Homeostasis and physiological variables Flashcards
What is physiology?
The study of how organisms function and how function is controlled and maintained in order to keep us alive and healthy.
What does normal function equate to?
Normal function = physiological = health
What does abnormal function equate to?
Abnormal function = pathophysiological = illness & disease.
What is a physiological variable?
A measure of a bodily condition or bodily function.
What is homeostasis?
The dynamic maintenance of physiological variables within a predictable range.
What is the set-point?
It is the normal ‘basal’ or ‘at rest’ value for a physiological variable
Set points may be temporarily over-ridden or may need to be adjusted to suit changing circumstances.
What is core temp and arterial CO2
- Core temperature = 37 degrees Celsius
- Arterial carbon dioxide = 5.3 KPa
what is the most common mechanism for the maintenance of physiological variables.
negative feedback
what are 2 types of homeostasis and why do we need them
- Short term - immediate survival.
- Medium - long term - health and well being reproductive capability.
What happens is a physiological variable is out of its normal range for too long?
Illness, disease or death.
E.g.
- Hypertension
- Hypoxemia
- Acidosis/alkalosis
- Hyperglycemia (diabetes)
- Excess cortisol (cushing syndrome)
- Hyperthyroidism (Grave’s disease)
What are two examples of physiological variables?
Blood glucose concentration
Blood pressure
in blood glucose concentration what is the set point
~90 mg/ml
what is the mean bp when diastolic and systolic
- diastolic = 80 mmHg
- systolic = 120 mmHg
when is the set point of blood pressure lower?
during sleep
what is more important to immediate survival than blood pressure
Osmolality (salt/water balance) is more important to immediate survival than blood pressure
3 types of control mechanisms
Negative feedback
Feed-forward
Positive feedback
what is negative feedback
A change is sensed, and a response is initiated to reverse that change,
The effect is therefore to maintain physiological variables within a predicted range
what is feed forward
Anticipation of a change brings about the response to that change before the change can be detected by negative feedback sensors
what is positive feedback
A change in a variable triggers a response that causes further change in that variable
The effect is therefore amplification of the change rather than normalisation
What are the key features of all negative feedback loops?
A physiological variable drifts away from it’s normal set-point
Sensors detect the change in the variable
Afferent pathway carries signals from sensors to integrating centre
integrating centre compares input from sensors against physiological set point and elicits a response
efferent pathway carries signals from integrating centre to effectors
effectors produce responses that tend to bring the variable back towards its set-point
What are the 3 main types of negative feedback?
- Neuronal
- Endocrine
- Paracrine
Where are many neuronal integrating centres found?
In the midbrain or brain stem.
What 4 things are neuronal integrating centres essential for in negative feedback?
- Temperature control
- Osmolality control
- Blood pressure/flow control
- Blood gas/breathing control
What is communication with effectors usually via? what does this result in?
Communication with effectors is usually via the sympathetic and parasympathetic nervous systems as they tend to have opposing actions on bodily functions.
This results in a fine tuning of physiological variables.
