Lecture 3: Homeostatic Control Flashcards
What does RMP stand for?
Resting membrane potential.
What is RMP?
RMP refers to the fact that the inside of the cell
membrane is negatively charged compared to its
external surface.
The resting membrane potential is an electrical potential that exists across the cell membrane and is due to different concentrations of ions on each side of the membrane and their respective permeabilities to it.
Consider a hypothetical cell with ICF [K+] = 150 mmol/L and ECF [K+] = 4mmol/L. (assume that no membrane potential initially exists)
What will happen over time?
When the amount of K+ leaving the cell down its conc. gradient is balanced by that moving back in due to the electrical gradient we have the RMP.
What is the typical RMP of a cell?
-70mV
Which ion is the major determinant in RMP?
K+
What is the ‘Regulated variable’? (AKA controlled variable)
The variable that the system senses and tries to keep stable.
[eg. the speed of a car on the motorway]
What is the ‘Reference (normal) range’?
Values of the regulated variable within acceptable limits.
[e.g. what speeds most ‘normal’ people are driving between]
What is the ‘Set point’?
The target value for variable.
[eg. the speed limit]
What is variation in homeostatic terms?
Variation in regulated variable values within and between ‘normal’ people (intra and inter individual variation).
Within an individual, variables fluctuate around a Set Point. This may occur in response to biological rhythms. Give two examples of such biological rhythms.
Circadian Rhythms (24hrs) Monthly Rhythms (eg. menstrual cycle).
Through which to processes is homeostasis achieved?
Feedback and feedfoward.
What is negative feedback?
Feedback that brings a variable back to a set point.
What is positive feedback?
Feedback that takes a variable further and further away from a set point.
What are the 4 key components of a negative feedback system?
- Sensor
- Integrator
- Effector/s
- Communication pathways
What does a homeostatic integrator do?
Compares actual and set point values, and generates an ‘error’ signal is any discrepancy occurs between these two. Then determines and controls the response.
Which two components of the negative feedback system can often be within the same cell?
The sensor and integrator.
What does a homeostatic effector do?
Produces the response(s) that restore the regulated variable to its ‘set point’.
What are the two Physiological Communication Pathways?
Neuronal and hormonal.
How do neuronal communication pathways work?
Action potentials in axons and neurotransmitter release at synapses.
How do hormonal communication pathways work?
Hormones are released into the blood (or the ECF).
What are the benefits of neuronal communication pathways?
– Fast (up to 100m/s)
– Specific
– Good for when conditions are changing rapidly and where an immediate response is required to prevent tissue damage or loss of homeostatic control
– Good for brief responses
What are the benefits of hormonal communication pathways?
– Target any cells that have receptors specific for the particular hormone (so one hormone can potentially affect several tissues or organs)
– Good for widespread, sustained responses e.g. fluid volume regulation
What is feed foward?
Feed-forward essentially involves detection or anticipation of external (or internal) conditions or situations that could alter a regulated variable (or disrupt homeostasis) if some sort of PREEMPTIVE action was not taken.
The integration centre establishes a future ‘predicted value’ for the regulated variable, compares this with the ‘set-point’ and makes anticipatory corrections.
What are the two types of feed forward?
Physiological (eg. goosebumps) and behavioral (eg. putting on a jacket)
In what circumstance may positive feedback be helpful?
In physiological situations when there is a specific end point or purpose, eg. childbirth or blood clotting. Must be carefully controlled to prevent inappropriate activation and to limit the outcome.
