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The wall of trachea is formed of following layers from within outwards

1. MUCOSA: It is comprised of the following layers.

a. Epithelium of trachea is pseudostratlfled ciliated tall columnar with goblet cells.

The ciliary activity produces constant movements of glandular secretions towards the pharynx. The epithelium is comprised of following cells.

I. Columnar ciliated cells (each cell bears 300 cilia)

II. Goblet cells (secrete mucous material)

III. Brush cells: These are sensory receptor cells, which are columnar and non- ciliated. Microvilli are present.

Iv. Basal or short cells (act as stem cells): These occur in the depth of epithelium

between the bases of the other types of cells and are undifferentiated cells that give rise to goblet cells or ciliated cells.

v. Neuroendocrine (Kulchltsky) cells

vl. Migrating lymphocytes and

vll. Migrating mast cells.

vlll. Dendritic cells: A network of dendritic cells lies along the base of tracheal epithelium which function as antigen-presenting cells, i.e.. these bind the antigens and then present it to the T-lymphocytes. All these cells are evident on electron microscope; while on light microscope, one can see'only columnar ciliated cells, goblet cells and basal cells.

 The tracheal epithelium is supported by a thick basement membrane.

Beneath basement membrane lamina propria consists of loose highly vascular connective tissue, which becomes condensed at its deeper aspects to form a band of fibroelastic tissue (clear elastic membrane).

II. SUBMUCOSA: It contains loose areolar C.T. numerous mixed seromucous and mucous tracheal glands (which decrease in number in lower part of trachea), nerves, vessels and lymphoid follicles.

III. CARTILAGE: The submucosa merges with the perichondrium of the underlying hyaline cartilage. These cartilages (16-20) are found in the form of C-shaped rings. Between the two ends of C-shaped cartilages the submucosa directlv merges with the external adventitial layer. Bands of smooth muscles (trachealls) join the free ends of the rings posteriorly. The contraction of muscle and resultant narrowing of the tracheal lumen are useful in cough reflex.

IV. ADVENTITIA/FIBROSA: it is formed of areolar C.T. containing small blood vessel and autonomic nerves to trachea.


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