(1) What are hormones?

A hormone can be defined as a chemical substance, produced by a gland and carried by the blood, which alters the activity of one or more specific target organs

Hormones are produced in the endocrine gland system and are transported by the blood to their target cells, tissues or organs

Many process within the body are coordinated and controlled by chemical substances called hormones.

You can think of hormones as chemical messengers sent around the bloodstream.

Hormones are often quite large organic molecules.

Hormones and the nervous system send information around the body.

Hormones, being directly released into the blood, are quite rapidly carried to all parts of the body BUT only affect the function of particular cells, tissue or organs - the 'targets''.

Hormones, in acting as 'chemical messages', trigger particular biochemical reactions in various types of tissue and organs.

Hormones control functions in cells, tissue and organs that need constant adjustment and their effect is relatively long-lasting compared to eg the nervous responses of a reflex arc.

The activated cells are called 'target cells' and have a chemical receptor that responds to the hormone - the hormones work on effectors.

You should appreciate that the nervous system and hormones enable us to respond to external changes and also help us to control conditions inside our bodies.

BUT, unlike the nervous system, the hormone response times are slower e.g. minutes or hours, an exception is adrenaline , which is the fastest acting hormone response.

Reminder: Homeostasis the function of self-regulating processes by which biological systems (organisms) tend to maintain physical and chemical stability while adjusting to conditions that are optimal for survival i.e. counteracting unfavourable conditions. These process can involve hormones secreted from the glands of the endocrine system.

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Summary of learning objectives and key words or phrases

Be able to describe and explain what hormones are and what do they do?

Be able to define and describe the function of hormones.

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