Control of Blood Glucose Conc

Glucose concentration in the blood

All cells need a constant energy suppy to work- so blood glucose concentration must be carefully controlled. the concentration of glucose in the blood is normally around 90mg per 100cm3 of blood.

It is monitored by cells in the pancreas. Blood glucose concentration rises after eeating food contatining carbohydrate. It falls after exercise, as more glucose is used in respiration to release energy.

Hormonal control of blood glucose concentration

The hormonal system controls blood glucose concentration using two hormones called insulin and glucagon. They are both secreted by clusters of cells in the pancreas called islets of Langerhan. 

The islets of Langerhan contain beta cells and alpha cells. 

Beta cells secrete insulin into the blood. Alpha cells secrete glucagon into the blood. 

Insulin and glucagon act on effectors, which respond to restore the blood glucose concentration to the normal level

Insulin

Insulin lowers blood glucose concentration when it is too high. It binds to specific receptors on the cell membranes of liver cells and muscle cells and increases the permeability of cell membranes to glucose, so the cells take up more glucose.

Insulin also activates enzymes that convert glucose into glycogen. Liver and muscle cells are able to store glycogen in their cytoplasm, as an energy source. The process of forming glycogen from glucose is called glycogenesis. Insulin also increases the rate of respiration of glucose, especially in muscle cells.

Glucagon

Glucagon raises blood glucose concentration when it is too low. It binds to specific receptors on the cell membranes of liver cells and activates enzymes that break down glycogen into glucose. the process of breaking down glycogen is called glycogenolysis. 

Glucagon also promotes the formation og glucose from glycerol and amino acids. The process of forming glucose from non-carbohydrates is called gluconeogenesis. Glucagon also decreases the rate of respiration.

Rise in blood glucose concentration 

When the pancreas detects blood glucose concentration isa too high, the beta cells secrete insulin and the alpha cells stop secreting glucagon. Insulin then binds to receptors on liver and muscle cells. The liver and muscle cells respond to decrease the blood glucose concentration, e.g. glycogenesis is activated. Blood glucose concentration then returns to normal.

Fall in blood glucose concentration

When the pancreas detects blood glucose is too low, the alpha cells secrete glucagon and the beta cells stop secreting insulin. Glucagon then binds to receptors on liver cells. The liver cells respond to increase the blood glucose concentration, e.g. glycogenolysis is activated. Blood glucose concentration then returns to normal.

Control of insulin secretion by beta cells

Beta cells contain insulin stored in vesicles. They have potassium ion channels and calcium ion channels in their membrane. When the blood glucose concentration is around normal level or lower, the potassium ion channels are open and the calcium ion channels are closed. Potassium ions diffuse out of the cell through the channel proteins, which makes the inside of the cell membrane more negatively charged compared to the outside. 

1) High blood glucose concentration detected- When the blood glucose concentration is high, more glucose enters the beta cells by facilitated diffusion. More glucose in a beta cell causes the rate of respiration to increase, making more ATP.

2) Potassium ion channels close- The rise in ATP triggers the potassium ion channels in the beta cell plasma membrane to close. This means that potassium ions can not enter the cell. The membrane becomes depolarised.

3) Calcium ion channels open- Depolarisation triggers calcium ion channels in the membrane to open, so calcium ions diffuse into the beta cells. This causes the vesicles to move to and fuse with the beta cell plasma membrane, releasing insulin by exocytosis.

Type 1 diabetes (insulin-dependent)

Type 1 diabetes is an auto-immune diseas, in which the body attacks and destroys the beta cells in the islets of Langerhans. This means people with Type 1 diabetes don't produce any insulin. After eating, the blood glucose level rises and stays high, which can result in death if left untreated. The kidneys can't reabsorb all this glucose, so some of it is excreted in the urine. 

Type 1 diabetes usually develops in children or young adults. A person's risk of developing Type 1 diabetes is slightly increased if there is a close family history of the disease.

Type 2 diabetes (non-insulin dependent)

Type 2 diabetes occurs when the beta cells don't produce enough insulin or when the body's cells don't respond to insulin. Cells don't respond because the insulin receptors in their membranes don't work, so the cells don't take up enough glucose.

Type 2 diabetes us usually acquired later in life than Type 1, and is often linked with obesity. The risk is also greatly increased in people from certain ethnic groups, e.g. African or Asian.

Treating Diabetes

Type 1 diabetes can be treated by regular injections of insulin. But this has to be carefully controlled because too much cna produce a dangerous drop in blood glucose levels. Eating regulary and controlling simple carbohydrate intake (sugar) helps to avoid a sudden rise in glucose. Type 2 diabetes can be treated by controlling simple carbohydrate intake and losing weight.

Insulin from GM bacteria

Insulin used to be extracted from animal pancreases (e.g. Pigs and cattle), to treat people with Type 1 diabetes. Human insulin can be made by genetically modified bacteria. Using GM bacteria to produce insulin is much better for many reasons:

• Producing insulin using GM bacteria is cheaper than extracting it from animal pancreases.
• Larger quantities of insulin can be produced using GM bacteria.
• Less likely to be rejected by the body

Curing Diabetes

Your body is made up of many different types of cells that are specialised for their functions, e.g. liver cells, beta cells. All specialised cekks originally came from stems cells. Stem cells are unspecialised- they have the ability to develop into any type of cell.

Using stem cells could potentially cure diabetes. Stem cells could be grown into beta cells, which would then be implanted into the pancreas of a person Type 1 diabetes. This means the person would be able to make insulin as normal. This treatment is still being developed but, if it is effective, it will cure people with Type 1 diabetes- they won't have to have regular injections of insulin.