Blood glucose homeostasis

Start with basic knowledge of GCSE/A-level content → an excellent candidate will cover most of the following…

Discuss mechanism of insulin  

• Should identify that glucose is a primary metabolite in the body,  though its homeostasis is crucial to maintain a functional state 

• Insulin is the main hormone that regulates glucose concentration 

Describe properties of insulin 

• Peptide hormone released from pancreatic beta-cells 

• Released in response to elevated blood glucose → due to entry of glucose into beta cells via GLUT2 transporters and activation of ATP- sensitive K+ channels 

• Released via exocytosis from vesicles 

Identify that insulin has different effects on different tissues 

• Muscle → stimulates glucose uptake and glycogen synthesis 

• Liver → increases glycogen synthesis, lipogenesis, glycolysis and inhibits gluconeogenesis 

• Adipose tissue → stimulates glucose uptake

Describing the data

• Use a systematic approach

• 1) Title → this graph shows the blood glucose measurements → you can then infer that these measurements were taken after participants consumed bread, mars bars or cheese

• 2) Axes → x-axis shows time in minutes (always mention units!), and y-axis shows blood glucose concentration in mM

• 3) Trends → work your way left to right and talk about any rises/falls in the data

• Starting from 0 minutes, the blood glucose began at a baseline of around 5mM, which then rose variably depending upon the type of food item consumed.

• The rate at which blood sugars rose also varied upon different types of food too.

• Mars bars caused the highest rise in blood glucose (from 5.00 to 6.50 within 20 minutes) at a steeper rate than all the other foods

• Bread caused a more steady rise from 5.00 to around 6.4/6.5 after 40 minutes, but cheese didn’t really seem to affect blood sugars much at all.

• After the initial rises, the blood glucose concentration then started to decrease after peaks back down to baseline

• 4) Underlying mechanisms → think about why blood glucose concentration rose variably with different foods (i.e. higher sugar content in mars bars, slow-release carbs present in bread) and why it reduced back down again (release of insulin)

• 5) Critical appraisal → excellent candidates will then try to comment on the reliability of the data and critique the experiment → think outside the box and question everything!

• e.g. how many study participants were there? how was the glucose level measured (was it done continuously via a glucose monitor, or was it measured at intervals via finger prick)? were the participants fasted before consuming each foods to ensure a fair test? was the participant diabetic or not? were the portion sizes equal for each food?

Experiment design: This is an experiment where participants consumed different types of food, and had their glucose measured at 10 minute intervals over an hour via finger pricks. Participants should ideally all be fasted to ensure standardised test conditions.

Suggests that insulin release is not purely glucose dependent 

• There is a feed-forward insulin release that happens during digestion of any food to prepare the body for a glucose spike 

An excellent candidate will then go on to compare the response of cheese with the other foods.

Explain differences in bread/chocolate:

• Slower increase in concentration in bread as the carbohydrates are stored as starch → takes longer to digest than simple sugars in chocolate 

• Smaller peak concentration with bread as carbs do not enter circulation all at once,  so the body has longer to remove them

• Chocolate (i.e. mars bars) on the other hand are simple sugars which are digested very quickly → causing a more rapid spike in blood glucose.

• These ideas are much easier to work out if you look at the graph and put yourself in the shoes of the person collecting the data → pretend you are carrying out the experiment yourself and see what’s missing

• Subjects may not consume entire portion → the portion sizes may not also be standardised (e.g. a loaf of bread is much bigger than a single slice of cheese or half a mars bar)

• Subjects may not wash hands so the needle prick may be contaminated with sugar from the skin 

• The glucose monitor may not be accurately calibrated, giving large error bars on the data (as shown on the graph)

• Subjects may have consumed food prior to experiment → this may tamper with feed-forward insulin release as mentioned earlier