Biol 72 Lab #1 HOMEOSTASIS Spring ‘17
I. Introduction
A. Homeostasis
Human cells have narrow tolerances. They’re divas. They’re like goldilocks. EVERYTHING has to be juuuuust right. If not, they might die and so might you. They function properly only within a narrow range of temperature, pH (acidity), water levels, etc. Thus, the body's internal environment needs to be kept pretty constant so the body's CELLS can live and function. This relative constancy of the internal environment is called HOMEOSTASIS. (It is one of the most important concepts we will learn about! So know it. Well. Seriously). The body's organs and organ systems cooperate to maintain the dynamic constancy of the internal environment. They do this by constantly making adjustments to keep body parameters (e.g. water content, blood pressure, blood sugar) within narrow limits that support life. The kidneys, for example, have to be regulated, so they will make the proper adjustments to maintain homeostasis whether you are becoming dehydrated from sweating or over hydrated from guzzling too much water. So, if you drank too much water, your kidneys will help you pee a lot. If you haven’t had enough water, they’ll conserve water and prevent you from peeing.
B. Negative Feedback loops
Homeostasis of the body parameters is maintained by what are called negative feedback loops within the body's organ systems. To explain what this means, let’s first think about how an air conditioning system regulates the temperature of a room. Together with your table mates, discuss (in as much detail as possible), what an A/C unit needs to have to keep the temperature at or around 70 degrees farenheit. That is, try designing an A/C unit to do this. Write your thoughts and your group’s thoughts below:
You see how in the example of the A/C unit, the A/C unit was always doing the opposite of what was happening? If temperature was FALLING, it would turn off to help INCREASE temperature. This is what is called “negating” or doing the “negative” or opposite, based on getting “feedback” about what the temperature in the room is. If temperature was RISING, the A/C would turn on to help DECREASE temperature. The A/C unit got “feedback” that the temperature was too HIGH, so it turned on to “negate” this trend and LOWER the temperature. Hence, this is called “negative feedback”.
As you all might have found out when you were designing an A/C unit on the previous page, there are 3 main components of a negative feed back loop: SENSOR, INTEGRATING CENTER, EFFECTOR.
The SENSOR detects changes in some important variable. In the A/C unit example, this would be a thermometer.
The INTEGRATING CENTER receives input from sensors. It processes this information and decides whether the variable (like temperature) is too high or too low.
The EFFECTOR receives input from the integrating center and then does something based on this info; it produces a correction in the variable that is needed to keep it relatively constant despite challenges to the system. For example, if temperature is too LOW, the effector can be a heater that is turned on to get temperature to increase.
C. Set point, Range and Sensitivity
Negative feedback systems cannot normally maintain absolute constancy. If you think about household examples, you might notice that A/C units don't usually maintain absolutely constant temperatures. Instead they maintain temperatures within some RANGE of values; when temperatures deviate beyond this range the negative feedback loop activates an effector to correct it.
The SET POINT is defined as the average value that the system maintains.
The RANGE is the difference between the maximum and minimum values.
The SENSITIVITY is the typical deviation from the Set Point that is needed to activate the Effector to produce a correction.
Heater OFF
Heater ON
2
The figure above shows temperature data from a hypothetical household A/C/heater unit over time. In this example, the set point is 680 F, the range is 40 F , and the sensitivity is 20 F.
II. Temperature regulation in a laboratory water bath
A. Components
A laboratory water bath contains 3 main electrical components, connected by wires, that make it function.
Sensor ______> Thermostat ______> Heater (sensor) (integrator) (effector)
The probe of a digital thermometer has been placed near the sensor of the system.
A light comes on when the heating element is activated.
You will observe these two devices to evaluate the functioning of the system.
III. Hot Plate vs. Water Bath experiment
A. Introduction
In this experiment, we will compare the temperature-regulating properties of two pieces of lab equipment. After turning them on, we will monitor their performance by recording water temperatures over an hour's time (probably less than that). Your goal is to determine which is a better negative feedback loop and which of the systems is displaying homeostasis.
