CELL, The Tissue Cell

THE BEGUSARAI POST 

 CELL

A cell is a minute (jelly-like) mass of protoplasm containing a nucleus held together by a cell membrane. In considering the structure of a cell, its component parts may usefully be related to its function.

Cells possess the qualities of all living matter, including those of self-preservation and reproduction.

Ingestion and assimilation.

Cells select from the intercellular Or interstitial fluid which surrounds them chemical substances such as amino-acids, which the cell builds up into the complicated substances, e.g., proteins, which make up protoplasm. Thus, a cell is a very active unit in which the nourishing food materials eaten by man are absorbed and assimilated.

Growth and repair

These materials brought to the cell may be used by the cell to synthesise new protoplasm, in which case the cell increases in size, that is, it grows. They may also be used to replace worn-out parts of the cell. These constructive activities, growth and cell repair, are spoken of as the anabolic functions of the cell, or anabolism.

Metabolism 

 On the other hand, the cell needs a supply of energy for its activities and it will use some absorbed food materials as a fuel. The food is broken down (catabolism) and the energy stored in it is released and used by the cell to provide heat, glandular secretion, movement, and nervous activity. Anabolism and catabolism make up the total activities of the cell, or metabolism

THE TISSUE CELL

Respiration

 Oxygen brought from the lungs by the blood and the removal of the gaseous waste-product, carbon dioxide, are essential for the functions and survival of the cell.

Excretion 

The waste materials resulting from the catabolic processes are eliminated from the cell into the interstitial fluid, and then  carried away by the blood. The blood transports the carbonic acid waste to the lungs, where it is removed from the body as carbon dioxide. The other waste substances are eliminated, via the kidneys, in the urine.

 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 (fibre); it may produce a secretion, 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.

Cell Structure

 In considering the structure of the cell it is essential to relate its parts to its function,

The protoplasm of the cell is composed of a centrally placed body, the nucleus, and the cytoplasm or remainder of the protoplasm, which surrounds the nucleus.

INTRODUCTION TO THE HUMAN BODY

Image of cell and its parts


Cytoplasm. This contains the following essential requirements:

1. Mitochondria, small rod-like structures which are closely connected with the catabolic, or respiratory, processes of the cell body

2. Golgi apparatus. A canal-like structure lying next to the nucleus and involved in the secretory activities of the cell.

3. Ground cytoplasm. A highly complex colloidal material in which the other structures are embedded. It is largely concerned with the anabolic, or synthetic, activities of the cell.

4. Centrosome. A minute, dense part of the cytoplasm, lying close to the nucleus. It plays an important part during cell division

5. Cell membrane. The cell boundary is no static envelope. Many important functions are connected with it, but in particular it acts as a selective sieve through which certain substances are allowed to pass into the cell, or which prevents other substances from gaining access to it. Thus, it is most important in maintaining the correct chemical composition of protoplasm

Nucleus. The nucleus consists of a more compact mass of protoplasm, 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 controls the cell and all its activities, Without a nucleus the cell would die.

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 of species of organism. In man, there are twenty-three pairs of forty-six chromosomes


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