Controlling Blood Glucose Concentration Flashcards
1
Q
How can glucose enter bloodstream?
A
- Absorption in gut
- Hydrolysis of glycogen
- Non-carbs like lipids, lactate and amino acids converted to glucose
2
Q
What happens (overview) if there is an increase in blood glucose concentration?
A
- β cells secrete insulin
- α cells stop secreting glucagon
- Increased glucose uptake into muscle and liver cells
- Increased glycogenesis
3
Q
What happens (overview) when there is a decrease in blood glucose concentration?
A
- α cells release glucagon
- β cells stop releasing insulin
- Rapidly released from storage molecules
- Led by glycogenolysis and gluconeogenesis
4
Q
2 main hormones in blood glucose regulation and their sites of secretion?
A
- Insulin, secreted by β cells
- Glucagon. secreted by α cells
- Found in the pancreas
- Tissue group called islets of Langerhans
5
Q
What are the α and β cells in the pancreas?
A
- α cells secrete glucagon
- β cells secrete insulin
- They are receptors and initiate responses in cell signalling
6
Q
A decrease in blood glucose concentration causes :
A
- Glucagon binds to receptors in cell surface membrane of liver cells
- Conformational changes in receptor proteins activating a G protein
- Activated G protein activates enzyme adenylyl cyclase
- Activated adenylyl cyclase catalyses conversion of ATP to cyclic AMP (cAMP, which is a second messenger)
- cAMP binds to protein kinase A enzymes
- Active protein kinase A enzymes activate phosphorylase kinase enzymes by adding phosphate groups to them
- Active phosphorylase kinase enzymes activate glycogen phosphorylase enzymes
- Active glycogen phosphorylase enzymes catalyse breakdown of glycogen to glucose
- THIS IS GLYCOGENOLYSIS
- This cascade results in release of extra glucose by liver to increase blood glucose concentration
7
Q
What effect does adrenaline have on blood glucose concentration?
A
- Increases BGC
- Binds to different receptors on surface of liver cells
- Activates the same enzyme cascade, and same end result (glycogen -> glucose) (glycogenolysis)
- Also stimulates breakdown of glycogen stores in muscles during exercise, where glucose remains in muscle cells for respiration
8
Q
An increase in blood glucose concentration causes :
A
- β cells detect
- When high concentration of glucose, it diffuses through Glut 2 Channel proteins by facilitated diffusion
- Glucose phosphorylated by glucokinase
- Glycolysis of glucose converts it to ATP
- High ATP concentration causes potassium channels to close
- Membrane potential decreases from -60 to -30 mv due to buildup of K+ ions
- Voltage-gated calcium channels open
- Influx of calcium ions causes vesicles containing insulin to fuse with cell surface membrane and by exocytosis release insulin into capillaries
- Insulin then stimulates UPTAKE OF GLUCOSE by muscle cells, fat cells and liver
9
Q
What does insulin do?
A
- Targets glucose transport proteins in fat, muscle and liver cells
- Glucose transport receptors are insulin sensitive
- Insulin binds to these receptors on target cells
- Stimulates them to activate more glucose transporter proteins to cell surface membrane, INCREASING PERMEABILITY OF CELLS TO GLUCOSE
- So rate of glucose diffusion increases, and blood glucose levels decrease
- It also stimulates increase of uptake of glucose in liver by stimulating glycogenesis
- Blood glucose level is lowered in liver cell
- Steep concentration gradient maintained so more glucose diffuses in
Converts glucose into fats
More glucose used in respiration
10
Q
What is negative feedback generally?
A
- Receptors detect whether X level is too low or high
- Hormonal or nervous system communicates to effectors
- Effectors react to counteract change
- Bringing X level back to normal
11
Q
In the control of blood glucose concentration, how does negative feedback apply?
A
- α and β cells act as receptors in pancreas
- Release hormones glucagon and insulin
- Liver cells are effectors in response to glucagon, and liver, muscle and fat cells respond to insulin.
12
Q
What does the liver do in controlling blood glucose concentration?
A
- Converts glycogen to glucose
Site of
- Glycogenesis
- Gluconeogenesis
- Glycogenolysis
13
Q
What is glycogenesis?
A
- Glucose to glycogen
- Triggered by insulin in response to high BGC
- Removes glucose from bloodstream, reducing BGC to normal range
14
Q
What is glycogenolysis?
A
- Glycogen to glucose
- Triggered by glucagon in response to low BGC
- Activates enzymes in liver to do this
- So more glucose released increasing BGC to normal range
15
Q
What is gluconeogenesis?
A
- Glucose from non-carb molecules
- Glucagon triggers (same enzyme cascade as glycogenolysis)
- Fatty acids and amino acids to glucose
- Glucose released to blood, increasing BGC to normal range
