How does the endocrine system work?

Nine small glands, from a pea under your brain to the islets in your pancreas, run your body by sending chemical messages in the blood. The hypothalamus, pituitary, pineal, thyroid, parathyroids, thymus, adrenals, pancreatic islets and ovaries or testes make more than 50 hormones.

Read how it works: How does the endocrine system work? · The history of the endocrine system · More boxes on Glassbox

Chapters in this interactive model

1. Glands that talk through your blood: Nine small glands, from your brain to your belly, run a chemical postal service.
2. A message for anyone with the right lock: Hormones reach every cell, but only cells with the matching receptor listen.
3. A thermostat in your head: The hypothalamus and pituitary switch glands on, and the glands’ own hormones switch them off.
4. Blood sugar, and a sudden scare: Insulin and glucagon keep your fuel steady; adrenaline and cortisol get you ready to run.
5. Hormones that grow you up: Growth hormone, thyroid hormone, puberty, melatonin, and the iodine in your salt.
6. When hormones go wrong: Diabetes, thyroid problems, goitre and growth disorders: what to notice, and why to see a doctor.