02 - Homeostasis Flashcards
Homeostasis Definition
A relatively stable state of equilibrium or a tendency toward such a state between the different but interdependent elements or groups of elements of an organism, population or group
- Bunch of “wheels” working together at the same time to keep you alive
Homeostasis
- The envelope of internal conditions which allows us to live
- Our bodies must maintain internal constancy (homeostasis) while meeting the constantly changing demands of life
- All cells and organs participate in homeostasis
- We must constantly change to maintain internal consistency (in order to stay constant we must be dynamic)
Perturbations in Homeostasis Examples
- External perturbations: environmental temperature change
- Internal perturbations: the sugar in the food we eat and the byproducts of metabolism
What system is dedicated to the whole process of homeostasis?
Autonomic nervous system
2 Ways of Maintenance of Homeostasis
- Positive feedback
- Negative feedback (more common)
Variable
The something that is required to regulate
Detector or Receptor
Detect change in the variable from its set point
Stimulus
The movement of the system away from its set point
Control center
Figure out what to do when the stimulus is detected
Effector
Move the variable back to normal
- The effector deprives the system of the stimulus and terminates the feedback loop (bring back to normal)
Oxygen homeostasis - Why might there not be enough oxygen?
- If the lungs cannot get enough from the air
- If the heart cannot move enough blood around
- If the blood vessels are too blocked up
Negative Feedback Loop
- Stimulus - a variable in homeostatic balance
- Detector/receptor: a change is detected in the variable
- Control center: response is initiated
- Effector: creates the response to the change
- Response decreases the departure from the set point
- Back to normal
Why might it be impossible to maintain homeostasis?
- Large deviations from the set point (too extreme conditions)
- You can not get yourself back to the normal range with extreme conditions but other people can help you (eg. warm you up or cool you down) to help you get back to the normal range
Examples of negative feedback loops
- Temperature
- Blood glucose
Positive Feedback Loop
A way to maintain homeostasis when a distinct event will facilitate the return to homeostasis
- The effector will move the variable FURTHER from the starting point and provide MORE stimulus
- The change in the variable stimulates additional change in the variable
- The positive feedback loop must terminate with some distinct event which deprives the feedback system of input
Examples of positive feedback loop
- Child born: uterine contractions in labour (uterine contractions causes further uterine contractions)
- Blood clotting (clotting causes more clotting)
- The APs in a neuron (changes in voltage trigger additional changes in voltage)
- Ovulation (increases in the hormone estrogen causes increases in estrogen which stimulate egg release)
- Orgasm (increases in sensory nervous input lead to an increase in sensitivity which lead to an increase in sensory nervous input which continues until there is a massive spinal cord reflex)
- Lactation (milk let down)
How does positive & negative feedback occur together?
- Positive feedback mechanisms are always found within other negative feedback mechanisms
- The positive feedback mechanism can be exploited to provide a signal or accomplish a distinct event
- Positive feedback events maintain homeostasis in the long run though they hardly look homeostatic when they are occurring
Homeostatic Imbalance
- Any prolonged departure from homeostasis results in some sort of disorder or disease
- These departures from homeostasis yield signs & symptoms
- With these signs & symptoms of the departure from homeostasis you can make a diagnosis of the disorder or disease
Signs
Objective measures of change
Eg. with diabetes that would be increased blood sugar and sugar in the urine
Symptoms
Subjective measures of change
Eg. diabetes: fatigue and thirst
