Topic 6: Blood Glucose Flashcards
What hormones are involved in the control of blood glucose concentration?
Insulin
Glucagon
Adrenaline
What is the average blood glucose concentration in a human?
90mg per 100cm3
There is a narrow range of 70-100mg
Why is it important that the blood concentration is maintained ?
Cells need a constant/consistent supply of glucose for respiration
Glucose is a major respiratory substrate
What is the source of glucose in the diet?
Carbohydrates
Summarise what will happen if the blood glucose level falls too low
Cells will die
Brain cells for example, can only respire glucose and not use other organic molecules as respiratory substrates so they would die
Summarise what would happen if the concentration of blood glucose what’s too high
It lowers the water potential of blood and creates osmotic problems that can cause dehydration
What are the sources of blood glucose
Absorption from the gut after the digestion of carbohydrates
The breakdown of glycogen stored in liver and muscle cells
The conversion of non-carbohydrates into glucose
What is the name given to the conversion of non-carbohydrates (e.g. lactate, fats and amino acids) into glucose?
Gluconeogenisis
What is the role of the pancreas?
It is mainly involved in producing enzymes for digestion
It is involved in regulations blood glucose by producing insulin and glucagon
How is the pancreas involved in regulating blood glucose?
1-2% of pancreatic tissue is made up of clusters of cells that produce hormones, known as the islets f langerhans
What are the Islets of Langerhans?
They are clusters of cells in the pancreas
They have 2 cell types: alpha and beta
Alpha produce glucagon
Beta produce insulin
What do alpha cells produce?
Glucagon
what do beta cells produce?
Insulin
What is the role of the liver?
The insulin and glucagon produced in the pancreas have effects in the liver
It is where glycogenesis, glycogenolysis and gluconeogenesis occur
Glycogenesis
Conversion of glucose to glycogen
Glycogenolysis
Breakdown of glycogen to glucose
Gluconeogenesis
Production of glucose from other sources than glucose
What happens when there is a rise in blood glucose?
- Rise is detected by beta cells, they then produce insulin
- Vesicles of insulin move to the membrane and release it into the capillaries
- Insulin diffuses into the blood
- Insulin attaches to receptor molecules on cell membranes- especially adipose storage tissue, muscles and liver
What does insulin do ?
- causes a change in the tertiary structure of channel proteins in the liver and muscle cells so they open
- increase in number of channel proteins in the membranes of muscle and adipose cells
-Activation of enzymes in the liver to convert glucose to glucose phosphate
-activation of enzymes in the liver and muscles for glycogenesis
-activation of enzymes in the adipose tissues to convert glucose to fat - an increase in the rate of aerobic respiration in cells
Insulin causes a change in the tertiary structure of channel proteins in the membranes of liver and muscle cells so they open. How does that lower the blood glucose concentration?
More glucose molecules enter the liver and muscle cells by facilitated diffusion
Insulin results in an increase in the number of channel proteins (GLUT-4) in the membranes of muscle and adipose cells. How does this lower blood glucose?
The rate of uptake of glucose from the blood by facilitated diffusion is increased because of the increased permeability of the cell membrane
Insulin results in enzymes being activates in the adipose tissue to convert glucose to fat. How does this lower the blood glucose concentration?
It maintains a steep diffusion gradient between the blood and cells, so the rate of uptake of glucose is increased
Insulin causes an increase in the rate of aerobic respiration in cells. How does this lower blood glucose?
Cells respire more glucose, so they increase their uptake from the blood
What does the action of insulin result in?
Blood glucose concentration returning to normal
Beta cells reduce their secretion of insulin
It’s an example of negative feedback
When does the blood concentration fall?
During exercise or when a person is fasting or starving
This is because glucose has been used for cellular respiration
What happens when the blood glucose drop?
When it drops below 90mg per 100cm3, the secretion of insulin stops
Alpha cells in the islets of Langerhans secrete glucagon
Glucagon diffuses into the blood and mainly affects liver cells
What does glucagon do?
