Lesson 1 of 11 · 6 min

Endocrine glands and hormones

NCERT §19 (opening text) and §19.1

On the morning of her biology board exam, Meher's hands are cold and her heart is racing, though no nerve told her fingers to go cold. Something in her blood is carrying the message. What is it?

The story this chapter follows: Meher's exam day

Meher sits her biology board exam today. She wakes after a late night, skips breakfast, freezes at the first question, recovers, and has rice and dal at lunch with her Nani, who has diabetes and takes insulin. Behind every one of these moments is a hormone carried in her blood, and this chapter follows each one to its gland.

The lesson in notes

In short

The neural system gives point-to-point coordination that is quick but does not last. Nerve fibres do not reach every cell, and cell functions need regulating all the time, so a second kind of coordination is needed; hormones provide it.

The neural and endocrine systems work together to coordinate and regulate the body's physiological functions.

Endocrine glands have no ducts, so they are called ductless glands. What they secrete is called a hormone.

The classical definition: a hormone is a chemical made by an endocrine gland, released into the blood and carried to a target organ some distance away.

The current definition is broader: hormones are non-nutrient chemicals, made in trace amounts, that carry messages between cells. It takes in many molecules that do not come from organised endocrine glands.

Invertebrates have very simple endocrine systems with only a few hormones, while in vertebrates a large number of chemicals act as hormones.