Topic 6- Control of blood glucose concentration Flashcards
what is negative feedback?
when any deviation from the normal values is restored to their original level
|> involves the nervous system and often hormones too
what is the normal concentration of blood glucose?
5mmol dm-3
what are the three sources that blood glucose comes from?
-directly from the diet in the form of glucose absorbed following hydrolysis of other carbohydrates such as starch, maltose, lactose and sucrose
-from the hydrolysis in the small intestine of glycogen
|> glycogenolysis
-from gluconeogenisis, production of glucose from other sources of carbohydrate
-intake of glucose in animals fluctuates-> animals do not eat continuously and diet varies
-glucose is used in respiration at different rates-> depending on physical demand
Describe the factors that influence blood glucose concentration
-consumption of carbohydrates-> glucose absorbed in the blood
-rate of respiration of glucose e.g increases during exercise due to muscle contraction
Glycogenesis
-Conversion of glucose-> glycogen
|> when blood glucose is higher than normal-> liver removes glucose from the blood and coverts to glycogen
Glycogenolysis
- hydrolysis of glycogen to glucose
|> when blood glucose concentration is lower than normal, liver converts glycogen back into glucose -> diffuses into blood to restore the normal blood glucose concentration
Gluconeogenesis
-production of glucose from sources other than carbohydrate
|> when glycogen supply is exhausted, liver can produce glucose from non-carbohydrate sources such as glycerol+ amino acids
Explain the action of insulin in decreasing blood glucose concentration
1)Beta cells in the islets of Langerhans in the pancreas have receptors that detect when blood glucose levels are too high
-> respond by secreting insulin
2)Insulin attaches to specific receptors on cell surface membranes of target cells e.g liver/ muscles
3)Causes a change in the tertiary structure of glucose channel proteins, change shape and open, allowing more glucose to enter cells by facilitated diffusion
4) There is also an increase in the number of channel proteins incorporated into the cell membranes
-at low insulin conc, the protein from which these channels are made is part of the membrane of vesicles
-increase in insulin causes these vesicles to fuse with cell surface membrane
|> more channel proteins are incorporated into cell membranes -> more glucose absorbed from blood into cells
5) Also activates enzymes involved in in the conversion of glucose to glycogen (glycogenesis
|> lowering glucose concentration in cells, creating a concentration gradient-> glucose enters cells by FD
As a result of insulin, blood glucose concentration is lowered in on or more of the following ways:
1.by increasing rate of absorption of glucose into cells-> especially muscle cells
2.by increasing respiratory rate of cells, which therefore use up more glucose-> increasing rate of glucose uptake ion the blood
3. increasing rate of conversion of glucose-> glycogen in the cells of liver and muscles
4. increase rate of conversion go glucose to fat
How is insulin secretion negative feedback?
-the effect of the processes of insulin is to remove glucose from the blood-> return its concentration to the optimum
-this decrease in blood glucose conc-> causes B cells to decrease secretion of insulin
|> negative feedback
What detects when blood glucose is too low?
Alpha cells in the islets of Langerhans in the pancreas detect when blood glucose concentration is too low
Explain the action go glucagon in increasing blood glucose concentration
1)Glucagon attaches to specific receptors on the cell surface membrane of target cells e.g liver
2)When glucagon binds it causes a protein to be activated into adenylate cyclase and to convert ATP into a molecule called cyclic AMP (cAMP)
-cAMP activates an enzyme, protein kinase-> involved in the hydrolysis of glycogen to glucose (glycogenlysis)
3) Also activates enzymes involved in the conversion of glycerol/ amino acids-> glucose (gluconeogenesis)
|> this establishes a concentration gradient -> glucose enters blood by FD
what is the overall effect of the action of glucagon?
- to increase concentration of glucose in the blood and return it to its optimum concentration
-> this raising of blood glucose concentration -> causes alpha cells to decrease the secretion of glucagon = negative feedback
Explain the role of adrenaline in increasing blood glucose concentration
-Fear/ stress/ exercise-> adrenal glands secrete adrenaline
1.Adrenaline attaches to specific receptors on the cell surface membrane of target cells e.g liver cells
2. Causes a protein to be activated and to convert ATP- cAMP
3.cAMP activate an enzyme that hydrolyses glycogen -> glucose
|>(activates enzymes involved in the hydrolysis of glycogen to glucose) glycogenolysis
4. This establishes a concentration gradient -> glucose enters blood by FD
-> known as the second messenger model of adrenaline and glucagon action
|> because the process results in the formation of cAMP-> acts as a second messenger
Describe the second messenger model of adrenaline and glucagon action
-adrenaline and glucagon (first messengers) attach to specific receptors on the cell membrane of a liver cell which:
1.The binding of adrenaline/ glucagon causes the change in shape of the enzyme adenylate cyclase (changes shape)
2.The activated adenyl cyclase converts ATP-> Cyclic AMP (cAMP)
3.cAMp acts as a second messenger -> binds to protein kinase enzyme, changing its shape and therefore activating it
4.Protein kinase enzyme catalyses the conversion of glycogen to glucose
|> which moves out of the liver cell by FD into the blood-> through channel proteins
