Growth and Development of the Child
The major physiologic problems of the child beyond the neonatal period are related to special metabolic needs for growth, which have been fully covered in the sec-tions of this book on metabolism and endocrinology.
Figure 83–8 shows the changes in heights of boys and girls from the time of birth until the age of 20 years. Note especially that these parallel each other almost exactly until the end of the first decade of life. Between the ages of 11 and 13 years, the female estrogens begin to be formed and cause rapid growth in height but early uniting of the epiphyses of the long bones at about the 14th to 16th year of life, so that growth in height then ceases. This contrasts with the effect of testosterone in the male, which causes extra growth at a slightly later age—mainly between ages 13 and 17 years. The male, however, undergoes much more prolonged growth because of much delayed uniting of the epiphyses, so that his final height is considerably greater than that of the female.
Behavioral growth is principally a problem of maturity of the nervous system. It is extremely difficult to dissociate maturity of the anatomical structures of the nervous system from maturity caused by training. Anatomical studies show that certain major tracts in the central nervous system are not completely myelinated until the end of the first year of life. For this reason, it is frequently stated that the nervous system is not fully functional at birth. The brain cortex and its associ-ated functions, such as vision, seem to require several months after birth for final functional development to occur.
At birth, the infant brain mass is only 26 per cent of the adult brain mass and 55 per cent at 1 year, but it reaches almost adult proportions by the end of the second year. This is also associated with closure of the fontanels and sutures of the skull, which allows only 20 per cent additional growth of the brain beyond the first 2 years of life. Figure 83–9 shows a normal progress chart for the infant during the first year of life. Com-parison of this chart with the baby’s actual development is used for clinical assessment of mental and behavioral growth.