Homeostasis & intracellular signaling Flashcards
Who coined the word “homeostasis” in 1963?
Walter Cannon
What is the definition of homeostasis?
Self-regulating process by which biological systems maintain stability while adjusting to changing external conditions.
What is stability?
A particular physiologic parameter that is monitored and maintained within a relatively narrow range at all times.
When a process proceeds in a forwards and backwards direction at the same rate-no net change occurs
Equilibrium
When a process or system exerts energy to maintain a particular state:
Dynamic steady state
ex) Na+/K+ pump moves sodium out of cell to prevent swelling
What are the components that define homeostasis?
-Sensor
-Error detector
-Controller
-Effectors
A parameter that is measured in the body with sensors and is kept within a set of limits:
Regulated variable
-Limit = low and high range
-The “thing” that homeostasis is devoted to regulating
A process that can measure the regulated variable and deliver a signal about that variable:
Sensor
-Sometimes signals only happen when the regulated variable falls out of the “normal” range
Has a controller and error detector:
Control centre
“calculates” the difference between the set-point value of the regulated variable and the actual value of the regulated variable and sends an error signal to the controller:
Error detector
Sends output signals to effectors that can change the regulated variable depending on data:
Controller
The range of values of the regulated variable that the system tries to maintain:
Set Point
-very difficult to “find where the set point exists” in a biological system
How does the brainstem “know” what the normal pH is supposed to be?
No one has really figured this out
What the controller manipulates to “get the job done”:
Effector
-Effectors respond to information from the controller and change the value of the regulated variable
Effectors usually change values of the _______________________ in order to bring the regulated variable closer to the set-point.
Non-regulated variable
ex) if your pH drops, then your respiratory rate increases in order to get rid of excess carbon dioxide. Regulated variable = pH, Non-regulated variable = respiratory rate
Are homeostasis and negative feedback the same?
Homeostasis can and usually does use negative feedback loops, not all negative feedback loops are homeostatic.
(photo is an example of a simple negative feedback loop)
What products are created in this simple negative feedback loop?
A + B + C
What product inhibits the process?
“B” inhibits ABCase, reaction slows down
Output of a system is fed back in a manner that tends to reduce the fluctuations in the output:
Negative Feedback
-products tend to oscillate between low and high points, depending on how “fast” the product inhibits the process
What does the negative feedback loop lack that does not consider it to be homeostasis?
-Control centre
-Set point
-Error Signal
-Regulated Variable
What are the major baroreceptors?
-Carotid arteries
-Arch of the aorta
what happens when:
pressure drops -> message sent to the brainstem via nerves->
1) activation of the sympathetic nervous system -> release of epinephrine, norepinephrine
2) Epi and NE -> Elevation in HR and constriction of arterioles and increase stroke volume
The proprioceptor that senses muscle stretch:
Muscle spindle
As the muscle is stretched, what happens?
-Activates the muscle to contract against the stretch by stimulating the motor neuron in the ventral horn
-inhibits the antagonist muscle
(stretch is caused by hitting the tendon with a reflex hammer)