QS Study

Physiology of Growth

Growth is the characteristic of living organisms which includes an increase in size and number of cells leading to human beings to increase height and weight. Infancy is a period of rapidly changing growth rate, from 20 cm/year during the first few months to 10–12 cm/year by 1 year of age.

Growth periods:

In human, there are two periods of rapid growth.

  1. Infancy as a continual fetal growth.
  2. In late puberty, just before the growth stops due to a cessation of Growth Hormone, androgen, and estrogen.

The growth of different types of cell

Differentiation of homogenous cells into cells with specialized function begins early in embryonic life and continues in parts of the body up to old age.

Some types of cells, eg., somatic, muscle and nerve cells cease to divide after 5-6 months of fetal life though they increase in size (length and weight) after birth.

Nerve cells ramify and myelin sheaths grow in postnatal life.

Fig: Rate of growth in boys and girls from birth to age 20.

Growth curves of different types of organ

(A) Neural type: There is a rapid initial increase in size so that the brain, spinal cord and the organs of special sense, together with the skull, reach 90% of adult size by about 6 years of age.

(B) Lymphoid type: The lymphoid tissue, including the thymus, tonsil, and lymph nodes, throughout the body, grow rapidly in early childhood and reach their minimum size at puberty after this lymphoid tissue degenerates.

(C) Reproductive type: The gonads and accessory organs of reproduction remain undeveloped till puberty then very rapid growth begins and continues throughout adolescence.

(D) Certain organs: Show different types of growth. The adrenal glands and uterus are relatively large at birth; they then lose weight rapidly and regain their birth weights just before puberty.

Catch-up growth

Following illness or starvation in children, there is a period of ‘catch-up-growth’, during which the growth rate is greater than normal. The accelerated growth rate usually continues until the previous growth curve is reached. Then the growth slows to normal. The mechanism is not known.