16.3 Control of blood glucose

Question 1

What are hormones

Answer 1

• Secreted by glands directly into the blood (endocrine glands)
• Carried in the blood plasma to the cells on which they act, known as target cells
• Effective at very low concentrations but often have widespread and long lasting effects

Question 2

What is the second messenger model

Answer 2

This mechanism is used by two hormones involved in the regulation of blood glucose concentration:
Adrenaline and glucagon

Question 3

How does the hormone adrenaline work using the second messenger model to control blood glucose

Answer 3

-Adrenaline binds to a transmembrane protein receptor within the cell surface membrane of liver cell

• This binding of adrenaline makes the protein change shape on inside of membrane
• When it changes shape it activates an enzyme called adenyl cyclase.
  This converts ATP to cyclic AMP also known as CAMP
• cAMP acts as a second messenger that binds to a protein kinase enzyme which changes its shape and activates it
• This activated kinase enzyme catalyses reaction that converts glycogen to glucose which moves out of liver by facilitated diffusion and into the blood through channel proteins

Question 4

What is the pancreas

Answer 4

It is a large pale coloured gland situated in upper abdomen, behind the stomach

It produces enzymes for digestion and hormones for regulating blood glucose concentration

Question 5

What are the islets of Langerhans

Answer 5

In the pancreas, these are hormone producing cells. Two types

Alpha cells: Larger and produce the hormone glucagon to increase blood glucose

Beta cells: Smaller and produce the hormone insulin

Question 6

What is the liver
What cells are in it

Answer 6

It is directly below diaphragm and is made up of cells called hepatocytes

Question 7

What 3 important processes occur in the liver

Answer 7

• Glycogenesis
• Glycogenolysis
• Gluconeogenesis

Question 8

What is glycogenesis

Answer 8

Conversion of glucose into glycogen
Think of it as creating glycogen (genesis)

When blood concentration is higher than normal in the blood the liver converts the glucose to glycogen to be stored

Question 9

What is glycogenolysis

Answer 9

The hydrolysing of glycogen to make glucose.

This occurs when blood glucose level is too low so glucagon is secreted by pancreas to make liver produce glucose

Question 10

What is gluconeogenesis

Answer 10

Making glucose from sources other than carbohydrate
Eg liver can make glucose with amino acids and glycerol when supply of glycogen is exhausted

Question 11

Why is control of blood glucose important

Answer 11

Glucose is substrate for respiration and provides a source of energy for all organisms.
If concentration is too low, cells are deprived of energy and die, especially brain cells as they can only respire glucose

If concentration of glucose rises too high, it lowers water potential of the blood and creates osmotic problems that cause dehydration and are equally dangerous

Question 12

What 3 places does blood glucose come from

Answer 12

• Directly from diet: It is produced by the hydrolysis of starch to maltose
• Glycogenolysis: Produced when glycogen is broken down into glucose. This occurs in small intestine
• Gluconeogenesis: Produced by sources other than carbohydrate

Question 13

What do beta cells in islets of langerhans in the pancreas do when glucose concentration in blood is too high

Answer 13

• They have receptors that detect a stimulus of a rise in blood glucose concentration
• Secrete insulin directly into blood: Insulin is globular protein
• Almost all cells have glycoprotein receptors on cell membrane so bind to insulin

Question 14

When cells in body bind to insulin what 3 things happen

Answer 14

• Change in tertiary structure of glucose transport carrier proteins causing them to change shape and open, allowing more glucose in by facilitated diffusion
• Increases number of carrier proteins in cell membrane: At low concentrations of insulin, the protein that makes up these channels is part of membrane of vesicles however they now fuse with cell membrane so increase number of glucose transport channels
• Activate enzymes that convert glucose to fat and glycogen

Question 15

So how is blood glucose lowered

Answer 15

• Increase rate of absorption of glucose into cells
• Increase rate of respiration in cells so they use up glucose so it diffuses in more readily
• Increase rate of converting glucose to glycogen in liver and muscles, and also to fats

Question 16

What do alpha cells in islets of langerhans in pancreas do

Answer 16

When theres a fall in blood glucose concentration they secrete glucagon into the blood

Question 17

What 3 ways does glucagon increase glucose concentration in the blood

Answer 17

• Attach to specific protein receptors on cell membrane of liver cells which makes it release glucose
• Activates enzymes that convert glycogen to glucose
• Activates enzymes in conversion of amino acids and glycerol into glucose