Homeostasis Flashcards
What is Homeostasis
Homeostasis is the maintenance of a relatively constant internal environment
Explain what is meant by a set point in homeostasis
Each variable regulated by homeostasis has a set point for example body temperature has a set point at 37 degrees.
However in reality, each variable has a working range. For example, although the set point of body temperature may be 37 degrees the working range may be 36.5 - 37.5
What are the 5 components of homeostatic control systems?
- Detectors are structures which monitor variables (e.g. thermoreceptors monitor temperature, baroreceptors monitor pressure in the cardiovascular system.)
- afferent neurons also called sensory neurones carry sensory information from the outside world to the CNS
- Comparator - This knows what the set point should be it is something that makes a decision on whether the measurement is normal e.g. brain
- efferent neurons also known as motor neurones carry signals from the CNS to other parts of the body e.g. muscles and glands
- Effectors are structures which produce a response e.g. muscle contraction
THESE COMPONENTS ARE FOUND IN ALL HOMEOSTATIC CONTROL SYSTEMS
The components of homeostatic control systems are arranged such that control is achieved by the process of negative feedback
What is negative feedback?
Negative Feedback is returning things in the opposite direction they have gone
It is when a variable is disturbed, changes are initiated which return it to its set point.
This can be illustrated with the example of regulation of blood pressure.
What is the set point for normal blood pressure
The set point for normal blood pressure is
120/80mmHg
Let us assume that blood pressure drops what detects it?
The drop is detected by specialized receptors in the walls of some arteries called baroreceptors
NOTE: They signal this drop back to the brainstem region of the brain via transmission of action potentials.
How is an error signal generated?
In the brainstem, the signal is compared with the normal or desired value if there is a mismatch between the two then an error signal is generated.
The error signal is conveyed via efferent neurons to effectors.
How is blood pressure returned back to normal (The process)
LOOK BACK TO THE BOOK PAGE 9
Limitation of negative feedback
While negative feedback is important, it can only correct changes after they have occurred.
What is feedforward
Feedforward is a process that limits changes in physiological variables, thus limiting the response required to bring them back to their set point.
FOR EXAMPLE wearing clothes appropriate for the weather. for example in cold weather coats and gloves are worn which would reduce any drop in body temperature that would be seen in a person wearing just a t shirt and shorts. Since the drop in body temperature is reduced fewer physiological responses are needed to maintain the body temperature at its set point.
IN SIMPLE WORDS: feedforward anticipates changes. It is anticipatory behaviour expecting things to happen in anticipation. E.g. anticipating eating so body may release to help with the absorption.
The opposite of negative feedback is positive feedback
What is positive feedback?
Positive feedback is increasing more in the same direction it is reinforcing things in the same direction.
In this case, a change in a regulated variable initiates responses which makes it change even more
For example, in the case of blood pressure, a drop in BP would initiate responses that would make it drop further.
ANOTHER EXAMPLE: Child birth keep contractions going so the birth of the baby can take place its reinforcing in the same direction.
EXTRA MARKS
Although physiological variables have a working range it is possible for them to be reset. For example resetting the hypothalamus ( part of the brain responsible for regulating many bodily functions) body temperature during infections resulting in a fever which helps fight off infection.
Why do cells need stability and what is kept stable?
For optimal function
ECF = Extracellular fluid, plasma and Interstitial Fluid
Examples of things needing to be stable include body temperature, blood pressure and BP
What is a regulated variable
A variable that has the potential to change in order to maintain homeostasis
What is a non - regulated variable
Can change to achieve control of regulated variable e.g. change blood pH by changing CO2 concentration.
