Regulation of CO Flashcards
(22 cards)
Frank-Starling mechanism
- intrinsic regulation of myocardial performance
- allows the heart to adapt to alterations in venous return
- heart pumps out whatever blood it receives (within limits)
- maintains precise balance of outputs from left and right hearts
ventricular filling increases diastolic fiber length –> number of myofilament cross bridges increases –> strength of contraction increases
Frank-Starling mechanism vs increased cardiac contractility
Frank-Starling mechanism: increase in CO is due to increased venous return
Increased contractility: increase in CO is due to increased stretch
ensures that the outputs from the right and left ventricle match
Frank-Starling mechanism
How does the Frank-Starling mechanism ensure that the outputs from the left/rights ventricles are the same?
change in output in one ventricle causes like change in venous return to its mate, which leads to matching output from the latter ventricle
Both _______ and _______ components are innervated by sympathetics and parasympathetics.
conductile (SA node) and contractile
Parasympathetic innervation is more dense on the atria. What does this mean?
it has a greater effect on HR than SV
effect of sympathetic nerves vs parasympathetic nerves on HR and strength of contraction
sympathetic nerves increase HR and increase strength of contraction
parasympathetic nerves decrease HR and decrease strength of contraction
Resting ______ tone predominates over ______ tone.
parasympathetic / sympathetic
intrinsic resting HR
100 bpm
stretch receptors located in carotid sinuses and aortic arch
baroreceptor reflex
Explain how the baroreceptor reflex works.
decreased stretch in the carotid sinus –> decreased impulses up sinus nerve and glossopharyngeal (IX) nerve
–> nucleus tractus solitarius (vasomotor center in medulla) –> increased sympathetic nerve impulses –> increased HR and decreased vagal firing
Bainbridge reflex
- increased cardiac filling elicits tachycardia (sensed by atrial volume stretch receptors)
- nervous reflex that passes through the vasomotor center and back to the heart via sympathetic nerves and vagi
- highly selective (no change in cardiac contractility)
- Bainbridge reflex only occurs with very gradual increases in cardiac filling
hormones that increase HR and SV
epinephrine
thyroxine
What is cardiac muscle hypertrophy?
marathon runners increase heart mass (increased cell size, not number) by 50-75%, which leads to increased contractility (and increased CO)
Pro-hypertrophic signals
- ) Muscle stretch
- ) Norepinephrine
- ) Angiotensin II
- ) Endothelin-1
- 1.) is preload-induced hypertrophy (increases contractile function)
- 2.) is afterload-induced hypertrophy (decreased contractile function)
Difference between preload-induced and afterload-induced hypertrophy.
Calcium-sensitive signaling pathways mediate the gene activation induced by pro-hypertrophic agents.
- Increased preload produces a gene switch from beta to alpha MyHC
- Increased afterload produces a gene switch from alpha to beta MyHC
*The alpha form accounts for only a small percentage of the cardiac mass, but has a high contractile velocity. This is a very efficient form.
If you increase afterload, you will decrease SV. Why doesn’t CO fall?
doesn’t fall until pressure exceeds 160 mmHg (between 100-150 mmHg, CO is largely determined by tissue blood flow and venous return)
increases in intrapleural or pericardial pressures shift cardiac function curve to the right; cardiac filling requires extra pressure to overcome this external force
extracardiac pressures
fluid accumulation in the pericardial sac
increased pericardial pressure
amount of blood flowing back to the heart per unit time
venous return
In the steady state, venous return = ________.
CO (@ RAP = 0)
Determinants of venous return:
- right atrial pressure (RAP)
- mean systemic filling pressure (Psf)
- resistance to venous return (RVR)
VR = Psf - RAP / RVR
