THE ENDOCRINE

SYSTEM

The endocrine system is another communication system. It uses

blood circulation to transmit its signals. The signals released by the

endocrine glands directly into the blood are called hormones.

Endocrine gland secretes hormones directly into the blood

and have no ducts

Exocrine gland secretes molecules into a duct which carries

them to where they are used

TARGET CELLS

Target cells are those that possess a specific receptor on their plasma

membrane. The shape of the receptor is complementary to the shape

of the hormone molecule. Many similar cells group together to form

target tissues.

HORMONES

There are two types of hormones

Protein and Peptide:

(and derivatives of amino acids)

Examples: adrenaline, insulin,

glucagon.

These are not soluble in the

phospholipid membrane and so

don’t enter the cell

Steroid:

Examples: sex hormones

These enter the cell and

have a direct effect on the

DNA in the nucleus

ADRENALINE

Adrenaline is an amino acid derivative and so can’t enter the target

cell. So, it may cause an effect inside the cell without entering it.

Adenyl Cyclase is the enzyme associated with the receptor for

adrenaline. It is found on the inside of the cell surface membrane.

THE ACTION OF ADRENALINE

1. Adrenaline (first messenger) in the blood binds to its specific receptor on

the cell surface membrane.

2. When it binds to the receptor, it activates adenyl cyclase.

3. The adenyl cyclase converts ATP to cyclic AMP (second messenger)

4. The cAMP then causes an effect inside the cell by activating enzyme action

THE ADRENAL

MEDULLA

This is found in the centre of the gland. The cells in it release, after manufacturing,

adrenaline in response to stress (e.g. pain and shock) to prepare the body for activity

Some Effects…

Dilate pupils

Body hair erects

Inhibit gut action

Increase mental awareness

Increase heart rate

THE ADRENAL CORTEX

This uses cholesterol to produce certain steroid hormones.

Roles in the body…

Mineralocorticoids: (e.g. adolsterone) to help control the

concentration of sodium and potassium in the blood

Glucocorticoids: (e.g. cortisol) to help control the metabolism of

carbohydrates and proteins in the liver