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Homeostasis and physiological control lecture notes
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Lecture notes for Homeostasis and physiological control
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L3: Homeostasis and physiological controlDr Greg Knock
List physiological variables and explain their importance
Homeostasis: the dynamic maintenance of physiological variables within a predictable
range.
Dynamic: the variable may fluctuate but still within a normal range and the average value
will be predictable over longer periods of time.
The size and frequency of fluctuations depends on the variable.
The purpose of homeostasis in the short term is: immediate survival. In the long term, the
purpose is: health and wellbeing as well as reproductive capability.
, L3: Homeostasis and physiological control
Dr Greg Knock
Explain the principles of homeostatic control, including negative feedback, sensors and effectors,
integrating centres, hierarchy of importance
The hierarchy of importance of physiological variables is such that a variable that is of
greater immediate importance may be maintained at the expense of other variables that are
of importance in the long term.
Negative feedback: a change in the variable being regulated is compared against a set-point,
causing a response that tends to move the variable back to the set-point (normalization).
Components:
- Sensors: detect changes from sensors to integrating centre.
- Afferent pathway: carry signals away from sensors to integrating centre.
- Integrating centre: compares inputs from sensors against physiological set- point and
elicit a response.
- Efferent pathway: carry signals from integrating centre to effectors.
- Effectors: produce a response that tends to normalise the physiological variable.
Types of negative feedback:
- Neuronal
- Endocrine
- Local (chemical/physical).
Feed- forward: anticipation of a change brings about the response to that change before the
change can be detected by negative feedback sensors. E.g. the Pavlovian response- salivating
before eating food.
Positive feedback: change in a variable triggers a response that causes further change in that
variable (amplification).
Understand the role of brain stem and autonomic nervous system in physiological control
Many neuronal negative feedback reflex arcs involve the ANS.
Neuronal integrating centres for physiological control are located in the midbrain and brain
stem (hypothalamus, pons, medulla).
Includes: temp control, osmolarity control, blood pressure/flow control, blood
gas/ventilation control.
Sympathetic (noradrenaline) and para- sympathetic (acetylcholine) nervous systems tend to
have opposing actions on various bodily functions. Results in fine- tuning of physiological
variables e.g. heart rate, blood vessel diameter, salivary secretion, sweat gland secretion and
endocrine secretions.
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