Hormones

In your body many organs have to work together even though they lie far apart. To make this work the body sends messages. Some of them travel as hormones through the blood. A hormone is a tiny messenger substance: it tells a cell what to do, even when the sender sits in a completely different part of the body.

Glands as senders

Hormones are made in special organs called glands. Examples are the thyroid gland in the neck and the pancreas behind the stomach. A gland releases its hormone directly into the blood. From there it spreads through the whole body and also reaches distant organs.

The matching receiver

Even though a hormone is everywhere in the blood, not all cells react to it. Only cells with the matching receiver take up the message. The hormone is the key, the receiver is the lock, and a key fits only one particular lock. Experts call this receiver a receptor. That is why a single hormone acts on just the right organs.

A control loop for blood sugar

The sugar in the blood is measured in milligrams per deciliter, mg/dl for short. Before a meal it sits at about 70 to 100 mg/dl, and after eating it rises. The pancreas notices the rise and releases the hormone insulin. Insulin makes the cells take up sugar from the blood, so the value drops again. If the sugar is too low, the same gland releases the hormone glucagon, which works in the opposite direction. This way the two hormones keep blood sugar in a good range.

Always in balance

A control loop works like a scale that balances itself. If a value is too high, the body slows it down, if it is too low, the body pushes it up. This keeps many things in the body stable: blood sugar, the amount of water, and even your growth are partly steered by hormones.