The Basis of Life 37 



cells such as those lining the inner surfaces of blood vessels. Cuhoidal 

 epithelium is found in the salivary glands and in the kidney tubules. 

 Tall cells known as columnar epithelium are found lining the intestine. 

 Epithelial tissue may be only a few cells thick. In that case, it is known 

 as simple epithelium; when it occurs in many layers, it is termed 

 stratified epithelium. 



2. Supporting and Connective Tissues. This is a very large 

 group of tissues (Fig. 4) which includes all those that in some way con- 

 nect or support. Many different types of these tissues are specialized 

 for many different functions. All are alike in one respect ; that is, they 

 have relatively scattered cells with a great amount of intercelluar 

 material. 



ETrm 



Fig. 4. Types of epithelial and connective tissues. A, Cuboidal epithelium; 



B, squamous epithelium; C, ciliated columnar epithelium; D, adipose tissue; E, elastic 

 connective tissue; F, areolar connective tissue. 



Areolar connective tissue has a few widely separated cells scattered 

 in a semifluid matrix. This matrix is strengthened by a network of 

 elastic and collagenous fibers. Collagenous fibers are composed of 

 manv fibrils closely cemented together. These fibrils are formed of 

 collagen, a protein material which when boiled in water yields gelatin. 

 This type of tissue is found under the skin, in mucous membranes, and 

 around blood vessels and nerves. A special kind of areolar connective 

 tissue, adipose Hssue, has many of the cells filled with fat. This tissue 

 is found throughout the body, but especially under the skin and around 

 certain organs. 



