3.6 - 3.6.4 - 3.6.4.2 Control of blood glucose concentration (A-level only) Flashcards
What changes the concentration of glucose in your blood? (The 2 E’s)
Eating and exercising.
What is the concentration of glucose in the blood monitored by?
Cells in the pancreas.
Does blood glucose concentration rise after eating food containing carbohydrate?
Yes.
Does blood glucose concentration fall after exercise? and why?
Yes because more glucose if used in respiration to release energy.
What are the name of the two hormones which control blood glucose concentration?
Insulin and glucagon.
What do insulin and glucagon travel in the blood to and act on?
Their target cells (effectors) which respond and restore the blood glucose concentration to the normal level.
What is the name of the clusters of cells, insulin and glucagon, are secreted by in the pancreas?
The islets of langerhans.
What do Beta cells in the islets of langerhans secrete into the blood?
Insulin.
What do Alpha cells in the islets of langerhans secrete into the blood?
Glucagon.
How does insulin lower blood glucose concentration when it is too high?
1 - Insulin binds to specific receptors on the cell membranes of liver cells and muscle cells.
2 - It increases the permeability of the muscle-cell membranes to glucose, so the cells take up more glucose. This involves increasing the number of channel proteins in the cell membranes.
3 - Insulin also activates enzymes in liver and muscle cells that convert glucose into glycogen.
4 - The cells are able to store glycogen in their cytoplasm, as an energy source.
5 - The process of forming glycogen from glucose is called glycogenesis.
6 - Insulin also increases the rate of respiration of glucose, especially in muscle cells.
What are liver cells also called?
Hepatocytes.
How does glucagon raise blood glucose concentration when it is too high?
1 - Glucagon binds to specific receptors on the cell membranes of liver cells.
2 - Glucagon activates enzymes in liver cells that break down glycogen into glucose.
3 - The process of breaking down glycogen is called glycogenolysis.
4 - Glucagon also activates enzymes that are involved in the formation of glucose from glycerol (a component of lipids) and amino acids.
5 - The process of forming glucose from non-carbohydrates is called gluconeogenesis.
6 - Glucagon decreases the rate of respiration of glucose in cells.
Why are the responses of the hormones insulin and glucagon lower than those produced by nervous impulses?
Because they travel in the blood to their target cells.
Why do the effects of hormones tend to last for longer?
Because hormones are not broken down as quickly as neurotransmitters.
What mechanisms keep blood glucose concentration normal?
Negative feedback mechanisms.
How does negative feedback respond to a rise in blood glucose concentration?
1 - Pancreas detects BGC is too high.
2 - B cells secrete insulin and A cells stop secreting glucagon.
3 - Insulin binds to receptors on liver and muscle cells.
4 - Cells take up more glucose, Glycogenesis is activated, Cells respire more glucose.
5 - Less glucose in the blood.
How does negative feedback respond to a fall in blood glucose concentration?
1 - Pancreas detects BGC is too low.
2 - A cells secrete glucagon and B cells stop secreting insulin.
3 - Glucagon binds to receptors on liver cells.
4 - Glycogenolysis is activated, Glyconeogenesis is activated, Cells respire less glucose.
5 - Cells release glucose into the blood.
What does lysis mean?
Splitting.
What does genesis mean?
Making.
Insulin makes glucose transporters available for what type of diffusion?
Facilitated.
What do skeletal and cardiac muscle cells contain?
A channel protein which is a glucose transporter.
What happens when insulin levels are low?
A channel protein which is a glucose transporter is stored in the vesicle in the cytoplasm of cells.
When insulin levels are low, the channel protein is stored in vesicles in the cytoplasm of cells.
When the insulin binds to receptors on the cell-surface membrane, it triggers the movement of the channel protein to the membrane.
Glucose can then be transported into the cell through the channel protein by facilitated diffusion.
What is another hormone apart from glycogon which increases blood glucose concentration?
Adrenaline.
Where is adrenaline secreted from?
The adrenal glands (found just above your kidneys).
When is adrenaline secreted?
When there is a low concentration of glucose in your blood (when you are stressed and when you are exercising).
What does adrenaline bind to?
Receptors in the cell membranes of liver cells.
When adrenaline binds to receptors in the cell membrane of liver cells, what does it activate?
Glycogenolysis (the breakdown of glycogen to glucose).
It also activates glucagon secretion and inhibits insulin secretion, which increases glucose concentration.
When adrenaline binds to receptors in the cell membrane of liver cells, what does it inhibit?
Glycogenesis (the synthesis of glycogen from glucose).
How does adrenaline get the body ready for action?
By making more glucose available for muscles to respire.
What do adrenaline and glucagon act via?
A second messenger.
Both adrenaline and glucagon can activate glycogenolysis inside a cell even though, what?
They bind to receptors on the outside of the cell.
How do adrenaline and glucagon activate glycogenolysis inside a cell even though they bind to receptors on the outside of the cell?
1) The receptors for A and G have specific tertiary structures that make them complementary in shape to their respective hormones. A and G bind to their receptors and activate an enzyme called adenylate cyclase (aka adenylyl cyclase).
2) Activated adenylate cyclase converts ATP into a chemical signal called second messenger.
3) The 2nd messenger is called cyclic AMP (cAMP).
4) cAMP activates an enzyme called protein kinase A. It activates a cascade (a chain of reactions) that breaks down glycogen into glucose (glycogenolysis).
When does diabetes occur?
When blood glucose concentration is not controlled.
What is the name of the condition where blood glucose concentration can’t be controlled properly? what are the two types?
Diabetes mellitus.
Type 1 and type 2.
What happens in type 1 diabetes?
The immune system attacks the B cells in the islets of langerhans so they can’t produce any insulin. Scientists have found that some people have a genetic predisposition to developing type 1 diabetes. They also think that the disease may be triggered by a viral infection.
What happens after eating if you have type 1 diabetes? why?
The blood glucose level rises and stays high - this is called hyperglycaemia and can result in death if left untreated. This is because the kidneys can’t reabsorb all this glucose, so some of it is excreted in the urine.
