B1 Hormones

What are hormones?

Hormones are basically chemicals that are made and released by glands called endocrine glands. These messages go into the bloodstream where they cause certain parts of the body to do something. Different messages for different parts of the body.

So where are these endocrine glands then?





There are lots of them and they send chemical messages to specific target organs.

1. Pituitary gland releases anti-diuretic hormone which causes the kidneys to produce more concentrated urine. This is part of homeostasis which helps keep our water levels constant.
2. Adrenal gland makes the hormone adrenaline which speeds up the heartbeat.
3. The pancreas releases the hormone glucagon which raises blood glucose levels and also the hormone insulin which lowers blood glucose levels. This is a big topic which you will have to learn especially linked to diabetes Types 1 and 2.
4. The male testes release the hormone testosterone which causes the development of the male reproductive organs during puberty.
5. The female ovaries make the hormone oestrogen which causes the development of the female reproductive organs during puberty.

Now, let's get back to the the control of blood sugar levels.

You eat, in fact you may usually eat your lunch at break-time. 

Carbohydrates in your food are mainly digested into a type of sugar called glucose. So, eating carbohydrates (like bread, flour, cakes. potatoes etc) increase the glucose levels whereas exercise, in fact respiration uses up glucose so the blood sugar levels drop.

Note, energy stored in food is released in respiration. Respiration is not breathing!

So, all the time your glucose levels are going up and down depending on what you are doing. Homeostasis is keeping the internal environment stable - in this case it is to do with keeping the blood sugar levels the same.

Now, this topic is about hormones,
so it's basically a gland sending a chemical message to tell something else what to do.

It's the pancreas that makes the hormones

.

The 2 hormones are called insulin and glucagon.

The target organ is the liver.

The pancreas then is telling the liver what to do by sending it 2 messages.

1. Insulin tells the liver that there is too much glucose in the blood so it has to remove some. The liver takes the glucose out and stores it as glycogen.
2. Glucagon tells the liver that there is not enough glucose in the blood (the glucose has gon!) so the liver breaks down the glycogen stored earlier back into glucose. 

B1 Responding to stimuli

When the brain gets impulses from the receptor cells it co-ordinates a response. What this means is that the brain sends impulses to effectors and these do something. Effectors could be muscles or glands. Like your brain could send an impulse to your sweat glands to make sweat to cool you down. So the effectors do something - they have an effect.

Right now, lets get the basics sorted.

The neurones that receive impulses from receptor cells are called sensory neurones.

That makes sense doesn't it - the sensory neurone senses things because it is receiving information.

The neuron in the diagram above has lots of dendrites - these are to receive the information. This information is passed along the neurone as an impulse. The impulse travels along the neurone along the axon. Remember, the myelin sheath is a fatty layer that insulates the axon so the impulse moves faster.

It does not protect the axon!

The neurones that take impulses to effectors are called motor neurones.

Effectors are the things that make an effect - they could be the muscles.

Motor neurones do not have a dendron, the dendrites are on the cell body.

Relay neurones are short neurones that join up the motor neurones and the sensory neurones. These neurones are found in the spinal cord and the brain.

Now, so you've got all these neurones joining with each other. Well, there is a bit of a problem. Where the neurones connect with each other there is a small gap called a synapse. Impuses are transmitted across the gaps in synapses by chemicals called neurotransmitters. Stimulants like caffeine speed up the neurotransmission of nerve impuses across the synapses.


The synapse actually slows down the impulse but they are useful because as the chemicals are only released from the axon endings the impulse can only go in one direction. Botox injections stop impulses from the motor neurones reaching the muscle cells. This stops the muscle cells working so the skin doesn't wrinkle.

The reflex arc - learn it!
The reflex arc lets you do things without thinking. The are responses that are very quick and automatic and they protect you. They use neurone pathways called reflex arcs where a sensory neurone directly controls a motor neurone. Reflex arcs bypass the brain so you don't decide what to do. Reflex arcs make you automatically blink if something gets in your eye or makes your pupils in your eyes get smaller in bright light.

