The Master Gland and Its Messengers
The pituitary gland sits at the base of your brain, about the size of a pea. But don't let its size fool you — it's called the "master gland" because it controls so many other glands in your body. Think of it as the CEO of a company: it doesn't do all the work itself, but it sends out orders that make other departments (thyroid, adrenal glands, ovaries, testes) do their jobs.
The pituitary has two distinct parts: the anterior lobe (front) and the posterior lobe (back). They're like two different departments that happen to share the same building. The anterior lobe makes its own hormones; the posterior lobe stores and releases hormones that were actually made in the brain (the hypothalamus).
Anterior Pituitary Hormones (Made Here)
The anterior pituitary produces six major hormones. Each one targets a specific organ or tissue elsewhere in the body.
Growth Hormone (GH)
GH stimulates growth in almost every tissue — especially bones and muscles. It's most active during childhood and adolescence. If too little is secreted, a child may have stunted growth (pituitary dwarfism). Too much can lead to gigantism in children or acromegaly (enlarged hands, feet, jaw) in adults.
Thyroid-Stimulating Hormone (TSH)
TSH travels to the thyroid gland in your neck and tells it to release thyroid hormones (T3 and T4). Those thyroid hormones then regulate your metabolism — how fast your body burns energy. Without TSH, your thyroid goes dormant.
Adrenocorticotropic Hormone (ACTH)
ACTH targets the adrenal cortex (the outer layer of the adrenal glands, which sit on top of your kidneys). It triggers the release of cortisol, a stress hormone that helps manage blood sugar, inflammation, and immune responses.
Luteinizing Hormone (LH) and Follicle-Stimulating Hormone (FSH)
These two work together as the gonadotropins — they control the reproductive system.
- In females: FSH stimulates the growth of ovarian follicles (which contain eggs); LH triggers ovulation (release of the egg) and helps form the corpus luteum.
- In males: FSH helps produce sperm; LH stimulates testosterone production from the testes.
Prolactin
Prolactin's main job is to initiate and maintain milk production in the mammary glands after childbirth. It's normally kept in check by dopamine from the hypothalamus — that's why prolactin levels stay low unless a woman is breastfeeding.
The anterior pituitary is sometimes called the adenohypophysis. Its hormones are all protein or peptide hormones — they can't cross cell membranes, so they bind to surface receptors and trigger second messengers inside the cell.
Posterior Pituitary Hormones (Stored Here, Made Upstairs)
The posterior pituitary doesn't make its own hormones. Instead, the hypothalamus (the brain region just above it) produces two hormones, which then travel down nerve fibres into the posterior pituitary for storage and release.
Oxytocin
Oxytocin is best known for two actions:
- Childbirth: It stimulates strong contractions of the uterine muscles during labour.
- Milk ejection: When a baby suckles, oxytocin is released, causing milk to be "let down" from the mammary glands.
It's also involved in bonding and social behaviour — sometimes called the "love hormone."
Vasopressin (Antidiuretic Hormone, ADH)
Vasopressin acts on the kidneys. It tells them to reabsorb more water back into the blood, producing more concentrated urine. This is how your body conserves water when you're dehydrated.
If vasopressin is deficient, you get diabetes insipidus — not the sugar-related diabetes, but a condition where you produce huge volumes of dilute urine and feel constantly thirsty.
Don't confuse diabetes insipidus (ADH deficiency) with diabetes mellitus (insulin deficiency). Both cause frequent urination, but the underlying hormones and mechanisms are completely different.
Summary Table
| Part | Hormone | Target | Main Effect |
|---|
| Anterior | GH | Bones, muscles, tissues | Growth |