Chapter 28. Homeostasis and Body Chemistry

Learning Objectives

glucose
type of sugar found in blood; main fuel burned by muscles and brain cells; low level of glucose triggers hunger
set point
the optimal level for each body system; the actual level fluctuates around the optimal level
homeostasis
the body’s tendency to regulate its physiological systems so that each component stays within an optimal range
Homeostasis and Body Chemistry
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Learning Objectives:

Describe the principle of homeostasis.

Compare the body’s homeostatic systems that regulate blood chemistry to a thermostatically controlled system for heating a room.

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There are three images of a person on a sea saw. The first image is a woman standing on the left side of a sea saw, with the right side up in the air. The second image is of a man standing on the right side of the sea saw, with the left side up in the air. The third image is a man standing in the middle of the sea saw with both sides at the same level off of the ground. The middle is labeled "set point"

1. Homeostasis is your body’s method of maintaining a balanced, or constant, internal state. The level of stable internal balance for a homeostatic system is called the set point.

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A cartoon caricature of a cell holding a sign with the words "Glucose running low; need food."

2. If some part of the system falls below its set point (as detected by specialized receptors), your body will try to correct the imbalance, and you will be motivated to engage in behaviors that will restore the system’s balance.

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The figure is a line graph. There are three lines in the graph: a green line labeled "Normal", an orange line labeled "Impaired regulation", and a red line labeled "Diabetic". The X axis is labeled "Time elapsed after snack in minutes", ranging from 0 to 120 in increments of 30. The Y axis is labeled "Blood glucose level", ranging from 50 to 250 in increments of 50. In the graph, the Normal line begins at a blood glucose level of 125 at time 0, rises gradually to a blood glucose level of 160 at 60 minutes, then falls gradually back to 125 blood glucose level at 120 minutes. In the graph, the Impaired regulation line begins at a blood glucose level of 125 at time 0, rises drastically to a blood glucose level of 210 at 30 minutes, then falls gradually down to a blood glucose level of 160 at 120 minutes. In the graph, the Diabetic line begins at a blood glucose level of 160 at time 0, rises gradually to a blood glucose level of 220 at 90 minutes, then falls down to a blood glucose level of 210 at 120 minutes. The data are summarized in the following table. All data are approximate.

3. For the body to function properly, every aspect of your blood chemistry must stay within a fairly narrow range. The green range on this graph shows that a healthy person’s blood glucose level returns to normal within two hours after eating a sugary snack. The orange line shows that a person with impaired glucose regulation recovers more slowly. But the snack might push a person with diabetes (the red line) to a dangerously high level of glucose.

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The figure is a line graph. There are three lines in the graph: a black line labeled "set point", a blue line labeled "temperature", and a red line labeled "heat source", The X axis is labeled "Time" with no increments or scale. The Y axis is labeled "On" at the top and "Off" at the bottom. In the graph, the Set point line is between On and Off on the Y axis and continues horizontally across time. In the graph, the Temperature line begins just below the set point line and curves above it. The line curves back down below the set point and then curves above the set point again. It finally curves back down below the set point at the end of the graph. The line resembles two small rolling hills or waves with the set point line splitting it in half vertically. In the graph, the Heat source line begins at On on the Y axis and continues until the Temperature curve is almost at its peak, then drops vertically to Off. The line stays at Off until the Temperature curve is almost at its lowest point, then it vertically rises to On. The line stays at On until the Temperature curve is almost at its peak again, then drops vertically to Off. The line stays at Off until the Temperature curve is almost at its lowest point again, then it vertically rises to On. After the temperature rises above the set point, the heat source switches off. Once the temperature falls below the set point, the heat source switches on. This cycle repeats over time.

4. Separate homeostatic systems regulate the levels of water, salt, sugar, protein, fat, calcium, and oxygen in our blood. They all work in a way roughly similar to our temperature-regulation system, which is the system we will use for our example.

Practice 1: Regulating Room Temperature

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Practice 1: Regulating Room Temperature

Select the PLAY button to watch how a heating system maintains a stable temperature.

The figure includes a thermostat and a heater. The thermostat has a knob that is turned to the right, indicating the ideal temperature setting or set point. The current temperature is indicated as below the set point by a red arrow in the thermostat window. The heater is turned off. The options for the animation include play, pause, and replay. When the Play button is selected, the thermostat indicates that the room temperature is below the ideal setting. The thermostat detects this. The thermostat signals the heater to produce more heat. An arrow moves from the thermostat to the heater. The heater turns on. The arrow continues to move from the thermostat to the heather, which produces more heat. The room temperature begins to rise. Then the thermometer on the thermostat begins to rise. The heater produces maximum heat as the temperature continues to rise. The thermometer rises beyond the ideal setting. The thermostat detects that the room temperature is now above the ideal setting. The thermostat signals the heater to shut down. An arrow moves from the thermostat to the heater. The heater turns off. The heater stops producing heat. The room temperature begins to fall. The thermometer begins to fall. Room temperature continues to fall and so does the thermometer. The room temperature is below the ideal setting and the cycle repeats itself.

Practice 2: Human Temperature Regulation

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Practice 2: Human Temperature Regulation

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Quiz 1

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Quiz 1

Answer the question. When the answer has been chosen, select the CHECK ANSWER button.

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In this temperature-regulation system, which component detects that an imbalance has occurred?
air temperature
thermostat
heater

Quiz 2

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Quiz 2

Answer the question. When the answer has been chosen, select the CHECK ANSWER button.

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Which of the following statements about the body’s homeostatic systems is true?
The body maintains a constant level of blood glucose throughout the day.
When the level of one substance in the blood goes above the set point, the body compensates by lowering the level of other substances.
The concentration of salt in the bloodstream fluctuates around an optimal level.

Conclusion

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Homeostasis and Body Chemistry!