Growth hormone is a protein hormone and is essentially a tissue building hormone produced and secreted by the anterior portion of the pituitary gland.
Growth hormone is extremely important piece of the body’s endocrine system and produce all our life, peaking through adolescence and progressively declining with age. It is secreted in six to twelve pulses each day with the largest pulse out about one hour after the onset of sleep. Levels of growth hormone in the blood are regulated two hormones produced in the hypothalamus called growth hormone releasing hormone and growth hormone inhibiting hormone. The powerful stimulus for the secretion of growth hormone is sleep.
Growth hormone (GH) has a variety of roles that it plays in the body, most known role is its role in skeletal muscle and muscle growth. In adolescents GH actively stimulates the growth plates of long bones of the arms and legs. Although most cells in the body have GH receptors, most growth-promoting effects mediated indirectly by insulin-like growth factors produced by the liver and secreted in response to GH, because of this the liver is the main target organ of GH.
GH also plays an important role in metabolism as it stimulates stored fats to break down into free fatty acids, and also reduces fatty tissues from accumulating more lipids. It also works in the opposite function of insulin and reduced glucose uptake and metabolism, and in the liver it encourages glycogen breakdown and release glucose to the blood.
GH also increases calcium retention and strengthens and increases bone formation in bone.
Excess secretion has a very visible effect on the body; this effect varies depending on the age of onset and is mainly caused by the growing tumor in the pituitary gland. In young children or adolescents this results in a rare condition called gigantism.
A famous case of gigantism was Robert Wadlow who holds the world record for being the tallest man. Robert Wadlow was born in 1918 weighing normal eight pounds, but by the time he was eight years old, he was six feet, two inches tall, and by the time he died at age 22, he had reached eight feet, eleven inches tall.
In older adults, excess growth hormone levels causes a condition known as acromegaly, which causes thickening of the jaw, fingers and toes. Other problems that can accompany this condition include enlarged organs, joint problems, insulin resistance and reduce sexual activity.
Under secretion (hypo secretion) also has a special effect on the body. In children, this leads to a condition called pituitary dwarfism, which leads to relatively normal proportions of the body, but a short height. In adults, the effect is much less noticeable and can include deficiencies in strength, energy, and bone mass increases risk of cardiovascular disease.
Under the secretion of growth hormone can be caused by mutations in specific genes, malformations in the hypothalamus and / or pituitary gland and also damage the pituitary from injury, surgery or disease.