THE TISSUES
Four main groups of tissues are known in the body. These are:
Epithelial tissues.
Connective tissues.
Muscular tissues.
Nervous tissues.
A- THE EPITHELIAL TISSUES
These tissues arise from any of the three primary germ layers, the ectoderm, endoderm or mesoderm. They are almost always found covering a surface, external or internal, thus mainly performing a protective function. But some of them are specialized in various ways to perform different other functions.
The epithelial tissues are characterized by having very little intercellular substance or matrix between their cells and by resting, in the majority of cases, on a basement membrane formed of the underlying connective tissues.
Classification of Epithelium
Cell arrangement and cell shape classify the epithelium, not by function
-Simple, when it is one cell layer thick
-Stratified, when it is two or more cell layers
The individual cells that compose an epithelium are described as:
Squamous, where the width of the cell is greater than its height
Cuboidal , where the width, depth ,and height are approximately the same
Columnar , where the height of the cell appreciably exceeds the width (the term low columnar is often used where a cells height only slightly exceeds its other dimensions ).
Pseudostratified epithelium has the appearance of being stratified. Some of cells do not reach the free surface; however, all rest on the basement membrane. Thus, it is actually a simple epithelium.
Transitional epithelium has several layers of cells, characterized by large, dome-shaped cells at the free surface, that help maintain the integrity of the epithelium during distention of the various components of the urinary tract.
CLASSIFICATION SOME TYPICAL LOCATIONS
Simple squamous Lining of vascular system (endothelium) Bowman ,s capsule (kidney)
Lining of respiratory spaces in lung
Simple cuboidal Small ducts of exocrine glands
Surface of ovary (germinal epithelium)
Kidney tubules
Simple columnar Lining of small intestine and colon stomach Lining and gastric glands lining of gallbladder
Pseudostratified Lining of trachea and bronchi
Lining of differences efferent ductules of epididymis
Stratified Squamous Epidermis
Lining oral cavity and esophagus
Lining of vagina
Stratified cuboidal Sweat gland , ducts larger ducts of exocrine glands
Anorectal junction
Stratified columnar Largest ducts of exocrine glands
Anorectal Junction
Transitional Renal calyces
Ureters
Bladder
Urethra
Glands
Glands are composed of epithelial cells specialized to synthesize and secrete a specific product. Typically, glands are classified into two major groups reflecting how their products are distributed:
Exocrine glands, secrete their products onto a surface through ducts or .The ducts, also composed of epithelial cells.
Endocrine glands, lack a duct system. They secrete their products into the connective tissue from which they enter the blood stream in order to reach their target cells. The products of endocrine glands are hormones.
Glands are composed of epithelial cells specialized to synthesize and secrete a specific product. Typically, glands are classified into two major groups reflecting how their products are distributed:Exocrine glands, secrete their products onto a surface through ducts or .The ducts, also composed of epithelial cells.Endocrine glands, lack a duct system. They secrete their products into the connective tissue from which they enter the blood stream in order to reach their target cells. The products of endocrine glands are hormones.