AQA GCSE Lungs (Biology)

Lungs

Learn the labels on the diagram of the gas exchange system below.

Structure	Function
Trachea	The trachea provides the airway that connects the mouth and nose to the lungs. Contains C shaped rings of cartilage which prevents the trachea collapsing, when breathing in. Trachea contains goblet cells that produce a sticky mucus to trap dust and pathogens from entering lungs. Cilliated cells line the trachea, they move mucus along with dust and pathogens up to the top of airways, where swallowing will take the mucus down the oesophagus into the stomach.
Bronchus or Bronchi	Bronchus is single, whilst bronchi is plural. The trachea splits into two bronchi, before entering the lungs. Both bronchi are lined with goblet cells and ciliated cells.
Bronchioles	"ioles" means subdivision in biology. So bronchioles are subdivisions of bronchi. These bronchioles will lead to the air sacs (alveoli).
Diaphragm	Sheet of muscle that separates the respiratory system from the digestive system. When breathing in the diaphragm contracts and flattens. When breathing out, the diaphragm relaxes and returns to its dome shape.
Ribs	Bone structures that are used to protect the gas exchange system.
Intercostal muscles	When the intercostal muscles contract it raises the rib cage during breathing in. During breathing out the intercostal muscles relax. (At a higher level than GCSE, you will learn about the difference between internal and external intercostal muscles, this is not needed for GCSE).
Alveoli	Alveoli are the air sacs where gas exchange occurs. These are surrounded by blood capillaries to aid diffusion of gases.

Breathing in and breathing out.

Structure	Breathing in	Breathing out
Intercostal muscles	Contract to raise the rib cage upwards and outwards	Relax to allow the rib cage to move downwards and inwards
Diaphragm	Contracts and flattens, increasing the volume of thorax (chest)	Relaxes and returns to its dome shape, decreasing the volume of the thorax (chest)
Chest (Thorax)	As volume of thorax increases, air pressure in lungs decreases, so air moves into the lungs.	As the volume of thorax decreases, air pressure in the lungs will increase, forcing air out of the lungs.

Understanding why the air moves in and out.

Students often have problems understanding the changes in pressure and why this causes air to move into or out of the lungs, so lets do a side step and explain it!

Gas pressure is caused by gas particles colliding with the walls of a container and exerting a force on the walls. This force is at 90 degrees as shown below!

If the volume of a container is made smaller, it will contain the same number of gas particles, but they will collide with walls of the container more often, so the gas pressure increases.

Lets relate this to the lungs, as the volume of the thorax decreases, gas pressure inside the lungs increases, so it will force the air out of the lungs!

Gas Exchange in Alveoli.

The alveoli allow gas exchange to occur, they are adapted for this process.

Once the air has been inhaled, oxygen will diffuse from the alveolus into the red blood cells.

Carbon dioxide from the red blood cells will diffuse into the alveolus.

During exhalation, carbon dioxide is removed from the body.