EPITHELIAL TISSUE 



75 



Problem. Study of certain epithelial cells. 



Take a toothpick and gently rub the inside of the cheek and gums. Mount 

 the material from the toothpick in water and add just enough fountain pen ink 

 to give a slightly-bluish tint to the water. Study with the low and high mag- 

 nification. 



I. Describe the shape, color, relative size, and structure of the cells. 



II. Draw a group of epithelial cells at least five times larger than they 

 appear. 



III. Write a brief description of epithelial cells. 



Epithelial tissue. Epithelial 

 cells cover and line the organs 

 of the body. They make very 

 little intercellular material. Their 

 function is protection and secre- 

 tion. They may protect certain 

 organs against invasion of foreign 

 material, or, by means of their 

 moist secretion, guard other or- 

 gans against friction. The epi- 

 thelial cells that line the nose, 

 throat, digestive system, and air 

 tubes or respiratory system make 

 up the tissue called mucoiis mem- 

 brane. (A membrane is a very 

 thin structure consisting of a 

 single layer or a few layers of 

 cells.) The cells lining the wind- 

 pipe have tiny projections of 

 protoplasm called cilia. Germs 

 are pushed or moved back into 

 the throat by means of this brush- 

 like arrangement. They work very much like the cilia of the 

 Paramecium. Because of the mucous epithelium in the alimentary 

 canal, food slips easily through the tube with no friction. In addi- 



Epithelial cells vary in shape. They may 

 appear as a single layer or groups of layers 

 of flattened, cubelike, or columnar units. 



The cheeks are lined with squamous epi- 

 thelial cells ; the respiratory tract with cili- 

 ated, epithelial cells. 



