Homeostasis- Control of Blood Glucose Concentration Flashcards
Why must blood glucose concentration be carefully controlled?
Because all cells need a constant energy supply to work
How is blood glucose concentration monitored?
By cells in the pancreas
When does blood glucose concentration rise?
After eating food containing carbohydrate
When does blood glucose concentration fall?
After exercise, as more glucose is used in respiration to release energy
How is blood glucose concentration controlled?
By insulin and glucagon
How is insulin secreted?
By Beta cells in the islets of Langerhans in the pancreas
How is glucagon secreted?
By Alpha cells in the islets of Langerhans in the pancreas
What does insulin do?
Lowers blood glucose concentration when it’s too high
How does insulin lower blood glucose concentration?
- Insulin binds to specific receptors on cell membranes of liver cells and muscle cells
- Increases permeability of muscle cell membranes to glucose so cells take up more glucose- involves increasing number of channel proteins in cell membranes
- Also activates enzymes in liver and muscle cells that convert glucose into glycogen
- Cells are able to store glycogen in cytoplasm as an energy store
- Glycogenesis= forming glycogen from glucose
- Insulin also increases rate of respiration of glucose
What does glucagon do?
Raises blood glucose concentration when it’s too low
How does glucagon raise blood glucose concentration?
- Glucagon binds to specific receptors on cell membranes of liver cells
- Activates enzymes in liver cells that break down glycogen into glucose
- Glycogenolysis= breaking down glycogen
- Also activates enzymes involved in formation of glucose from glycerol and amino acids
- Gluconeogenesis= forming glucose from non-carbohydrates
- Glucagon decreases rate of respiration of glucose
What is glycogenesis?
Process of forming glycogen from glucose
What is glycogenolysis?
Breaking down glycogen
What is gluconeogenesis?
Forming glucose from non-carbohydrates
Why are responses produced by hormones slower than those produced by nervous impulses?
Because hormones travel in the blood
Why do effects from hormones last longer?
They are not broken down as neurotransmitters are
How do negative feedback mechanisms work when they detect a rise in blood glucose concentration?
- Pancreas detects blood glucose concentration is too high
- Beta cells secrete insulin and alpha cells stop secreting glucagon
- Insulin binds to receptors on liver and muscle cells
- Cells take up more glucose, glycogenesis is activated, cells respire more glucose
- Less glucose in the blood —> return to normal blood glucose concentration
How do negative feedback mechanisms work when they detect a fall in blood glucose levels?
- Pancreas detects blood glucose concentration is too low
- Alpha cells secrete glucagon and beta cells stop secreting insulin
- Glucagon binds to receptors on liver cells
- Glycogenolysis is activated, gluconeogenesis is activated, cells respire less glucose
- Cells release glucose into the blood —> return to normal blood glucose concentration
What is GLUT4?
A glucose transporter- a channel protein in skeletal and cardiac muscle cells
When is GLUT4 stored in vesicles in the cytoplasm of cells?
When insulin levels are low
When is the movement of GLUT4 to the membrane triggered?
When insulin binds to receptors on the cell-surface membrane
How is glucose transported into the cell?
Through the GLUT4 protein by facilitated diffusion
What is adrenaline?
A hormone secreted from your adrenal glands
When is adrenaline secreted?
When there’s a low concentration of glucose in your blood, when your stressed and when your exercising
