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
1-These tissues arise from any of the three primary germ layers, the ectoderm, endoderm or mesoderm.
2-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.
3- The epithelial tissues are characterized by having very little intercellular substance or matrix between their cells and by
4- Resting, in the majority of cases, on a basement membrane formed of the underlying connective tissues.
Cell arrangement and cell shape classify the epithelium, not by function
1- Simple, when it is one cell layer thick
2 -Stratified, when it is two or more cell layers



The individual cells that compose an epithelium are described as:
Simple Squamous epithelium :-
where the width of the cell is greater than its height


Lining of vascular system (endothelium) Bowman ,s capsule (kidney)
Lining of respiratory spaces in lung
Simple Cuboidal epithelium :-
where the depth, width, and height are approximately the same



Small ducts of exocrine glands
Surface of ovary (germinal epithelium)
Kidney tubules
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.









Lining of trachea and bronchi
Lining of differences efferent ductules of epididymis
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.







Renal calyces Ureters Bladder Urethra
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.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.

Exocrine glands are classified as either unicellular or multicellular:
Unicellular glands: are the simplest in structure, the secretory component consists of single cells distributed among other cells that are not secretory. A typical example is the goblet cell, mucus-secreting cell positioned among other columnar cells.

Multicellular glands: are composed of more than one cell and exhibit varying degrees of complexity. Their structural organization allows for sub classification according to the arrangement of the secretory cells and the presence or absence of branching of the duct elements
Tubular secretory portions may be single or branched. Thus, exocrine glands may be described as:
Simple tubular, as in the intestinal glands of the colon
Simple coiled tubular, as in the eccrine sweat glands
Simple branched tubular, as in the submucosal glands of Brunner in the duodenum
Simple branched acinar, as in the cardiac glands of the stomach
Compound acinar, as in the pancreas
Compound tubuloacinar, as in the submandibular gland
Mucous and serous glands, are so named because of the type of secretion produced .The secretory cells of exocrine glands associated with the various body tubes, i.e., the alimentary canal, respiratory passages, and urogenital system, are often described as being mucous, serous, or both.