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Hormones are a diverse group of compounds that act as an intercellular messengers and regulate cell function.

So how do they work

Hormones are produced by cells and transported through the internal transport system (blood stream). They affect specific cells and alter specific biochemical reactions within these cells.

As hormones are spread throughout the body, only cells with specific receptors are effected.

Hormones can either pass through the plasma membrane to the cell (directly) or interact with receptors on the plasma membrane (indirectly).


 A key difference between the nervous and endocrine systems is the speed of the reactions. Unlike the nervous system, hormonal effects:

- Are slow

- Are longer in duration

- And can be widely distributed throughout the body.


 Hormonal communication is specific for two reasons:

1. Only a particular stimuli will affect a specific group of hormone-secreting cells.

2. Hormones only act on cell that possess specific receptors.

Fatty acids:

o Small, lipid soluble and able to pass through the cellular membranes.

o They pass into the cytoplasm of the cell, binding to specific receptors molecules. The signal continues into the nucleus where they act directly on the DNA.

o Examples are: Testosterone and Oestrogen

Amino acids:

o Water-soluble and cannot pass through the cell membrane.

o They act by binding to the receptors on the cell membrane, triggering a physiological response within the cell.

o Examples are: adrenaline and growth hormones.

Types of hormones

Some hormones may have different effects in different cells. For example epinephrine (adrenaline) produces a different response in smooth muscles compared to the liver cells.

In liver cells epinephrine causes a release of glucose, however in smooth muscle cell it causes them to relax. This is because there are different secondary molecules within the cell.

Click here to continue onto the endocrine system

As you can see in the animation to the left, the hormone attaches to a receptor on the surface of the cell.

It then triggers a reaction, stimulating another receptor within the cell, which then causes an effect in the cell.

This method of chain signalling is called signal transduction.

Bellow is a video of signal transduction

Click here to continue onto pheromones

Click here for a test on hormones and the endocrine system

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