Vascular pt 3 Flashcards
(38 cards)
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
