Growth Curve

When the change in the body weight is plotted against time the curve is sigmoid, the characteristic of all higher animals including man.

Growth passes through following phases:

Lag phase : It mainly shows cell division. It is beginning of growth.
Log phase / Exponential phase : It is the period of rapid growth.
Decelerating growth phase : Growth slows down generally due to differentiation.
Steady state : There is no growth due to achievement of maturity.
Inflexion point : The point were exponential growth begins to slow down.

The difference between initial and final weight (or size) of an individual for any period of time is the absolute increase.A new born baby has disproportionately larger head compared to the rest body part. The ratio of head then decreases with increasing age as  given in the diagram. Human embryo is about 150 µm at the time of implantation. In 9 months grows to about 50 cm. During first two months the basic plan is laid. After 4 months embryo grows at the rate of 10 cm per month. During first year after birth grows @ 2 cm per month then declines steadily and  again shoots at puberty. After puberty the physical growth declines and stops after 23 years.

Fig. Characteristic age changes in the proportion of various parts of the body

At 9 weeks of development head of human embryo constitutes more than one third of body length then becomes 1/4^th, and after birth, since rest  of the body grows at very fast rate, the head in adult becomes 1/8^th of the body. Infantile It is growth period from birth to 10 months of age. Growth is very slow. Early childhood It is growth period between 10 months to 5 years. Development of brain takes place. Juvenile stage It is growth period between 5 to 14 years. Growth of legs comparatively more. Adolescent stage Growth period between 14 to 17 years. Growth is maximum. The body attains sexual maturity.