Microstructure of the lungs and pleura

Question 1

Describe the development of the lungs

Answer 1

Develop from epithelial mesenchymal outgrowths of the anterior foregut

Tubes form branch as they grow. These tubes becomes the bronchioles

This occurs late in the prenatal period and suffacent is produced in the 3rd trimester

Question 2

1. Describe the layers of the trache
2. Describe the outer supportive structure of the trachea
3. What cell types are in the mucosa of the trachea
4. What layers does the submucosa consist of?

Answer 2

1.

• It consists of the following layers
  
  • MUCOSA
    
    1. Respiratory epithilium- cilliated pseudostatified columnar epithilium
    2. Lamina propria- thin later of connective tissue
    3. Elastic lamina- longitudinally arranged elastic fibres with some blood vessles
  • SUBMUCOSA
  • OUTER ADVENTITIA

2. Supported by cartilagenous rings (2/3 of the diameter) anteriorly

Posterior wall of the trachea consists of smooth muscle and collagen

3.

The following cell types are present in the mucosa:

• Ciliated columnar cells form the mainstay of secretion and clearance. Cilial beating rate varies with mechanical stimulation and inflammatory mediator presence.
• Goblet cells contain secretory vacuoles filled with mucinogen. The number of goblet cells increases when the epithelium is irritated.
• Basal cells are the mitotic stem cells for other epithelial cell types.
• Brush cells are slender non-ciliated cells with stiff microvilli. They are in contact with afferent nerve fibres and so may have a sensory function.
• Lymphocytes and mast cells migrate into the epithelium

4.

• smooth muscle
• glands (serous and mucous cells)
• blood vessels
• lymphoid tissue
• nerves

Question 3

1. There are two main differences in the structure of the bronchi compared to the trachea. Can you name them?
2. Describe the structural features of the bronchi

Answer 3

1. Smooth muscle is present in a spiral arrangement (constriction produces bronchospasm)

Cartilagenous rings are replaced by plates which reduce in size as the bronchial diameter reduces

2. The structural features:

Epithelium: pseudostratified columnar with or without cilia

simple columnar to cuboidal, goblet cells only present in larger bronchioles

Smooth muscle

No glands or cartilage

Question 4

1. Describe the structure of the respiratory bronchioles
2. What cell types make up the alveoli?

Answer 4

1.

• made up from isolated alveoli in the walls of the respiratory bronchioles
• overall alveolar area is >140m2 and contain >3 million alveoli

2.

The walls of alveoli consist of a single layer of squamous epithelial cells called type 1 cells surrounded by basal lamina

Scattered among the type 1 cells are smaller cuboidal cells called type 2 cells

contain secretory granules full of surfactant which is important in reducing the surface tension of alveoli and prevent collapse

Question 5

1. Does the pleura originate?
2. Where does the parietal pleura cover and extend to?
3. Where does the visceral pleura cover and what is it made off?
4. What is its blood and nerve supply?

Answer 5

1. From an invaginated sac
2. Parietal pleura covers the internal surface of the chest wall, diaphragm extending to the lung root where it becomes continuous with the visceral pleura
3. Visceral pleura covers the entire lung. Single layer of mesothelial cells separated by basal lamina

4.

Blood supply is from the bronchial arteries which drain into bronchial veins.

Nerve supply is via the anterior and posterior pulmonary plexi