Growth hormone (GH) is a protein hormone composed of 191 amino acids, produced by somatotropic cells in the anterior pituitary gland. The release of GH into the bloodstream occurs in pulses every three to five hours. This process is regulated by hormones from the hypothalamus and influenced by factors like sleep, exercise, and stress. While known for its role in growth, this hormone contributes to bodily regulation throughout life.
Role in Childhood Growth and Development
The most recognized contribution of growth hormone is facilitating linear growth during childhood and adolescence. GH does not directly cause bones to lengthen; instead, it travels to the liver and stimulates the production of another hormone called insulin-like growth factor 1 (IGF-1).
Once released, IGF-1 is the primary actor that promotes the growth of long bones by targeting the growth plates, which are areas of new cartilage in the bones of children and teens. IGF-1 stimulates the multiplication of cartilage cells (chondrocytes), leading to bone elongation and an increase in height. This process continues until the growth plates fuse after puberty, at which point an increase in height is no longer possible.
Metabolic Functions in Adulthood
After linear bone growth ceases, growth hormone continues to perform functions related to metabolism and body composition. In adults, GH helps regulate the body’s ratio of muscle to fat by increasing muscle mass through protein synthesis and encouraging lipolysis, the breakdown of fat for energy.
GH’s metabolic influence also extends to maintaining bone density and managing how the body processes fats and sugars. It supports bone mineralization, which helps keep bones strong. The hormone also plays a part in homeostasis by reducing the liver’s uptake of glucose while promoting its production, a process known as gluconeogenesis.
Consequences of Imbalance
Proper levels of growth hormone are necessary for normal development, as both excesses and deficiencies can lead to significant conditions. In children, a deficiency of GH can impair growth, leading to a condition sometimes known as pituitary dwarfism. For adults, a lack of GH can result in reduced muscle mass, an increase in body fat, and lower bone density.
An overproduction of growth hormone also has distinct effects depending on age. If GH levels are excessively high during childhood before the bone growth plates have closed, it results in gigantism. In adulthood, after bone growth is complete, excessive GH leads to acromegaly, a condition characterized by the enlargement of bones in the hands, feet, and face, along with organ enlargement.