Homeostasis: Some Common Student Misconceptions
September 2012 (from faculty surveys and workshops at HAPS & NWBio in 2012)
Naïve misconceptions (does not understand the concept or principle)
- Negative feedback is detrimental for the body; positive is better for the body.
- Negative feedback means less.
- Homeostasis means that the body always does what is best for itself. (Students might not have a good mental model of how this happens and be content in thinking that this is an adequate explanation).
- Homeostasis means keeping things ‘normal’ (students may think that the body takes care of itself and may think this in the absence of any understanding of the process).
- Homeostatically regulated variables are more important than variables that are not homeostatically regulated. (HR & SV are important even if they are not homeostatically regulated.)
Anatomical misconceptions (assuming anatomical constraints)
- Distance matters (e.g. students may think that the blood sodium sensor in the kidney is too far away from the brain to have an effect).
- The sensor control center and effector are in different anatomical structures and/or locations. (Students may not understand that a sensor, control center and effector can be in the same place even same entity. They may believe that these must be fragmented and disparate).
Misconceptions regarding regulated variables
- Any physiological (physical or chemical) variable that is held constant most of the time must be regulated (e.g. heart rate). So, if a variable doesn’t change during a period of observation, then it must be regulated.
- If you can change a variable (e.g. heart rate), then it is ‘regulated’ (Students may not realize that if you don’t have a sensor, you can’t regulate that variable.)
- If an individual can measure a variable, then the human body must be able to measure it, i.e. there must be a sensor for that variable (e.g. students had palpate and count their heart rate but there is no internal heart rate sensor).
- If a variable is not absolutely constant (i.e., if it varies at all), like blood glucose, then it is not regulated. Only variables that are absolutely constant are regulated.
- Any variable that changes can be regulated. Students don't always understand that if there is no sensor for it, it can't be regulated and they often confuse a controlled (or manipulated) variable with the regulated variable.
- Only one variable is controlled at a time. Students may understand that multiple variables are resulted, but may think that they are controlled one at a time.
Other incomplete understandings (has some understanding of the concept)
- Regulatory or compensatory mechanisms are "on" or "off” (all or none), like a light switch, rather adjusted up or down like a volume knob.
- The body's interior is static, rather than dynamic.
- The set-point is a discrete value rather than a defined range of values with some ranges being narrow and others being rather wide.
- Homeostasis is maintained only by the nervous system or the nervous system is always involved.
This is work in progress and the we are in the process of organizing these into a theoretical scheme