Biology Homeostasis - Blood Glucose

All cells need a constant energy supply to work - so blood glucose concentration must be carefully controlled.

The concentration of glucose in the blood is usually around 90mg per 100cm3 of blood. this is monitored by cells in the pancreas.

blood glucose concentration rises after eating foods containing carbohydrates

blood glucose concentration falls after exercise, as more glucose is used up in respiration to release energy.

Beta cells secrete insulin into the blood. This causes a decrease in blood glucose concentration when its too high.

Insulin binds to specific receptors on the cell membranes of liver cells and muscle cells.

It increases the permeability of cell membranes to glucose, therefore the cells take up more glucose.

Insulin also activates enzymes that convert glucose into glycogen

Cells store glycogen in their cytoplasm as an energy store

The process of forming glycogen from glucose is glycogenesis.

Insulin can also increase the rate of respiration of glucose, especially in muscle cells.

Alpha cells secrete glucagon into the blood

Glucagon raises blood glucose concentration when its too low

Glucagon binds to specific receptors on the cell membranes of liver cells

Glucagon activates enzymes that break down glycogen into glucose

The process of breaking down glycogen is caled glycogenolysis

Glucagon also promotes the formation of glucose from fatty acids and amino acids

The process of forming glucose from non-carbohydrates is called gluconeogenesis

Glucagon decreases the rate of respiration of glucose in cells

Adrenaline is a hormone secreted from your adrenal glands

It is secreted when there is a low concentration of glucose in your blood, when your stressed and when you are exercising

Adrenaline binds to receptors in the cell membrane of liver cells:

- It activates glycogenolysis
- It inhibits glycogenesis

It also activates glucagon secretion and inhibits insulin secretion, which increase glucose concentration 

Adrenaline gets the body ready for action by making more glucose available for muslces to repsire

Both adrenaline and glucagon can activate glycogenolysis inside a cell even though they bind to receptors outside the cell.

Adrenaline and glucagon bind to their specific receptors and activate an enzyme called adenylate cyclase

activated adenylate cyclase converts ATP into a chemical signal called a "second messenger"

the second messenger is called cyclic AMP (cAMP)

cAMP activates a cascade (a chain of reactions) that break down glycogen into glucose (glycogenolysis)

The Beta cells in the islets of langerhans dont produce any insulin

After eating the blood glucose level rises and stays high - this is called hyperglycaemia and can result in death if left untreated. The kidneys cant reabsorb all this glucose so some of it is excreted in the urine

It can be treated by regular injections of insulin. But this had to be carefully controlled because too much can produce a dangerous drop in blood glucose levels - this is called hypoglycaemia.

Eating regularly and controlling simple carbohydate intake helps to avoid a sudden rise in glucose.

Type 2 diabetes is usually aquired later in life than type 1 and it is often linked with obesity

It occurs when the Beta cells dont produce enough insulin or when the bodys cells dont respond properly to insulin. cells dont respond properly because the insulin receptors on their membranes dont work properly, so the cells dont take up enough glucose. This means the blood glucose concentration is higher than normal

It can be treated by controlling simple carbohydrate intake and losing weight. glucose lowering tablets can be take if diet and weight loss cant control it.