Free Mammalian Gaseous Exchange System revision notes for OCR A Level Biology – covering specification points 3.1.1(a), 3.1.1(b), 3.1.1(c) and 3.1.1(f).
Gaseous Exchange
For the effective exchange of oxygen and carbon dioxide, mammals have a highly specialised gaseous exchange system consisting of a series of airways that filter, warm, and moisten air before it reaches the alveoli.
The pathway that air follows during inhalation is:
The table below provides an overview of some functions and features of these structures:
Part
Structure
Function(s)
Trachea
– Single-wide tube supported by C-shaped cartilage rings.
– Lined with ciliated epithelium and goblet cells.
– Contains smooth muscle and elastic fibres.
– Cartilage prevents the collapse of the airway.
– Cilia and mucus trap and remove debris.
– Smooth muscle regulates airway diameter.
– Elastic fibres recoil after stretching.
Bronchi
– Two tubes branching from the trachea into each lung.
– Supported by cartilage plates.
– Lined with ciliated epithelium and goblet cells.
– Contains smooth muscle and elastic fibres.
– Cartilage prevents airway collapse.
– Cilia and mucus trap and remove debris and microorganisms.
– Smooth muscle controls airway diameter.
– Elastic fibres provide recoil after stretching.
Bronchioles
– Narrower tubes containing smooth muscle and elastic fibres.
– Ciliated epithelium and goblet cells are present in larger bronchioles.
– Elastic fibres help keep airways open and allow recoil after stretching.
– Cilia and mucus trap and remove debris and microorganisms.
Alveoli
– Large surface area with an extensive capillary network.
– Short diffusion distance (~0.5 μm).
– Microscopic air sacs with squamous epithelium and many elastic fibres.
– Main site of gas exchange.
– Elastic fibres allow recoil to expel air during exhalation.
