The major endocrine glands
From the master gland in the brain to the adrenal glands above the kidneys, each endocrine gland has distinct jobs.
The hypothalamus and pituitary
The hypothalamus links the nervous and endocrine systems. It sends releasing and inhibiting hormones to the anterior pituitary through a special blood portal system, and its neurons extend into the posterior pituitary, which releases oxytocin and antidiuretic hormone (ADH). The pituitary is often called the master gland because it controls several other glands.
Anterior pituitary hormones
The anterior pituitary makes growth hormone (GH), stimulating growth and metabolism; thyroid-stimulating hormone (TSH); adrenocorticotropic hormone (ACTH), stimulating the adrenal cortex; follicle-stimulating hormone (FSH) and luteinising hormone (LH), controlling the gonads; and prolactin, stimulating milk production.
Posterior pituitary hormones
Antidiuretic hormone (ADH) makes the kidneys retain water, concentrating urine; alcohol suppresses ADH, which is why it increases urination. Oxytocin triggers uterine contractions during childbirth and milk release during breastfeeding, and plays a role in social bonding.
The thyroid and parathyroids
The thyroid gland in the neck makes thyroid hormones (T3 and T4), which set the body's metabolic rate and require iodine; iodine deficiency can cause goitre, an enlarged thyroid. It also makes calcitonin, which lowers blood calcium. The four small parathyroid glands make parathyroid hormone (PTH), which raises blood calcium by releasing it from bone.
The adrenal glands
Each adrenal gland, above a kidney, has two parts. The adrenal cortex makes steroid hormones: cortisol, which helps the body cope with long-term stress by raising blood glucose and suppressing inflammation; aldosterone, which makes kidneys retain sodium and water; and small amounts of sex hormones. The adrenal medulla makes adrenaline and noradrenaline for short-term stress.
The pancreas
The pancreas is both exocrine and endocrine. Its endocrine cells, in clusters called the islets of Langerhans, include beta cells making insulin (lowering blood glucose) and alpha cells making glucagon (raising it). These two hormones act antagonistically to keep glucose near 4-6 mmol/L between meals.
Gonads and other glands
The ovaries make oestrogen and progesterone; the testes make testosterone. The pineal gland makes melatonin, which helps regulate sleep-wake cycles and is released in darkness. The thymus helps T cells mature in childhood. Many other organs, such as the heart, kidneys, stomach, and fat tissue, also release hormones.
Worked example
A person is dehydrated after exercising. Blood becomes more concentrated; the hypothalamus detects this and the posterior pituitary releases ADH. The kidneys reabsorb more water, producing small amounts of dark urine. Thirst is also triggered. When water balance is restored, ADH release falls.
Key takeaways
The hypothalamus controls the pituitary. The anterior pituitary makes GH, TSH, ACTH, FSH, LH, and prolactin; the posterior pituitary releases ADH and oxytocin. The thyroid sets metabolic rate; PTH raises blood calcium. The adrenal cortex makes cortisol and aldosterone; the medulla makes adrenaline. Pancreatic islets make insulin and glucagon. Gonads, pineal, and thymus have further roles.
Flashcard
Links nervous and endocrine systems
Check your understanding
Blood calcium falls too low. Which hormone will be released to raise it?