Lecture 3: Homeostatic Control

Question 1

What does RMP stand for?

Answer 1

Resting membrane potential.

Question 2

What is RMP?

Answer 2

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.

Question 3

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?

Answer 3

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.

Question 4

What is the typical RMP of a cell?

Answer 4

-70mV

Question 5

Which ion is the major determinant in RMP?

Answer 5

K+

Question 6

What is the ‘Regulated variable’? (AKA controlled variable)

Answer 6

The variable that the system senses and tries to keep stable.

[eg. the speed of a car on the motorway]

Question 7

What is the ‘Reference (normal) range’?

Answer 7

Values of the regulated variable within acceptable limits.

[e.g. what speeds most ‘normal’ people are driving between]

Question 8

What is the ‘Set point’?

Answer 8

The target value for variable.

[eg. the speed limit]

Question 9

What is variation in homeostatic terms?

Answer 9

Variation in regulated variable values within and between ‘normal’ people (intra and inter individual variation).

Question 10

Within an individual, variables fluctuate around a Set Point. This may occur in response to biological rhythms. Give two examples of such biological rhythms.

Answer 10

Circadian Rhythms (24hrs)
Monthly Rhythms (eg. menstrual cycle).

Question 11

Through which to processes is homeostasis achieved?

Answer 11

Feedback and feedfoward.

Question 12

What is negative feedback?

Answer 12

Feedback that brings a variable back to a set point.

Question 13

What is positive feedback?

Answer 13

Feedback that takes a variable further and further away from a set point.

Question 14

What are the 4 key components of a negative feedback system?

Answer 14

1. Sensor
2. Integrator
3. Effector/s
4. Communication pathways

Question 15

What does a homeostatic integrator do?

Answer 15

Compares actual and set point values, and generates an ‘error’ signal is any discrepancy occurs between these two. Then determines and controls the response.

Question 16

Which two components of the negative feedback system can often be within the same cell?

Answer 16

The sensor and integrator.

Question 17

What does a homeostatic effector do?

Answer 17

Produces the response(s) that restore the regulated variable to its ‘set point’.

Question 18

What are the two Physiological Communication Pathways?

Answer 18

Neuronal and hormonal.

Question 19

How do neuronal communication pathways work?

Answer 19

Action potentials in axons and neurotransmitter release at synapses.

Question 20

How do hormonal communication pathways work?

Answer 20

Hormones are released into the blood (or the ECF).

Question 21

What are the benefits of neuronal communication pathways?

Answer 21

– 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

Question 22

What are the benefits of hormonal communication pathways?

Answer 22

– 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

Question 23

What is feed foward?

Answer 23

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.

Question 24

What are the two types of feed forward?

Answer 24

Physiological (eg. goosebumps) and behavioral (eg. putting on a jacket)

Question 25

In what circumstance may positive feedback be helpful?

Answer 25

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.