- A hormone is a chemical substance produced by a gland and carried by the blood, which alters the activity of one or more specific target organs i.e. they are chemicals which transmit information from one part of the organism to another and bring about a change
- The glands that produce hormones in animals are known collectively as the endocrine system
Table of endocrine hormones
- Endocrine glands have a good blood supply as when they make hormones they need to get them into the bloodstream (specifically the blood plasma) as soon as possible so they can travel around the body to the target organs to bring about the response
- Hormones only affect cells with target receptors that the hormone can bind to.
- These are either found on the cell membrane, or inside cells.
- Receptors have to be complementary to hormones for there to be an effect.
- The liver regulates levels of hormones in the blood; transforming or breaking down any that are in excess.
Only cells with complementary receptors can bind with and respond to the hormone
Hormones v's nervous impulses
- Hormones are used to control functions that do not need instant responses
- Compared to the nervous system the effects of hormones are slower but they act for longer
Table to compare responses of the nervous and endocrine system
You will come across hormones at various points throughout the course, so remember to refer back to what you have learnt here about hormonal action as it will help you understand their effects