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Epithelial Tissues 
Epithelial tissues
cover the outside of organs and structures in the body and line the lumens 
of organs in a single layer or multiple layers of cells. The shapes of the cells that are present and the 
number of cell layers are used to categorize the different types of epithelia. 
Simple epithelia
is a type 
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(credit: modification of work by NCI)

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of epithelium made up of a single layer of cells; epithelial tissue composed of multiple layers is called 
stratified epithelia
Table 1 summarizes the different types of epithelial tissues. 
 
Cell shape 
Description 
Location 
Squamous 
Flat, irregular round shape 
Simple: lung alveoli, capillaries; 
stratified: skin, mouth, vagina 
Cuboidal 
Cube shaped, central nucleus 
Glands, renal tubules 
Columnar 
Tall, narrow, nucleus toward base; tall, 
narrow, nucleus along cell 
Simple: digestive tract; 
pseudostratified: respiratory tract 
Transitional 
Round, simple but appear stratified 
Urinary bladder 
Table 1. 
Various epithelial tissue types
 
Connective Tissues 
Connective tissues
are made up of a matrix consisting of living cells and a nonliving 
substance, called the ground substance. An organic substance (typically a protein) and an inorganic 
substance combine to form the ground substance (usually a mineral or water). The fibroblast is the 
main cell of connective tissues. The fibers that are present in almost all connective tissues are 
produced by this cell. Fibroblasts can produce any type of connective tissue that is required, are 
mobile, and are capable of going through mitosis. Some of the tissues contain lymphocytes, 
macrophages, and occasionally leukocytes. Specialized cells are present in some tissues but not in 
others. The 
matrix
in connective tissues gives the tissue its density. A connective tissue's matrix is 
proportionally less dense when there are many cells or fibers present. 
Collagen, elastic, or reticular fibers make up the organic portion of protein fibers found in 
connective tissues. Collagen fibers give the tissue strength, preventing tearing or separation from the 
tissues around it. The protein elastin is used to make elastic fibers, which can stretch to one and a half 
times their original length before snapping back to their original dimensions. The tissues are flexible 
thanks to elastic fibers. The third kind of protein fiber found in connective tissues are reticular fibers. 
Collagen is broken down into tiny strands to create a network of fibers in this fiber, which supports 
the tissue and other organs to which it is connected. The various types of connective tissues, the types 
of cells and fibers they are made of, and sample locations of the tissues is summarized in Table 2.