Control of blood glucose levels

Question 1

What are hormones?

Answer 1

• Hormones are produced by glands and are secreted directly into the blood
• They are carried by blood plasma to target cells which have specific receptors on their cell surface membrane which are complementary to specific hormones
• They are effective in very low concentrations and have long lasting effects

Question 2

What is the mechanism of adrenaline?

Answer 2

• Adrenaline binds to a transmembrane protein receptor within the cell membrane of a liver cell
• The binding of adrenaline causes the protein to change shape on the inside of the membrane
• The change in shape leads to the activation of an enzyme called adenyl cyclase. The activated adenyl cyclase converts ATP to cAMP
• The cAMP acts as a second messenger and binds to the protein kinase enzyme, changing its shape and therefore activating it
• The active protein Kinase enzyme catalyses the conversion of glycogen to glucose which then moves out of the liver by facillitated diffusion into the blood through channel proteins

Question 3

What is the role of the pancreas in regulating glucose?

Answer 3

• The pancreas is a large, pale gland that produces enzymes for digestion and hormones for regulating blood glucose concentration
• Scattered through pancreatic cells are groups of hormone - producing cells known as islets of langerhan
• The cells of the islets of langerhan include:
  a cells = these are larger and produce the hormone glucagon
  b cells = these are smaller and produce the hormone insulin

Question 4

What is the role of the liver in regulating glucose?

Answer 4

• The liver is located below the diagraphm and is made of hepatocytes
• The liver is a target cell for the hormones insulin and glucagon

Question 5

What are the three processes which regulate blood sugar in the liver?

Answer 5

Glucogenesis = this is the conversion of glucose into glycogen. This occurs when blood glucose is higher than normal, causing the liver to convert excess glucose into glycogen

Glycogenolysis = this is the breakdown of glycogen into glucose. This occurs when blood glucose concentration is lower than normal, causing the liver to convert stored glycogen to glucose which diffuses into the blood and restores normal blood glucose concentration

Glyconeogeneis = This is the production of glucose from other sources which are not carbohydrates. When the supply of glycogen is exhausted, the liver can produce glucose from non - carbohydrate sources such as glycerol and amino acids

Question 6

What are factors that influence blood glucose concentrations?

Answer 6

• directly from our diets, glucose is absorbed following the hydrolysis of other carbohydrates such as starch, maltose, lactose and sucrose
• the hydrolysis in the small intestine of glycogen = glycogenolysis
• from gluconeogenesis = the production of glucose from sources other than carbohydrates

Question 7

What is the mechanism of insulin?

Answer 7

• The B cells in the islets of langerhan in the pancreas have receptors that detect the stimulus of a rise in blood glucose and respond by secreting insulin
• hepatocytes and other cells have glycoprotein receptors on their cell surface membranes that are complementary to insulin
• the binding of insulin causes vesicles to fuse with the cell surface membrane, causing the display of glucose transport carrier proteins
• This increases the facilliated diffusion of glucose into cells down a concentration gradient
• ## This also results in the activation of enzymes which convert glucose to glycogen

Question 8

What are the four results of the action of insulin?

Answer 8

• increases the rate of absorption of glucose into cells, especially in muscle cells
• Increases the rate of respiration of cells and phosphorylates glucose which increases the uptake of glucose from the blood
• increases glycogenesis
• increases the rate of conversion of glucose into fat

Question 9

What cells detect a fall in blood glucose concentration?

Answer 9

a cells in the islets of langerhan

Question 10

What is the mechanism of glucagon?

Answer 10

• Glucagon binds to a transmembrane protein receptor within the cell membrane of a liver cell
• The binding of adrenaline causes the protein to change shape on the inside of the membrane
• The change in shape leads to the activation of an enzyme called adenyl cyclase. The activated adenyl cyclase converts ATP to cAMP
• The cAMP acts as a second messenger and binds to the protein kinase enzyme, changing its shape and therefore activating it
• The active protein Kinase enzyme catalyses the conversion of glycogen to glucose which then moves out of the liver by facillitated diffusion into the blood through channel proteins

Question 11

What are the actions of glucagon?

Answer 11

• activates glucogenesis
• activates gluconeogenesis