Control of blood glucose concentration

Question 1

What is hyperglycemia and what happens during it?

Answer 1

• When the blood glucose concentration is too high (more than 200mg/100cm3
• Blood WP drops, water moves into blood from cells
• Some tissues begin to metabolize fats as glucose stays in this blood, this lowers the pH of blood

Question 2

What is hypoglycemia and what happens during it?

Answer 2

• When the blood glucose concentration is too low (less than 72mg/100cm3)
• There is not enough glucose for respiring tissues and nerves can only use glucose for respiration hence these nerves shut down which leads to unconsciousness and then coma.

Question 3

How is glucose stored in
- Skeletal muscles
- Adipose cells
- Liver

Answer 3

Skeletal muscles - stores glucose as glycogen for later use
Adipose cells (fat cells) - glucose is converted to triglycerides for long term storage
Liver - stores excess glucose a glycogen which it returns when levels drop

Question 4

What is glycogenolysis and when does it occur?

Answer 4

The hydrolysis of glycogen back into glucose in the liver. This occurs when blood glucose levels are lower than normal

Question 5

What is glycogenesis and when does it occur?

Answer 5

Muscles and liver cells take up excess glucose and converted it into glycogen for later storage. This occurs when blood glucose levels are higher than normal and usually in the liver.

Question 6

What is gluconeogenesis and when does it occur?

Answer 6

The production of glucose from non-carbohydrate stores in the liver such as amino acids. This occurs when all the glycogen has been hydrolysed into glucose but your body still needs more glucose.

Question 7

What is glycolysis and when does it occur?

Answer 7

The conversion of glucose into pyruvate which occurs in the 1st stage of respiration.

Question 8

What is fatty acid synthesis and when does it occur?

Answer 8

Adipose take up glucose and convert it into fatty acids to store as triglycerides. Occurs when there is no more space in the liver.

Question 9

How does the pancreas work in blood glucose control?

Answer 9

The pancreas detects changes in blood glucose levels by the endocrine cells in the Isle of Langerhans which release the hormone insulin from beta cells and glucagon from alpha cells to bring the levels back to normal.

Question 10

What happens when blood glucose levels rise?

Answer 10

• The rise in blood glucose level is detected by the beta cells in the Isle of Langerhans in the pancreas which cause beta cells to release insulin. Insulin causes the liver cells to become more permeable to glucose hence there is an increase in glucose uptake in muscles, adipose and liver cells. Enzymes are also activated to convert glucose to glycogen. This means that glucose is removed from the blood and stored as glycogen in the cells hence blood glucose levels return to normal.

Question 11

What happens when blood glucose levels drop?

Answer 11

• The drop in blood glucose level in detected by alpha cells in the Isle of Langerhans in the pancreas which cause alpha cells to release glucagon. Adrenaline will also be released from the adrenal glands. The second messenger model occurs which activates enzymes to hydrolyse glycogen into glucose. This means more glucose is being released into the blood hence blood glucose levels return to normal.

Question 12

How does insulin decrease blood glucose levels?

Answer 12

1. Insulin diffuses from the capillaries to the muscle and adipose cells where it will bind to a complementary receptor protein.
2. This causes intracellular chemicals to be released which cause vesicles containing protein channels and phospholipids to fuse with the cell surface membrane of the liver cell. This makes the membrane more permeable to glucose.
3. The protein channels will embed into the membrane which means more glucose can be taken up by facilitated diffusion

Question 13

How does glucagon increase blood glucose levels?

Answer 13

1. Glucagon binds to glucagon receptors on the liver cells which changes the shape of the enzyme adenyl cyclase which also activates this enzyme
2. The enzyme catalyses the reaction of ATP converting into cyclic AMP (cAMP) which is the second messenger.
3. cAMP will activate the protein kinase which catalyses the hydrolysis of glycogen into glucose.

Question 14

Which reactions do insulin and glucagon inhibit and stimulate

Answer 14

Insulin
- Stimulate glycogenesis
- Inhibits glycogenolysis and gluconeogenesis

Glucagon
- Stimulates glycogenolysis and gluconeogenesis
- Inhibits glycogenesis

Question 15

What is gluconeogenesis