18 11-15 Flashcards
Energy requirements/metabolism of the heart?
- Relies exclusively on aerobic respiration for energy metabolism 2. Has a very extensive blood supply 3. Many mitochondria 4. Myoglobin/creatine kinase 5. Uses multiple fuel molecules . Capable of switching nutrient pathways - uses fat under
Intrinsic cardiac conduction system
Consists of noncontractile cardiac cells specialized to initiate and distribute impulses throughout the heart so it contracts in an orderly and sequential manner. Myogenic rather than neurogenic.
Autorythmic cells?
Have an unstable resting potential, spontaneously depolarize to fire action APs (“pacemaker potentials”) then spontaneously repolarize, connected via conduction fibers with larger diameters than muscle fibers and can conduct APs more rapidly
SA node
“pacemaker” (because it depolarizes faster than other component it sets the pace.) sinoatrial node Will spontaneously depolarize 100x/min. However, vagus nerve slows it to 75/min Depolarizes the atria and the AV node.
AV node
“gatekeeper” atrioventricular node Will spontaneously depolarize about 40-50x/min Inferior to entrance of SVC
AV bundle
“bundle of His” superior part of the interventricular septum
R/L bundle branches
No nickname…
Purkinje fibers
“subdenoardial conducting network”
Pacemaker/autorythmic cells
Unstable resting potential that continuously drifts towards depolarization . These spontaneously changing membrane potentials (pacemaker potentials/prepotentials) initiate Aps.
Order of the impulses passing through the heart?
SA node –> AV node –> AV bundle –> R/L bundle branches –> Purkinje fibers
5 steps in intrinsic conduction system showing the sequence of electrical excitation.
- SA node generates impulse
- The impulses pause 0.1s at the AV node (allowing the atria to respond and contract, delay is cause by smaller diameter fibers/fewer gap junctions)
- AV bundle connects the atria to the ventricles (no gap junctions, AV bundle is only connection between atria and ventricle)
- Splits into the R+L bundle branches, impulse conducted through the interatrial septum
- Purjinke fibers/subendocardial cunducting network depolarizes the contractile cells of both ventricles.
Ectopic focus
A pacemaker other than the SA node
Arrythmia
Irregular heart rhythm
Fibrillation
Rapid and irregular or out of phase contractions in which control of the heart rhythm is taken away from the SA node by rapid activity in other heart regions
EKG/ECG
A graphic record of heart activity - reflects patterns of Ap firings in the entire population of cells (nodal and contractile) that make up the heart. Electrocardiogram
P wave
(Patrial depolarization) Lasts 0.08s, results from movement of the depolarization wave from the SA node through the atria. Appx. 0.1s after P wave begins, the atria contract.
QRS wave
(Ventricular depolarization) Lasts 0.08s, results from ventricular depolarization and precedes ventricular contraction.
T wave
(Ventricular repolarization) Lasts 0.16s, caused by ventricular repolarization
S-T segment
corresponds to plateau, elevation here is called tombstoning. A disruption of rhythm/calcium
Heart sounds are the?
Valves closing.
First the AV valves (when ventricular pressure rises above atrial pressure, ventricle systole) lub or S1 - soft, low pitched.
Then the SL valves (snap shut at the beginning of ventricular diastole) Dup or S2 - sharper, louder, higher-pitched.
What kind of abnormalities can be traced on an ECG?
Junctional rhythm, heart block, ventricular fibrillation, flatline
heart murmurs
When blood flow becomes turbulent and generates abnormal heart sounds.
Common in young with healthy hearts but thin heart walls which vibrate.
Can indicate valve problems though.–
- Insufficient/Incomplete valves fail to close completely and the sound is swishing as blood backflows.
- Stenotic valves fail to open completely and narrowness restricts blood flow resulting in a high pitched click.
Heart sounds are the?
Valves closing. First the AV valves (when ventricular pressure rises above atrial pressure, ventricle systole) lub or S1 - soft, low pitched. Then the SL valves (snap shut at the beginning of ventricular diastole) Dup or S2 - sharper, louder, higher-pit
Duration of a heartbeat?
0.8s - 0.5s in diastole, 0.3s in systole
heart murmurs
When blood flow becomes turbulent and generates abnormal heart sounds. Common in young with healthy hearts but thin heart walls which vibrate. Can indicate valve problems though. Insufficient/Incomplete valves fail to close completely and the sound is s
Sign of a heart attack?
Creatine kinase and troponin in the blood (from cardiac cells rupturing)
Junctional rhythm
Sa node is nonfunctional, P waves absent, AV node paces heart at 40-60
Heart block
Some P waves are not conducted thru the AV node, hence more P than QRS waves are seen
Ventricular fibrillation
Chaotic irregular ect deflections
