Recognising Structures (CIE A Level Biology)

Trachea

• 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

Cross section of a trachea diagram

Trachea cross-section as shown under a light microscope

• The cells of the ciliated epithelium are shown here – the cells are tightly packed and interspersed with goblet cells, which are shown in light grey

Tissues of the trachea diagram

A light micrograph image showing tissue of the trachea

• 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

Trachea electron micrograph diagram

An electron micrograph of the tissues that can be found inside the trachea

Bronchi

• 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

Cross section of a bronchi diagram

A light micrograph image showing tissue of the bronchi in cross section

Bronchioles

• Bronchioles are approximately 1mm or less in diameter
• Smooth muscle and cuboidal epithelium are found in their walls

Cross section of a bronchiole diagram

A photomicrograph showing bronchiole tissues in the gas exchange system

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

Light micrograph of an alveolus diagram

The cells surrounding the alveolus air sac as viewed by a light microscope

 

Alveoli damaged by emphysema diagram

Several alveoli are damaged due to the medical condition emphysema

Walls of the trachea & bronchus

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

Parts of the trachea wall diagram

Labelled diagram of a cross section of the trachea

 

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

Parts of a bronchus wall diagram

Parts of the cross section of a bronchus. This would be the same in both bronchi