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Growth is a complex process and requires the coordination of several hormones of which the main one is growth hormone. It is produced by the pituitary gland and acts on the liver, stimulating it to produce another hormone. It is this second hormone, which directly affects the growth of bone and muscle. Growth hormone also helps to control the body´s use of proteins, carbohydrates and fats.
Babies' length, mass and head size are routinely measured during the first few months of life. Growth problems may be highlighted when the results are plotted on Average Growth Charts, although such charts are used only as a guide.
A percentile is a score below which a certain percentage of the scores may be found in a set of data, or distribution. For example, 98% of the data points are found below the 98th percentile, whereas only 2% are found below the 2nd percentile.
In children, if there is not enough growth hormone, growth does not happen at the normal rate and this can result in dwarfism. The treatment for this deficiency is to give the child growth hormone which, nowadays, is produced by genetic engineering.
If too much growth hormone is produced in childhood, then giantism results. The most famous case of giantism is that of Robert Wadlow. He weighed a normal 8.5 pounds at birth but by 5 years of age he weighed 7.5 stones and was 5 ft 4 tall. As an adult he weighed 35 stones and was 8 ft 11 tall. He died aged 22 years.
Extremes in height (dwarfism and giantism) can also be inherited from parents in the genes. Too much growth hormone in adults results in a disease called acromegaly in which there is an overgrowth of bone giving the person a change of appearance. This happens slowly over a long period of time.
Genetic engineering means that there is a plentiful supply of growth hormone for everyone who needs it. Growth hormone might have a role in anti-aging treatments and this is being researched at present. The cow version, bovine growth hormone, and the pig version, porcine growth hormone, have been used in animals to increase yields of milk and of leaner meat without any harmful effects on humans who eat the meat.
Robert Wadlow in 1936 next to his brother (Photo used with permission of The (Alton, IL) Telegraph)