tiny blood vessels called capillaries, which are located in the walls of the alveoli

To access more topics go to the Combined Science Notes page.

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