Lab 2: Glucose tolerance test

Question 1

Explain the “health and safety” precautions associated with taking and handling blood

Answer 1

• All clinical waste is deposed of in a designated bins for subsequent incineration
• Lab coat and apron must be woren when handling and taking blood

Question 2

Describe how the glucose tolerance test of a person with diabetes would differ from that of a healthy individual

Answer 2

Question 3

In a healthy individual, blood glucose will be ____ after ingestion of a fixed dose of glucose but within ___ hours the concentration of blood glucose should have returned to normal

Answer 3

A) Elevated

B) Two

Question 4

In a healthy individual, blood glucose will be elevated after ingestion of a fixed dose of glucose but within two hours the concentration of blood glucose should have returned to normal.

How is this statement different for those with diabetes

Answer 4

Ingestion of the same fixed dose of glucose will result in an abnormally high concentration of glucose in the blood which will be sustained for an extended period of time.

Question 5

Descibe the method of using a blood glucose sensor

Answer 5

• Put the test strip into the sensor
• Clean the target site with an antiseptic swab
• Allow the target site to dry
• Punture the skin of the target site with a sterile disposable lancet- encourage the blood to flow to the punture site.
• Allow the drop of blood from the punture site to be absorbed by capillary action by the test time.
• The sensor will now give a reading of the blood glucose level (in mmol/l)

Question 6

How does the “ExacTech Blood Glucose Monitoring” system work in measuring blood glucose levels

Answer 6

Glucose (along with water and oxygen) are converted by glucose oxidase in the sensor to gluconic acid and hydrogen peroxide.

As a result, a minute current is generated- this current is proportional to the glucose concentration

Question 7

How does the clinistix work in measuring blood glucose levels

Answer 7

Glucose (along with water and oxygen) are converted by glucose oxidase in the sensor to gluconic acid and hydrogen peroxide.

The hydrogen peroxide is used by the enzyme, peroxidase, to catalyse the oxidation of a colourless dye to the coloured oxidised form

The colour is produced only if glucose is present

Question 8

What contains more glucose:

Lucozade or the Mars Bar

Answer 8

Lucozade (34g), as mars bar only contains 23.6g of glucose

Question 9

Where does most of the glucose go two hours after ingestion? (if fasted beforehand)

Answer 9

Goes to the liver

In the fasted state, glycogen stores are used as fuel

When glucose is ingested it is absorbed in the small intestine and enters the bloodstream (in the portal vein). The portal vein drains into the liver therefore this is the place glucose will be (to replenish the glucogen stores)

Question 10

Describe what happens to glucose at the kidneys

Answer 10

Glucose is filtered freely at the glomerulus

It is rebsorbed at the proximal convoluted tubule (90%) with the remaining being absorbed at the distal convoluted tubule

Question 11

Define the term renal threshold

Answer 11

This is the capacity the kidneys are able to reabsorb glucose. If blood glucose level exceeds this threshold, glucose will be lost in urine

Question 12

What is the normal value for the renal threshold

Answer 12

11 mmol/L

Question 13

When, during the period of the glucose tolerance test, would you expect the highest concentration of insulin?

Answer 13

After the peak of glucose

Appears to lag behind the glucose as insulin is produced in response to glucose

Question 14

Fill in the blanks

Answer 14

Question 15

When, during the period of the glucose tolerance test, would you expect the highest concentration of glucagon?

Answer 15

At the start of the experiment as this was the longest period of fasting

Question 16

Glucose reabsorption is two-fold:

1. Apical membrane (from tubule to cell)
2. Basal membrane (from cell to the bloodstream)

Describe the process of the glucose reabsorption across the apical membrane.

Answer 16

Utilises the sodium glucose linked transporter (SGLT 2)

Solutes dissolved in water naturally tend to diffuse from areas of high to low concentration, which causes the sodium ions to flow back into the cell. The cell takes advantage of this concentration gradient using SGLT2, which couples the cross-membrane transport of a sodium ion to the transport of a glucose molecule.

Question 17

Which SGLT receptor is found in the kidneys and is important in the reabsorption of glucose

Answer 17

SGLT-2

Question 18

Glucose reabsorption is two-fold:

1. Apical membrane (from tubule to cell)
2. Basal membrane (from cell to the bloodstream)

Describe the process of the glucose reabsorption across the basal membrane.

Answer 18

Once the glucose is in the renal epithelial cell it leaves the cell into the bloodstream via GLUT-2 receptor.

