Free response · Unit 4 Beta

Blood glucose and hormone levels after a meal

Analyze Model or Visual Representation · 4 points

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The question

Name: ______________________   Date: ____________   Blood glucose and hormone levels after a meal (4 points)

Model

A model of glucose control, and one meal

The diagram is a model of how blood glucose is regulated. The graph shows blood glucose (mg/dL), insulin (µU/mL) and glucagon (pg/mL) in a healthy teenager during the 3 hours after a meal rich in carbohydrate, eaten at time 0. Each is plotted in its own unit.

0204060801001201401600306090120150180Time after the meal (min)Level (unit in the key)

Glucose (mg/dL)Insulin (µU/mL)Glucagon (pg/mL)

Data table
Time after the meal (min)Glucose (mg/dL)Insulin (µU/mL)Glucagon (pg/mL)
085890
151102584
301355078
451406272
601305870
901104074
120952282
150881288
18085990
Negative feedback loops that hold blood glucose near its set point A box on the left shows blood glucose near its set point, about 70 to 100 milligrams per deciliter when fasting. Top loop: after a meal glucose rises above the range; beta cells in the pancreas sense the rise and release insulin; muscle and fat cells take up glucose and the liver stores it as glycogen; glucose falls back to the range. Bottom loop: during fasting or exercise glucose falls below the range; alpha cells in the pancreas sense the fall and release glucagon; the liver breaks down glycogen and releases glucose; glucose rises back to the range. In each loop the response cancels the change that started it. Blood glucosenear its set point(about 70-100mg/dL fasting) Glucose risesabove the range(after a meal) Beta cells in thepancreas sense it andrelease insulin Muscle and fat cellstake up glucose; liverstores it as glycogen stimulussensor and control centereffectors (response) Glucose fallsbelow the range(fasting, exercise) Alpha cells in thepancreas sense it andrelease glucagon Liver breaks downglycogen and releasesglucose into the blood stimulussensor and control centereffector (response) glucose falls backglucose rises back

  1. (a) Describe the role of the beta cells in the model. [1 point]

  2. (b) Using the graph, explain how the data show that glucose is regulated by negative feedback. [1 point]

  3. (c) Glucagon falls after the meal. Using the model, explain why the fall in glucagon helps return blood glucose to its set point. [1 point]

  4. (d) In type 2 diabetes, muscle and fat cells respond weakly to insulin. Predict how the glucose and insulin curves after the same meal would differ from those shown. Justify your prediction using the model. [1 point]