Communication and homeostasis

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Regulation of insulin levels

The control of insulin secretion

The cell membranes of beta cells contain both calcium ion channels and potassium ion channels

The potassium ion channels are normally open and the calcium ion channels are normally closed. potassium ions diffuse out of the cell making the inside of the cell more negative. the potential difference of the membrane is about -70mV

When glucose concentrations outside the cellar high, glucose molecules diffuse into the cell

The glucose is quickly used in metabolism to produce ATP

The extra ATP causes the potassium channels to close

The potassium can no longer diffuse out and this alters the potential difference across the cell membrane - it becomes less native inside

This change in potential difference opens the calcium ion channels

Calcium ions enter the cell and cause the secretion of insulin by making the vesicles continuing insulin move to the cell surface membrane and fuse with it, releasing insulin by exocytosis.

Diabetes Mellitus - disease in which the body is nob longer able to control its blood glucose concentration which can lead to high concentrations (hyperglycaemia) or low concentrations (hypoglycaemia) of blood glucose.

Type I

Aka insulin dependent diabetes. it is juvenile onset diabetes because it starts in childhood. it is thought to be the result of an autoimmune response in which the body's own immune system attacks the b cells and destroys them. It may also be a result from a viral attack. the body is no longer able to manufacture sufficient insulin and cannot store excess glucose as glycogen.

this is treated using insulin injections. The BGC must be closely monitored and the correct dose of insulin most be correctly administered to ensure a stable glucose concentration.

Type II

This is where people's responsiveness to insulin declines due to the specific receptors on the surface of the liver and muscle cells decline and lose their ability to respond to insulin in the blood. The levels of insulin secreted by b cells may also decline.

This is treated by careful monitoring and control of diet.

The source of insulin

It can be extracted from pigs but more recently it can be produced by a bacteria that have been genetically engineered to manufacture human insulin.

Advantages:

it is an exact copy of human insulin therefore it is faster acting and more effective

less chance of rejection due to an immune response

there is a lower risk of infection

it is cheaper to manufacture

the manufacturing process is more adaptable to demand

some people are less likely to have moral objections to using the insulin produced from bacteria than the ones extracted from animals

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Control of heart rate in humans

The requirements of the cell vary according to the level of their activity. When you are active your muscle cells need more oxygen and glucose and your heart muscle cells need more oxygen and fatty acids. These cells also need to remove more carbon dioxide. Therefore the heart needs to adapt to meet the requirements of the body.

How the heart adapts to supply more oxygen and glucose:

increase in the number of beats per minute - increase heart rate

increase the strength of its contractions

increase the stroke volume

Control of heart rate:

The heart muscle is myogenic which means that the muscle tissue can initiate its own contractions.

The heart has its own pacemaker called the sinoatrial node (SAN). this is a region of tissue that can initiate an action potential which travel as a wave of excitation over the atria walls thought the AVN and down the Purkyne fibres to the ventricles, causing them to contract.

The heart is supplied by nerves from the medulla oblongata of the brain which connect to the SAN. They can affect the frequency of the contractions. Action potentials sent down the accelerator nerve increase the heart rate. Action potentials sent down the vagus nerve reduce the heart rate.

The heart muscle responds to the presence of the hormone adrenaline in the blood.

Interactions between control mechanisms

Under resting conditions the heart rate is controlled by the SAN. this has a set frequency at which it initiates waves of excitation. The frequency of these excitation waves can be controlled by the cardiovascular centre in the medulla oblongata.

Factors:

Movement of the limbs is detected by stretch receptors in the muscles. These send impulses to the cardiovascular centre informing it that extra oxygen may soon be needed. This tends to increase heart rate.

when muscles produce more carbon dioxide, some reacts with the the water in the blood plasma and reduces pH. The change in pH is detected by chemoreceptors in the carotid arteries, the aorta and the brain. the chemoreceptors send impulses to the cardiovascular centre, which increases heart rate, which increases heart rate.

when carbon dioxide concentration in the blood falls, it reduces the activity of the accelerator pathway. Therefore the heart rate declines.

adrenaline is secreted in response to stress, shock anticipation or excitement. The presence of adrenaline in the blood increases the heart rate. This helps the body prepare for activity.

blood pressure is monitored by stretch receptors in the walls of the carotid sinus (small swelling in the carotid artery). If the blood pressure rises too high e.g. during vigorous exercise, the stretch receptors send signals to the cardiovascular centre. This responds by reducing the heart rate.

Cardiovascular centre - a specific region of the medulla oblongata that receives sensory inputs about levels of physical activity, blood carbon dioxide concentration and blood pressure. it sends nerve impulses to the SAN in the heart to alter the frequency of excitation waves.