6.4.2 Control of blood glucose concentration Flashcards
What are hormones?
- Produced in glands, which secrete the hormone directly into the blood (endocrine glands)
- Carried in the blood plasma to the target cells - which have specific receptors on their cell-surface membranes that are complementary to a specific hormone
- Effective in low concentration, but often have widespread and long-lasting effects
Describe what happens when adrenaline binds to a transmembrane protein receptor (secondary messenger mechanism):
- Binding of adrenaline causes the protein to change shape on the inside of the membrane
- Leads to activation of an enzyme called adenyl cyclase
- The activated adenyl cyclase converts ATP to cyclic AMP (cAMP)
- The cAMP acts as a second messenger that binds to protein kinase enzyme, changing its shape and therefore activating it
- Active protein kinase catalyses the conversion of glycogen to glucose which moves out of the liver cell by facilitated diffusion and into blood, through channel proteins
Why does blood glucose need to be controlled?
- Effects water potential of blood plasma
- Cells need a constant supply for respiration
What are the hormones and organs involved in this control of blood glucose?
HORMONES:
- Insulin
- Glucagon
- (Adrenaline)
ORGANS:
- Liver - stores glucose as glycogen
- Pancreas - secreting insulin and glucagon, monitoring blood glucose
- Muscle - also store glucose as glycogen
What happens when there is a rise in blood glucose?
- Detected by beta cells in pancreas
- Beta cells secrete insulin into the blood
- Insulin binds to receptors on liver, muscle and other cells
- Mechanisms out in place to lower blood glucose
What happens when blood glucose levels fall?
- Detected by alpha cells in pancreas
- Alpha cells secrete glucagon into the blood
- Glucagon detected by receptors on liver and cells
- Liver cells convert glycogen back to glucose and release it into the blood
How does insulin work?
- Binds to receptors (made of protein/glycoprotein) on cells
- Causes glucose transporter proteins to change shape and open
- Increases the number of glucose carrier molecule of surface of cells (increases uptake of glucose from the blood)
- Activates the enzymes that convert glucose into glycogen and fat
What are the effects on insulin?
- Increase in uptake of glucose out of the blood and into cells (particularly in muscles) increase conversion of glucose into glycogen in muscles and liver (GLYCOGENESIS)
- Increase conversion of glucose into fat for storage
- Increases respiratory rate
How does glucagon work?
- Binds to receptors on liver cells
- Activates enzymes that convert Glycogen into glucose
- Activates enzymes that convert glycerol and amino acids into glucose.
What are the effects of glucagon?
- Increase in conversion of stored glycogen –> glucose (GLYCOGENOLYSIS)
- Increase conversion of glycerol and amino acids into glucose (GLUCONEOGENESIS)
Where is adrenaline produced?
Adrenal glands in response to stress.
It causes the fight or flight response, preparing the body for action
How does adrenaline raise blood glucose?
- Attaching to receptors on cell surface membrane
- Activating enzymes that cause the breakdown of glycogen –> glucose
What is diabetes?
A disorder in which the blood glucose concentration cannot be effectively controlled
What is type I diabetes?
- Early onset or insulin dependent diabetes
- Body does not produce insulin (due to an autoimmune response - that destroys the beta cell)
- Treated by injecting insulin after food
What is type II diabetes?
- Obesity, diets high in sugar
- Insulin no longer works properly - due to glycoprotein receptors on body cells being lost/losing responsiveness to insulin
- Treated by controlling diet
- Develops slowly
