Control of Blood Glucose Concentration

Question 1

what monitors the blood glucose concentration?

Answer 1

the pancreas

Question 2

when does blood glucose concentration increase?

Answer 2

after eating food containing carbohydrate

Question 3

when might blood glucose concentration decrease?

Answer 3

it falls after exercise, as more glucose is used in respiration to release energy

Question 4

what are the hormones used to control blood glucose concentration?

Answer 4

• insulin
• glucagon

Question 5

how are insulin and glucagon secreted?

Answer 5

• secreted by clusters of cells in the pancreas called the islets of Langerhans

Question 6

what types of cells do the islets of Langerhans contain?

Answer 6

• alpha cells
• beta cells

Question 7

what do beta cells secrete?

Answer 7

insulin into the blood

Question 8

what do alpha cells secrete?

Answer 8

glucagon into the blood

Question 9

what does insulin and glucagon do?

Answer 9

• act on effectors, which reasons to restore the blood glucose concentration

Question 10

what is the role of insulin in regulating blood glucose concentration?

Answer 10

• insulin lowers blood glucose concentration when it’s too high
• insulin also activates enzymes in muscle and liver cells that convert glucose into glycogen

Question 11

how does insulin lower blood glucose concentration?

Answer 11

• insulin lowers blood glucose concentration when it’s too high
• insulin binds to receptors on the cell membrane of muscle cells and liver cells
• increases he permeability of muscle cell membranes to glucose
• so cells take up more glucose, which involves increasing the number of channel proteins in the cell membranes

Question 12

how does insulin activate enzymes when blood glucose concentration is too high?

Answer 12

• activates enzymes in muscle and liver cells that convert glucose to glycogen
• cells are able to store glycogen in their cytoplasm as an energy source
• forming glycogen from glucose is called glycogenesis
• insulin also increases the rate of respiration of glucose, especially in muscle cells

Question 13

what activates glycogenesis?

Answer 13

insulin

Question 14

what is the role of glucagon in regulating blood glucose concentration?

Answer 14

• glucagon raises blood glucose concentration when it’s too low
• it binds to receptors on the cell membranes of liver cells and activates enzymes that break down glycogen into glucose

Question 15

what is the process of breaking down glycogen called?

Answer 15

glycogenolysis

Question 16

what other enzymes may glucagon activate?

Answer 16

• enzymes involved in the formation of glucose from glycerol and amino acids

Question 17

what does insulin do to the rate of respiration in muscle cells?

Answer 17

• insulin increases the rate of respiration of glucose, especially in muscle cells

Question 18

what is gluconeogenesis?

Answer 18

• forming glucose from non-carbohydrates

Question 19

what does glucagon do to the rate of respiration of glucose?

Answer 19

glucagon decreases the rate of respiration of glucose in cells

Question 20

how does hormones differ to nerve impulses?

Answer 20

• hormones travel in blood to target cells, so responses are slower than nerve impulses
• hormones create responses which are more widespread, whilst nerve impulses are localised in one area
• hormones are not broken down as quickly as neurotransmitters, so the effects from hormones tend to last longer

Question 21

explain the negative feedback mechanism when there is a rise in blood glucose concentration.

Answer 21

• pancreas detects blood glucose concentration as too high
• beta cells secrete insulin and alpha cells stop secreting glucagon
• insulin binds to receptors on liver and muscle cells
• liver and muscle cells respond to decrease the blood glucose concentration, by activating glycogenesis, cells taking up more glucose or cells respiring more glucose
• blood glucose concentration then returns to normal

Question 22

explain the negative feedback mechanism when there is a fall in blood glucose concentration.

Answer 22

• pancreas detect blood glucose concentration to too low
• alpha cells secrete glucagon and beta cells stop secreting insulin
• glucagon binds to receptors on the liver cells
• liver cells respond to increase blood glucose concentration, by activating glycogenolysis or gluconeogenesis, cells respire less glucose
• blood glucose concentration returns to normal

Question 23

what is used to transport glucose across the cell membrane?

Answer 23

• glucose transporters which are channel proteins

Question 24

give the name of the glucose transporter.

Answer 24

GLUT4

Question 25

where is GLUT4 contained?

Answer 25

skeletal and cardiac muscle

Question 26

what does GLUT4 do when insulin levels are low?

Answer 26

• GLUT4 is stored in vesicles in the cytoplasm of cells, when insulin binds to receptors on the cell-surface membrane it triggers the movement of GLUT4 to the membrane
• glucose can then be transported into the cell through the GLUT protein by facilitated diffusion (high insulin levels)

Question 27

explain the second messenger model.

Answer 27

• receptors of adrenaline and glucagon have a specific tertiary structure
• to activate glycogenolysis, adrenaline and glucagon have to bind to receptors and activate the enzyme adenylate cyclase
• activated adenylate cyclase converts ATP to a chemical called cyclic AMP cAMP
• cAMP activates enzyme protein kinase A
• protein kinase A activates a chain of reactions which break down glycogen to glucose