Growth hormone is a protein hormone and is essentially a tissue building hormone which is produced and secreted by the anterior portion of the pituitary gland. Growth hormone works by producing direct and indirect effects on target organs and cells. |
Growth hormone is an extremely important piece of the body’s endocrine system and is produced throughout our life, peaking through adolescence and progressively declining with age. It is secreted in six to twelve pulses each day with the largest pulse released around one hour after the onset of sleep. Levels of growth hormone in the blood are regulated by two hormones produced in the hypothalamus called growth hormone releasing hormone and growth hormone inhibiting hormone. The most powerful stimulus for the secretion of growth hormone is sleep. ___
Growth hormone has a variety of roles that it plays within the body, the most widely known role is its function in skeletal and muscle growth. In adolescents growth hormone actively stimulates the growth plates in the long bones of the arms and legs. Although most cells in the body have growth hormone receptors, most growth promoting effects are mediated indirectly by insulin-like growth factors produced in the liver and secreted in response to growth hormone, because of this the liver is the main target organ of growth hormone.
Growth hormone also plays an important role in metabolism as it stimulates stored fats to break down into free fatty acids, and also suppresses fatty tissues from accumulating more lipids. It also acts in the opposite function of insulin and decreases the rate of glucose uptake and metabolism, and in the liver it encourages glycogen breakdown and release of glucose to the blood.
Growth hormone also increases calcium retention and strengthens and increases the mineralization of bone.
Excess secretion (hypersecretion) of growth hormone has a very visible impact on the body; this impact is different according to the age of onset and is mainly caused by a tumour growing in the pituitary gland. In young children or adolescents this results in a very rare condition known as 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 a 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 the age of 22, he had reached eight feet, eleven inches in height.
In older people an excess of 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 reduced sexual functioning.
Hyposecretion of growth hormone: Under secretion (hyposecretion) of growth hormone also has a distinct impact on the body. In children this results in a condition known as pituitary dwarfism, which results in relatively normal body proportions, but a short height. In adults the effects are much less noticeable and can include deficiencies in strength, energy, and bone mass as well as an increased risk of cardiovascular disease.
Under secretion of growth hormone may be caused by mutations of specific genes, malformations in the hypothalamus and/or pituitary gland and also damage to the pituitary gland from injury, surgery or disease.
Growth hormone and exercise: Through research I discovered that physical exercise is the most powerful stimulus apart from sleep for secretion of growth hormone.
The exercise-induced growth hormone response is well recognised, and although the exact mechanisms remain unclear, a number of implicating factors have been acknowledged by researchers, including stimulation by catecholamines, neural stimulation, and lactate and nitric oxide levels.
Several studies that I have looked at suggest that growth hormone levels after exercise are largely determined by the length of time, intensity and type of exercise undertaken.
These studies have suggested that training above the lactate threshold for a minimum of 10 minutes appears to elicit the greatest stimulus to the secretion of growth hormone.
Researchers acknowledge that more studies need to be undertaken in this area in order to develop a better understanding of growth hormone response to exercise and the need to be able to define the ideal method of provoking the maximum response as a way to curb the growing practice of growth hormone doping in the sports industry by giving potential abusers a safer alternative.
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