Physiology 1 Flashcards
Which part of the nervous system increases HR?
Sympathetic
Which part of the nervous system decreases HR?
Parasympathetic
Which nerve provides parasympathetic supply to the heart?
Vagus
Which neurotransmitter is responsible for slowing the heart rate (parasympathetic) and through which receptors?
Acetyl choline through
muscarinic M2 receptors
Which drug can be used to treat extreme bradycardia by speeding up the heart and how does it work?
Atropine
Competitive inhibitor of acetylcholine
Which neurotransmitter is responsible for increasing HR (sympathetic) and through which receptors?
Noradrenaline through
Beta-1 adrenoceptors
How does normal cardiac excitation spread through the heart?
SA node –> AV node –> Bundle of His –> Bundle of His left and right branches –> Purkinje fibres
What is stroke volume?
The volume of blood ejected by each ventricle per heart beat
SV = end diastolic volume (EDV) - end systolic volume (ESV)
What determines the cardiac preload?
End diastolic volume (venous return)
What is afterload?
Resistance into which the heart is pumping
What happens if there is a persistently increased afterload e.g. hypertension?
Ventricular muscle mass increases to overcome the resistance
–> ventricular hypertrophy
What is an inotropic effect?
Effect on force of contraction
What is a chronotropic effect?
Effect on heart rate
e.g. positive chronotropic effect = increases HR
What is cardiac output and how is it calculated?
The volume of blood pumped by each ventricle per minute
CO = SV x HR
When do normal heart valves produce a sound?
When they shut
not normally when they open
What are the 5 stages of the cardiac cycle?
- Passive filling
- Atrial contraction
- Ventricular contraction
- Ventricular ejection
- Ventricular relaxation
What produces the first heart sound?
When the ventricular pressure exceeds atrial pressure, the AV valves shut (mitral and tricuspid)
What produces the second heart sound?
After ventricular ejection, when the ventricular pressure falls below the aortic/pulmonary pressure –> aortic and pulmonary valves shut
Where does S1 fall in systole and diastole?
Beginning of systole
Where does S2 fall in systole and diastole?
End of systole/beginning of diastole
What does the P wave represent on an ECG?
Atrial depolarisation