Chap. Ill] EPITHELIAL TISSUE 31 



Function. — The most important functions of epithelial tissue 

 are as follows : 



1. Protection. — Some varieties are specially modified so as to 

 form protective membranes. Example — • skin. Other varieties 

 form the top layer of the mucous membranes, and mucous mem- 

 branes are found lining passages that communicate with the ex- 

 terior of the body. Serous membranes are also lined by epithelial 

 cells. These serous membranes line passages that do not com- 

 municate w4th the exterior of the body. 



2. Motion. — This is seen in the cilia, which tend to keep the 

 passages to w^hich they are attached clean, and free from foreign 

 material. 



3. Absorption. — This is particularly well seen in the digestive 

 tract. To some extent the skin also is capable of absorption. 



4. Secretion. — Every secreting organ must contain epithelial 

 cells. Mucous and serous membranes are examples of secreting 

 organs. 



5. Special Sensation. — The organs of the special senses contain 

 epithelial cells. Examples — eye, ear, nose, etc. 



