The human growth hormone (GH) is well known for stimulating the height growth of children and adolescents. Hormones are chemical “messengers” that are produced in one part of the body and travel to another part to create some sort of change.
GH, also known as somatotropin or human growth hormone (HGH), is synthesized, stored and secreted in the anterior pituitary gland, which is located near the base of our brain. The growth hormone has the central function of stimulating the growth of all body tissues, bones and regulating the metabolism. Biochemically, growth hormone stimulates protein synthesis and promotes fat breakdown to provide the energy needed for tissue growth. Growth hormone secretion is controlled by the hypothalamus which is similar to most anterior pituitary gland hormones. Every day one or two milligrams of the hormone is released. Alterations in the GH secretion can lead to disorders of growth and metabolism.
The production of the growth hormone is influenced by many factors such as nutrition, sleep, exercise, stress or the growth hormone itself. However, GH secretion is mainly stimulated by growth hormone-releasing hormone (GHRH) and is inhibited by somatostatin. Ghrelin, a peptide that is produced primarily by the endocrine stomach, has as well an influence on the secretion of GH. The secretion of Ghrelin is understood as a response to eating behavior, which shows a direct connection between nutrition and growth.
How Does the Growth Hormone Work?
Growth is a complex process and requires good coordination of several hormones. The growth hormone works in two different ways. Partly, it acts directly on the tissues, but it mainly stimulates the liver to create a protein called insulin-like growth factor 1 (IGF-1). IGF-1 stimulates the proliferation of cartilage cells, resulting in bone growth and muscle growth. The Serum IGF-1 level considerably increases and accelerates during puberty. After puberty, the IGF-1 level gradually decreases, in the same way as the growth hormone level. It is decreasing by about 14% every 10 years. GH deficiency in adults is related to fatigue, decreased energy, depressed mood, decreased muscle strength and mass, and osteoporosis.
The Impact of Sleep and Exercise on the GH Secretion
The human growth hormone is generally secreted along with the circulatory rhythm. Many physiological stimuli cause GH secretion, sleep and exercise play an essential role. At night, humans go through four to five stages in their sleep. In adults, GH release has the strongest impulse during the first phase of slow-wave sleep (stages three and four). In men, about 70% of the GH pulses occur during the slow-wave sleep (SWS) phase. Sleep-related GH secretion seems to be mainly associated with the secretion of growth hormone-releasing hormone (GHRH). When we are between 30 to 40 years old, the total amount of GH secreted drops by two- or threefold. Interestingly, the amount of SWS decreases similarily. Exercise strengthens the cardiovascular system, increases muscle strength and maintains bone minerals. Additionally, acute exercise stimulates the release of GH and multiple other hormones and metabolites. Factors such as aging or obesity can affect GH secretion and GH reaction to an exercise stimulus. However, for healthy young adults, exercise has the unique ability to generate recurrent GH elevations during the same day. High-intensity training for only 10 minutes typically evokes a already substantial GH release.
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