the epithial tissues

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.Classification of Epithelium
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:
? Squamous, 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
? Cuboidal , where the width, depth ,and height are
approximately the same
Small ducts of exocrine glands
Surface of ovary (germinal epithelium)
Kidney tubules
? Columnar , where the height of the cell appreciably
exceeds the width.
Lining of small intestine and colon stomach
Lining and gastric glands
lining of gallbladder
? 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