Hormones and endocrine glands explained: the body's chemical messengers

What hormones are and how they travel

Unlike the nervous system, which sends fast electrical signals along nerves, the endocrine system sends slow chemical signals through the blood. A gland releases its hormone into the bloodstream, the hormone circulates through the whole body, and only the tissues with matching receptors respond. The effects build slowly and last longer than a nerve impulse.

This is also why hormones are powerful in small doses. A tiny concentration in the blood can switch on growth, change how fast the body burns energy, or alter mood and reproduction. Doctors can measure hormone levels in blood, urine or saliva, and abnormal results often point to a gland making too much or too little.

The major endocrine glands

The main endocrine glands are the pituitary, pineal, thyroid, parathyroid, thymus and adrenal glands, plus hormone-making tissue in the pancreas, the ovaries in women and the testes in men. The hypothalamus, a small region of the brain, sits above the system and controls it, which is why the nervous and endocrine systems are often described together as the neuroendocrine system.

The pituitary, a pea-sized gland hanging below the hypothalamus, is called the master gland because its hormones direct several other glands. The thyroid, following pituitary instructions, sets the pace of metabolism: more thyroid hormone speeds up chemical activity in the body, less slows it down. The pancreas releases insulin, which lets the body regulate blood sugar, and the adrenals, sitting on top of the kidneys, make hormones for stress response and salt and water balance.

Feedback: how the body keeps hormones balanced

The system regulates itself through negative feedback, much like a thermostat. When the hypothalamus senses that a target gland's hormone has risen high enough, it signals the pituitary to stop stimulating that gland, and production falls. When levels drop too low, the signal switches back on.

This constant adjustment is called homeostasis, the body's way of holding its internal conditions steady while the outside world changes. When feedback fails, disorders follow: an overactive thyroid speeds the body up, an underactive one slows it down, and a pancreas that cannot make or use insulin properly leads to diabetes.

Why this matters for exams and health

For GK, the exam-ready points are the gland-hormone pairs: pituitary as master gland, thyroid for metabolism, pancreas (islets of Langerhans) for insulin and blood sugar, adrenals for stress and salt balance, and ovaries and testes for sex hormones. The pineal gland, which helps regulate sleep cycles, and the thymus, active in immune development, complete the classic list.

Hormone disorders are common exam and real-life examples of feedback gone wrong, from diabetes to thyroid disease, and they are diagnosed with laboratory tests rather than guesswork. This article gives general educational information only, not personal medical advice.

Editorial disclosure

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