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Hemodynamic Defense Response
Dr. Cunningham's lecture on Hemodynamic Defense Response
32
Veterinary Medicine
03/08/2012

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Cards

Term
What's the first line of defense against rapid changes in BP?
Definition
Baroreceptor reflex.
Term
Name the key systems (4 of them) involved in controlling BP.
Definition
1. Baroreceptor reflex
2. SNS (vasoconstriction, increased HR)
3. RAAS (immediate and long term vasoconstriction and Na+ retention to increase blood volume)
4. ADH (aka Arginine Vasopressin): chronic vasoconstriction and water retention
Term
What are the 3 arms of the cardiovascular adaptive mechanism?
Definition
1. Hemodynamic response (both physiologic and pathologic)
2. Inflammatory
3. Growth/remodeling
Term
How does the heart increase diastolic reserve (ventricular filling pressure)?
Definition
1. Increase Blood volume
2. Decrease venous capacity (via venous constriction)
Term
How does the heart increase systolic reserve?
Definition
Increase contractility, which decreases ESV.
Term
Why is adequate cerebral blood flow dependent on systemic BP?
Definition
Brain has limited capacity for vasodilation.
Term
What is the relationship between BP and TPR?
Definition
MAP = CO x TPR
Term
What are the stimulus and pathway for carotid sinus and aortic arch (high pressure) baroreceptors?
Definition
Stimulus: increased pressure (mean or rate of change).
Pathway: afferent in CN IX or X to solitary tract nucleus. Inhibits SNS efferent (excitatory to vagus).
"Reset" occurs after 1-2 days, so less important in chronic BP control.
Term
What are the stimuli and pathways for the carotid and aortic body chemoreceptors?
Definition
Stimuli: decreased PO2, increased PCO2, decreased pH
Pathway: afferents in IX, X stimulate both SNS and PNS efferents to increase resp. rate and depth, decrease HR, peripheral vasoconstriction.
Term
What are stimuli and pathway of medullary (central) chemoreceptors?
Definition
Hypercapnia or hypoxia centrally; SNS efferents result in in increased resp rate and depth, increased HR, inotropy.
Term
Stimulus and response of low pressure baroreceptors ("volume receptors") of large vessels and heart?
Definition
Stimulus: increased stretch/volume
Response: bradycardia, hypotension
Term
Define respiratory sinus arrythmia.
Definition
Physiologic response to changing conditions within a respiratory cycle: HR and BP increase at the end of inspiration
Term
What's the Cushing reflex?
Definition
Under CNS ischemic conditions (MAP <50mmHg), response is increase in BP. This increase in BP is Cushing reflex.
Term
Where is the vasomotor center located? What does it do?
Definition
Floor of 4th ventricle, in medulla. Contains pressor area, depressor area (causing vasoconstriction and dilation, respectively), and sensory area (solitary tract nucleus, receiving afferents from CN IX and X).
Term
What is the dorsal motor nucleus of the vagus?
Definition
Cardioinhibitory center. Sends tonically active fibers to PNS ganglia in heart.
Term
What causes degranulation of atrial ANP granules?
Definition
Atrial stretch.
Term
What leads to the release of BNP?
Definition
Cardiac pathology.
Term
WHat stimulates aldosterone release? How does it work? What are its effects?
Definition
AT II, decreased Na+, increased K+, ACTH all stimulate aldosterone secretion.
It works via upregulating production of Na+/K+ pumps in DT and CD, resulting in Na+ and H2O retention, and K+ excretion.
Term
How long do Epi and NE last in the bloodstream?
Definition
1-3 minutes!
Term
What causes renin release?
Definition
1. Decreased stretch of glomerular afferent arterioles
2. Decreased Na+ concentration reaching macula densa
3. SNS stimulation at kidney
Term
Review the RAAS.
Definition
Renin released by JG cells catalyzes conversion of angiotensinogen (made in liver) to AT I (decapeptide). ACE then converts AT I to AT II (octapeptide, mostly in endothelium of lung; also blood vessels). All this takes about 20 min.
Term
What are the effects of AT II?
Definition
1. Direct vasoconstriction
2. Stimulates aldosterone release (-> fluid retention)
3. stimulates thirst (hypothalamus)
4. Intra-renal vasoactivity resulting in Na+ and H2O conservation.
5. Long-term effect on heart, promoting hypertrophy and fibrosis.
Term
Where does ADH come from and what does it respond to?
Definition
Hypothalamus, released by posterior pituitary. Responds to decreased atrial stretch (sensed at atria) and increased plasma osmolarity (sensed at hypothalamus - no BBB there, remember!) and AT II. Takes hours to be activated (steroids work by upregulating genes involved in enzyme production): increase aquaporin production, which increases reabsorption of water in CD. V1 receptors restore blood pressure; V2 receptors restore blood volume.
Term
What are ATII receptor subtypes? What about ADH subtypes?
Definition
A and B. A is regulatory (increase BP, growth, etc.) and B is counterreg. A is found in adult, B in fetus.
V1 exerts vasoconstrictive effects and V2 vasodilation.
Term
What's ADHs role in heart failure?
Definition
ADH release increases thirst and water retention, resulting in volume overload, dilutional hyponatremia.
Term
What is endothelin?
Definition
Vasoconstrictor (works on intermediate/long term).
Term
How does capillary fluid shift work in the context of restoring BP?
Definition
Sympathetic stimulation selectively constricts arterioles and dilates venules, reducing capillary pressure and driving fluid INTO the vasculature from the interstitium.
Term
Does MAP change during exercise? Why/how?
Definition
NO. MAP = CO x TPR. CO increases, but TPR decreases (vasodilation at skeletal muscle beds) so MAP doesn't change.
Term
What is the major determinant of resistance in a vessel?
Definition
Radius. Remember Poiseuilles equation? R = 8nL/πr^4
Term
What are Alpha 1 effects? What are they mediated by primarily?
Definition
Alpha 1 effects:
Arteriolar (splanchnic) vasoconstriction
Venous vasoconstriction

Mediated by NE, primarily.
Term
What are Beta 1 effects? What are they mediated by primarily?
Definition
Increased dromotropy (conduction speed), chronotropy (HR), inotropy (contractility), and lusitropy (relaxation).
Mediated primarily by Epi.
Term
What kind of molecules are ANP and BNP?
Definition
Peptides cleaved to active forms.