Function of the heart Flashcards
What is the difference in the stimulus for contraction between a cardiac and skeletal muscle?
cardiac:
- involuntary / auto-rhythmic / myogenic (no stimulus needed)
- nodal cells start AP
skeletal:
- voluntary contraction initiated by motor nerves
- at neuromuscular junction
What is the difference in the duration of the AP between a cardiac and skeletal muscle?
cardiac: 250-300 mSec (longer)
skeletal: 1-2 mSec (shorter)
What is the difference in the refractory period between a cardiac and skeletal muscle?
refractory period = period of time muscle fiber is unresponsive to stimulus
cardiac:
- long
- unable to summate
- prevent tetanic contractions
skeletal:
- short
- summation and tetany
What is the difference in the source of intracellular Ca2+ for contraction between a cardiac and skeletal muscle?
cardiac:
- sarcoplasmic reticulum
- extracellular fluid
skeletal:
- Sarcoplasmic reticulum
What is the difference in the coordination of contraction between a cardiac and skeletal muscle?
cardiac:
- intercalated discs allow rapid spread of electrical signal
- syncytium (contract as single unit)
skeletal:
- inidividual muscle fibers are stimulated by single motor nerve
- motor units
What is the electrocardiogram (ECG)?
the ECG is the measurement of voltage between points on the surface of the body and reflects the electrical activity of the heart
Draw a sketch of the general output from the ECG
(slide 10)
- P wave: depolarization of the atria
- QRS complex: depolarization of the ventricles
- T wave: repolarization of the ventricles
- RR interval: used to calculate heart rate (from one R to next R)
- PR interval: indicates conduction from the SA node to ventricles
- QT interval: ventricular depolarization and repolarization
What is the cardiac cycle?
The cardiac cycle is the sequence of events that occurs during one complete heartbeat
What are systole and diastole?
Systole - phase of the cardiac cycle in which the heart muscle contracts and pumps blood out of the heart.
Diastole - phase of the cardiac cycle in which the heart muscle relaxes and fills with blood
How does blood move during the cardiac cycle?
Blood moves from areas of high pressure during systole to areas of lower pressure during diastole
What is excitation-contraction coupling in cardiac muscle?
Excitation-contraction coupling is the process by which an electrical signal triggers the contraction of cardiac muscle cells
What are the five stages of the cardiac cycle?
1) Ventricular diastole: active ventricular filling (atrial systole)
2) Ventricular systole: isovolumetric contraction
3) Ventricular systole: ejection phase
3) Ventricular diastole: isovolumetric relaxation
4) Ventricular diastole: passive ventricular filling
What happens during stage 1 of the cardiac cycle?
- Ventricular diastole: active ventricular filling (atrial systole)
- at the start of atrial systole, the ventricles are already ~ 70% full
- left and right atria contract, normally at the same time
- atrial pressure increases to force additional blood into the ventricles through open AV valves
- at the end of atrial systole, each ventricle contains the maximum amount of blood in the cardiac cycle = end-diastolic volume (EDV ~130 ml)
What happens during stage 2 of the cardiac cycle?
- Ventricular systole: isovolumetric contraction
- the first phase of ventricular systole / contraction
- increased pressure in ventricles closes the AV valves, but not enough pressure to open the SL valves
- rapid increase in ventricular pressure with no change in volume
- SL valves open when ventricular pressure > arterial pressure
What happens during stage 3 of the cardiac cycle?
- Ventricular systole: ejection phase
- ventricular pressure > arterial pressure opens the SL valves and blood ejects into the arterial circulation
- each ventricle ejects ~70ml of blood (stroke volume, SV) which is ~55% of the EDV = ejection fraction
- ventricular pressures decline at the end of ventricular systole
- ventricular pressure < arterial blood pressure closes the SL valves
