Human Phys: Chapter 8: Hormones - draft 1

What is a hormone?

A hormone is a chemical messenger.

the four big criteria of a hormone are:

1. Made and secreted by a cell or group of cells

2. Secreted into the blood

3. Travels to a distant target

4. Works at a very low concentration

And most importantly:

The target cell must have the right receptor.

What do hormones control?

Hormones are especially important for long-term body functions like:

• metabolism

• temperature regulation

• water balance

• ion balance

• reproduction

• growth

• development

They can also cause faster responses depending on the hormone.

How can a hormone change a cell?

(There are 3 basic ways:)

A. Change enzyme activity

B. Change membrane transport

C. Change gene expression

ETG: Enzymes — Transport — Genes

A. Change enzyme activity

The hormone makes certain chemical reactions happen faster or slower.

B. Change membrane transport

The hormone changes what ions or molecules can enter or leave the cell.

Example idea:
glucose entering a cell

C. Change gene expression

The hormone changes which genes are being used.

Endocrine

Travels through blood to a distant target

Endo = distant

Paracrine

Acts on nearby cells

Para = neighbor

Autocrine

Acts back on the same cell that secreted it

Auto = self

Neurohormone

a hormone made by a neuron

So it is basically a nerve cell sending a chemical message into the blood.

Ectohormone

An ectohormone is a chemical signal released outside the body.

instead of sending a message inside your body, you send it into the outside world.

Pheromone

A pheromone is a type of ectohormone that affects another member of the same species.

Example:

Ants leave a chemical trail that basically says:

“Food is this way.”

Other ants smell it and follow.

That is a pheromone.

Hormones work in tiny amounts

Hormones are powerful because you do not need much of them.

Even a tiny amount can cause a big effect.

Think of food coloring:

One little drop can change a whole glass of water.

Hormones are kind of like that.

Hormones need receptors

A hormone only works if the target cell has the right receptor.

Best example:

hormone = key

receptor = lock

If the key does not fit the lock, nothing happens.

So even if a hormone reaches lots of cells, only the cells with the correct receptor respond.

One hormone can do different things in different cells

The same hormone can cause different effects depending on the cell.

Think of one teacher saying:

“Get ready.”

A basketball player might grab a ball.

A student might grab a notebook.

Same message, different response.

That is what can happen with hormones.

The cell's response depends on what kind of receptors and machinery it has.

Insulin example

Insulin does not do exactly the same thing everywhere.

In some tissues, it helps change:

• glucose transport

• glucose metabolism

In other tissues, it mainly changes enzyme activity.

The big point is:

Same hormone does not always mean same effect.

Cellular mechanism of action

What happens inside the cell after the hormone binds to its receptor.

So:

Hormone binds receptor → cell does something

That “something” is the mechanism of action.

Candidate hormone

A candidate hormone is basically:

“We think this might be a hormone, but we are not 100% sure yet.”

It has not met every rule clearly enough.

Growth factors

Growth factors help cells:

grow

divide

But many work only on nearby cells, so they do not always fit the classic hormone definition.

Think:

They act more like local messages than long-distance messages.

Cytokines

Cytokines are also chemical messengers.

They can act a lot like hormones, but scientists usually put them in a different group.

The main point from your textbook:

The line between “hormone” and “other chemical messenger” is sometimes blurry.

Berthold rooster experiment

This is basically the first big proof that glands can send messages through the blood.

He removed the roosters' testes.

The roosters became:

less aggressive

less sexual

had smaller combs

Then he put testes back in.

Those traits came back.

The important part:

The testes were not connected to nerves.

So the testes had to be releasing something into the blood.

That “something” was a hormone-type signal.