Growth in height: how it happens and what it depends on
During childhood and adolescence, the bones of the human body are affected by continuous phenomena of growth and remodeling, some of which cease in adulthood; others remain for life, so that every 10 years the skeleton is completely renewed.
The increase in height during development is the result of the longitudinal growth of long bones. This growth is guaranteed by the presence of the so-called conjugation cartilage, whose welding at the end of the development precludes any further statural increase.
In childhood and adolescence it is possible to distinguish two small regions, called epiphyseal plates, interposed between the epiphysis and the diaphysis of long bones, and also present in some short bones.
These plaques - also known as cartilaginous disks, bone growth nuclei, metaphyses or conjugation cartilages - host particular cells, called chondrogenic cells. It is a cell population in continuous division, responsible for the production of chondroblasts, of which they represent the natural precursors.
The chondrogenic populations give rise to the chondroblasts (cells deputed to the deposition of cartilage), which, once this function is fulfilled, turn themselves into chondrocytes (inactive cells). We then witness a gradual resorption of the cartilage thus produced, the calcification of the residual matrix and the gradual conversion of the newly formed fibrous bone tissue into lamellar bone tissue.
The whole process allows the growth of long bones.
Hormonal influences and growth arrest
Statural growth is regulated by different hormones; before puberty the stimulus for the lengthening of long bones is mainly given by GH (or somatotropic hormone), in synergy with thyroid hormones, as well as with insulin and similar insulin growth factors (which enhance their effects).
A defect or an excess of these hormones, in particular of GH, T3 and T4, determines alterations of growth (dwarfism or gigantism).
At the end of puberty, roughly around 16-17 years for females and around 18-20 for males, statural growth freezes. Growth stops because the epiphyses connect to the metaphyses and the growth cartilages cease to function. From this moment on it is no longer possible to increase one's bone length.
Responsible for this block are the sex hormones, which after having prompted a rapid acceleration of growth in the pubertal period, determine their definitive arrest.
In females, the massive secretion of estrogens in the puberty period induces the closure of the cartilages of conjugation of the long bones, ending in fact, the phase of statural growth. An analogous speech in the male, where the incretion of androgens also increases the production of estrogens (due to the peripheral activity of the aromatase enzyme), determining the welding of the intercartilaginous discs and the arrest of growth.
Hypogonadism (reduced synthesis of sex hormones) causes gigantism due to failure to close the epiphyseal plates in puberty.
It should be noted that GH secretion is positively influenced by physical exercise and negatively by obesity (another reason to inculcate a healthy sporting culture to our children).
Among the environmental factors capable of influencing height growth, a predominant role is played by nutrition, as evidenced by the so-called secular trend (or secular trend of growth). In the last century, in fact, children who live in developing countries have reached ever greater stature, hand in hand with the progress of national economic well-being. In Italy, for example, the stature of military recruits increased by about 10 cm between 1861 and 1961.
