Vascular pt 3 Flashcards
What effect does decreasing resistance in one organ have on the MAP of the entire system?
A decrease in resistance means a decrease in MAP of the entire system.
MAP must be maintained, therefore it is restored by baroreflexes the elicit vasoconstriction and increased cardiac output.
What two primary mechanisms regulate MAP?
Cardiovascular (baroflex): fast, short term response
Renal: slow, long term response
Where are baroreceptors found?
What do they respond to?
In the aortic arch and carotid sinus.
They respond to the change in tension of the carotid artery and aortic arch b/c of changes in blood pressure.
What is a baroreceptor reflex to an increase and decrease in blood pressure?
(inverse relationship)
Increase elicits a decrease in heart rate and blood pressure
Decrease elicits an increase in heart rate and blood pressure
Baroreceptor afferents project to where? And where do they project excitatory activity to?
Solitary Nucleus (NTS) - the caudal ventrolateral medulla and the nucleus ambiguus
What do the baroreceptors of the caudal ventrolateral medulla inhibit?
the rostral ventrolateral medulla (RVLM)
What is the role of the RVLM baroreceptor pathway?
- Acts as a pacemaker for the basal sympathetic activity
- Projects to sympathetic preganglionic neurons in the spinal chord
What is the role of the nucleus ambiguus baroreceptors?
The parasympathetic neurons in the vagus nerve (CNX) decelerate the heart rate
What is the role of the sympathetic baroreceptor pathway?
Preganglionic and postganglionic neurons go to blood vessels
Baroreception is what kind of system?
A negative feedback system
A homeostatic system
What affect does an increased MAP have?
- Stimulation of the CVLM neurons, reducing tonic sympathetic activity in the RVLM
- Reduction of HR and MAP
- Stimulation of the parasympathetic neurons in nucleus ambiguus, decreasing HR
What is the set operating point?
What determines the set point?
- Where the baroreflex is the most sensitive and produces the max response for a shift in BP
- Determined by sensitivity of RVLM neurons to baroreceptive input
How is RVLM sensitivity to BP altered?
- Top down: cerebral input
- Bottom up: sensory input via brain stem centers
What are the characteristics of the negative feedback system of baroreceptors?
- Only works when BP has already changed; occurs as a response
- Time delay between disturbance and homeostatic restoration; produces changes in vascular function
What are the characteristics of the feedforward control system of baroreceptors?
- Signal associated with disturbance sent to RVLM to anticipate a change in BP; creates a pre-emptive compensatory response to BP
- Reduces changes in the vascular system by stabilizing responses
What are the characteristics of CNS baroreflex regulation?
- Long term BP is tightly regulated
- CNS generates a vascular tone (baseline) of BP for specific behavioral or emotional contexts
How does the RVLM maintain BP with pacemaker-like cells?
- Continuous activity projected to preganglionic sympathetic neurons
- Bottom up regulation (baroreceptors adjust RVLM to stabilize BP)
- Top down regulation (cerebral cortex and limbic system activity)
What do the cerebral cortex and the limbic system affect? What are they responsible for?
- Anticipatory, emotional or cognitive responses to environmental stress/threats (project into the hypothalamus; paraventricular nucleus)
- Responsible for behavior- related adjustments to sympathetic tone (feedforward control of baroreflexes)
What does the paraventricular nucleus do?
Regulates ANS control of BP and baroreflex sensitivity
What do paraventricular and supraoptic nuclei do?
What does their destruction cause?
Where does the paraventricular nucleus project into?
- Regulate water balance; produce ADH and oxytocin
- Destruction causes diabetes insipidus
- PVN projects into autonomic nuclei of brainstem and spinal cord
What does the anterior nucleus do?
What does its destruction result in?
- Thermal regulation via heat dissipation; stimulates PNS
- Destruction causes hypothermia
What does the preoptic area contain?
What does it do?
- Contains sexually dimorphic nucleus.
- Regulates release of gonadotrophic hormones
What does the suprachiasmatic nucleus do?
Receives input from retina, controls circadian rhythms
What does the dorsomedial nucleus stimulation result in?
Obesity and savage behavior
What does the posterior nucleus do?
What does its destruction result in?
- Thermal regulation; stimulation of SNS
- Destruction results in inability to thermoregulate
What does the stimulation of the lateral nucleus do?
What about its destruction?
- Stimulation induces eating
- Destruction induces starving
What does the mammillary body do?
- Recieves input from the hippocampal formation
- Projects to anterior nucleus of thalamus
- Contains hemorrhagic lesions in Wernicke’s encephalopathy
What is the ventromedial nucleus?
What does its destruction do?
- Satiety center
- Destruction results in obesity and savage behavior
What does the Arcuate nucleus do?
What does it contain?
- Produces hypothalamic releasing factors
- Contains DOPA-ergic neurons that inhibit prolactin release
How does the PVN nucleus regulate RVLM and baroreflex sensitivity?
- Specific pathways from PVN to RVLM and spinal cord preganglionics
- Subgroup regulates heart, vascular system, and kidney to estabilsh BP and HR baselines of behavioral contexts
What is the internal control of the PVN?
What is the result of hypertension in the PVN?
- GABA and NO inhibit RVLM pathways
- Decreased inhibition by GABA and NO permit higher sympathetic activity and BP
How does the CNS reset the baroreflex to maintain different levels of BP?
What is the affect of changing baroreceptor sensitivity to higher BP levels?
- PVN temporarily enhances sympathetic vasoconstriction or desensitizes baroreceptors to changes in BP
- Rightward shift in equilibrium point of baroreception
How does exercise increase BP?
- Decreases baroreflex sensitivity
- Anticipatory limbic and PVN during exercise resets the baroreflex equilibrium to the right
What is transient orthostatic hypotension?
Sudden downward flow of blood via gravity; causes momentary lightheadedness; ANS responds with a baroreceptor reflex
How does aging affect baroreflex capacity?
- Carotid artery stiffness decreases baroreflex sensitivity (reduces response magnitude)
- Delayed peak cardiovascular responses to acute carotid baroreceptor loading
What does high frequency in power spectral analysis correspond to?
respiratory activity
- increased pulmonary circulation during O2 intake, decreased circulation during CO2 release
- primarily a result of parasympathetic activity
What does low frequency in power spectral analysis correspond to?
(Meyer Waves)
- Both HR and BP variability
- Related to feedback changes of baroreflexes
What is sinus arrhythmia?
- HR increases with inspiration, decreases with expiration
