Homeostasis & control systems Flashcards
def of homeostasis
The maintenance of a constant internal environment
Mechanism of homeostatic regulation - Autoregulation
cell, tussue, organ or organ system adjusts in response to environmental change - e.g. dec O2 om tissue = cells release chemicals that dilate clood vessels = more blood gloe = more O2
Mechanism of homeostatic regulation - Extrinsic
Activities of nervous system or endorcrine system -
these organ systems detect change
either electrical signal or chemical signal tries to adjust it
e.g. excerise = nervous system increases heart rate, direccts blood flow to right places etc.
Diff between effects of nervous sysrems response and endrocrine systems response
Nervous - rapid, short term, specific
Endocrine - slower, longer lastin, affects organs/tissues throughout the body e.g. adustment of organ system during starvation
What does a homeostatic regulatory mechanism consist of?
Receptor - sensor for stimuli/environmental changes
Control centre - receives and processes info, sends out commands
Effector - cell or organ that respons to commands, activity opposes or enhances the stimuli
def of negative feedback
Aims to maintain a controlled variable at its set point
typically negates the original stimuli in order to minimise change
Thermoregulation as a process in -ve feedback
Receptor = skin
Control center = hypothalamus
if int temp rises above 37.2C
Two effectors are activated by CC: -muscle tissue lining of blood (relax, blood vess dilate, inc blood flow near skin suface vessels, - sweat glands (secrete sweat, evap cools)
When back to normal temp, all these processes are signalled to stop
Also remmeber set point for temp changes depending on time of day, individual differences etc.
regulation of BP
- BP lowers
- Sensor = baroreceptors
- glosso pharyngeal nerve sends signal to
- medulla oblongata in brain (CC) (at base connected to spinal cord)
- autonomic nerves send signal to
- Heart, blood vessels (effectors)
- increase in cardiac output (heart rate)
- inc vasoconstriction
raises BP
process stopped
def of positive feedback
initial stimulus produces a response that amplifies/enhances/reinforces itself (rahter than oposing it)
example of positive feedback - blood clotting
Damage to blood vessel
Activates clotting factors (chemicals released)
Activation of Thrombin - starts chain reaction
As clotting continues, each step releases chemicals that further accelerate process
When bleeding stops and clot is formed, the loop ends
Branches of the peripheral nervous system
Somatic:
Skeletal muscle = concious movement
Autonomic:
- Parasympathetic
- Sypathetic
=smooth & cardiac muscle, glands
(subconscious movement)
general mechanism of autonomic nervous system
CNS = Preganglionic neuron –>
Peripheral ganglion = postganglionic –>
target cell
Sympathetic
- more active in stressful situations e.g. fight or flight
- From CNS = Thoracic & Lumbar
- preganglionic are SHORT - releases ACETYLCHOLINE to the NICOTINE receptor on the postganglionic
Ganglionic trnasmitter = ACh (N2) - postganglionic are LONG - releases NORADRENALINE to alpha/beta adrenergic receptors (=Neuroeffector transmittor)
Parasympathetic
- active during rest - e.g. digestion etc.
- From CNS - Cranial & sacral
- preganglionic fibre are LONG - releases ACETYLCHOLINE to NICOTINIC receptors on postganglionic
Ganglionic trnasmitter = ACh (N2) - postganglionic fibre are SHORT - release ACETYLCHOLINE to muscarinic acetylecholine receptor (=Neuroeffector transmittor)
Adrenal Medulla
Instead of the regular sypathetic pathway, preganglionic fiber releases acetylcholine to Nicotinic receptor IN THE ADRENAL MEDULLA - contains chromaffin cell
this releases Adrenaline into circulation
