Regulation Of Heart Rate And Arterial Pressure Flashcards
Vagal signal is (?) to sympathetic stimulation when it comes to heart rate
Vagal = dominant signal
Vagal = more rapid signal than sympathetic (rapid response and decline)
Sympathetic = slow to decline***
Para vs. sym stimulation effect on Frank-Sterling Curve
Parasympathetic = shift curve downwards
Sympathetic = shift curve upwards —> more of a increase in CO as you increase right atrial pressure (preload)
Antidieuretic hormone (vasopressin)
Hypothalamus recieves input (like hyperosmolality, decreased atrial function, or sympathetic stimulation) —> a.k.a body tissues are getting poor perfusion…NEED TO RAISE BP!!!
—> signals the posterior pituitary to release vasopressin —> constriction
Receptors in kidneys —> drive up fluid resorption…retain fluid, increase blood volume
Atrial Natriuretic Peptide (ANP)
Released from atrium smooth muscle in responses to increase preload
Drives vasodilation in arterioles… to reduce BP
In kidneys…lowers blood volume, decrease preload
Renin-angiotensin II-aldosterone system
Liver produces angiotensinogen constitutively, a pre-protein
When kidney senses poor perfusion, release renin (which cleaves angiotensinogen —> angiotensin I)
Angiotensin I —> II in lungs (active form)
Series of effects that ultimately increase perfusion to the kidney
- increase in sympathetic activty
- drives fluid resorption
- stimulate adrenal gland to release aldosterone
- drives vasoconstriction in cells
- stimulates pituitary gland to relase ADH
(When bp goes up, kidney sees more perfusion, and lowers renin release)
Baroreceptor reflex
Senses changes in stretch in aortic arch and carotid sinus
Baroreceptors decreases HR in response to increasing arterial pressure in a sigmoidal manner (HR = y axis)
Low pressure = less baroreceptor firing = allows more sympathetic innervation = increase HR
Occurs very rapidly…keeps pressure constant and minimizes fluctuation
If you vasodilate your arm muscles…baroreceptor detects this drop in BP and…
Reduces firing
Allowing more sympathetic activation - to keep bp…
Further decrease in receptor firing if start using legs as well
Most important in our daily physiological activity
Bainbridge reflex
Responds to changes in blood volume (not pressure like the baroreceptors)
Detects an IV fluid infusion (like an IV from hospital)
Responds to atrial stretch —> increases heart rate
And increases urine volume by lowering vasopressin
Acts very quickly…dominant over baroreceptor
Chemoreceptor reflex
Looks for systemic ischemia
May raise or lower HR…depending on lung activity
Activated by:
- increased pCO2
- decreased pO2
- decreased pH
Depends on lung function to increase HR
…if no lung function -> will decrease HR because chemoreceptors realize there is no O2 in blood
Chemorecptors attempt to increase O2 intake in the lungs…with lungs in tact this results in increase RR…which restores Oxygenation
—> increased heart rate…as long as lungs are functioning, the chemoreceptors will drive up heart rate
Coordination of the reflexes that regulate the heart rate
Baroreceptors: responds immediately
Chemo: respond a bit slower
CNS response: brain is very sensitive to CO2 levels…if CO2 increasing, it will response robustly
Renin/angiotensin: a bit slower, may not stimulate until hours later —> leads to increase in aldosterone
Capillary fluid shift: occurs when low pressure in capillary…capillaries pick up interstitial fluid to restore blood volume…takes ~15 min to kick in
Pressure ranges of the heart rate reflexes
Baro: nice sigmoidal curve…increase pressure will increase firing…only operates within 75-175mmHg
Chemo: kicks in below 75mmHg…increase sympathetic activity
CNS response: kicks in at 50mmHg…ramp up sympathetic —> this is when the MYOGENIC TONE is not longer working!!!
Clinical problem:
Woman has 96/60mmHg with HR of 120
Mildly anemic
Why tachycardic?
—> reflexes have kicked in to increase perfusion (baro)
Why bp low with hr high?
—> total peripheral resistance is too low ( BP = CO* TPR
What is likely the status of CO?
—> decreased due to decrease in TPR
Baroreceptor vs. Brainbridge reflex
During increases in blood volume = Bainbridge is dominant….leading to increase in heart (senses high atrial stretch)
During decreasing volumes = baroreceptor is dominant…stimulating increase in heart rate when blood pressure is lowering
Sympathetic and parasympathetic innervation on heart
Regulation against each other?
Sympathetic =
NE -(+)—> beta-1
&
Neuropeptide Y -(-)—> M2 receptor
Parasympathetic=
AcH stimulates M2 and inhibits beta1
