Module 2 The Endocrine System

Lessonn 1.2.5

1.2.5 page 3

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Pancreatic Hormones

Like calcitonin and PTH, produced by the thyroid and parathyroid glands, insulin and glucagon produced by the pancreas are antagonistic hormones, responsible for regulating blood glucose. Insulin, through its mechanisms, lowers blood glucose levels while glucagon, through its mechanisms, raises levels of blood glucose. Together, these hormones maintain homeostasis by way of negative feedback. Restoration to a range of normal glucose levels acts to control hormone secretion.

Read and make notes from pp. 456 – 457 of your textbook, which describes how pancreatic hormones maintain blood glucose levels. A good summary of negative feedback is given in Figure 13.25 on p. 457 of the textbook. File your notes, including the feedback loop diagram, in your course folder.

Try This

TR 2.

Now that you know about blood glucose regulation by insulin and glucagon, complete the following closed written response question which has four parts. Notice that mark values have been assigned for each part. The key to this exercise will explain how the mark values are assigned, and when you check your answers, mark each part accordingly. After checking this exercise, file it in your course folder. Consult your instructor if you require clarification or help.

Use the following information to answer the following question.

Blood glucose concentrations of one individual were monitored over several hours. The following data was collected. The blood glucose level of a healthy person is approximately 90 mg/100 mL.

Time	Blood Glucose Levels (mg/100 mL)
7:00 am	80
8:00 am	120
9:00 am	90
10:00 am	75
11:00 am	100
12:00 noon	80
1:00 pm	125
2:00 pm	100
3:00 pm	90

Plot this data on the grid provided below. Draw a curved line through the points and label your graph appropriately. Draw a horizontal dotted line showing the approximate blood glucose level of a healthy individual. (6 marks)

On the graph, indicate with an arrow, two places where a blood test would reveal high levels of insulin. Explain why insulin would be at high levels at these times. (4 marks)
Predict what would happen to this person’s blood glucose levels if he/she worked out at the gym from 9:00 am to 10:00 am. With respect to blood glucose levels, how would his/her body respond?
The graph shows that this person’s glucose levels fluctuate throughout the day. Is this person healthy or does he/she have a malfunctioning pancreas? Explain your answer. (3 marks)

Check your work.

Self-Check Answers

The graph should look similar to the one shown below.

The marks would be assigned as follows.

1 mark for the title – include the manipulated and responding variable
1 mark for correct labels and units on the x-axis
1 mark for correct labels and units on the y-axis
1 mark for using suitable scales for each axis – graph should use the whole grid
1 mark for drawing a smooth curved line through the points rather than a jagged line
1 mark for showing the approximate blood glucose level of a healthy individual

First place that insulin would be high – A time selected somewhere between 7:00am and 8:00am and marked on the graph with an arrow. (1 mark) This is a time shortly after breakfast. The absorption of glucose from the meal would raise blood glucose levels and the high glucose levels would stimulate the beta cells in the pancreas to release insulin to lower blood glucose levels back to the normal range. (1 mark for the explanation)

Second place that insulin would be high – A time selected somewhere between 12:00 noon and 1:00pm and marked on the graph with an arrow. (1 mark) This is a time shortly after lunch. Absorption of glucose from the meal would raise blood glucose levels and the high glucose levels would stimulate the beta cells in the pancreas to release insulin to lower blood glucose levels back to the normal range. (1 mark for explanation). Since the explanation is the same for both places, award two marks if you explained the reason correctly.
The muscle cells would use increased amounts of glucose for cellular respiration. (1 mark) As a result, blood glucose levels would start to drop. (1 mark) In response to lower blood glucose levels, the alpha cells in the pancreas would secrete glucagon into the bloodstream. Glucagon stimulates the liver to convert glycogen into glucose, which would be released into the blood to raise blood glucose levels. (1 mark) (Total 3 marks)
This individual is healthy according to the levels of blood glucose indicated. (1 mark) If 90 mg/100 mL is considered to be a normal set value, then small fluctuations around the set value are to be expected. (1 mark) It is only if the fluctuations are large and stay above or below the set value continually that the person is considered as having pancreatic dysfunction. (1 mark) (Total 3 marks)