Hormones, adrenaline and blood glucose

Last time

Before we start: last time, in Control of body temperature, you learned these points. Here they are again on one card. Keep them in mind, because today builds on them.

Chemical messages

A sudden loud bang and your heart pounds, your breathing speeds up, and you feel ready to run. That is adrenaline, a hormone. Today: what hormones are, how adrenaline prepares you for action, and how insulin and glucagon keep your blood glucose steady.

Hormones

A hormone is a chemical substance, produced by a gland and carried by the blood, which alters the activity of one or more target organs. The glands that make hormones are called endocrine glands. Each hormone affects only its target organs, which have the right receptors.

Glands and hormones

Learn these four glands and their hormones. Adrenal glands make adrenaline, the pancreas makes insulin and glucagon, the testes make testosterone, and the ovaries make oestrogen.

Adrenaline

Adrenaline is released in frightening or stressful situations. It increases the heart rate and breathing rate, and widens the pupils. It increases the blood glucose concentration, giving muscles more glucose for respiration.

Nerves or hormones?

Here is the comparison. Nerves are fast and short-lived. Hormones are slower and longer-lasting. Nerves send electrical impulses; hormones are chemicals in the blood.

Homeostasis

Homeostasis is the maintenance of a constant internal environment. Blood glucose, body temperature and water content are all kept within narrow limits. It uses negative feedback: a change away from the normal level causes a response that brings it back.

Too much glucose

After a meal, blood glucose rises. The pancreas detects this and releases insulin. Insulin makes the liver and muscles take in glucose and convert it into glycogen, so the blood glucose falls.

Too little glucose

During exercise or when you have not eaten, blood glucose falls. The pancreas releases glucagon. Glucagon makes the liver convert glycogen back into glucose, so the blood glucose rises.

Type 1 diabetes

In type 1 diabetes, the pancreas does not make enough insulin. Blood glucose can rise very high, and glucose may appear in the urine. It is treated with insulin injections, a careful diet, and regular blood glucose tests.