Insulin

Insulin brings about effects that reduce the blood glucose concentration. If blood glucose concentration is too high then insulin is released from beta cells. However, if the blood glucose concentration drops too low it is important that insulin secretion stops.

1. The cell membrane of Beta cells contain both calcium ion channels and potassium ion channels

1. 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; at rest the potential difference across the cell membrane is -70mV

1. When glucose concentrations outside the cell are high, glucose molecules diffuse into the cell.

1. The glucose is quickly used in metabolism to produce ATP

1. The extra ATP causes the potassium channels to close

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

1. This change in potential difference opens the calcium ion channels.

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

Diabetes Mellitus is a disease in which blood glucose concentrations cannot be controlled effectively.

It is thought to be the result of an autoimmune response in which the body’s own immune system attacks the beta cells and destroys them. It may also result from a viral attack. The body is no longer able to manufacture sufficient insulin and cannot store excess glucose as glycogen.

A person with type 2 diabetes can still produce insulin. However, as people age, their responsiveness to insulin declines. This is probably because the specific receptors on the surface of the liver and muscle cells lose their ability to respond to the insulin in the blood. The levels of insulin secreted by the beta cells may also decline. It is thought that anyone who lives long enough will eventually become diabetic . However, certain factors may bring it on earlier

• Obesity
• A diet high in sugars, particularly refined sugars
• Being Asian or Afron Caribbean origin
• Family history

• Type 2 diabetes is usually treated by careful monitoring and control of the diet. Also insulin injections.
• Type one diabetes is treated using insulin injections. The blood glucose concentration must be monitored and the correct does on insulin must be administered to ensure that the glucose concentration remains fairly stable.

• The heart pumps blood around the circulatory system
• Blood supplies the tissue with oxygen and nutrients
• It also removes waste products
• The heart must adapt to meet the requirements of the body

1. Increase the number of beats per minute
2. increase the strength of its contractions
3. increase the stroke volume

• The heart rate is myogenic- the muscle tissue can  initiate its own contractions
• The heart contains its own pacemaker called the sinoatrial node- this is a region of tissue which can initiate an action potential which travels as a wave of excitation over the atria walls, through the atrioventricular node 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. These nerves connect to the SAN. These do not initiate a contraction, but 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.

The heart rate must interact in a coordinated way to ensure that the heart beats at the most appropriate rate. There are many factors that affect the heart rate.

     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 we exercise the muscle produces more carbon dioxide. Some of this reacts with the water in the blood plasma  and reduces its PH. The change in PH is detected by chemoreceptor’s  in the carotid arteries, the aorta and brain. The chemoreceptor’s send impulses to the cardiovascular centre, which increases the heart rate.

     When we stop exercising the concentration of carbon dioxide in the blood falls. This 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 to prepare the body for activity

·         Blood pressure is monitored by stretch receptors in the walls of the carotid sinus. This is a smaller swelling in the carotid artery. If blood pressure rises to high, perhaps during vigorous exercise, the stretch receptors send signals to the cardiovascular centre. This responds by reducing the heart rate.