Growth hormone (GH) is a substance that influences various bodily functions beyond increasing stature. It acts as a chemical messenger, orchestrating complex processes. It regulates how the body uses energy and maintains tissues.
Growth Hormone Basics: What It Is and Where It’s Made
Growth hormone, also known as somatotropin, is a protein hormone composed of 191 amino acids. It is synthesized, stored, and released by specialized cells called somatotrophs within the anterior pituitary gland, a small structure at the base of the brain.
The release of growth hormone into the bloodstream is not continuous; instead, it occurs in bursts or pulses throughout the day. This pulsatile secretion is influenced by various factors, including sleep, stress, exercise, and the body’s glucose levels. Two other hormones, growth hormone-releasing hormone (GHRH) from the hypothalamus and somatostatin, primarily regulate GH release, with GHRH stimulating and somatostatin inhibiting its secretion.
How Growth Hormone Triggers Effects
Once released, growth hormone travels through the bloodstream and binds to specific receptors on target cells. This binding initiates a series of intracellular signals. These signals activate various pathways within the cells, leading to changes in gene expression and cellular activity.
Growth hormone’s influence is largely mediated indirectly through insulin-like growth factor 1 (IGF-1). Growth hormone stimulates the liver to produce and release IGF-1. IGF-1 then acts on its own receptors, triggering cellular responses that mirror many of growth hormone’s effects, particularly those related to growth and anabolism. This interplay between GH and IGF-1 is often referred to as the GH/IGF-1 axis, forming a feedback loop where IGF-1 can also inhibit GH release.
Growth Hormone’s Diverse Roles in the Body
Growth hormone’s most recognized function is its role in physical growth, particularly during childhood and adolescence. It promotes the lengthening of long bones by stimulating the activity of cells in the growth plates. This process involves increased protein deposition and cell reproduction within cartilage and bone tissue. Once the growth plates fuse after puberty, GH no longer increases height, but it continues to maintain normal body structure.
Beyond its growth-promoting effects, growth hormone impacts the body’s metabolism. It influences protein synthesis, which is important for building and repairing muscle tissue. Growth hormone also promotes the breakdown of fats (lipolysis), making stored energy available for use, and helps regulate how the body uses glucose. These metabolic actions contribute to overall body composition, including the maintenance of muscle mass and the distribution of fat.
Understanding Growth Hormone Imbalances
When growth hormone levels are either too low or too high, various health conditions can arise. Growth hormone deficiency (GHD) in children manifests as a slow growth rate and short stature. In adults, GHD can lead to reduced muscle mass, increased body fat, lower energy levels, and decreased bone density.
Conversely, an excess of growth hormone can also cause health issues. If this overproduction occurs in childhood before the growth plates have fused, it results in gigantism, characterized by excessive height and overall body size. In adults, after the growth plates have closed, excessive growth hormone leads to acromegaly, a condition where bones and soft tissues gradually enlarge and deform. These imbalances show the importance of regulated growth hormone levels for bodily health.