Controlling blood glucose concentration 5.4.3

Question 1

What are three ways in which glucose can enter the bloodstream?

Answer 1

• Absorption in the gut following carbohydrate digestion
• Hydrolysis of glycogen stores
• Non carbohydrates such as lipids, lactate and amino acids that have been converted to glucose

Question 2

How does the amount of glucose absorbed in the blood vary?

Answer 2

Through digestion - as some meals may be much more carbohydrate rich than others

Question 3

What are the hormones that control blood glucose concentration?

Answer 3

Insulin and glucagon

Question 4

What happens when blood glucose concentration decreases?

Answer 4

Detected by a and b cells in the pancreas (a=glucagon rise, b=insulin stops)
- Decrease in insulin reduces use of glucose by muscles and livers
- Glucagon binds to receptors in liver membrane, causing a conformational change
- This activates a G protein which activates the enzyme adenylyl cyclase
- Adenylyl cyclase catalyses the conversion of ATP to cyclic AMP
- cAMP binds to protein kinase A enzymes
- Activate protein kinase A activates phosphorylase kinase enzymes by adding phosphate groups to them
- Active phosphorylase kinase enzymes activate glycogen phosphorylase enzymes
- Active glycogen phoshorylase enzymes catalyse the breakdown of glycogen to glucose

Question 5

How do B cells respond when blood glucose concentration is too low?

Answer 5

By stopping the secretion of insulin

Question 6

How do a cells respond when blood glucose concentration is too low?

Answer 6

By secreting glucagon

Question 7

What is glycogenolysis?

Answer 7

Breakdown of glycogen to glucose

Question 8

How does adrenaline increase the concentration of blood glucose?

Answer 8

It binds to different receptors on the surface of liver cells that activate the same enzyme cascade and lead to the same end result - which is the breakdown of glycogen by glycogen phosphorylase (glycogenolysis)
It also stimulates the breakdown of glycogen stores in muscle during exercise

Question 9

What happens when blood glucose concentration increases?

Answer 9

• B cells detect this rise
• When the concentration of glucose is high, glucose molecules enter the B cells by facilitated diffusion
• The cells respire this glucose and produce ATP
• High concentrations of ATP causes the potassium channels in the B cells to close, producing a change in the membrane potential
• This causes voltage gates calcium channels to open
• In response to the influx of calcium ions, the B cells secrete insulin and insulin containing vesicles move towards the cell surface membrane where theyre released by exocytosis
• Once in the bloodstream, insulin circulates around the body
• It stimulates the uptake of glucose by muscle, fat, and liver cells

Question 10

What cells possess glucose transporter proteins

Answer 10

Muscle cells, fat storage cells, adipose tissue, and liver cells
Which are the target cells of insulin

Question 11

What do glucose transporter proteins allow for?

Answer 11

Facilitated diffusion of the uptake of glucose molecules

Question 12

What is the rate of glucose uptake limited by?

Answer 12

The number of glucose transporter proteins

Question 13

What happens when insulin binds to specific receptors on the membranes of target cells?

Answer 13

• Stimulates them to activate/add more glucose transporter proteins to their cell surface membrane which increases the permeability of their cells
• As a result the rate of facilitated diffusion increases

Question 14

What is blood glucose concentration regulated by?

Answer 14

Negative feedback control mechanisms

Question 15

What happens in the negative feedback systems

Answer 15

• Receptors detect whether a specific level is too low or too high
• This information is communicated through the hormonal or nervous system to effectors
• Effectors react to counteract the change by bringing the level back to normal

Question 16

Describe the negative feedback mechanism of blood glucose concentration

Answer 16

• a and b cells in the pancreas act as the receptors
• They release the hormones glucagon (secreted by a cells) and insulin (secreted by B cells)
• Liver cells act as the effectors in response to glucagon and fat cells act as the effectors in response to insulin

Question 17

What is the role of the liver in hormonal communication

Answer 17

Plays a vital role in the conversion between glycogen and glucose, which helps to regulate glucose concentration

Question 18

What is glycogenesis?

Answer 18

The synthesis of glycogen from glucose molecules

Question 19

What triggers glycogenesis?

Answer 19

Insulin after it detects an increased blood glucose concentration

Question 20

What does the synthesis of glycogen do?

Answer 20

Removes glucose molecules from the bloodstream and decreases blood glucose concentration to within a normal range

Question 21

What does the breakdown of glycogen do?

Answer 21

Releases more glucose molecules to the bloodstream and increases the blood glucose concentration to within the normal range

Question 22

What is gluconeogenesis?

Answer 22

The synthesis of glucose molecules from non carbohydrate molecules

Question 23

What triggers gluconeogenesis?

Answer 23

Glucagon

Question 24

Describe gluconeogenesis

Answer 24

• Glucagon triggers this by activating enzymes within the liver
• These enzymes convert other molecules, such as fatty acids and amino acids, into glucose molecules
• Glucose molecules are released into the bloodstream

Question 25

What is the function of insulin?

Answer 25

It decreases blood glucose concentration

Question 26

What is the function of glucagon?

Answer 26

It increases blood glucose concentration