B1 Skin and receptor cells

Your skin can detect many different stimuli, including touch, heat, cold, pain and pressure. Remembering THCPP might help you learn the different stimuli.

For each of these stimuli you have different receptor cells. The cells are adapted to become specialised cells to detect different things.

B1 Sensitivity

Are you a sensitive person? You are - we all are!

We all have sense organs which detect changes inside and outside the body. This is not just your five senses, sight, smell, hearing, taste and touch (SSHTT) - but other things like heat and cold, pain etc.

Now then you sensitive person, anything that you are sensitive to is called a stimulus. It stimulates you. You detect the stimulus because your sense organs contain receptor cells. So, back to homeostasis, your skin has receptor cells to detect changes in temperature. Hopefully you have worked out that this leading up to the nervous system.

These receptor cells make electrical signals called impulses. These usually go to the brain, unless it is a reflex action,. The brain then sends impulses to other organs or muscles to make the changes that the body needs to stay the same - back to homeostasis again eh?!

So what happens. Well the electrical impulses travel along neurones (or nerve cells). This movement of impulses is called neurotransmission. This links up nicely to how drugs called stimulants speed up the neurotransmissions. Now if you look at the diagram below, it has a cell body and long extension bits that look like tentacles (but they are not). These are called dendrites and they receive impulses from the receptor cells or other neurones. The impulse then moves along the dendron to the axon. Here it then goes to other neurones and so on.

So, the receptor cells receive the impulse and sends it along the axon. If the receptor cells are damaged no signal is got so no impulse is sent.

Remember that you are a big organism and there are millions and millions of neurones. Groups or bundles of these neurones are packed together into nerves. We are vertebrates and so we have an organ called the spinal cord. The spinal cord contains many nerves packed together and this connects to the brain. The brain and the spinal cord together make up the central nervous system (CNS) which controls your body.

B1 Homeostasis

This is a big topic and lends itself to questions worth a lot of marks.

So, what is homeostasis?

Well the, homeostasis is where the conditions inside the body are kept the same. It is all about keeping the internal environment the same regardless of what is happening.

There are 3 main things that you need to know how they are controlled.

1. Water - osmoregulation.
2. Temperature - thermoregulation.
3. Glucose - Blood glucose regulation.

Basically, water is to do with your sweat glands, kidneys and urine. Temperature is to do with your skin, sweating and blood vessels and glucose is about your pancreas and liver.

But, and it's a big but, you have to learn the various diagrams that go along with these 3 things to control. So let's start with water control.

You lose water by breathing and sweating. You also lose water in urine. If you drink too much water then your kidneys will produce more dilute urine - obviously. If you do not drink enough water then you will produce less urine and your brain tells you that you are thirsty. Again, common sense really.

Now, thermoregulation is a big topic to learn and you must include the diagrams that show what the skin does when you are hot or cold. Your body works best at 370C which is the optimum temperature for many chemical reactions and enzymes to work. Your body under the control of the hypothalamus which is a small part of the brain that monitors temperature.

So, what happens then?

When you are cold:

1. The hypothalamus causes muscles to shiver. This makes heat which warms you up.
2. The hypothalamus also causes erector muscles in the skins dermis to contract. This causes the skin hairs to stand up. This traps a layer of air for insulation. Note: it traps air not eat!
3. The hypothalamus constricts the blood vessels called capillaries near the skins surface. This means that less warm blood is near the surface so you lose less heat to the air. The fancy word for this is vasoconstriction.

When you are warm:

1. The hypothalamus causes sweating. You use heat to evaporate the sweat and so you cool down.
2. The hypothalamus increases the amount of blood flow to the blood vessels - capillaries - near the surface of the skin. I does this by making the blood vessels wider, it dilates them, so more warm blood flows near the surface of the skin so more heat is lost to the air - so you cool down. This is called vasodilation.

                                                Vasoconstriction                  Vasodilation


Diagram of the skin

Note where the sweat gland, capillary and hair is.

Negative feedback.

The control of body temperature is an example of negative feedback. This means that if you get too hot your body will work to make it colder, and if your are too cold then your body will make it warmer. All this, remember, is under the control of the hypothalamus and it is happening all the time without you thinking about it.