- Normal Blood glucose concentration: 90 mg/100cm-3
- Monitored by the pancreas
- Increases due to consumption of carbohydrates
- Decreases due to exercise
Hormonal Control of Blood Glucose Concentration
- Blood glucose concentration is the result of the hormones insulin and glucagon
- Insulin and glucagon are secreted by islet of Langerhans found in the pancreas.
- 2 types Islet of Langerhans
- Alpha Cells
- Secretes glucagon into the blood
- Beta cells
- Secretes insulin into the blood
- Alpha Cells
Insulin
- Lower blood glucoses concentrations (when too high)
- Binds to specific receptors on cell membranes on muscle cells and hepatocytes (liver cells)
- Increases permeability of muscle-cell membranes to glucose so that the cells take up more glucose
- It does this by increasing the number of channel proteins on the cell membrane
- Glycogenesis is the activation of an enzyme in muscle and liver cells that convert glucose à glycogen
- Cells are able to store glycogen in cytoplasm
Glucagon
- Raises blood glucose concentration (when too low)
- Binds to specific rececptors on the cell membrane of liver cells
- Glycogenolysis is the activation of an enzyme that break down Glycogen à Glucose
- Gluconeogenesis is the activation of a different enzyme which is involved in the formation of glucose from glycerol and amino acids
Overall Process of glycogenolysis and gluconeogenesis
Rise in Glucose Blood Concentration
- Pancreas detect blood glucose concentration is too high
- Beta cells secrete insulin and the alpha cells stop secreting glucagon
- Insulin binds to receptors on liver and muscle cells
- Liver and muscle cells respond to decrease the blood glucose concentration (glycogenesis)
- Blood glucose concentrations return back to normal
Fall In Glucose Blood Concentration
- Pancreas detect blood glucose concentration is too low
- alpha cells secrete glucagon and beta cells stop secreting insulin
- Glucagon binds to receptors on liver
- Liver respond to increase the blood glucose concentration (glycogenolysis)
- Blood glucose concentrations return back to normal
Glucose Transporters
- Type of channel protein
- Allows glucose to be transported across cell membrane
- Skeletal and cardiac muscles contain a type of glucose transporter (GLUT4)
- Insulin levels are low:
- GLUT4 is stored in vesicles in the cytoplasm
- Insulin Levels are high:
- GLUT4 moves to the cell membrane
- Glucose can be transported into the cell using the GLUT4 protein via facilitated diffusion
Adrenaline
- A hormone that is secreted from the adrenal gland (kidneys)
- Secreted when low concentration of glucose in blood during stressed activity
- Adrenaline binds to receptors on cell membrane of liver cells to:
- Activates glycogenolysis
- Inhibits glycogenesis
- Activates glucagon secretion
- Inhibitors insulin secretion
- Overall adrenaline increase the glucose concentration for muscle response
- Type of second messenger
- Both adrenaline and glucagon activate glycogenolysis inside a cell despite there only being binding to receptors on the outside of the cell
- Second messenger model is the binding of the hormone to cell receptors which activate an enzyme on the inside of the cell membrane which bring about a response