Regulation of stroke volume & heart rate Flashcards
What do the sympathetic nerves release?
Noradrenaline
Where is circulating adrenaline coming from?
Adrenal medulla
What does noradrenaline act on?
- B1-receptors
- Sinoatrial
What does noradrenaline do to the slope of the regulation of the heart?
Increases it
-meaning faster depolarisation
What is the name for increased heart rate?
-Tachycardia
What nerve in the parasympathetic system innervates the heart?
Vagus
What does the vagus nerve release?
Acetylcholine
What is a decreased heart heart rate called?
Bradycardia
What is starlings law?
The energy of contraction is proportional to the intiail length of the cardiac muscle
What is another way of thinking about preload?
length
What determines preload?
EDV
What happens if venous return is increased?
increase in EDV= Increase in stroke volume
What does this reaction to preload mean in vivo?
Matches SV of left & right ventricles
What is after load?
Load against which the muscle tries to contract
-in vivo against aortaic valve and peripheral resistance of arterioles
What happens to stroke volume if total peripheral resistance is increased?
L ventricle has to work harder to open aortic valve and therefore has less energy to pump out blood. Lower stroke volume
What kind of vessels affect preload?
-Capacitancy vessels ie venules and veins
What vessels affect afterload?
Resistance vessels ie arteries and arterioles
What happens if you constrict veins?
Lager EDV larger preload larger stroke volume
What does inotopic mean?
Effecting strength
What does Chronotopic mean?
Effecting rate
What happens to contraction when sympathetic innervation takes over?
-Gives stronger and shorter contraction
What is the effect of the parasympathetic system on the stroke volume of the heart?
-Little effect
Why does the parasympathetic system have little effect on stroke volume?
Vagus nerve does not innervate the ventricle muscle
What effect does hypercalcemia have on starlings curve?
-Shifts curve up and left
higher stroke volume with lower EDV
What effect does hypocalcemia have on starlings curve?
Shifts curve down and to the right
lower SV and larger EDV
What effect does ischaemia have on starlings curve?
Shirts curve down and right
lower SV and larger EDV
How does heart react to lower SV?
Increases EDV if only left side is effected
What numerical value tells you where youre working on starlings curve?
Ejection fraction
EDV/SV
What effects do barbiturates have on starling curve?
Down and to the right
How do you measure cardiac output?
Heart rate x stroke volume
What does increasing heart rate with an electrical pacemaker do and why?
Small increase in CO but the SV decreases
WHY?
Shortening cardiac interval cuts into the rapid filling phase.
Reduces EDV and reduces preload so lower SV
What happens to HR and how when you exercise?
HR increases
- Via decreased vagal tone
- & Increased sympatheic tone
What happens to Contractility and how when you exercise?
Contractility increases
- via increased sympathetic tone
- alters inotropic state & shortens systole
What happens to venous return and how when you exercise?
Increases
- Via venoconstriction
- & skeletal/respiratory
- maintains preload
What happens to Total peripheral resistance and how when you exercise?
falls
- Due to arteriolar dilation in muscle skin &heart
- Reduces aterload
CO increases by how much when exercising?
4-6 times
