TH1.H2.3 +D1 Bronchial tree
Bronchial Tree:
- The bronchial tree is the term often used to describe the series of divisions, within the lung, of the primary bronchus which enters the hilus of the lung
- These divisions are:
- Secondary bronchi
- Tertiary bronchi
- Terminal bonchioles
- Respiratory bronchioles
- Hyalin cartilage plates:
- Irregular plates in secondary bronchus, reduction in size of plates in tertiary bronchus, absent in terminal bronchioles
- Smooth muscle:
- Lies internal to cartilage plates present in tertiary bronchi, and in terminal bronchioles where counters expansion of lung tissue during inspiration in order to control flow of air to area of lung
- Epithelium:
- Pseudostratified ciliated columnar epithelium with goblet cells in secondary and tertiary bronchi becomes simple columnar ciliated epithelium with goblet cells in terminal bronchioles, reducing to simple cuboidal without goblet cells or cilia in respiratory bronchioles
- Important to note that goblet cells lost from epithelium before cilia
- Submucosal glands:
- Reduced in number and size through bronchial tree
- Absent in terminal bronchioles and beyond
- Lymphoid tissue
- Lymphoid tissue present in walls as either lymphatic nodules or as scattered lymphoid cells to protect against pathogens
Progressive changes occur in the structure of the walls of the bronchial tree
Question:
Micrograph of Bronchi:
- As can be seen from the surrounding alveoli, this is occurring within the substance of the lung
- There is still some hyalin cartilage (H) supporting the walls of the bronchi at this stage but the plates are small
- The epithelium is not as tall as in the trachea and primary bronchi and can now be described as tall columnar epithelium
- It is still ciliated and has mucus secreting goblet cells between the ciliated cells
- Can you identify the layer of smooth muscle in the walls of the bronchi?
- Does it lie internal, or external, to the plates of hyalin cartilage?
- The numerous small round densely packed nuclei are lymphocytes: it is normal to see accumulations of lymphoid tissue in the respiratory tract
- Lymphatic nodules are common, particularly where the bronchi bifurcate
This micrograph shows a division of the bronchial tree
