Cardiac Rhythm & Cardiac Cycle Flashcards
Describe the special features of cardiac myocytes
- striated & branching with centrally located nuclei
- no terminal cisterna
- almost exclusively aerobic metabolism
- intercalated discs (made up of desmosomes and gap junctions) connect myocytes
Describe the anatomy of intercalated discs, desmosomes and gap junctions in cardiac myocytes
Intercalated discs:
- connect adjacent myocytes
- made up of desmosomes and gap junctions
Desmosomes:
- intercellular junctions
- create strong adhesions between cells to maintain tissue integrity and resist mechanical stress
Gap junctions:
- protein lined tunnels
- allow direct transmission of action potential from cell to cell
Describe the importance of calcium for generating action potentials in cardiac myocytes
Stage 1:
- depolarization of cardiac myocytes opens calcium channels in plasma membrane (10-20% of calcium needed for contraction)
Stage 2:
- influx of calcium triggers the opening of calcium channels in sarcoplasmic reticulum (80-90% of calcium needed for contraction)
What are the two circuits in the cardiovascular system?
Pulmonary - between heart and lungs
Systemic - between heart and the rest of the body
What is the intrinsic conduction system and the direction of conduction?
Intrinsic conduction = wave of depolarization / contractions that is generated by pacemaker cells and spreads through gap junctions in the heart
- SA node (pacemaker cells) - in right atrial wall inferior to SVC
- AV node
- in inferior interatrial septum superior to tricuspid valve - AV bundle
- superior interventricular septum - AV bundle branches
- interventricular septum - Purkinje Fibres
- from apex of heart superiorly along ventricular walls
Describe the main events of the cardiac ECG and what they correlate to.
P: atrial systole / atrial depolarization
QRS: ventricular systole / ventricular depolarization
T: ventricular diastole / ventricular repolarization begins at apex
Describe the events of the cardiac cycle
- Atrial systole / ventricular diastole
- atria contract (early phase)
- atria relax (mid-late)
- ventricles relaxed & filling with blood through open AV valve - Ventricular systole
- atria relaxed
- ventricles contract and empty (isometric contraction)
- AV valves close (S1 beat)
- semilunar valves open - Early ventricular diastole
- atria & ventricles relaxed
- atria passively filling (isovolumetric relaxation)
- semilunar valves closed (S2 beat)
- AV valves open
Describe what is happening in (mid-late) ventricular diastole
- atria in systole: contracting & pumping blood to ventricle
- AV valves open & semilunar valves closed
- ventricle in diastole & filling with blood
- P wave
Describe what is happening in ventricular systole
- atria in diastole
- AV valves close (S1 beat)
- ventricles in systole & pumping blood through open semilunar valves
- QRS wave
Describe what is happening in (early) ventricular diastole
- atria in diastole & filling with blood passively
- ventricles in diastole
- semilunar valves close (S2 beat)
- AV valves open
What is the difference between an electrocardiograph and an elecrogardiogram?
Graph = machine Gram = image produced
What are the locations of the SA node and AV node?
SA node:
in right atrial wall
(inferior to SVC)
AV node:
inferior interatrial septum (above tricuspid valve)
What does the QRS complex represent?
Electrical event:
ventricular depolarization
Mechanical event:
ventricular contraction
What does the P wave represent?
Electrical event:
atrial depolarization
Mechanical event
atrial contraction
What does the T wave represent?
Electrical event:
ventricular repolarization
Mechanical event
ventricular relaxation
