Regulation of blood glucose concentration

Question 1

WHy does blood glucose concentration need to be controlled?

Answer 1

• to remain healthy it needs to be constant
• w/o control, blood glucose conc. would range from very high levels after a meal, to very low levels several hours later
• at these low levels cells would not have enough glucose for respiration

Question 2

How can blood glucose conc. increase?

Answer 2

• diet - when you eat carbohydrate rich foods - carbs. broken down to release glucose - abosrbed into blood stream
• glycogenolysis - glycogen stored in the liver and muscle cells is broken down into glucose which is released into the bloodstream increasing blood glucose conc.
• glucogenesis - production of glucose from non-carbohydrate sources - e.g. the liver is able to make glucose from glycerol (from lipids) and amino aids - released into bloodstream

Question 3

How is blood glucose concentration decreased?

Answer 3

• respiration - some of the glucose in the blood is used by cells to release energy - increases rate of glucose usage as activity increases
• glycogenesis - production of glycogen - when blood glucose conc. is too high, excess glucose taken in through diet is convered into glycogen which is stored in the liver

Question 4

What cells produce insulin and where are they?

Answer 4

beta cells of the islets of Langerhans in the pancreas

Question 5

How is insulin released?

Answer 5

• beta cells detect a rise in blood glucose conc. and respond by secreting insulin directly into the blood streeam

Question 6

How does insulin cause an effect in cells?

Answer 6

• virtually all body cells have insulin receptors on their surface membrane (except erythrocytes_
• when insulin binds to its glycoprotein receptor, it causes a change in the tertiary structure of the glucose transport protein channels
• this causes the channels to open allowing more glucose to enter
• insulin also acitvates the enzymes within some cells to convert glucose to glycogen and fat

Question 7

How does insulin lower blood glucose conc.

Answer 7

• increases rate of absorbtion of glucose by cells - in particular the skeletal muscle cells
• increasing the respiratory rate of cells - increases their need for glucose and causes a higher uptake of glucose from the blood
• increasing the rate of glycogenisis - stimlates the liver to remove glucose from the blood by turning the glucose into glycogen and storing it in the liver and muscle cells
• increasing the rate of glucose to fat conversion
• inhibiting the release of glucagon from the alpha cells in the islets of Langerhands

Question 8

Why does insulin secretion need to be sustained?

Answer 8

it is broken down by enzymes in the cells of the liver

Question 9

How are the beta cells an example of negative feedback?

Answer 9

• beta cells detect the blood glucose concentration returns to normal
• when it falls below a set level, beta cells reduce their secretion of insulin
• negative feedback ensures that, in any control system, changes are reversed and returned back to the set level