The Physiology of Growth Hormone in the body.

Growth hormone is one of the essential hormones secreted by the anterior pituitary gland in the brain.

As the name suggests, its primary role is to promote the body’s growth.

It is one of the peptide hormones, consisting of 191 amino acids. It is also called a Somatotropin hormone.

Physiology of Human Growth Hormone

Regulation of Secretion

• It is secreted under the influence of Growth hormone-releasing hormone (GHRH) and

• Suppressed by Growth hormone release inhibiting hormone (GHRIH) (somatostatin). Both GHRH and GHRIH are secreted by the hypothalamus.

• The growth hormone-releasing hormone (GHRH) stimulates the pituitary to release growth hormone.

• While the growth hormone release inhibiting hormone (GHRIH) inhibits the secretion of growth hormone from the pituitary.

• The hormone somatostatin, which inhibits growth hormone secretion, is also produced by pancreatic islets.

Timing and stimulation of secretion

• Growth hormone secretion is highest during the night sleep.

• Its blood levels are high during adolscence and decline with age.

• Its secretion is also triggered by exercise, fasting, stress, anxiety, and hypoglycemia.

• Further, infusion of arginine stimulates the release of growth hormone.

Effect on the body’s growth

• GH promotes a person’s growth during early life. It is believed that a person’s height continues to grow until age 18 and ceases thereafter.

• It exerts its action by stimulating the cells and tissues of the body.

• This stimulation of cells is predominant in the bone, cartilage, and other cells responsible for the body’s linear growth in height and overall body mass.

This involves

1. Enlargement of the cell size
2. Increase in mitosis and
3. differentiation of bone and muscle cells.

• During childhood and adolescence, growth hormone predominantly promotes linear growth by enhancing the growth of bone cells and skeletal muscles.

• Once adolescence is over, it maintains the mass of cells and tissues of bones and muscles for the rest of life.

• It also regulates the metabolism in the organs like the intestine, liver, and pancreas.

• It promotes growth and repair, the breakdown of fats, and increases blood glucose levels.

Effect on protein synthesis.

• Growth hormone increases the rate of protein synthesis by
  • Enhancing the DNA transcription to form mRNA for protein formation.
  • Increasing the translocation of mRNA from the nucleus into the cytoplasm.
  • Enhancing the uptake of amino acids across the cell membrane.
  • Decreasing protein catabolism by GH induced promotion of lipolysis, which provides alternative energy, thereby sparing amino acids from being used for gluconeogenesis.

Effects on fat metabolism and lean body mass.

• GH increases fat metabolism and maintains lean body mass. This done through
  • The GH promotes the release of fatty acids from adipose tissue.
  • Enhancing the utilization of fatty acids for energy generation.
  • Thus, its ability to improve fat metabolism and protein deposition causes lean body mass.

Effect on body height

• Its effects are seen in terms of height growth until age 18. Then height growth stops at around 18 due to the epiphyseal plate closure (fusion of the growth plates) in the long bones.

• During this phase, the epiphysis of the long bones unites with the shafts. Once done, no further rise in height is possible.

• So growth in height is freely possible till the age of 18 to 19. After that, though the growth hormone is secreted, there is no growth in height. Instead, the body tissue mass grows.

• So the best chance of height growth by this hormone is before the end of height growth.

Growth Hormone Disorders

Growth hormone disorders occur as a consequence of excess, insufficient, or absent release.

Hypersecretion of GH causes either

1. Gigantism or
2. Acromegaly

While Hyposecretion causes

• Dwarfism

Gigantism leads to excess height, like 2.1 to 2.4 meters, in the individual compared to the normal average height. This is seen when GH secretion is excessive during childhood.

Acromegaly leads to large extremities with thickening of soft tissues. This occurs when GH secretion is high after the ossification (bone growth) is complete. The individual tends to have large hands and feet.

Dwarfism causes short stature. Though the person has grown up, his height remains small.

Growth Hormone Supplements

GH supplements are synthetic or recombinant forms of human growth hormone that are medically used for:

• GH deficiency in children and adults

• Turner’s syndrome and chronic renal insufficiency

• Muscle wasting in HIV patients

However, self-use for bodybuilding or anti-aging is risky, as it may cause insulin resistance, joint pain, or abnormal tissue growth.

Growth hormone antagonists

These are agents that block the effects of GH. They include

• Somatostatin is a natural hormone produced in the body that inhibits GH effects.

• Octreotide is a synthetic substance that is longer-acting and used to treat acromegaly and certain GH-secreting tumors.

FAQ’s

References

• Normal Pituitary Gland Function in Children — Children’s Hospital of Philadelphia.
• Growth Disorders — University of Texas Medical Branch (UTMB) Pediatrics Endocrine Module
• Growth Hormone Deficiency — University of California, San Francisco (UCSF) California Center for Pituitary Disorders
• Physiology, Growth Hormone.
• Regulation of human growth hormone secretion and its disorders — PubMed.