Lecture 14 Flashcards
What part of the heart receives blood from the body/ lungs?
Atria
What is the mechanics of the heart?
A dual pump with valves
What is the pathway of blood through the heart?
R- atrium receives blood from body via sup. Inf. Venacave
R - ventricle pushes blood to lungs via left pulmonary artery
L - atrium receives blood from lungs via right pulmonary artery
L - Ventricle pushes blood to body via aortic arch
How do cardiac muscles work together?
By communicating by gap junctions and allowing AP to spread equally
What part of the heart does not participate in contraction?
The conduction system
What is the role of the conduction system of the heart?
Initiates and distributes impulses
Spontaneously produces action potentials
What is the conduction system of the heart?
Sinoatrial node -> atrioventricular node -> bundle of His (av bundle) -> purkinje fibers
Where is the SA and AV nodes located?
Upper right atrium
Lower right atrium
What is the SA rate of AP/min?
100 AP/min
Produces AP faster than other areas
AKA pacemaker
How is the heart rate modified?
It is modified by PSNS
What is the AV rate of AP/min?
50 AP/min
Why do AV node, His bundle and purkinje fibers have their own AP/min?
This allows the heart to still beat if the SA nodes OR AV node OR his bundle fails
But are all over ridden by the SA node and the pace that is set by PSNS
What is the AP/min of bundle of his and purkinje fibers?
30 AP/min
Where is the bundle of his located?
At AV node and travels down from the atria to ventricles L and R
Where is the purkinje fibers located?
At terminal fibers of the ventricles to stimulate the contraction
What is the pathway of action potentials?
SA node at atria -> contract -> AV node signal delay and allows vents to fill -> bundle of His (rapid signal) -> bundle branches (rapid signal) -> purkinje fibers (rapid signal) -> vents contract
What is the difference between AP in nodes vs AP in myocardium?
AP in nodes occur quick
AP in myo had a plateau period to allow time to contract
How are AP in SA and AV nodes different from myocardium?
SA and AV are non contractile, auto rhythmic
Self excitable
Threshold of -40 mv
What are the phases in pace maker activity?
Pacemaker potential (-60) opens Na -> depolarizes at threshold (-40) -> action potential occurs and Na channels close while Ca channels open -> peak AP closes Ca channels and K open and leaves -> below threshold closes K channels -> at pacemaker potential Na opens at -60
What is the difference of AP in the heart and AP in neurons?
It is a continuous cycle with no resting membrane potential `
What occurs during AP of the myocardium?
Cells contract
AP of purkinje fibers make ventricle contract by spreading AP through gap junctions
What are the phases of ventricular myocardial action potentials?
Depolarization occurs from Na opening quickly -> at +30 Na close making a dip and Ca and K open slowly balancing + leaving cell -> repolarization closes Ca channels and K opens to restore RMP
What type of stimulus opens the Ca and K channels of the ventricular myocardia?
Slow voltage gated channels
How is absolute refractory period in myocardium muscle different from neurons and skeletal muscles?
It’s longer than neurons and skeletal muscles because the Na are inactivated until MP is near -70 mv
What is the excitation contraction coupling of myocardium?
The same as skeletal muscles
Require Ca to bind to troponin and move tropomyosin out of the way
What is the AP duration of skeletal muscles vs myocardial?
1 to 2 msec
250 msec or 0.25 sec
How are myocardial action potentials different from skeletal muscles?
The muscle contraction occurs before the AP is over
Lasts 300msec or 0.3 sec
No wave summation because it is a smooth muscle and will alternate contraction and relaxation
What are the 3 components of the cardiac cycle?
Electrical activity
Mechanical activity
Blood flow through heart
What is an ECG?
Measures small electrical currents from de/repolarization of myocardia
Measured in waves = sum of electrical activity
What do the ECG waves represent?
P wave - atrium depolarizing
QRS - ventricular depolarization
R - atrial repolarizing and ventricle depolarizing
T - ventricular repolarization
What part of ECG does the atria and ventricle contract?
P-Q => atria by AV node
S-T => atria relax/ ventricle contract
What segment of the ECG is the heart at rest?
T-P
What are the 2 abnormalities in heart beat?
Tachycardia - resting heart is greater than 100 bpm
Bradycardia - resting heart is less than 60 bpm
What happens with a heart block?
Conduction through A/V node is slowed/ increased P-Q interval
How is the systole and diastole initiated?
By electrical activity
How long is the cardiac cycle?
75 bpm divided by 60 sec = 0.8 sec/beat
How long is the atria in diastole?
For 0.7 sec
How long are ventricles in systole compared to atria for?
0.3 sec compared to 0.1 seconds in the atria
What are the 3 causes of blood flow throughout the heart?
Pressure changes (high pressure to low pressure)
Valves
Myocardial contractions
What does the LUB and DUB sounds occur?
LUB - the sound of atrial valves closing by blood pressure (mitral and bicusp valves)
DUB - the sound of ventricle valves closing (semilunar) and blood pushing them closed
How does pressure force the movement of blood from one chamber to another?
Valves open when the pressure is greater than the next chamber and pushes it open
What does the stop of korotkoff sounds represent?
The diastolic pressure
