Question

Pseudostratified columnar epithelium ( depicts a section through the wall of the trachea – the same structure seen on your slide) a. What criteria must be satisfied for an epithelium to be considered stratified?

1. Why is the pseudostratified columnar epithelium lining the trachea not considered a true stratified epithelium?

2. Identify goblet cells in the epithelium lining the trachea. What is the function of the product secreted by these unicellular glands within the epithelium? [Note; The function of the product secreted by these goblet cells is not the same as the function of the product secreted by the cells in the intestinal lining.]

3. What apical surface specialization is characteristic of the epithelial cells lining the trachea? What is the significance of this specialization in this particular location?

4. Superficially the apical surface of the pseudostratified epithelium lining the trachea resembles the apical surface of the brush border (composed of microvilli) associated with the simple columnar epithelium lining the small intestine. Be sure you have a good understanding of the nature of the apical surface in each case; appreciate the differences in structure of the surface specializations, as well as the differences in function of these specializations (particularly in these two specific locations).

5. Is it easy to convince yourself that the epithelium lining the trachea is a pseudostratified columnar epithelium? Explain why or why not.

Answer 1

Epithelium is found on almost all body parts and it’s main function are absorption and secretion. In the histological cross section, pseudostratified columnar epithelia tissues look like a multilayer tissue however it is not. This type of epithelium found in upper respiratory track and in a trachea. Mainly two types of epithelium are classified: simple epithelium and stratified.

A. criteria for stratified epithelium:

It is made up for more than two layers of cells. These types of cells have capacity to regenerate as compared to simple epithelia cells. Generally, stratified epithelium present in esophagus and skin.

Their main functions are protection, mainly against water loss, chemical and mechanical damage.

Simple epithelial are single layered cells and have different sub types. Major function of simple epithelium are: secretion, absorption and lubrication.

1. pseudo-stratified epithelia are generally appeared as a stratified epithelial but it is not a true stratified epithelial. Trachea and bronchi of respiratory system consist of pseudo- stratified epithelia. All the cells present on lumen have cilia on the outer surface. Mucus secreting cells are interspersed in ciliate cells which are unicellular goblet cells hence it is consider are a pseudo- stratified and not as a true stratified epithelia.

2. Goblet cells are columnar and granular cells present on most epithelium. It has “goblet-like” shape. Generally goblet cell are round at early life and it secrets mucus. As shown in the figure A, goblet cells have large nucleus, Golgi body and endoplasmic reticulum present on base.

Function of goblet cells.

Goblet cells secrets Mucus. It is a gel like substance which is composed of mucins, glycoprotein and carbohydrate. In the respiratory track epithelium (trachea) it reacts directly when any foreign particles are inhaled (which are harmful for body). In epithelium cells it tracks foreign particles and transport to create allergen reaction.

3. The lining of trachea is made up of pseudo- stratified epithelial cells. As we discuss previously, goblet cells are interspersed between this cells which produce mucus. Cilia are present on their free apical surface which is the main characteristic of epithelium in trachea. Significantly it helps goblet cells to secret mucus which helps in trapping foreign particles.

4. Small intestine is composed of simple epithelial lining where as the tracheal lining is stratified. Hence the epithelia layer of small intestine is single layer and epithelial layer of trachea is multilayer. The outer surface of small intestine is covered with micro villi where as outer surface of trachea is covered with cilia.

The epithelium of small intestine act as a selective filter for nutrients, electrolyte and water. Which is main function of epithelium in small intestinal lining. It is also work as an entry barrier for foreign particles and antigens. Whereas epithelium in trachea work as trapping foreign particles and generates allergic effect in respiratory system.

5. we can called the tracheal epithelium as pseudo stratified epithelium but exactly it is not a true stratified epithelium. Actually it is a single layer of epithelia cells. In which goblet cells are dispersed. Hence we can say it is not a true pseudo stratified epithelium.