Control of blood glucose concentration

What are the 3 factors that influence the concentration of blood glucose?

• Food intake

• Exercise

• Metabolic rate

How does food intake influence concentration of blood glucose?

Glucose is absorbed into blood during digestion

How does exercise influence concentration of blood glucose?

Demand for glucose increases

How does metabolic rate influence concentration of blood glucose?

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What are the 3 key processes in the control of blood glucose?

• Glycogenesis

• Glycogenolysis

• Gluconeogenesis

Glycogenesis

Conversion of glucose into glycogen

Glycogenolysis

Hydrolysis of glycogen into glucose

Glyconeogenesis

Conversion of non-carbohydrates (e.g: amino acids, glycerol) into glucose (Useful when glycogen stores are low)

Where are alpha cells and beta cells found?

Islets of Langerhans in the pancreas

What is the role of alpha cells and what do they secrete?

• Detect low blood glucose concentration

• Secrete glucagon

What is the role of beta cells and what do they secrete?

• Detect high blood glucose concentration

• Secrete insulin

When blood glucose concentration is too high what happens in detection? (2 steps)

1. Glucose is absorbed from the small intestines, increasing blood glucose levels

2. The beta cells in the Islets of Langhans in the pancreas detect increase in blood glucose levels

When blood glucose concentration is too high what happens in hormone release? (1 step)

Beta cells secrete more insulin into the blood in response to the increase in blood glucose concentration

When blood glucose concentration is too high what happens during cell signalling and glucose entry? (7 steps)

1. More insulin binds to receptor sites located on glucose channel proteins and membranes of cells throughout the body

2. The binding of insulin causes a change in tertiary structure of channel proteins that causes the more channel proteins to open

3. Blood glucose concentration is higher than cell glucose concentration so glucose diffuses into cells down a concentration gradient

4. Within cells glucose is used for respiration

5. The respiration within the cells maintains the concentration gradient for glucose to diffuse into the cells

6. The binding of insulin to the receptors on the cell surface membrane lead to the release of chemicals within the cell that stimulate the movement and fusion of vesicles with the cell surface membrane

7. The fusion of these vesicles adds additional glucose channels into the cell surface membrane to give a quicker rate of uptake of glucose

When blood glucose concentration is too high what happens during glucose use within the liver? (4 steps)

1. In liver and muscle cells the increased binding of insulin to receptors in the cell membrane activates more enzymes within the cell

2. Activated glycogen synthase has an active site complementary to glucose

3. Glycogen synthase catalyses the condensation reaction required to form glycosidic bonds between glucose units to produce glycogen, a store of glucose within the cell

4. The formation of glycogen lowers glucose concentration within the cell so there is a concentration gradient for glucose to diffuse into the cell

When blood glucose concentration is too high what happens during glucose use within adipose cells? (1 step)

In adipose cells the binding of insulin to receptors in the cell membrane stimulates enzymes that catalyse the formation of lipids from glucose units

When blood glucose concentration is too high what happens during the negative feedback? (5 steps)

1. The corrective actions stimulated by insulin lower blood glucose levels

2. The beta cells of the pancreas continually monitor blood glucose levels

3. The return to normal blood glucose levels lead to insulin production stopping

4. This is an example of a negative feedback as switching on of a corrective action leads to return to normal.

5. Leading the corrective action being switched off

When blood glucose concentration is too low what happens when the blood glucose concentration falls? (2 steps)

1. During activity, glucose is used in respiration to produce ATP in cells

2. This lowers blood glucose concentration as glucose diffuses into cells from blood

When blood glucose concentration is too low what happens during detection? (2 steps)

1. Alpha cells in the islets of Langerhans detect the decrease in blood glucose concentration

2. They respond by secreting more glucagon into the bloodstream

When blood glucose concentration is too low what happens during transport and binding? (2 steps)

1. The glucagon is transported in the blood plasma to target cells (mainly muscle and liver cells)

2. It binds to many complementary shaped receptors on the cell surface membrane to form many glucagon-receptor complexes

When blood glucose concentration is too low what happens during the signal cascade? (6 steps)

1. Binding activates an enzyme on the other side of the membrane within the cell called adenylate cyclase

2. Adenylate cyclase’s substrate is ATP

3. The ATP is converted into cyclic AMPs which we call a second messenger

4. cAMP activates protein kinase enzyme

5. The product of the reaction protein kinase catalyses then activates the next reaction

6. This triggers a cascade of enzyme controlled reactions

When blood glucose concentration is too low what happens during glycogenolysis? (6 steps)

1. Glycogen phosphorylases are activated

2. These catalyse the hydrolysis of glycogen to glucose-6-phosphate

3. This process is called glycogenolysis

When blood glucose concentration is too low what happens in liver cells? (4 steps)

1. Liver cells produce glucose-6-phosphate enzyme

2. The enzyme hydrolyzes glucose-6-phosphate into a phosphate group and glucose

3. The increase in cell glucose concentration means glucose diffuses out of the liver cells into the blood

4. This raises blood glucose levels back up to normal

When blood glucose concentration is too low what happens in muscle cells? (2 steps)

1. The glucose-6-phosphate which was produced from hydrolyzing glycogen is used in glycolysis

2. Muscle cells do not release glucose into the blood

When blood glucose concentration is too low what happens during gluconeogenesis? (2 steps)

1. Hormone glucagon also stimulates enzymes to produce glucose from non-carbohydrate sources (e.g: glycerol and amino acids)

2. This occurs when glycogen stores are low

How is the hormone adrenaline used in control of glucose concentration?

1. In hormonal control of glucose concentration, adrenaline is released

2. Adrenaline binds to specific receptors on cell surface membrane of target cells

3. This activates enzymes that convert glycogen into glucose (glycogenesis)

What is the cause of Type I diabetes?

1. Pancreas doesn’t produce enough insulin

2. Thought to be caused by autoimmune disease that destroys insulin-producing cells

What are the 2 treatments for Type I diabetes?

• Regular insulin injections

• Careful management of diet and exercise

What are the 3 symptoms for Type I and Type II diabetes?

• Thirsty → Increase blood glucose concentration → Water potential decreases

• Excess urination → Higher fluid intake

• Weight loss → Respire lipids instead

What is the 2 causes of Type II diabetes? What is Type II diabetes associated with

• Glyco-receptors on cell surface membrane of target cells become less responsive to insulin

• Pancreas may not produce enough insulin

Associated with obesity

What are the 2 treatments for Type II diabetes?

• Losing weight

• Careful management of diet and exercise