The effects of the hormones Insulin, Glucagon, T3 and T4 on Metabolism.

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TAQ 1.

a) & b)

Brain and spinal cord The central nervous system (CNS). This is where every action and reaction is processed via information received through the nervous system.

The brain consists of three major areas, the cerebral cortex which is divided in to two lobes and deals with emotions, perception, memory and, via the limbic system, primitive cognitive functions such as the fear and reward systems including the control of sex.

The spinal cord contains fibres that carry nerve signals from around the body to the brain for processing. It is what links the brain to the rest of the body. It uses a 31 pairs of spinal nerves that branch out to the rest of the body and carries the nerve signals and impulses via these branches.

Somatic System Responsible for voluntary actions e.g. lifting a book. It contains all the nerves that deal with sensory input and is responsible for carrying those signals to the CNS.

The somatic system carries signals to the brain for the brain to send signals, via the spinal cord, to the groups of muscles that will carry out the action etc. If the item is too heavy it will carry the signal to quickly put the item down.

Autonomic System The area of the nervous system maintains the constant conditions within the body i.e. homeostasis. It deals with sweating, breathing, control of the bowels and heart rate. It uses various hormones to regulate the body and the majority of its functions are dealt with without consciousness.

Sympathetic System – The main function is tom make adjustments to the body when we need energy or when we are in danger. For example, when threatened with danger, this system will make adjustments so that the pupil dilates to help us see better, causes the airways to open and dilate allowing more oxygen in to the body etc.

Parasympathetic System Contradicts the sympathetic system. This enhances actions such as digestion to build resources within the body when in “safe” situations.

TAQ 2.

Sensory neuron.

These carry signals from the outside world via eyes, ears, tongue, nose, skin to the brain via the spinal cord.

Using a variety of different receptors e.g. thremoceptors (cold and warmth), nocireceptors (pain and damage) the appropriate nerve impulses are triggered allowing the brain to respond appropriately using the nerve impulses.

Relay neurones (or intraneurons).

These carry messages from one part of the CNS to another – i.e. between the brain and spinal cord.

Relay neurons are neither sensory nor motor, but act as a link between the two.

The relay neurons are responsible for sending signals direct to the effector neurones during reflex action, this message never actually reaches the brain for a response.

Motor neurones.

These carry signals from the CNS to effectors. They originate from the CNS and project their axons to the target tissues, which are always skeletal muscle or glands. This means motor neurons axons terminate in muscle which causes movement.

Diagram of the different neurons.

TAQ 3.


When the nerves and neurons are stimulated, they undergo a chemical change which causes a small electrical current – this is known as a nerve impulse. The nerve impulse travels along the dendrites or axons to the synapse.

When a cell is unstimulated or resting it is in a steady sate of polarisation. This means there is a different electrical charge inside and outside the cell.

This polarisation is maintained by keeping an excess of positive potassium ions on the outside of the cell and an excess of positive sodium ions on the inside. This produces a resting membrane potential of -70 millivolts.

When the nerve cell or neuron is stimulated, via the senses, it causes a change in the membrane to occur. The membrane allows potassium ions to flow into the neuron. This causes a state of depolarisation i.e. the polarity inside changes because there are too many positive ions inside the cell and the cell is “action potential” which produces a current of +30 millivolts. This change in the charge in that part of the nerve causes a reaction along the nerve.

The reaction it causes is that the cell needs to re-establish the polarisation of the cell – this is referred to as repolarisation. The cell needs to “pump” out some of the positive ions. This action means that when restoring the charge balance at that point of the membrane it stimulates the next section of membrane. This in effect causes a ripple effect along the membrane and a change in the polarity along the length of the nerve. As the ripple effect is causing the cell to depolarise and enter a state of action ready the electrical impulse is carried along as the ripple effect travels the length of the nerve.


As the neurons are not tightly packed there is a tiny gap between them called a “synapse”.


As the neurons do not touch, the electrical impulse cannot travel from one to the other. They are separated by a gap called a synapse.

When the nerve impulse reaches the end of the dendrite or axon they come to the terminal button. The impulse causes pockets within the terminal button to travel to the end of the synapse, burst and release chemicals.

These pockets are called vesicles and the chemicals that they release are called neurotransmitters, these can either be quick acting or slow acting. The main neurotransmitter is Acetyl Choline (Ach) which is normally used within the muscle systems.

When the vesicles release the neurotransmitters they travel across the synaptic cleft to the adjacent synaptic membrane. The synaptic membrane has receptors on it that detect molecules from the neurotransmitter and match them. The combination of the receptors and the molecules, albeit briefly, causes another electro chemical impulse and if there are enough of these impulses then they will travel along that nerve setting off the process in that nerve.

