The pituitary gland, a pea-sized structure at the base of your brain, is the primary gland that controls growth. It produces growth hormone, a protein made up of about 190 amino acids, which drives the lengthening of bones, the building of muscle, and overall body development from infancy through adolescence. But the pituitary doesn’t work alone. It operates within a network of signals from the brain, the thyroid, the adrenal glands, and even the stomach.
How the Pituitary Produces Growth Hormone
Specialized cells called somatotrophs in the front portion of the pituitary gland synthesize and release growth hormone. These cells don’t release it in a steady stream. Instead, growth hormone comes out in pulses, with a major burst roughly every three to three and a half hours. The largest pulse typically happens during deep sleep, which is why adequate sleep during childhood and adolescence matters so much for healthy development.
Several factors influence how much growth hormone the pituitary releases at any given time: physical activity, stress levels, nutrition, blood sugar, and sleep quality all play a role. Even a hormone produced in the stomach called ghrelin (the same one that makes you feel hungry) binds directly to somatotrophs and stimulates them to release more growth hormone.
The Brain Controls the Pituitary
The pituitary is often called the “master gland,” but it takes orders from a region of the brain called the hypothalamus. The hypothalamus acts like a thermostat for growth hormone production, using two chemical signals to keep output in the right range.
The first signal is growth hormone-releasing hormone, or GHRH, which tells the pituitary to make and release more growth hormone. The second is somatostatin, which does the opposite, putting the brakes on release. When growth hormone levels in the blood rise too high, the hypothalamus ramps up somatostatin to bring them back down. When levels drop, GHRH production increases. This back-and-forth feedback loop is what creates the pulsatile pattern of release throughout the day and night.
What Growth Hormone Actually Does in the Body
Growth hormone doesn’t act on bones and muscles directly in most cases. Instead, it travels to the liver, where it triggers the production of a second messenger called insulin-like growth factor 1, or IGF-1. The liver is the primary source of IGF-1 circulating in the bloodstream, though growth hormone can also stimulate IGF-1 production locally in other tissues.
Together, growth hormone and IGF-1 have powerful effects throughout the body. They stimulate bone lengthening by acting on growth plates (the bands of developing cartilage near the ends of long bones), build and maintain muscle mass, reduce body fat (particularly around the organs), and improve how cells use insulin for energy. IGF-1 also supports healthy cell function at a deeper level, helping regulate energy production inside cells and improving insulin sensitivity in both muscle and liver tissue.
Other Glands That Support Growth
While the pituitary is the lead player, two other glands make essential contributions to normal growth.
The Thyroid Gland
The thyroid, located in the front of your neck, produces hormones that are direct biological regulators of the growth plates in bones. Thyroid hormones stimulate the cartilage cells in growth plates to multiply, mature, and eventually be replaced by hard bone. They also appear to amplify the effects of growth hormone and IGF-1, essentially making the whole growth system work more efficiently.
When the thyroid is underactive during childhood, the consequences are severe. Untreated hypothyroidism causes profound growth retardation and delayed skeletal maturation. On X-rays, the bones of affected children show delayed appearance of the hardening centers that signal normal development, along with deformed and irregular bone shapes. Treatment can partially reverse the damage: in one study of older children with long-neglected hypothyroidism, a year of thyroid hormone therapy reduced their bone age delay from 4.7 years behind schedule to 3.1 years behind.
The Adrenal Glands
Sitting on top of each kidney, the adrenal glands produce androgens, a group of hormones that become especially important during puberty. Adrenal androgens help trigger the pubertal growth spurt and contribute to the development of adult body characteristics: increased height, deeper voice, body hair growth, and muscle development. These hormones work alongside the surge in growth hormone that also occurs during puberty, creating the rapid increase in height that most teenagers experience.
When Growth Stops
Growth in height is only possible while the growth plates at the ends of your long bones remain open. These plates are made of cartilage that gradually hardens into solid bone as you mature. For girls, growth plates typically close between ages 13 and 15. For boys, closure happens between ages 15 and 17. Once they fuse completely, no amount of growth hormone can make bones longer.
This timing is why excess growth hormone has very different effects depending on when it occurs. If overproduction starts in childhood before the plates close, bones grow enormously in length, a condition called gigantism. In adults, the same excess can’t increase bone length because the plates are already fused. Instead, bones become thicker and deformed, particularly in the hands, feet, and face. This adult condition, called acromegaly, most commonly begins between ages 30 and 50 and is usually caused by a benign tumor on the pituitary gland.
Signs of Growth Hormone Deficiency
In children, the most obvious sign of growth hormone deficiency is falling behind on expected growth curves. A child may be significantly shorter than peers, gain height unusually slowly, or look younger than their actual age because of delayed facial maturation and a tendency to carry more body fat around the midsection.
Diagnosis involves stimulation testing, where doctors give a substance that should trigger the pituitary to release growth hormone, then measure the response through blood draws. In children, a peak growth hormone level below about 7 to 10 micrograms per liter during testing (depending on the specific test and assay used) generally confirms the diagnosis. For adults, the threshold is lower, typically 3 to 5 micrograms per liter. Testing in adults is more complex because body weight significantly affects results, with higher BMI naturally blunting the growth hormone response.
Growth hormone deficiency in adults doesn’t affect height, but it does cause changes in body composition, energy, and overall well-being. Adults with this condition tend to accumulate more abdominal fat, lose muscle mass, and may experience fatigue, reduced bone density, and changes in cholesterol levels.