Respiratory system III

Histology 2016-2017
Department of Anatomy &Histology: Dr.Rajaa Ali
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Respiratory System III
Lung:
? Lungs are the principal organs of respiration, situated in the thoracic cavity one on either side of the mediastinum.
? Each lung is conical in shape and is covered with visceral pleura.
? It contains the terminal parts of the bronchial tree, namely, intrapulmonary bronchus, bronchiole, respiratory bronchiole and lung parenchyma (alveolar ducts and alveoli) along with blood vessels.
Intrapulmonary bronchus (secondary and tertiary bronchi)
? In the lung each principal bronchus divides into secondary or lobar bronchi which in turn divide into tertiary or segmental bronchi
Secondary and Tertiary Bronchi
They are similar to the primary bronchus except for the following:
? ? The number of goblet cells is further reduced in the epithelium.
? ? The number of glands in the submucosa is also reduced.
? ? The cartilage is present as irregular plates.

Mucosa
– It consists of epithelium and lamina propria.
– The epithelium is pseudostratified ciliated columnar variety with few goblet cells.
– The lamina propria is rich in elastic fibres (longitudinally oriented).
– Mucosa is thrown into folds by the contraction of underlying smooth muscle.
(b) Smooth muscle layer
– This layer consists of spirally running criss-cross bundles of smooth muscle. Thus, in section the muscle layer appears to be discontinuous.
(c) Submucosa
– It contains few seromucous glands.
(d) Cartilage layer and adventitia
In contrast to C-shaped cartilage present in the trachea, the intrapulmonary bronchus contains isolated plates of hyaline cartilage.