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Biology HL (Option H): Types of Hormones

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HL Biology (Option G): What is the definition of a hormone, what different types are there (with an example of each) and how do these differ in their modes of action?

A Hormone is defined as a chemical messenger secreted by endocrine glands into the blood and transported to specific target cells. You need to memorise all the parts of this definition off by heart!

Types of hormone include:

1. Steroid hormones such as Oestrogen and Testosterone

2. Peptide hormones such as Insulin, Glucagon and Anti-Diuretic Hormone (also known as Vasopressin)

3. Tyrosine derivative hormones such as Thyroxine (T4), Adrenaline and Noradrenaline

(Obviously there are other examples!)

Steroid hormones work by passing through the lipid bilayer of the cell membrane and travelling directly to the nucleus of the cell. Here they have a direct effect on genes by altering the pattern of gene expression (specifically, transcription).

You don't need to know this, but it might help you to remember how steroid hormones work if you know that steroids (synthetic versions which are given as a treatment for some diseases) often take a few days to have an effect. This is because they're altering gene expression directly and it takes a little while for the genes to be up-regulated or down-regulated in order to see the effects.

Peptide hormones do not enter the cell! Instead they work by binding to receptors on the outside of cells. Receptors are themselves glycoproteins. The hormones attach to the receptor which in turn activates a series of intracellular messengers. These messengers set off cascades of reactions which overall change the actions of the cell.

Again you don't need to know this, but I think it helps to remember the difference between steroid and peptide hormones - if you think that things like insulin, glucagon and ADH all need to have very rapid effects in order to maintain important things like blood sugar and blood volume, then you can't afford to spend a few days waiting for the patterns of gene transcription to change (as with steroid hormones). You need a much more instant reaction mediated by secondary messengers setting off cascades within the cell.

You only need to be able to distinguish between the actions of steroid and peptide hormones, so don't worry about the tyrosine derivative hormones (although for the record, they basically act just like the peptide hormones do).

Revision tip!

The best way I found to remember which hormones are of what type and their mode of action is as I described above. Think of steroid hormones as these slow acting things due to the fact they're altering gene transcription and the results take a while to see. Hormones which we don't need quickly and which have effects in lots of different places such as Oestrogen and Testosterone will belong to this group.

Peptide hormones are the speed machines with rapid secondary messengers that help us keep a very fine-tuned level of control over things like blood sugar with Insulin and Glucagon both rapidly released.

As for the Tyrosine-derivatives, perhaps just that Thyroxine and Tyrosine both start (almost) with Ty!

As ever, please ask any questions on this thread or in the Biology forum ;)

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