Hormones in Humans (Cambridge O Level Biology)

What is a Hormone?

• A hormone is a chemical substance produced by a gland and carried by the blood
• The hormone 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

The endocrine system diagram

The endocrine glands secrete hormones into the blood

 Important hormones in the human body table

Hormone	Source	Effect
Adrenaline	Adrenal glands	Increases heart and breathing rate, dilates pupils
Insulin	Pancreas	Lowers blood glucose levels
Glucagon	Pancreas	Raises blood glucose levels
Testosterone	Testes	Male sex hormone that develops secondary male sexual characteristics
Oestrogen	Ovaries	Female sex hormone that develops secondary female sexual characteristics
Progesterone	Ovaries	Female sex hormone that plays a role in the menstrual cycle
LH	The pituitary gland	Female sex hormone that plays a role in the menstrual cycle
FSH	The pituitary gland	Female sex hormone that plays a role in the menstrual cycle

Transport around the body

• 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. 

Hormones travel in the blood to target organs