Growth

A complex process is affected by genetics, growth hormone, somatomedins, thyroid hormone, androgens, estrogens, glucocorticoids, insulin and adequate nutrition.

Nutrition is the most important extrinsic factor affecting growth.

Nutrition must be adequate in protein content, essential vitamins, minerals and calories to maintain adequate growth.

There are two periods of rapid growth, first in infancy, and the second in late puberty just before growth stops.

The first period of rapid growth is a continuance of the fetal growth period.

The second growth spurt is due to growth hormone, androgens and estrogens, at the time of puberty.

Growth cessation is largely due to closure of epiphyses by androgens.

Girls mature earlier than boys with their growth spurt appearing earlier.

During infancy growth is episodic, with increases in length of human infants of 0.5-2.5 cm in a few days, while separated by periods of 2-63 days during which no growth is measurable.

In utero growth is independent of growth hormone.

Plasma growth hormone is elevated in newborns.

Subsequently resting levels of plasma growth hormone fall with spikes during puberty.

Pubertal growth spurt is due in part to protein anabolic effects of androgens, and the secretion of adrenal androgens, interactionof sex hormones, growth hormone, and Insulin-growth factor-1 (IGF-1.

Sex hormones increase the amplitude of growth hormone spikes, and the latter increases IGF-1 secretion, and this in turn causes growth.

Estrogen causes cessation of growth by fusing epiphyses to the long bones.

This explains why individuals with sexual precocity are dwarfed, and why individuals castrated prior to puberty are tall.

Thyroid hormone essential for function of growth hormone, and for its rate of secretion.

Thyroid hormones have effects on ossification of cartilage, growth of teeth, facial contours, and body proportion.

Cretins therefore appear dwarfed with infantile features.

Glucocorticoids inhibit cellular growth by direct action of cells.

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