Physiology Flashcards
What is the function of the heart?
It allows blood to circulate
Approximately how many times does the heart beat per day?
100,000 times
Where does the cardiac AP start?
In the SA node
Why do action potentials pass slower through the nodes?
To allow atrial contraction prior to ventricular contraction
What is the pacemaker of the heart?
The SA node
What shortens the refractory period in cardiac automatism?
The lack of phase 1-2
What makes the SA node the pacemaker?
It has a faster rate (80 bpm)
What makes electric conduction in the heart one way?
Cells that have sent the AP are already excited and are already in phase 2,3 or the refractory period
How does the parasympathetic nervous system innervate the heart?
Through the vagus nerve
What receptors are used by the parasympathetic nervous system in the heart?
M2 ACh receptors
How does the parasympathetic nervous system affect the rest potential in cardiac cells?
It causes it to be more negative
How does the parasympathetic nervous system inhibit the AP of cardiac cells?
It inhibits Na+ and Ca2+ entry
How does the sympathetic nervous system innervate the heart?
Through the sympathetic chain
What receptors are used by the sympathetic nervous system in the heart?
β2 Ad receptors
How does the sympathetic nervous system stimulate the cardiac muscles?
It activates Na+ and Ca2+ entry
How does the sympathetic nervous system affect the rest potential of cardiac cells?
It causes it to be less negative
What are the effects of positive isotropism?
It causes stronger contraction
What are the effects of negative isotropism?
It causes weaker contraction
What are the effects of positive cronotropism?
It causes the heart to beat faster
What are the effects of negative cronotropism?
It causes the heart to beat slower
What are the 3 types of myocardial fibres?
The atrial, ventricular and specialised excitation and conduction fibres
What myocardial fibres are responsible for cardiac contraction?
The atrial and ventricular fibres
What myocardial fibres are responsible for forming the excitatory system that controls the rhythmic heartbeat?
The specialised fibres
What is inotropism?
The ability to develop strength at a given length
How is inotropism regulated by the sympathetic nervous system?
Through β1 receptors
How does the sympathetic nervous system cause increased contractile capacity?
It increases Ca2+ uptake
How is inotropism regulated by the parasympathetic nervous system?
Through Muscarinic (M2) receptors and ACh
How does the parasympathetic nervous system decrease contractile capacity?
It decrease Ca2+ uptake and increases the output of K+
What does the frank-starling mechanism state?
That within physiological limits the heart pumps all the blood that comes from the veins
What is cardiac output?
It is the amount of blood that the heart pumps into the Aorta every minute
What is venous return?
It is the amount of blood flow that returns from the systemic veins
What should be the relationship between the cardiac output and the venous return?
It should be the same
What is the average value for cardiac output?
5L/min
What part of the volume-pressure diagram represents ventricular filling?
A > B
When does the mitral valve open?
When the pressure of the atrium exceeds that inside the ventricle
What part of the volume-pressure diagram represents isovolumetric contraction?
B > C
Which of the heart valves are open during isovolumetric contraction?
None of them
What part of the volume-pressure diagram represents ventricular ejection?
C > D
What does the width of the curve in the C > D portion of the volume pressure diaphragm represent?
The stroke volume
What part of the volume-pressure diagram represents isovolumetric relaxation?
D > A
What is preload?
The force that stretches the cardiac muscle prior to contraction
What happens if preload increases?
Venous return increases
What is afterload?
The ventricular wall stress or tension that develops during systolic contraction and ejection of blood into the aorta.
What is contractility?
The relative ability of the heart to eject a stroke volume
What happens if contractility increases?
Increased pressure during systole
Increased blood ejection
What happens if afterload increases?
The aortic valve opens at higher pressures and closes earlier
How is coronary blood flow in comparison to the rest of the organism?
The changes in systole and diastole are opposite
What happens if more oxygen is needed in the coronary circulation?
The blood flow is increased
What can be a result of insufficient flow in the coronary circulation?
Angina pectoris or myocardial ischemia
What is the coronary blood flow reserve?
It is the capacity to increase flow
How does blood return to from the left ventricular muscle?
Mostly through the coronary sinus (75%)
How does blood return from the right ventricular muscle?
Through the small anterior cardiac vein that flows directly into the right atrium
What is Phase 1 of the cardiac cycle?
Diastole
What is phase 2 of the cardiac cycle?
Isovolumetric contraction (systole) 2nd half of QRS: ventricular depolarisation
What is phase 3 of the cardiac cycle?
Rapid ventricular ejection (systole)
ST segment
What is phase 4 of the cardiac cycle?
Slow ventricular ejection (systole)
T wave: ventricular repolarization
What is phase 5 of the cardiac cycle?
Isovolumetric relaxation (diastole) T wave end
What is phase 6 of the cardiac cycle?
Rapid ventricular filling (diastole)
TP segment
What is phase 7 of the cardiac cycle?
Slow ventricular filling (diastole)
Post-T wave
What are the ECG derivations of the lateral wall?
I
aVL
-aVR
What are the ECG derivations of the anterolateral wall?
V5
V6
What are the ECG derivations of the anterior wall?
V3, V4
What are the ECG derivations of the inferior wall?
II
III
aVF
What are the ECG derivations of the Interventricular septum?
V1
V2
What is the normal heart rate?
60 - 100
How is heart rate counted down according to each square on the ECG chart?
300, 150, 100, 75, 60, 50
How many small boxes are required for ST depression on the ECG graph?
At least 3 small boxes
How does the sympathetic nervous system affect blood vessels?
It causes vasoconstriction
What is tachycardia?
When heart rate is above 100 bpm
How is tachycardia found on an ECG graph?
The cardiac cycle is 3 squares or less (100 bpm)
What is brachycardia?
When heart rates is less than 60 bpm
How is brachycardia identified on an ECG graph?
The cardiac cycle is 5 squares or more (60 bpm)
How is heart block identified on an ECG graph?
The PR interval is lenghtened (sign of abnormal contraction)
How is previous myocardial infarction identified on an ECG graph?
The Q wave is 25% of the R wave
How is current myocardial infarction detected on an ECG graph?
Elevations and depressions on the ST segment
What is the normal electrical axis range?
Between -30° and 90°
What is the electrical axis of the aVL lead?
-30°
What is the electrical axis of lead I?
0°
What is the electrical axis of the -aVR lead?
30°
What is the electrical axis of lead II?
60°
What is the electrical axis of the aVF lead?
90°
