Gas Exchange

• Structure of the lungs, trachea, bronchi, bronchioles, alveoli and capillary network.
• Distribution of cartilage, ciliated epithelium, goblet cells, squamous epithelium, smooth muscle and capillaries.
• Recognising these tissues and airways in slides and micrographs; plan diagrams of trachea and bronchus walls.
• Functions of ciliated cells, goblet cells and mucous glands.
• Functions of cartilage, smooth muscle, elastic fibres and squamous epithelium.
• Gas exchange between alveolar air and blood.

From trachea to alveoli

• Lungs: a pair of organs in the thorax, enclosed by the ribs and diaphragm, containing the branching airways and alveoli.
• Trachea: the windpipe, supported by C-shaped rings of cartilage; branches into two bronchi.
• Bronchi: one to each lung, supported by irregular plates of cartilage; branch repeatedly.
• Bronchioles: small airways with no cartilage; walls of smooth muscle; the smallest end in alveoli.
• Alveoli: tiny air sacs with walls of thin squamous epithelium and elastic fibres; the site of gas exchange.
• Capillary network: a dense network of capillaries wraps around every alveolus.

Which tissue is found where

Recognising tissues and airways in sections

• Cartilage: pale, glassy-looking matrix with scattered cells (chondrocytes) in small spaces.
• Ciliated epithelium: column-shaped cells with a fringe of cilia on the free surface, lining the airway.
• Goblet cells: cup-shaped cells among the ciliated cells, full of pale-staining mucus.
• Squamous epithelium: very thin, flattened cells forming the alveolar walls.
• Smooth muscle: bands of spindle-shaped cells, often in a ring around a bronchiole.
• Trachea: large, with a thick C-shaped band of cartilage. Bronchus: smaller, with separate pieces of cartilage. Bronchiole: no cartilage, ring of smooth muscle, folded lining. Alveoli: lace-like spaces with very thin walls.

Plan diagram of the trachea or bronchus wall (TS)

Draw the layers as bands, from the lumen outwards: ciliated epithelium with goblet cells → loose tissue containing mucous glands, blood vessels and elastic fibres → cartilage (a continuous C-shaped band in the trachea; separate plates in a bronchus) with smooth muscle → outer connective tissue. No individual cells; correct proportions.

Keeping the system healthy and working