Structure of the Gas Exchange System

The gas exchange system primarily consists of the nose, mouth, trachea, bronchi, bronchioles and alveoli.
The trachea, or windpipe, is a tube that connects the mouth and nose to the lungs. It splits into the bronchi.
Each bronchus then further subdivides into smaller tubes called bronchioles.
At the end of each bronchiole are small air sacs known as alveoli. These are the primary sites for gas exchange in the body.
The lungs contain millions of alveoli, providing a vast surface area for gas exchange.

Function of the Gas Exchange System

The primary function of the gas exchange system is to exchange oxygen and carbon dioxide between the body and the environment.
Oxygen from the air we breathe is transferred into the blood in the alveoli, while carbon dioxide, a waste product of respiration, is transferred from the blood to the alveoli to be exhaled.
This process relies on diffusion, which is the movement of molecules from an area of high concentration to an area of low concentration.
Ventilation, the process of inhaling and exhaling, maintains a high concentration of oxygen and low concentration of carbon dioxide in the alveoli, ensuring efficient gas exchange.

The wall of an alveolus is only one cell thick, allowing for the rapid diffusion of gases.
The internal surface of alveoli is covered with a thin layer of water, creating a moist environment which assists in gas diffusion.
Alveoli are surrounded by a dense network of capillaries, the small blood vessels through which oxygen and carbon dioxide are transported.
Oxygen diffuses from the alveoli into the capillaries, where it binds to haemoglobin in red blood cells.
Carbon dioxide, produced during cell respiration, diffuses from the blood into the alveoli to be exhaled.

The process of inhaling and exhaling involves multiple structures including the diaphragm, intercostal muscles, and rib cage.
During inhalation, the diaphragm contracts and flattens, pulling down and increasing the volume of the thoracic cavity.
The intercostal muscles contract to move the rib cage upwards and outwards, further increasing the volume of the thoracic cavity.
A decrease in pressure within the thoracic cavity results in the rushing in of air into the lungs.
During exhalation, the diaphragm and intercostal muscles relax, decreasing the volume of the thoracic cavity, thus increasing the pressure and forcing air out of the lungs.