Blood Sugar Regulation
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At what level must blood sugar be maintained?
What happens to cells that rise above the optimum blood sugar level?
They become hypertonic and water is drawn out of them down a water potential gradient
What happens to cells that fall below the optimum blood sugar level?
The glycolysis stage of respiration is slowed down so brain activity is reduced
Describe stage 1 of a glucose surplus response
The change in blood glucose levels is detected by the beta cells in the islets of langerhans within the pancreas
Describe stage 2 of a glucose surplus response
The beta cells release insulin into the blood
Describe stage 3 of a glucose surplus response
The insulin binds to specific protein receptors in the membrane of liver cells
Describe stage 4 of a glucose surplus response
- Liver cells increase their permeability to glucose by transporting protein channels into the membrane meaning more glucose enters the cells
- Enzymes responsible for converting glucose into glycogen in a process of glycogenesis are also activated
Describe stage 5 of a glucose surplus response
Insulin also causes the liver to convert excess glucose into fats to be stored in adipose tissue under the skin
Describe stage 1 of a glucose deficiency response
The change in glucose levels is detected by alpha cells in the islets of langerhans within the pancreas
Describe stage 2 of a glucose deficiency response
Alpha cells release glucagon into the blood
Describe stage 3 of a glucose deficiency response
Glucagon binds to specific protein receptors in the membrane of liver cells
Describe stage 4 of a glucose deficiency response
- Liver cells activate the enzyme glycogen phosphorylase to hydrolyse the glycogen back into glucose
- This process is known as glycogenolysis
Describe stage 5 of a glucose deficiency response
- In times of stress or excitement, adrenaline from adrenal glands
- Adrenaline also stimulated glycogenolysis
Describe stage 6 of a glucose deficiency response
- If glycogen reserves are empty (due to fasting or otherwise) the liver cells produce new glycogen
- This process is known as gluconeogenesis and is controlled by glucagon
From where is new glucose synthesised by the liver?
- Lactic acid from anaerobic respiration in muscles
- Glycerol from fatty acid breakdown
- Amino acid from body proteins
Describe stage 1 of the second messenger model
- The hormone (messenger no1) binds to a protein receptor on the membrane of the target cell to form a hormone receptor complex
Describe stage 2 of the second messenger model
- A membrane bound enzyme know as adenylate cyclase is activated
- This enzyme converts many ATP molecules to cyclic AMP (messenger no2)
Describe stage 3 of the second messenger model
In the case of adrenaline and glucagon, each secondary messenger activates many enzymes that convert glycogen into glucose
Describe stage 4 of the second messenger model
A cascade reaction is formed with a single hormone resulting in a large number of activated enzymes
What is diabetes?
A disease caused by an inability to control blood glucose levels
What effects does diabetes have on bodily cells
- Glucose remains in the blood and is not absorbed by cells
- This means cells lack glucose for respiration leading to weight loss and fatigue
- The glucose in the blood lowers water potentials causing water to move out of cells down a water potential gradient via osmosis resulting in thirst and increased urine production
- Any urine produced contains glucose due to incomplete reabsorption in the kidneys
What is type 1 diabetes
- Insulin dependent diabetes
- The pancreas is unable to produce insulin in response to high blood glucose levels
How is type 1 diabetes treated?
With regular injections of insulin
What is type 2 diabetes?
- Insulin independent diabetes
- Insulin is produced but the cells of the body fail to respond to it
How is type 2 diabetes treated?
- Reducing the amount of soluble sugar in the diet
- Eating carbohydrates in the form of insoluble starch which is absorbed more slowly as it needs to be digested first
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