Synapses can either be “excitatory” causing the receiving neuron to fire or “inhibitory” which instructs the neuron not to fire. However, as each neuron as between 1,000 and 10,000 synapses, the decision is dependent on the combined effect of all the receiving synapses.

To ensure that the neurotransmitter does not continue to cause the same excitery response over and over, they are split up using another chemical. In the most common neurotransmitter, Acetyl Choline, the chemical is cholinesterase. The cholinesterase causes the neurotransmitter chemical to be broken up so it can be absorbed by the presynaptic membrane and back in to the vesicles.

TAQ 4.

When the body has to respond quickly to protect itself it is due to a receptor being excited. In the diagram below, this is demonstrated as someone having a nail in their hand.

The simplest way to describe this is that the stimulus is detected by the receptor cells and transmitted to the central nervous system (CNS) via the sensory neurons.

It is at this point that the signal is recognised by the intern-neurons in the spinal cord as a threat to the body and therefore stimulates a motor neuron that sends a signal to the effector – in this case the muscle to contract thereby drawing the hand away.

A signal is still transmitted to the brain for learning purposes as the brain cannot react fast enough to protect the body – unlike when carrying our normal functions when the brain is able to “consider” the information the body has assimilated.

nervous system reflex arc

TAQ 5.

Name of endocrine gland.


Hormones released.

Function(s) of hormones released.



  1. Adrenocorticotrophic;
  2. Thyroid-stimulating hormone;
  3. Luteinising;
  4. Follicle-stimulating;
  5. Prolactin;
  6. Growth hormone;
  7. Melanocyte-stimulating;
  8. Anti-diuretic;
  9. Oxytocin.
  1. Stimulates the adrenal gland;
  1. Stimulates the thyroid gland;
  1. Stimulates the testes to produce testosterone in men. In women is stimulates the ovaries in the menstrual cycle to produce hormones and release the egg;
  1. Regulates functions of the ovaries and testes. Essential for the pubertal development;
  1. Stimulates the breasts to produce milk;
  1. Stimulates growth and repair;
  1. Affects mood;
  1. Controls the blood fluid and mineral levels affecting water retention by the kidneys;
  1. Affects uterine contractions in pregnancy and birth.




Controls metabolism including the maintenance of body weight, the rate energy is used and the heart rate.




Regulates the amount of calcium in the blood and within the bones. Can be located on the surface of the thyroid gland – shares the same blood supply as the thyroid gland.




Promotes hormones involved in the development of white blood cell production (T cells) that are part of the immune system.


Top of kidney.



Acts as a steroid and maintains metabolism including blood sugar levels, acting as an anti-inflammatory, controlling salt and water balance.

Prepares the body in emergencies (fight or flight). Key actions of include increasing the heart rate, blood pressure, expanding the air passages of the lungs, enlarging the pupil in the eye, redistributing blood to the muscles and altering the body’s metabolism, so as to maximise blood glucose levels.





Regulates blood sugar levels. Insulin converts excess glucose in to glycogen in the liver and glucagon converts the glycogen back to glucose.





Regulates menstrual cycle and ovulation.

Progesterone is essential to support the early stages of pregnancy once fertilisation has occurred.


Testes (Scrotum).


Production of sperm and secondary sexual characteristics in men such as facial hair, deepening of the voice, bone and muscle density i.e. strength.

TAQ 6.

The effects of Insulin, Glucagon, T3 and T4 on the Metabolism.

Metabolism is the term we can use that covers the breaking down, storage and speed at which we digest our food and turn it in to energy – we either use this immediately or we store it within our bodies.

When we take in food, our digestive system breaks down our food using enzymes, turning it in to amino acids, fatty acids and sugars.

Whether we store this food or use it as needed is dependent on chemical reactions within our body.

As we eat our food and digest it, the raised glucose level in our blood triggers a reaction in the pancreas that causes it to release the hormone insulin. The increase in our insulin levels causes our cells to increase their anabolic activity, anabolism or constructive metabolism. This activity causes excess glucose to be stored within our liver as glycogen, ready to be converted back to glucose when the body needs it or to simply be used in our cell maintenance and maintenance of our body tissues.

Anabolism involves the small molecules being changed in to larger, more complex molecules of carbohydrate, protein and fat.

The thyroid gland is responsible for determining how much energy we need to keep alive – this is known as the basal metabolic rate and is usually around 60% of the energy we consume via our food. The thyroid controls our metabolism using the hormone thyroxin (T4) and triiodothyronine (T3)– the higher the levels of these hormones the quicker the metabolism burns calories. The levels of T3 and T4 in our blood stream are control from the hypothalamus and pituitary gland as they release the thyroid stimulating hormone.

