Plasma glucose regulation PDF

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Flow chart of plasma glucose control...

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Glucose Tolerance Test When performed under rigid clinical conditions this test is used to diagnose diabetes. This test has largely been replaced with a single blood test known as the A1C . A1C tests for the amount of glycosylated proteins on red blood cells. We will use a procedure similar to the glucose tolerance test to demonstrate the action of insulin on plasma glucose levels. This lab involves working with blood. Remember to follow all precautions for working with biohazardous materials. You should not be the subject for this lab if you have a known issue with plasma glucose regulation. Most cells of the body acquire most of their energy from the oxidative metabolism of glucose. Plasma glucose levels typically range between 60 and 140 mg/dl in adults. This level of glucose provides a consistent supply of energy to the body’s cells. If plasma glucose levels are elevated insulin is released from the beta cells of the pancreas into the blood. Insulin acts to lower plasma glucose levels primarily by increasing the uptake of glucose into cells. Hypoglycemia occurs if plasma glucose levels fall below 50 mg/dl. Hypoglycemia is characterized by feeling of faintness, irritability, or anxiety. Brain cells are especially dependent on glucose for energy and these symptoms arise due to the lack of glucose to the brain cells. Hypoglycemia is typically produced by excess insulin levels. Hyperglycemia occurs if plasma glucose levels exceed 180 mg/dl. High plasma glucose levels create an osmotic gradient that causes dehydration in the tissue as water leaves the tissue and passes into the plasma. This is further complicated when glucose is lost in the urine. When plasma levels exceed 180 mg/dl the kidney’s ability to reabsorb glucose from the filtrate is exceeded and glucose is lost in the urine. The osmotic gradient produced by glucose in the urine causes an increase in urine volume and subsequent water loss. Procedure A glucose tolerance test is best performed on a subject who has not eaten for the 8 hours prior to the test. For our demonstration it will be adequate if you have not eaten for 2-4 hours before the lab period. Only 1 student per table should do the test. 1. Determine a normal blood glucose level using a glucometer. (directions below) 2. Immediately after taking the baseline sample drink approximately 8 ounces of a beverage of your choice such as soda, tea, coffee or fruit juice. Record the amount of sugar and calculate the number of grams of sugar consumed per kilogram of body weight. Record the form of sugar used to sweeten the drink (sucrose, high fructose corn syrup, honey ect.). If you chose a diet drink record the type of sweetener it contains. This information is typically available on the beverage bottle or online. For reference purposes the instructions for a glucose tolerance test follow. Immediately drink enogh of the glucose drink to supply 1g of glucose per kilogram of body weight. Each ounce of drink contains 10 grams of glucose. There is a metric

scale in the back of the room or you can convert your weight from pounds to kilograms by dividing by 2.2. If you weigh 100 pounds (45 kg) you should drink about 4.5 ounces (about half a bottle) of the drink. Dosage does not have to be exact. You should drink the glucose solution quickly (don’t gulp it down) since timing of your plasma glucose levels does not begin until you have finished the drink. 3. Measure plasma glucose levels every 30 minutes for the entire lab period. 4. If the plasma levels exceed 200 mg/dg perform a test for glucose in the urine. 5. Record your results on the data sheet and answer the questions.

Instructions for the glucometer 1. Make sure that the number on the glucometer insert and test strip match. If you use the wrong test strip the reading will be in error. 2. Insert the test strip and wait until the machine signals that it is ready for a sample. The screen will show a drop of blood rotating around the screen. 3. Prick your finger and touch the drop of blood to the side of the test strip when there is a semicircular indentation. The blood will flow into a space between the top and bottom of the strip. Do not place blood on the top of the test strip. 4. The glucometer should now display the plasma glucose level on the screen.

Instructions for testing urine glucose. 1. Obtain a urine sample in the sample cups provided. Only a small sample is needed for this test. 2. Obtain a urinalysis test strip 3. Dip the test strip into the urine sample until the pads on the test strip are saturated. 4. Compare the color of the pads on the test strip to the key on the side of the bottle.

Data Sheet and Questions Graph your results

300 Blood Glucose mg/dl

250 200 150 100

50 _____________________________________________________________________ Time 0 30 60 90 120

Did the plasma glucose levels exceed 200 mg/dl? If so what was the urine level of glucose?

1. From your knowledge of glucose transport across membranes what is the mechanism used to recover glucose filtered by the kidney? Hint ..typically the glucose level of the filtrate in the proximal convoluted tubule is greater than the glucose in the adjacent peritubular capillaries.

2. What is the cellular mechanism for glucose to appear in the urine when plasma glucose levels are high?

3. Type I diabetes mellitus is caused by a lack of insulin. Explain the cellular mechanism of the classic symptoms of diabetes mellitus . glucosuria (glucose in urine) polyuria (high urine production) polydipsia (high water intake)

4. Type II diabetes is a hyporesponsiveness to insulin. Would the systems of these disease be any different than those for Type I diabetes?

5. What test would you need to perform to confirm whether the problem was Type I or Type II diabetes?

6. When plasma glucose levels are high due to a lack of insulin cells increase their metabolism of fats and proteins. Why?

7. The increased metabolism of fats in diabetes causes the production of ketone bodies such as acetone (2 carbons in the carbon skeleton). Ketone bodies are acidic and have a characteristic “fruity” odor. An increased level of one of the intermediates of cellular respiration is responsible for ketoacidosis and a fruity breath. Which of the intermediates that we discussed in class would be responsible?

8. Compare your results with the results of your classmates. Does choice in beverage make a difference on plasma glucose levels? Is the amount of sugar or the form of sugar more important? What additional information would you need to better answer these questions?...