5.4.4: Regulating blood glucose Flashcards
What is the normal blood concentration of blood glucose?
Between 4 and 6 mmol dm-3
What happens If a person’s blood glucose concentration is allowed to drop below 4mmol dm-3 and remain too low for long periods?
The person is said to be hypoglycemic.
What is the main problem caused by hypoglycemia?
There is an inadequate delivery of glucose to the body tissues and, in particular, to the brain.
What can mild hypoglycemia cause?
tiredness and irritability.
What happens in severe cases of hypoglycemia?
There may be impairment of brain function and confusion, which may lead on to seizures, unconsciousness and even death.
What happens if blood glucose concentration is allowed to rise too high for long periods?
Hyperglycemia.
What can permanently high blood glucose concentrations lead to?
Significant organ damage.
What is a blood glucose concentration that is consistently higher than 7 mmol dm-3 used as the diagnosis for?
Diabetes mellitus
Which cells constantly monitor the blood glucose concentrations?
The cells in the islets of Langerhans.
What happens if blood glucose concentrations rise or fall away from the acceptable concentrations.
The alpha and beta cells in the islets of Langerhans detect the change and respond by releasing the relevant hormone.
Too high - insulin
Too low - glucagon
What do the hormones released by the islets of Langerhans act on?
Cells in the liver (hepatocytes) which can store glucose in the form of glycogen.
When there is excess glucose in the blood, what happens to it?
It is converted to glycogen.
What happens if blood glucose concentration needs to be raised?
The glycogen is converted back into glucose.
Which cells in the islets of Langerhans detect high blood glucose concentration?
The beta cells.
How do the beta cells respond to high blood glucose concentrations?
-They excrete insulin into the blood.
-Insulin travels through the body in the circulatory system .
The target cells are the liver cells, muscle cells and some other body cells including the brain.
Why is insulin unable to pass through the cell surface membrane?
Because it is a small protein of 51 amino acids.
Describe the action of insulin on the liver cells.
- The target cell possesses the specific membrane bound receptors for insulin.
- When insulin binds to the insulin receptor, this activates the enzyme tyrosine kinase which is associated with the receptor on the inside of the membrane.
- Tyrosine kinase causes phosphorylation of inactive enzymes in the cell.
- This activates the enzymes leading to a cascade of enzyme-controlled reactions inside the cell.
What effects does insulin have on the cell?
- More transporter proteins specific to glucose are placed into the cell surface membrane. This is achieved by causing vesicles containing these transporter proteins to fuse with the membrane.
- More glucose enters the cells.
- Glucose in the cell is converted to glycogen for storage (glycogenesis).
- More glucose is converted into fats.
- More glucose is used in respiration.
Which cells in the islets of Langerhans detect low blood glucose concentration?
alpha cells
How do the alpha cells respond to low blood glucose concentrations?
They secrete the hormone glucagon into the blood
Why is glucagon unable to pass through the cell surface membrane?
Glucagon is a small protein containing 29 amino acids.
What are the target cells of glucagon?
Hepatocytes which possess the specific receptor for glucagon.
What is the effect of glucagon on a cell?
-Glycogen is converted into glucose (glycogenesis)
What is the effect of glucagon on a cell?
- Glycogen is converted into glucose (glycogenolysis) by phosphorylase A, which is one of the enzymes activated in the cascade.
- More fatty acids used in respiration.
- Amino acids and fats converted into additional glucose, by gluconeogenesis.
- Overall=increase in blood glucose concentration
The concentration of blood glucose is controlled by a negative feedback mechanism involving which hormones?
Describe how these hormones are antagonistic.
- Insulin and glucagon.
- They have opposite effects on blood glucose concentration.
- One of the effects is to inhibit the effects of the opposing hormone.