GLUT-2 moves glucose down its concentration gradient

The sodium is removed from the epithelial cell by the sodium potassium pump.

Question 19

Which GLUT receptor is found in the kidneys and is important in the reabsorption of glucose

Answer 19

GLUT 2

Important for the reabsorption of glucose from the renal epithelial cell to the bloodstream

Question 20

In which form is glucose stored in the liver

Answer 20

As glycogen

Question 21

In which form is glucose stored in the adipose tissue

Answer 21

As triglyceride

Question 22

In which form is glucose stored in the skeletal muscle

Answer 22

As glycogen

Question 23

The renal threshold is caused by the saturation of which receptor in the kidneys

Answer 23

SGLT- 2 receptor

Therefore, if blood glucose level is above 11mmol/L, the SGLT-2 receptors become saturated and no more glucose can be reabsorbed

Question 24

Why is the presence of glucosuria not used diagnostically

Answer 24

This is because of the multiple factors that can cause the presence of glucose in the urine.

Cna be because the patient has exceeded their glucose threshold but could also beause of the presence of a infect or/and kidney disease

Question 25

Fill in the blanks regarding the reabsorption of glucose in the kidneys

Answer 25

Question 26

The release of which hormones and/or neuotransmitters will be increased by the procedure of taking blood? Will they affect the blood glucose result?

Answer 26

* **Adrenaline** **and** **noradrenaline**- yes will effect the blood glucose level as it stimulates the blood glucose level from the breakdown of glycogen * **Cortisol**- will cause the upregulation/downregulation of genes but will not effect the blood glucose result as it takes time for it to have an effect. Not immediate more like days * **Inflammatory** **markers** - will effect the glucose levels locally only. Therefore, we change the location of the puncture area after each one to prevent it effecting the level.

Question 27

What is the difference between brown and white adipocytes?

Answer 27

_White adipocytes_ - used to store lipids _Brown adipocytes_ - used to burn lipids to provide heat (contains lots of mitchondria). Little to absent in humans

Question 28

Where are SGLT 1 and 2 located?

Answer 28

_SGLT-1:_ found in the gut _SGLT-2:_ found in the kidneys

Question 29

What processes does adrenaline effect (in relation to glucose levels)

Answer 29

↑ gluconeogenesis ↑ glycolysis ↑ lipolysis ↓ glycogenesis

Question 30

List the tissues that are totally dependent on glucose as an energy source. Why?

Answer 30

**Brain** - as only glucose can pass the blood brain barrier **Erthyrocyte** - no mitchondria **Testes** - as only glucose can pass the testes blood barrier

Question 31

Why might a patient with diabetes have [glucose]\>11mM after an over-night fast?

Answer 31

They are unable to take up glucose into the cell (either by insulin resistance (T2) or insulin deficiency (T1)) Therefore even when they have high levels of blood glucose, the body starts to produce more glucose. As a result, they have high levels of glucose even when they are fasting as these glucose levels cannot go down.

Question 32

What effect would you expect if an average meal were accompanied by oral administration of an inhibitor of alpha-glucosidase activity?

Answer 32

Alpha-glycosidase is an enzyme that breaks alpha 1,4- glycosidic bonds. These bonds are important in the starch and maltose. Therefore, by inhibiting this enzyme you will lower the glycaemic index of the food

Question 33

Fill in the hormones

Answer 33

Question 34

Fill in the intermediates

Answer 34

Question 35

Which parts of these pathways does insulin effect

Answer 35

Question 36

What parts of these pathways does glucagon effect

Answer 36

Question 37

Why do patients with diabetes tend to have nocturnal polyuria?

Answer 37

They have hyperlgycaemia (as the cells cannot take up the glucose despite having high blood glucose levels). Therefore, the hypergylcaemia causes the glucose level to exceed the ability of the kidney to reabsorb glucose (over the renal threshold). Glucose is osmolarity active solute so draws water with it therefore you get a high water loss (osmotic diuresis) This is the reason for increase in urination at night

Question 38

Describe the fate of glucose ingested in the test dose for the glucose tolerance test in patients with diabetes

Answer 38

The glucose will be absorbed into the bloodstream. The cells in the body cannot take up this glucose (either due to insulin resistance or insulin deficiency). Therefore, the test dose stays in the bloodstream. Leads to the kidneys where it is reabsorbed. However, if the total blood glucose exceeds that of the renal threshold, the glucose cannot be reabsored and causes glucosuria. As time passes, the cells will produce more glucose (via glucogenesis and glycolysis and lipolysis)- so will lead to glucosuria