homeostasis Flashcards
conformers
more ‘primitive’ organisms that are restricted to more constant environments
homeostasis
the control or stabilisation of the internal environment
regulators
able to control internal environment and therefore able to exploit physiologically hostile and variable environments
internal environment
the environment surrounding cells inside the body (extracellular fluid)
body water
about 60% of total body weight (for a 70kg man: ~42 lites)
extracellular fluid
~33%, represents internal environment, (interstitial fluid, plasma + transcellular fluid)
interstitial fluid
fluid surrounding cells (~24%)
plasma
fluid component of blood (~8%)
intracellular fluid
~67%, fluid within cells (cytosol)
transcellular fluid
‘other’ fluid (e.g. CSF, joints, ocular) (~1%)
O2 levels
normal: 40 mmHg
range: 34-45 mmHg
non-lethal limit: 10-1000 mmHg
CO2 levels
normal: 40 mmHg
range: 35-45 mmHg
non-lethal limit: 5-80 mmHg
Na+ levels
normal: 142 mmol/l
range: 138-146 mmol/l
non-lethal limit: 115-175 mmol/l
K+ levels
normal: 4.2 mmol/l
range: 3.8-5.0 mmol/l
non-lethal limit: 1.5-9.0 mmol/l
Ca2+ levels
normal: 1.2 mmol/l
range: 1.0-1.4 mmol/l
non-lethal limit: 0.5-2.0 mmol/l
glucose levels
normal: 6 mmol/l
range: 4-7 mmol/l
non-lethal limit: 0.11-80 mmol/l
blood pH levels
normal: 7.4 pH
range: 7.35-7.45 pH
non-lethal limit: 6.9-8.0 pH
temperature levels
normal: 37 °C
range: 36.5-37.5 °C
non-lethal limit: 18-43 °C
O2 buffering function of haemoglobin
Hb has a high affinity for O2 and only releases O2 when the local concentration is low
respiratory control of CO2
end product of aerobic respiration:
C6H12O6 + 6O2 -> H2O + 6CO2
ΔHc 2880 KJ
HYPERventilation DEcreases plasma [CO2]
HYPOventilation INcreases plasma [CO2]
temperature regulation
hypothalamus (body’s thermostat) receives afferent inputs from peripheral and central thermoreceptors which initiate thermoregulatory responses (e.g. shivering, sweating, vascular changes)
negative feedback
effector system opposes the initiating stimuli
(e.g. an increase in blood pressure causes a compensatory decrease in blood pressure)
positive feedback
effector system reinforces or amplifies the initiating stimuli
(e.g. formation of a blood clot stimulates further clotting)
characteristics of negative feedback
-a SETPOINT for the physiological parameter being regulated
-a SENSOR to monitor the regulated variable
-the ability to detect any error between the sensor and the setpoint by a COMPARATOR
-an EFFECTOR to bring about a compensatory change
(-VE) blood pressure regulation (stimulus)
change in BP away from setpoint
(-VE) blood pressure regulation (sensor)
baroreceptors in aortic arch and carotid sinus
(-VE) blood pressure regulation (comparator)
vasomotor centres in the medulla
(-VE) blood pressure regulation (effector)
change in sympathetic and parasympathetic nervous system activity
(-VE) blood pressure regulation (response)
change in heart rate/vaso-response to return to setpoint
(+VE) oxytocin stimulation of uterine contraction during labour (stimulus)
as baby moves deeper into birth canal the cervix is stretched
(+VE) oxytocin stimulation of uterine contraction during labour (sensor)
stretch receptors send nerve impulses to hypothalamus
(+VE) oxytocin stimulation of uterine contraction during labour (effector)
hypothalamus sends impulses to posterior pituitary which releases oxytocin to blood (travels to uterine muscle)
(+VE) oxytocin stimulation of uterine contraction during labour (response)
uterus contracts more vigorously until baby is born; at birth, stretching of cervix lessens and the +ve feedback loop is broken
why do most physiological systems use -ve feedback ?
+ve feedback provides an unstable, increasing stimulus-response cycle, if not stopped, it can be dangerous and sometimes lethal
