ANATOMY&PHYSIOLOGY FOR NURSES

COMPOUND EPITHELIUM.  Consists of more than one layer of cells. Stratified Epithelium forms the epidermal layers of the skin.  It also lines the mouth, pharynx, oesophagus, the lower part of the urethra, the anal canal and the vagina, and covers the surface of the cornea. In these areas it does not become cornified. The outer layers of cells near the surface comprise the horny layer of the skin; these cells are flatterned and resemble scales.  The deepest layer of cells are columnar in shape.  These form the germinative layer and here the cells multiply by karyokinesis, pushing those above them nearer the surface until the superficial ones are cast off.  The cells between the basal layer and the horny zone are called 'prickly cells' they are connected to each other by fine tendrils which give them a prickly appearance when examined under the microscope. Transitional Epithelium is a compound stratified epithelium consisting of several layers of cells. It lines the urinary bladder, the pelvis of the kidney, the ureters and the upper part of the urethra. The deeper layers of cells in traditional epithelium are of the columnar type of cell with rounded ends which make them pyriform or pear-shaped. As the cells in the deeper layers multiply by dividing, the superficial layers of cells are cast off. The superficial cell layers in transitional epithelium are less scale- like than those of stratified epithelium.

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ANATOMY&PHYSIOLOGY FOR NURSES

REPRODUCTION.

A cell does  not go on growing indefinitely in size but at a certain optimum point divides into two daughter cells. Further, certain cells will undergo division to replace worn - out cells or those destroyed by disease.  This kind of cell division is called mitosis, or karyokinesis. Activity begins in the nucleus, the nuclear membrane disappears and the chromatin changes character and becomes long filaments called chromosomes.The chromosomes are then attracted to the poles and lie near the new centrosomes. The chromatin of which the nucleus is formed now comes to rest and two new nuclei exist. Finally the protoplasm of the cell constricts and divides and the two new cell resulting from mitosis contains fortysix chromosomes,  which means that during mitosis each chromosomal duplication is one of the least understood of the cell's activities.      However, mitosis is not the only kind of cell division. in the sex organs, the ovary and testis, another kind of cell division occurs called metosis.  During the formation of the sex cells, or gametes, the number of chromosomes is halved, so that the spermatozoon contains only twenty- three chromosomes and the egg- cell, or ovum, twenty - three.When fertilization occurs, that is when spermatozoon and ovum fuse to form the cell (zygote) which develops into a new individual, the normal chromosomal complement of forty-six is restored.  By this means a mixing of the hereditary determinants, or genes, from male and female is achieved.

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