16- Control of Blood Glucose Concentration

Where are hormones produced?

In glands

Describe what occurs in the second messenger model of adrenaline and glucagon. (7 marks)

• Adrenaline or glucagon bind to transmembrane protein receptor within the cell-surface membrane of a liver cell

• Causes the protein to change shape on the inside of the membrane

• Shape change leads to the activation of adenyl cyclase enzyme

• Activated adenyl cyclase converts ATP to cyclic AMP (cAMP)

• cAMP acts as a second messenger that binds to a protein kinase enzyme, changing its shape and activating it

• Active protein kinase catalyses the conversion of glycogen to glucose (glycogenolysis)

• Glucose moves out of the liver cell by facilitated diffusion and into the blood through channel proteins

What are the groups of hormone-producing cells in the pancreas known as?

Islets of Langerhans

What are the two types of cells found in the islets of Langerhans?

• α cells

• β cells

What do α cells in the islets of Langerhans produce?

Glucagon

What do β cells in the islets of Langerhans produce?

Insulin

Which are larger, β cells or α cells?

α cells

What are the three processes involved in regulating blood glucose in the liver?

• Glycogenesis

• Glycogenolysis

• Gluconeogenesis

What is glycogenesis?

The conversion of glucose into glycogen

What is glycogenolysis?

The breakdown of glycogen to glucose

What is gluconeogenesis?

The production of glucose from non-carbohydrate sources (such as amino acids and glycerol)

When would the liver perform glycogenesis?

When blood glucose concentration is higher than normal

When would the liver perform glycogenolysis?

When blood glucose concentration is lower than normal

When would the liver perform gluconeogenesis?

When blood glucose concentration is lower than normal and the liver’s supply of glycogen is exhausted

Which organ produces insulin and glucagon?

The pancreas

Which organ responds to insulin and glucagon?

The liver

What would happen if blood glucose concentration was too low?

Cells would be deprived of energy and die

What would happen if blood glucose concentration was too high?

The water potential of the blood would be lowered, causing osmotic problems such as dehydration

What is the normal concentration of blood glucose?

5 mmol dm^-3

What are the three sources of blood glucose?

• Diet

• Glycogenolysis

• Gluconeogenesis

What are the three main hormones involved in regulating blood glucose concentration?

• Insulin

• Glucagon

• Adrenaline

What happens in the pancreas when blood glucose concentration is too high? (4 marks)

• Receptors of the β cells in the islets of Langerhans detect that blood glucose concentration is too high

• They secrete insulin into the blood plasma

• Blood glucose concentration decreases and returns to optimum

• β cells reduce insulin secretion (negative feedback)

What happens in the pancreas when blood glucose concentration is too low? (4 marks)

• Receptors of the α cells in the islets of Langerhans detect that blood glucose concentration is too low

• They secrete glucagon into the blood plasma

• Blood glucose concentration increases and returns to optimum

• α cells reduce glucagon secretion (negative feedback)

What is the overall effect of insulin?

It decreases blood glucose concentration

What is the overall effect of glucagon?

It increases blood glucose concentration

What three things can glucagon do?

• Attaches to specific protein receptors on the cell-surface membrane of liver cells

• Activates enzymes involved in glycogenolysis

• Activates enzymes involved in gluconeogenesis

Where is adrenaline produced?

The adrenal glands

What is the overall effect of adrenaline?

It increases blood glucose concentration

When is adrenaline produced?

When excited or stressed

What two things can adrenaline do?

• Attach to protein receptors on the cell-surface membrane of target cells

• Activate enzymes involved in glycogenolysis (the breakdown of glycogen to glucose) in the liver

What word is used to describe how insulin and glucagon act to oppose one another’s actions?

Antagonistic

What three things can insulin do?

• Attach to receptors on the surfaces of target cells

• Activate enzymes involved in glycogenesis

• Increase the number of glucose channel proteins in the cell-surface membrane

How does insulin regulate the inclusion of channel proteins in the cell-surface membrane, and what effect does this have on blood glucose concentration? (4 marks)

• At low insulin concentrations, glucose channel proteins are contained in vesicles

• As insulin concentration increases, vesicles fuse with the cell-surface membrane

• This increases the number of glucose channel proteins in the cell-surface membrane

• More glucose enters cells via facilitated diffusion through channel proteins, lowering blood glucose concentration

What are the two types of diabetes mellitus/ sugar diabetes?

• Type I diabetes

• Type II diabetes

Describe what occurs in type I diabetes.

• Immune system attacks β cells in the islets of Langerhans

• This means they are unable to produce insulin

Describe what occurs in type II diabetes.

• Insulin receptors are lost from cells or lose their responsiveness to insulin

• It may also be due to an inadequate supply of insulin from the pancreas

What are three risk factors of type II diabetes?

• Age

• Obesity

• Poor diet

How is type I diabetes controlled?

• Insulin injections

• Controlled glucose diet

How is type II diabetes controlled?

• Balanced diet/ weight loss

• May be supplemented by insulin injections also

Where do the adrenal glands lie?

Above the kidneys

Where is the pancreas situated?

In the upper abdomen, behind the stomach

Where is the liver located?

Immediately below the diaphragm