TYPES OF BODY CELLS ON THE BASIS OF GROWTH

According to growth pattern, cells can be categorized as:

Renewing type which continuously lost and replaced by new cells, e.g., epidermis, endometrium, skel­etal tissue (partly).

Expanding type which expand continuously until the adult size of the organ is reached, e.g., liver, kidney, glands (endocrine and exocrine), skeletal tissue (partly).

Static type which is a part of the expanding system in which cell division is restricted to early stages of development. Later, only hypertrophy may occur, e.g., neurons, retinal rods and cones, muscle fibers.

23.2.1 Types of Growth

Compensatory Growth: If one organ or a part of an organ is removed, then remaining part grows faster to compensate the function of the other organ or part of the organ. This is known as compensatory growth. For example, if one kidney is removed, the other kidney increases the number and size of nephrons to normalize body function to normal. If a part of the liver is cut, it grows faster to compen­sate for liver functioning.

Differential Growth: When the growth in different organs of the body takes place during different stages of life. For e.g. Nervous system grows up to the age of 5 years, while reproductive organs grow up to puberty.

Negative Growth: It is a natural process and usually occurs during old age when cells are gradually lost and are not replaced. More catabolism than anabo­lism, Decrease in body weight, Irreversible change Growth Retardation: This is the failure of DNA rep­lication and protein synthesis due to exogenous processes. Factors causing growth retardation include hormonal imbalance (e.g., GH, T₃, T₄, Chromosomal abnormality, Radiations, Toxins, Hypoxia, Drugs, Infections.

Sympathetic nervous system also influences the rate of body growth. In case of stress, increased sympathetic activity leads to growth retardation as epinephrine released during stress may alter the secretion of growth hormones.

Growth retardation accompanies metabolic dis­eases in which the body is unable to synthesize or use protein, there is an abnormal ratio of amino acids in the extracellular fluid, and impaired trans­port of amino acids from the GIT to plasma or into body cells. Reduced protein synthesis is due to low intake of protein or increased loss of protein (nephrosis).

Catch up growth The growth of an individual which does not take place when normal condition is not provided. When suitable environment is provided, normal growth resumes. For example, in poultry used in case of poultry for meat purposes, this needs to be with great precaution. If used for lon­ger periods, it causes permanent damage to animal.

23.3