Causes the activation of enzymes in the liver that:
- breakdown stored glycogen into glucose(glycogenolysis)
-convert other substances to glucose (gluconeogenesis)
What happens as a result of glucagon acting?
Blood glucose increases
Alpha cells reduce secretion of glucagon (example of negative feedback)
What is the relationship between insulin and glucagon?
They act antagonistically (in opposite directions)
Where and when is adrenaline produced?
By the adrenal glands
In times of excitement,stress,exercise, when blood concentration is low
Explain the role of adrenaline in the control of blood glucose concentration
-it binds to protein receptors on the cell surface membrane of liver cells
-activates enzymes in the liver to cause glycogenolysis, and inhibit enzymes that carry out glycogenesis
- activates secretion of glucagon but inhibits insulin
What happens as a result of adrenaline in the control of blood glucose?
More glucose is available for respiring muscles
It allows a boost of respiratiory substrate for more respiration and more muscle contraction for fight or flight
What is the second messenger model?
The mechanism used by adrenaline and glucagon which both activate glycogenolysis inside cells
Summarise what the second messenger model does
It works where hormones bind to cell receptors which activate enzymes on the inside of cell membranes, which then produces a chemical known as a second messenger
The second messenger activates other enzymes to in the cell to bring a response
What is the first messenger ?
Adrenaline
Adrenaline is the first messenger, what does it do?
It and glucagon bind to the specific receptors on the cell surface membrane of target cells to form a hormone receptor complex
The hormones receptor complex activates an enzyme inside the cell
What enzyme is activated by the hormone-receptor complex in the second messenger model?
Adenylate cyclase
What does adenylate cyclase do in the second messenger model?
It converts ATP into cAMP by removing 2 phosphate groups
CAMP acts as a second messenger
What is the second messenger?
cAMP
What does cAMP do in the second messenger model?
It activates protein kinase which activates a set of chain reactions to bring about the breakdown of glycogen to glucose
Why is ADP more common than AMP, when more energy would be released from the hydrolysis of AMP?
It isnt as energy efficient to resynthesise 2 phosphates
How many types of diabetes are there?
2
Which type of diabetes is insulin dependent?
Type 1
What type of diabetes is insulin independent?
Type 2
Causes of type 1 diabetes
It is an auto immune condition
The body’s T cells attack and destroy beta cells so there is a shortage of insulin
Pancreas cannot produce insulin
It begins in childhood
What is the effect of type 1 diabetes?
It can lea to high levels of blood glucose concentration after a meal and it can affect the brain, leading to coma or death
What are the symptoms of type 1 diabetes?
Glucose appears in urine (kidney cannot absorb it all)
Urinating frequently
Thirst
Tiredness
Weight loss
Why does someone with type 1 diabetes urinate frequently and feel thirsty?
More glucose in urine means less water is reabsorbed
How is type 1 diabetes treated?
Insulin injections- fast acting and slow acting insulin is available
Management of exercise and carbohydrate intake
Why does insulin have to be injected in the treatment of type 1 diabetes?
It is a protein
If it was ingested it would be digested
What is the hazard of treatment for type 1?
If a diabetic takes too much insulin, it could lower blood glucose too much which results in unconsciousness
What is the cause of type 2 diabetes?
Glycoprotein receptors in the body, especially in liver and fat storage tissue lose their responsiveness to insulin
May also be due to inadequate supply of insulin from the pancreas
What is type 2 diabetes related to and how is this seen?
Often related to obesity
Tends to occur in over 40s, but more and more common in obese adolescents
90% of UK diabetes cases are type 2
What are the symptoms of type 2 diabetes?
Symptoms develop slowly and may be unnoticed
Possible symptoms: tiredness, blurred vision, sugar in urine
How is type 2 diabetes treated?
Regulation of carbohydrate intake
Lower fat content of diet
Exercise is needed
Drugs may be needed to stimulate insulin production
May need insulin injections