BEFORE YOU BEGIN: Assign different ROLES and TASKS to your group members:
a. One person should serve as TIMER, monitoring the ELAPSED TIME on a watch or stopwatch.
b. TWO people should be OBSERVERS; one monitors the temperature of the Water Bath, the other reads the thermometer in the Hot Plate Beaker.
c. DATA RECORDER(s), who record the temperatures in Table 1. 3
C. Method:
1. Be sure the water bath is switched to ON and that it is UNCOVERED. This is super duper important. 2. You also have a hot plate. It should be OFF to start. Fill the beaker about half full with water and ensure the automatic thermometer (looks like a suction cup) is inserted into the water. 3. Cover the beaker with the upside down watchglass and turn the hotplate on to level 5. 4. Also, turn the water bath to ON as well. 3. Begin recording the TIME and TEMPERATURE (shown on the water bath display or on the thermometer inserted in the hot plate) in the table below for ~20 minutes. 4. Every minute, as indicated by the TIMER, RECORD the water bath and hot plate temperatures in Table 1. Also note whether the 'heating' light for the water bath is On or Off. When the light is on, this means that the heater in the water bath is on and trying to heat the water.
Time WB HP light? Time WB HP light? 0 12
1 13
2 14
3 15
4 16
5 17
6 18
7 19
8 20
9
10
11
4
E. Graphing data
1. On the graph below, draw out two curves, one representing the data for the hot plate and the other representing the data for the water bath. On the x-axis put time and on the y-axis put temperature:
5
DATA ANALYSIS
1. Compare the graphs of the Water Bath vs the Hot Plate Beaker so assess differences in how they 'behave.'
2. Use the data from the water bath example to calculate the following:
RANGE of temperature permitted by water bath: ______
SET POINT of water bath: ______
SENSITIVITY or RANGE of water bath: ______
6
REVIEW QUESTIONS FOR HOT PLATE VS WATER BATH EXPERIMENTS:
What the heck is negative feedback? Explain in your own words.
Does the Graph for the covered beaker/hot plate experiment suggest the presence of negative feedback mechanisms? EXPLAIN why or why not?
Does the Graph for the Water Bath suggest the presence of negative feedback mechanisms? Why or why not?
Which system is better at HEATING water? Using your data, defend your choice and explain why it’s better at heating water. That is, what does it have or what does it lack that makes it better?
Which system is better at homeostatically regulating temperature? Using your data, defend your choice and explain what it has that makes it better.
Based on what “negative feedback” means, what do you think a “positive feedback loop” might do to water temperature?
7
In the water bath example, explain what each of the following components was doing (if you think the water bath likely did not have a particular component, say “not present”):
Sensor ______
Integrating Center ______
Effector ______
In the hot plate example, explain what each of the following components was doing (if you think the hot plate did not have a particular component, say “not present”):
Sensor ______
Integrating Center ______
Effector ______
8
Exam style questions:
Which of the following systems do you think would be best at keeping the water temperature around a set point (explain your choice very clearly – if you think both would stink, say so and explain why): A: a system that has a sensor and integrating center but no effector or B: a system that has no sensor, but does have an integrating center and an effector
So we saw how we might be able to regulate water temperature. In our body, we need to regulate key variables like blood pressure, temperature, blood sugar levels, etc. Based on what you know right now about homeostasis and negative feedback loops, list the components that are necessary to ensure that your blood pressure stays within its normal range. For example:
1.) What does the sensor for blood pressure regulation do?
2.) What does the integrating center for blood sugar regulation do?
3.) What does the effector for blood pressure regulation do?
4.) What happens if blood pressure gets too high? Too low? That is, why is it important to regulate blood pressure via negative feedback? (We’ll get into this later in the semester, but just discuss with your group for now to get your brain thinkin’)
9