Recognising Structures in the Gas Exchange System
Trachea
Trachea cross-section
- A tracheal cross-section shows the large lumen which air has to travel through
- The innermost cells of the trachea are the ciliated epithelia with projections called cilia
Trachea – light micrograph
- The cells of the ciliated epithelium are shown here – the cells are tightly packed and interspersed with goblet cells, which are shown in white
Trachea – electron micrograph
- The density of the cilia are shown in this electron micrograph
- The cilia are essential for sweeping bacteria and dust-filled mucus away from the lungs and up the trachea into the back of the mouth
- This mucus is then swallowed, with any pathogens hopefully destroyed by the acidic conditions in the stomach
Bronchi
Bronchi cross-section
- Bronchi are distinctive from the trachea because their lumen is narrower; 8.7mm instead of 18mm
- However, like the trachea, they are lined by ciliated epithelium
Bronchioles
Bronchiole – photomicrograph
- Bronchioles are approximately 1mm or less in diameter
- Smooth muscle and cuboidal epithelium are found in their walls
Alveoli
Alveoli
Emphysema alveoli
- Alveoli have a sponge-like appearance under a microscope due to their air spaces.
- They are surrounded by an extensive capillary network and are lined by squamous epithelium
Walls of the trachea & bronchus
Walls of the trachea
- The tracheal lumen is around 15 to 20 mm and is lined by ciliated epithelia
- The tracheal wall is surrounded by strong and flexible cartilage which flexes during breathing
- The smooth muscle of the trachea constricts and allows air to be expelled with more force
Walls of the bronchus
- Like the trachea, the bronchus is lined with ciliated epithelium
- The cartilage hoops provide structural support to the bronchi and the gland ducts secrete mucus in the bronchial tubes
