6.4.2 - Control of blood glucose concentration

Question 1

Using your knowledge of the kidney, explain why glucose is found in the urine of a person with untreated diabetes. (3)

Answer 1

• High concentration of glucose in blood/filtrate
  ‘accept tubule for filtrate’
• Not all the glucose is (re)absorbed at the proximal convoluted tubule
• Carrier/co-transport proteins are working at maximum rate/ Carrier/co-transport proteins/ are saturated

Question 2

Describe the role of glucagon in gluconeogenesis. Do not include in your answer details on the second messenger model of glucagon action. (2)

Answer 2

• (Attaches to receptors on target cells and) activates/stimulates enzymes
• Glycerol/amino acids/fatty acids into glucose

Question 3

Explain how increasing a cell’s sensitivity to insulin will lower the blood glucose concentration. (2)

Answer 3

• (More) insulin binds to receptors
• (Stimulates) uptake of glucose by channel/transport proteins /Activates enzymes which convert glucose to glycogen

Question 4

Explain how inhibiting adenylate cyclase may help to lower the blood glucose concentration. (3)

Answer 4

• Less/no ATP is converted to cyclic AMP/cAMP
• Less/no kinase is activated
• Less/no glycogen is converted to glucose / Less/no glycogenolysis

Question 5

Give two reasons why pancreas transplants are not used for the treatment of type II diabetes. (2)

Answer 5

• (Usually) Type II produce insulin
• Cells / receptors less sensitive / responsive (to insulin) / Faulty (insulin) receptors
• (Treated / controlled by) diet / exercise
  ‘accept: cells / receptors do not respond , fewer receptors, (Treated / controlled by) weight loss / medication / drugs’

Question 6

Give two ways in which people with type 1 diabetes control their blood glucose concentration. (2)

Answer 6

• Treat with insulin (injection/infusion)
• (Control) diet/control sugar intake

Question 7

Give one reason why blood glucose regulation is important. (1)

Answer 7

• It is a respiratory substrate / it is needed for respiration / energy can be released from it during respiration
• It can affect the water potential of the blood

Question 8

Describe two of the effects of insulin that lead to a fall in blood glucose. (2)

Answer 8

• An increase in the uptake of glucose by the cells / an increase in glucose transporter proteins in cell surface membranes (especially for the cells of the liver and muscles)
• Conversion of glucose to glycogen / glycogenesis (this maintains the glucose diffusion gradient between the cells and the blood)
• Increased metabolism / respiration (increasing the rate at which glucose is used by the cells)

Question 9

Describe two of the effects of glucagon that lead to an increase in blood glucose. (2)

Answer 9

• Conversion/breakdown of glycogen to glucose / glycogenolysis
• Production/synthesis of glucose from other molecules (such as fatty acids and amino acids) / gluconeogenesis
• Reduced metabolism / respiration (reducing the rate at which glucose is used up)

Question 10

High blood pressure is a possible side effect of poorly controlled diabetes. Use your knowledge of osmosis to explain why. (3)

Answer 10

• When glucose concentration in the blood is high, it lowers the water potential of the blood
• Therefore, water will enter the blood from the body tissues/cells via osmosis
• This means there will be a greater volume of blood in the circulatory system (therefore blood pressure increases)

Question 11

The molecules glucagon and glycogen are both involved in regulating blood glucose concentration. Explain the different roles they play. (4)

Answer 11

• Glucagon is a hormone
• That stimulates conversion of glycogen to glucose
• Glycogen is a storage carbohydrate/polysaccharide
• It is formed from glucose by action of insulin

Question 12

Some diabetics have to inject themselves with insulin to keep their diabetes under control. Suggest why insulin has to be injected and cannot be taken orally. (1)

Answer 12

• It is a protein and so would be digested by protease/enzymes in the gut

Question 13

Describe the mechanism by which insulin reduces the glucose concentration in the blood. (5)

Answer 13

• When blood glucose is too high, cells in the pancreas detect the high blood glucose levels and stimulate beta cells in the islets of Langerhans to secrete insulin
• Insulin travels in the bloodstream to liver and muscle cells
• Insulin binds to specific receptors (on cell membranes)
• This activates carrier proteins / opens channels / causes more channels to form
• Which increases the permeability of liver/muscle cells/tissues to glucose
• Insulin activates enzymes involved in the conversion of glucose to glycogen /insulin activates glycogenesis enzymes

Question 14

Glucagon is another hormone that can cause an increase in blood glucose concentration. After glucagon is secreted by alpha cells in the pancreas, it breaks down within a matter of minutes. Suggest the benefit of this. (2)

Answer 14

• It prevents glucagon from having a prolonged effect
• So blood glucose concentration does not increase too much / too high

Question 15

Describe the effect adrenaline has on blood glucose concentration. (3)

Answer 15

• Adrenaline increases the concentration of blood glucose
• It binds to different receptors on the surface of liver cells that activates glycogenolysis (break down of glycogen into glucose) and inhibits glycogenesis (synthesis of glycogen from glucose)
• Adrenaline gets the body ready for action by making more glucose available for muscles to respire

Question 16

State what cells are insulin and glycogen secreted from. (2)

Answer 16

• Insulin is secreted from Beta (β) cells
• Glucagon is secreted form Alpha (α) cells

Question 17

Describe the mechanism by which glucagon increases the glucose concentration in the blood. (5)

Answer 17

• When blood glucose is too low cells in the pancreas detect the low blood glucose and stimulate alpha cells in the islets of Langerhans to secrete glucagon
• Glucagon travels in the bloodstream to liver cells, where it binds to specific glucagon receptors on their cell surface membrane
• Glucagon activates enzymes in liver cells that break down glycogen into glucose (glycogenolysis)
• It triggers the production of glucose from non-carbohydrates such as lipids and amino acids (gluconeogenesis)
• Glucagon also decreases the rate of respiration in cells

Question 18

Describe and explain the second messenger model. (5)

Answer 18

• The receptors for adrenaline and glucagon have specific tertiary structures that make them complementary in shape to their hormones
• To activate glycogenolysis, adrenaline and glucagon bind to their 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 an enzyme called protein kinase A
• Protein kinase A activates a cascade (a chain of reactions) that breaks down glycogen into glucose