When our glucose levels drop or we have an increased need for energy, the pancreas detects this change or need and releases the hormone glucagon into the blood system. This causes a reaction to occur in the liver where the stored glucose, in the form of glycogen, is broken down and converted back to glucose – which is the bodies most adaptable and the most readily available source of energy. This process involves the breaking down of the larger cells that have been created in the anabolism process to release the energy.

In the simplest terms, anabolism is responsible for the storage of excess energy and catabolism is responsible for converting the stored energy back in to a useable form i.e. glucose when the body needs more energy, either for maintenance of our cells and body tissues (using anabolism) or additional energy due to increased activites etc.

All of the hormones are inter dependant one each other within the endocrine system – if there is a deficiency in the ability to effectively control the hormone levels then this can lead to difficulty in the ability to store unused energy and therefore potential catabolism of body tissues, muscle etc. to release energy when needed. This can therefore cause problems with an individual’s wellbeing and health.

TAQ 7.

The Structure and Function of the Eye and Ear.

We use our eyes and ear as part of our sensory ability – the others are the nose –smell, tongue – taste and the last being touch. All of these senses help the body assimilate, accommodate and adapt to our environment.

The eye is responsible for the majority of information the brain receives. The eye is basically a sphere that that takes in light information and converts this in to a nerve signal that is sent to the brain and is full of a jelly like substance called aqueous humour that nourishes the eye.

The first stage of that process is light rays enter the front of the eye via the cornea. This is the domed transparent part at the front of the eye and refracts, bends, the rays slightly. Sitting underneath the cornea is the pupil that contains the amount of light that enters the eyeball – it does this by contracting or relaxing the iris. The iris is the coloured part of the eye.

Once the light rays have passed in to the eye, the lens then changes shape to enable the “image” to be focused on to the back of the eye – the retina. The lens is able to change shape to fine tune the rays that have already been refracted by the cornea, a process known as “accommodation”. The lens changes shape by using the ciliary muscles. If the object is close, the ciliary muscle contracts causing the lens to become thicker. If the object is in the distance, then the muscle relaxes causing the lens to become flatter and thinner. This all helps “accommodate” the image within the eyeball and focus it on to the retina.

The region of the retina where the light rays are focused is called the fovea. The fovea has a highly concentrated covering of light sensitive cells called cones. Cones are responsible for distinguishing the fine detail of an image and are responsible for the colour of that image as they are sensitive to colour. As you move away from the centre of the visual field, the fovea has fewer cones but is covered with rods. Rods are sensitive to black and white and operate in lower light than cones, therefore allowing us to see when the lighting is poor, but in a monochrome fashion.

At the back of the retina is the optic nerve which conveys the nerve signals to the brain where the image is received.

Each eye transmits a slightly different aspect or position of an image, this helps the brain interpret depth and distance of that image.

The ear is responsible for two main functions which are hearing and balance. To understand how we hear, we first need to understand that sound is the vibration of air molecules that can vary in frequency and amplitude.

Sound enters the ear through the pinna, this is the large flap of skin and cartilage that helps direct the sound in to the outer ear. The sound wave travels down the ear canal and causes vibrations on the tympanic membrane, which is commonly referred to as the ear drum.

As the ear drum vibrates, it causes three tiny bones behind the ear drum to also vibrate. These bones are known as the ossicles. The first of these bones, the malleus, is attached to the ear drum, the second bone is called incus and the third is the stapes.

The way the ossicles are connected causes the amplification of the sound which is converted into electrical impulses that is transmitted to the middle ear to the cochlea. The cochlea is surrounded, inside and out, by a fluid that is made to vibrate by the stapes.

The cochlea is made up of a series of fluid filled tubes that have fibres running the length of the tubes. When these fibres resonate the ganglia become excited, the corti translates this stimulation along the auditory nerve to the brain.

Our balance is also controlled from the inner ear via two small organs called the utriculus and the semicircular canal. The utriculus senses tilting motions and is responsible for keeping us upright whilst the semicircular canal senses twisting movements and helps keep our balance when twisting.

Each of the semicircular canals are at right angles to each other and are filled with a jelly like fluid (endolymph) and are lined with fine hairs inside the cupula. As we move our head, the jelly like fluid lags behind slightly and then swirls past the cupula moves causing fine hairs inside to be pulled and triggering the nerve signals.

These signals are then sent to the brain that signals the actions necessary to maintain our balance.


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