ANATOMY&PHYSIOLOGY FOR NURSES

Columnar Epithelium    forms a single layer of cells which line the ducts of most glands, the gall bladder, nerly the whole of the digestive tract, in which goblet cells are interspersed,and parts of the genito- urinary tract. The illustration columnar cells from the interstine; these have a slightly striated border. In some situations, as when lining the alveoli of secreting glands, the cells of columnar epithelium are short and have a cubical appearance they are then described as cubical cells. Ciliated Epithelium, is found lining the air-passages and their ramifications such as the frontal and maxillary sinuses. It also lines the uterine tubes or oviducts and part of the uterus and the ventricles of the brain. Ciliated cells are like columnar cells in shape,but they have in addition fine hair like processes attached to their free edge.  These processes are called cilia.  The ciliary processes keep up a continual movement directed towards the external opening.  This movement has been likened to the movement seen in a field of corn, blown in one direction by the wind. In the respiratory passages the constant movement prevents dust, mucus, etc., entering the lungs, and in the uterine tubes the movement conveys the ovum into the uterus. Goblet Cells are mucus - secreting cells which lie in the walls of glands and ducts lined by columnar cells, either plain or ciliated. Goblet cells secrete mucus or mucin and express it on to the surface; they act as mucus-secreting glands and are most numerous where a considerable amount of mucus covers the surface as in the stomach, colon, and trachea.

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ANATOMY&PHYSIOLOGY FOR NURSES

THE ELEMENTARY TISSUES OF THE BODY Four groups of tissue in the body are known as the elementary tissues. These are epithelial tissue, muscular tissue, nervous tissue,and connective tissue. Types of epithelial Tissue.     An epithelium consists of cells which cover surfaces of the body,  e.g skin; or line hollow organs, tubes or cavities, e.g. blood vessels, and the air cells. There are two main classes of epithelial tissue, each containing several varieties. all epithelial cells lie on and held together by a homogeneous substances called a basement membrane. Simple Epithelium. This class consists of a single layer of cells, and is subdivided into three varieties. Pavement or Squamous Epithelium. Pavement epithelial cells are fine thin plates placed edge to edge like the particles in a mosaic pattern or the stones of a pavement. These cells form the alveoli of the lungs. They are found whenever a very smooth surface is essential as in the lining of the heart, lining of blood vessels and lymphatics, the serous membranes. when lining these structures the epithelial covering or lining is called endothelium.      ............

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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. Actively begins in the nucleus, the nuclear membrane disappears and the chromatin changes character and becomes long filaments called chromosomes. The centrosome divides and the two new centrosomes move away from each other to each end of the nucleus called the poles. 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 cells are complete. Each new daughter cell resulting from mitosis contains forty six chromosomes, which means that during mitosis each somal 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 meiosis.  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 individuals, 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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ANATOMY&PHYSIOLOGY FOR NURSES

NUCLEUS.   The nucleus is separated from the cytoplasm by the nuclear membrane which is also selectively porous , allowing substances to escape from the nucleus into the cytoplasm or substances to pass into it. The nucleus contains many protein-rich threads lying in a nuclear sap. In the "resting cell" the threads are collectively spoken of as chromatin, These threads or chromosomes are vital to the everyday activities of the cell and are responsible for determining the hereditary characteristics of the human body.  On the chromosomes in linear arrangement sit the genetic or hereditary determinants, the genes. The number of chromosomes in a body cell is constant for a particular forty-six chromosomes. Irritability and Conductivity. Mention has been made of some of these cells' characteristic functional properties, their metabolic activities and powers of growth. By these two properties the cell is active.  When a cell is stimulated either by chemical, physical, mechanical, or nervous means, the cell responds: it may contract as does a muscle cell; it may produce a secreation, as do the cells of the stomach, pancreas, and other organs and glands; or it may conduct an impulse, as in the case of the nerve cell.  This last is the best example of cell conductivity as a nerve impulse generated by the stimulation of a nerve cell may be conducted for a considerable distance, a yard or more, according to the length of the nerve fibre.  But in all cases, a stimulus which excites a cell to action is conducted along the entire length from end to end of the cell. .....

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