Structure and function of the human gas exchange system

In a nutshell

The respiratory system is made up of different organs and structures which allow for gas exchange. Gas exchange enables oxygen from the air to be absorbed into the blood whilst removing carbon dioxide from the blood.

The respiratory system

The gas exchange system is also known as the respiratory system. It is made up of special organs and structures that each have different functions.

1.	Nasal cavity	Air that is breathed in through the nose passes through the nasal cavity.
2.	Throat (pharynx)	The throat connects the mouth and nose to the larynx.
3.	Larynx	The larynx is a hollow tube which allows air to pass from the throat to the trachea.
4.	Trachea	The trachea is also known as the windpipe. Air that is breathed in goes through the trachea.
5.	Bronchi	The trachea splits into two tubes. Each bronchus enters one of the lungs.
6.	Lungs	The main organ of the respiratory system. The lungs are protected by the ribcage.
7.	Bronchioles	The bronchi split into smaller tubes in the lungs. These are the bronchioles.
8.	Diaphragm	A muscle that sits under the lungs. The diaphragm helps air to get into and out of the lungs by moving up (contracting) and down (relaxing).
9.	Alveoli	The site of gas exchange. The bronchioles end at the alveoli which are small air sacs.

Gas exchange

In humans, gas exchange occurs when air is inhaled into the lungs. The lungs are well adapted for gas exchange because they are moist, have a rich blood supply and the alveoli give the lungs a big surface area inside.

The process of gas exchange

1.	Humans breathe in air which travels via the respiratory system into the lungs.
2.	The inhaled air contains oxygen. This oxygen passes into the bloodstream to be used in respiration.
3.	Carbon dioxide is produced during respiration and is a waste product. It passes out of the blood in the lungs and is exhaled.

Diffusion

Definition

Diffusion is when a substance moves from an area of high concentration to an area of low concentration.

The gases, oxygen and carbon dioxide, are able to pass into and out of the bloodstream by diffusion. This occurs at the alveoli in the lungs.

Science; Human gas exchange systems; KS3 Year 7; Structure and function of the human gas exchange system

1.	Air containing oxygen flows through the respiratory system into the lungs during inhalation. At the alveoli in the lungs, the oxygen diffuses into the red blood cells and carbon dioxide diffuses out of the red blood cells into the air which will be exhaled.
2.	The arrow points to a red blood cell which carries oxygen around the body into cells for respiration. Carbon dioxide is also carried in the blood to be taken back to the lungs for exhalation. Both these gases move in and out of cells via diffusion.
3.	The arrow points to a blood vessel which carries the blood containing red blood cells.