Homeostatic regulation
Homeostatic regulation
● Homeostatic regulation
= organism’s ability to keep its internal environment stable despite changes in the external
environment
→ temperature, blood pH, oxygen pressure, blood glucose, …
● Central nervous system
= interface for interaction with external environment
● Stress is a threat to homeostasis
→ stressor: physical or psychological
→ compensatory stress response
● Physical vs. psychological stress:
● Feedback control for temperature:
● Feedback control for blood pressure:
1
,● Feedback control for blood pH levels (arterial carbon dioxide pressure, PaCO2):
● Feedforward control
→ perturbations are being anticipated and corrected before they occur
→ classical conditioning as a viable mechanism
→ ex.: exercise hyperpnea
→ increases in ventilation and heart rate occur at the onset of physical exercise even before an
increase in PaCO2
● A hierarchy of homeostatic controls:
● Intrinsic control mechanisms (organ level):
organ adapts its functioning on its own in response to slow local changes
→ only possible when conditions are relatively stable
→ ex.: Frank Starling mechanisms:
2
,Autonomic nervous system
● Autonomic nervous system (ANS)
→ viscera: limited awareness and voluntary control
→ negative feedback
→ parts: 1. sensory pathways (afferent)
2. motor pathways (efferent)
→ divisions: 1. sympathetic nervous system (SNS)
2. parasympathetic nervous system (PNS)
→ reciprocal regulation of organic function
●
● Each division has sensory pathways from organs via ganglia to brainstem (afferent)
● Response component of each division (efferent):
1. descending autonomic and pre-ganglionic fibers
→ hypothalamus or brain stem → intermediolateral cell column of spinal cord
2. ganglion
→ relay station for ascending and descending signals
→ part of local regulation system and reflexes
3. postganglionic fibers
→ more elaborated messages than in preganglionic fibers
4. neuroeffector junctions
→ postganglionic fiber
→ receptor at target tissue
→ nerve impulse → motor action
3
, ●
● Sympathetic nervous system
→ ratio of 1:10 pre- vs. postganglionic nerves
→ general broad influence on viscera
→ extensive linkages across widely distributed ganglia
→ closely integrated actions across different organs
→ neurotransmission
→ acetylcholine (preganglionic)
→ sympathetic preganglionic nerves release acetylcholine at adrenal medulla
→ release of catecholamines (nor- and epinephrine) into blood
→ sympathetic nerves release acetylcholine at sweat glands
→ norepinephrine (postganglionic):
smooth muscle cells, cardiac muscles and pace maker
→ activating function
→ more active during stress
→ crucial for fight/flight response
● Parasympathetic nervous system
→ ganglia more specific and nearer to target organ
→ ratio of 1:3 pre- vs. postganglionic nerves
→ localized specific actions directed at one organ
→ neurotransmission
→ acetylcholine (preganglionic)
→ acetylcholine (postganglionic):
smooth muscle cells, cardiac muscle and pace maker
→ inhibitory influence
4
Homeostatic regulation
● Homeostatic regulation
= organism’s ability to keep its internal environment stable despite changes in the external
environment
→ temperature, blood pH, oxygen pressure, blood glucose, …
● Central nervous system
= interface for interaction with external environment
● Stress is a threat to homeostasis
→ stressor: physical or psychological
→ compensatory stress response
● Physical vs. psychological stress:
● Feedback control for temperature:
● Feedback control for blood pressure:
1
,● Feedback control for blood pH levels (arterial carbon dioxide pressure, PaCO2):
● Feedforward control
→ perturbations are being anticipated and corrected before they occur
→ classical conditioning as a viable mechanism
→ ex.: exercise hyperpnea
→ increases in ventilation and heart rate occur at the onset of physical exercise even before an
increase in PaCO2
● A hierarchy of homeostatic controls:
● Intrinsic control mechanisms (organ level):
organ adapts its functioning on its own in response to slow local changes
→ only possible when conditions are relatively stable
→ ex.: Frank Starling mechanisms:
2
,Autonomic nervous system
● Autonomic nervous system (ANS)
→ viscera: limited awareness and voluntary control
→ negative feedback
→ parts: 1. sensory pathways (afferent)
2. motor pathways (efferent)
→ divisions: 1. sympathetic nervous system (SNS)
2. parasympathetic nervous system (PNS)
→ reciprocal regulation of organic function
●
● Each division has sensory pathways from organs via ganglia to brainstem (afferent)
● Response component of each division (efferent):
1. descending autonomic and pre-ganglionic fibers
→ hypothalamus or brain stem → intermediolateral cell column of spinal cord
2. ganglion
→ relay station for ascending and descending signals
→ part of local regulation system and reflexes
3. postganglionic fibers
→ more elaborated messages than in preganglionic fibers
4. neuroeffector junctions
→ postganglionic fiber
→ receptor at target tissue
→ nerve impulse → motor action
3
, ●
● Sympathetic nervous system
→ ratio of 1:10 pre- vs. postganglionic nerves
→ general broad influence on viscera
→ extensive linkages across widely distributed ganglia
→ closely integrated actions across different organs
→ neurotransmission
→ acetylcholine (preganglionic)
→ sympathetic preganglionic nerves release acetylcholine at adrenal medulla
→ release of catecholamines (nor- and epinephrine) into blood
→ sympathetic nerves release acetylcholine at sweat glands
→ norepinephrine (postganglionic):
smooth muscle cells, cardiac muscles and pace maker
→ activating function
→ more active during stress
→ crucial for fight/flight response
● Parasympathetic nervous system
→ ganglia more specific and nearer to target organ
→ ratio of 1:3 pre- vs. postganglionic nerves
→ localized specific actions directed at one organ
→ neurotransmission
→ acetylcholine (preganglionic)
→ acetylcholine (postganglionic):
smooth muscle cells, cardiac muscle and pace maker
→ inhibitory influence
4
