The anterior pituitary gland produces six hormones that regulate growth, metabolism, stress responses, reproduction, and milk production. Sitting at the base of the brain and roughly the size of a pea, it acts as a central relay station, receiving chemical signals from the hypothalamus above it and dispatching hormones into the bloodstream that tell distant organs what to do and when. It’s often called the “master gland” because so many essential body functions depend on it.
How the Hypothalamus Controls It
The anterior pituitary doesn’t act on its own. It takes orders from the hypothalamus, a small region in the brain that monitors conditions throughout the body. The two are connected by a specialized network of blood vessels called the hypothalamic-hypophyseal portal system. The hypothalamus releases tiny amounts of stimulating or inhibiting hormones into these vessels, and within seconds those chemical messages reach the anterior pituitary cells and either ramp up or dial down hormone production. This arrangement lets the brain fine-tune hormone output in response to stress, sleep, body temperature, blood sugar, and dozens of other signals.
The Six Hormones It Produces
Five distinct cell types inside the anterior pituitary are responsible for six different hormones. Somatotrophs, the most abundant cells (roughly half of the gland’s total), produce growth hormone. Lactotrophs (15 to 20% of cells) produce prolactin. Corticotrophs (another 15 to 20%) produce ACTH, the hormone that drives cortisol release. Gonadotrophs (10 to 15%) produce both FSH and LH, the two hormones that govern reproduction. Thyrotrophs, the smallest group at about 5%, produce TSH, which controls the thyroid.
Each of these hormones enters the bloodstream and travels to a specific target organ, where it triggers a cascade of effects. The sections below cover what each one actually does in the body.
Growth Hormone and Metabolism
Growth hormone is the anterior pituitary’s signature product. It works in two ways: directly, by binding to cells throughout the body, and indirectly, by prompting the liver to release a secondary messenger called insulin-like growth factor-1 (IGF-1). Together, these signals stimulate growth in nearly every tissue and organ, but the effects on bone and cartilage are the most dramatic, especially during childhood and adolescence. Growth hormone activates the cells responsible for building new bone and cartilage, driving increases in height and skeletal size.
Beyond growth, this hormone reshapes metabolism around the clock. It pushes cells into an anabolic state, increasing amino acid uptake and protein synthesis while reducing protein breakdown. It also triggers the breakdown and burning of stored fat in fat cells. The net effect is a body that builds lean tissue and uses fat for fuel, which is why growth hormone levels matter for body composition throughout life, not just during the growing years.
ACTH and the Stress Response
When you face a threat, whether physical danger or psychological pressure, the hypothalamus releases a signaling hormone that tells corticotroph cells in the anterior pituitary to secrete ACTH. ACTH travels through the blood to the adrenal glands, which sit on top of your kidneys, and stimulates them to produce cortisol.
Cortisol is the body’s primary stress hormone and has wide-ranging effects. It raises blood sugar and free fatty acid levels so your muscles and brain have quick energy. It increases cardiac output and narrows blood vessels, raising blood pressure. It suppresses inflammation and dampens parts of the immune system that aren’t immediately useful during a crisis. This entire chain, from hypothalamus to anterior pituitary to adrenal glands, is known as the HPA axis, and it’s one of the most important feedback loops in the body. Once cortisol levels rise high enough, cortisol itself signals the hypothalamus and pituitary to stop releasing more ACTH, preventing the system from overshooting.
TSH and Thyroid Regulation
Thyroid-stimulating hormone is the primary signal that tells your thyroid gland to produce thyroid hormones. The thyroid responds by releasing T4 (about 80% of its output) and T3 (about 20%). These thyroid hormones regulate your metabolic rate, body temperature, heart rate, and energy levels. Without TSH from the anterior pituitary, the thyroid essentially goes quiet.
This system runs on a negative feedback loop. When T3 and T4 levels in the blood climb too high, they act directly on the anterior pituitary to suppress TSH release, so the thyroid slows down. When thyroid hormone levels drop, TSH secretion increases, pushing the thyroid to make more. T3 is the stronger of the two at suppressing TSH, making it the main thermostat in this feedback cycle. This is why doctors measure TSH levels as a first step in checking thyroid function: an abnormal TSH reading usually reveals whether the thyroid is overactive or underactive before other symptoms become obvious.
FSH, LH, and Reproduction
The anterior pituitary’s gonadotroph cells produce two hormones, FSH and LH, that are essential for fertility in both sexes.
In women, FSH drives the growth and maturation of ovarian follicles, the tiny sacs that contain developing eggs. Without functional FSH signaling, follicles stall at an early stage and ovulation doesn’t occur. LH works alongside FSH during follicle development and triggers ovulation itself through a mid-cycle surge. After ovulation, LH supports the structure left behind (the corpus luteum), which produces progesterone to prepare the uterine lining for pregnancy.
In men, LH stimulates cells in the testes to produce testosterone, which is essential for male characteristics and, together with FSH, for sperm production. FSH acts on the supporting cells within the seminiferous tubules, maintaining the environment that developing sperm need to mature properly. Both hormones are required: testosterone alone isn’t enough for normal sperm production without FSH’s contribution.
Prolactin and Milk Production
Prolactin is unusual among the anterior pituitary hormones because it’s kept under constant suppression rather than waiting for a “go” signal. The hypothalamus continuously releases dopamine, which acts on lactotroph cells to block prolactin synthesis. This tonic inhibition means prolactin stays low unless something overrides the dopamine brake.
The strongest override is nipple stimulation during breastfeeding. Sensory nerves in the nipple send signals through the spinal cord to the hypothalamus, which temporarily stops dopamine release. With the brake lifted, prolactin floods the bloodstream and reaches the breast, where it stimulates the milk-producing cells to synthesize lactose, casein, and lipids, the core components of breast milk. During pregnancy, rising estrogen levels also increase prolactin to prepare the mammary glands for nursing. Outside of pregnancy and breastfeeding, dopamine keeps prolactin suppressed in the background.
What Happens When It Malfunctions
Because the anterior pituitary controls so many downstream organs, problems here can ripple outward. The most common culprit is a pituitary adenoma, a usually benign tumor that grows from one of the gland’s cell types. These tumors can cause trouble in two ways: by overproducing a specific hormone, or by growing large enough to compress and damage the surrounding normal tissue, leading to underproduction of other hormones.
Excess growth hormone in adults leads to acromegaly, a condition marked by gradual enlargement of the hands, feet, and facial features. Excess ACTH drives the adrenal glands to overproduce cortisol, resulting in Cushing’s disease, which causes weight gain concentrated around the midsection and face, thinning skin, high blood sugar, and weakened bones. A prolactin-secreting tumor can cause unexpected milk production and disrupt menstrual cycles or fertility.
On the underproduction side, the condition is called hypopituitarism. Depending on which hormones are affected, symptoms can include fatigue and cold intolerance (low TSH leading to low thyroid hormones), loss of muscle mass and increased body fat (low growth hormone), infertility or loss of sex drive (low FSH and LH), or an inability to handle physical stress (low ACTH and therefore low cortisol). Large tumors sometimes knock out multiple hormone lines at once while simultaneously overproducing the hormone from the tumor cells themselves.