The Breathing System (Leaving Cert Biology): Revision Notes

The Breathing System

Nose

• Air enters the body through the nasal cavity when we breathe in.
• The nasal cavity is moist, which warms and moistens the air. Warm, moist air can diffuse more easily from the lungs into the blood.
• Tiny hairs (cilia) in the nasal cavity philtre the air as it passes through.
• The sinuses are close to the nasal cavity. When we have a cold or flu, the sinuses can swell and cause a 'blocked nose'.
• Air taken in through the mouth is not warmed, moistened, or filtered. During exercise, we often breathe through the mouth to take in a larger volume of air.

Pharynx (Throat)

• The pharynx connects the nose and mouth to the larynx.
• The epiglottis is located in the pharynx, at the top of the trachea.
• The epiglottis closes over the trachea when we swallow to prevent food or liquid from entering the airway.

Larynx

• The larynx, or voice box, contains the vocal cords.
• The larynx produces sound.

Trachea

• The trachea (windpipe) carries air into the lungs.
• It branches into bronchi and bronchioles, which are made of muscle and elastic fibres, supported by rings of cartilage.
• Cartilage prevents the airways from collapsing as air flows through.
• The walls of the lower bronchioles are made of muscle and elastic fibres only.
• All of the air pipes are lined with mucous secreting cells and tiny hairs called cilia.
• The airways are lined with mucous-secreting cells and tiny hairs called cilia.
  • Mucous traps dust, bacteria, and viruses.
  • Cilia beat in an upward current, moving mucous to the oesophagus, where it is swallowed into the stomach. Clearing the throat helps force mucous upwards.

Lungs

• Gaseous exchange occurs in the lungs, primarily in the alveoli.
• The lungs are enclosed by two pleural membranes which are filled with a fluid to reduce friction during breathing.
• The lungs are protected by the rib cage.