Homeostasis Flashcards
Review of the basics of homeostasis
How do you define homeostasis?
All variables must operate within a narrow range of values
Is homeostasis of one variable independent of other variables?
No, balance is needed between different variables
What are the two degrees of control of variables?
Tight and loose controls
What is tight control of variables?
At any given time a variable will be close to a predicted value, and very rarely fluctuates
What is an example of tight control of a variable?
Concentration of oxygen in blood; constant even when a person exercises
What is looser control of variables?
Variable may fluctuate in response to diurnal rhythms; will average over the day to the normal value; mechanisms return variable to normal levels over a longer period of time
What is an example of looser control of a variable?
Blood glucose; peaks after meal, falls during fasting
What is the definition of a set point?
Point where we expect a variable to be at
What is an example of a set point?
Body temperature at 37 Celsius
How is a set point reset?
Temporarily stabilises at a different value; has a functional reason to change (is not a problem)
What is an example of a set point being reset?
When fighting an infection, stabilises to higher body temperature. When exercising, muscles are more efficient at higher temperature which is caused by contraction/aerobic respiration
Why are changes typically transient?
Mechanisms immediately start being triggered when a variable falls out of normal range
What does the gain of a variable measure?
The precision by which a control system can prevent deviation from homeostasis
What is the equation for the gain of a variable?
Amount of correction needed/ amount of abnormality after correction
What does a larger gain signify?
More sensitive regulation/ more accurate
What is negative feedback?
Signals “fine tune” the body’s response to a stimulus so that homeostasis can be achieved under the new conditions
Where does negative feedback occur?
On all levels (cellular, tissue, organ, system)
How does end-point inhibition/ competitive inhibition work as negative feedback?
Concentrations of final product block metabolism of initial enzyme/ concentrations of final product compete with initial enzyme
What are reflex responses?
Requires knowledge from an integrating centre and a circuitry that connects receptor and effector; most are negative feedback
What is an example of a reflex response?
Blood pressure regulation
What are local responses?
Allow individual parts of body to self-regulate
What is an example of a local response?
Vasodilation of vessels near contracting muscles during exercise, but not facial muscles
What are the types of communication?
Hormonal, neuronal, local
What types of communication are reflex responses?
Can be a combo of neuro and hormonal
What do local responses do?
Release chemical for receptor; can be paracrine or autocrine
