The Heart Flashcards
(78 cards)
1
Q
What is the cardiac cycle?
A
The sequence of mechanical and electrical events that repeats with each heart beat
2
Q
How do you calculate the duration of the cardiac cycle?
A
60/heart rate
3
Q
What are the 2 major phases of the cardiac cycle?
A
- Filling phase
- Emptying phase
4
Q
What are the 4 phases of the cardiac cycle (with respect to the ventricles)?
A
- Inflow phase
- Isovolumetric contraction
- Outflow phase
- Isovolumetric relaxation
5
Q
What happens during the inflow phase? (2)
A
- Blood enters the ventricles from the atria
- Atrioventricular valves open, semi-lunar valves closed
6
Q
What happens during the isovolumetric contraction phase? (2)
A
- Both valves closed
- Ventricles contract
7
Q
What does isovolumetric mean?
A
With no volume change
8
Q
What happens during the outflow phase? (2)
A
- Atrioventricular valves are closed, semi-lunar valves are open
- Blood leaves the ventricles into aorta/pulmonary artery
9
Q
What happens during the isovolumetric relaxation phase? (2)
A
- Ventricles relax
- Both valves closed
10
Q
What does diastole mean?
A
Ventricles relaxing
11
Q
What does systole mean?
A
Ventricles contracting
12
Q
During which phases of the cardiac cycle are the ventricles in diastole? (2)
A
- Inflow phase
- Isovolumetric relaxation
13
Q
During which phases of the cardiac cycle are the ventricles in systole? (2)
A
- Isovolumetric contraction
- Outflow phase
14
Q
What happens to the duration of the cardiac cycle when your heart rate increases?
A
Time spent in diastole decreases
15
Q
What does the dicrotic notch indicate?
A
Closing of the aortic valve
16
Q
What is the name of the atrioventricular valve in the left side of the heart
A
Mitral valve
17
Q
Where is the mitral valve?
A
Between the left atrium and left ventricle
18
Q
What happens during the end of the inflow phase in the left side of the heart? (3)
A
- Mitral valve is open due to higher pressure in the atrium than the ventricle
- Small, slow increase in ventricular volume
- Atrium contracts (systole) causing small increase in pressure in atrium and ventricle
19
Q
What happens during the isovolumetric contraction phase in the left side of the heart? (3)
A
- No change in ventricular volume
- Ventricle contracts so ventricular pressure rises above atrial pressure which closes the mitral valve (both valves shut)
- Ventricular pressure rises above aortic pressure which opens the semi-lunar valve (end of phase)
20
Q
What happens during the outflow phase in the left side of the heart? (3)
A
- Rapid ejection of blood from the ventricle causing decrease in ventricular volume
- Aortic pressure rises above ventricular pressure
- Small increase in atrial pressure as they start to fill
21
Q
What happens during the isovolumetric relaxation phase in the left side of the heart? (3)
A
- Ventricles relax so pressure falls rapidly
- Small amount of backflow of blood from aorta into the ventricle causing the semi-lunar valve to shut (dicrotic notch)
- Both valves closed
22
Q
What happens during the start of the inflow phase in the left side of the heart? (3)
A
- Ventricular pressure drops below atrial pressure so mitral valve opens
- Blood enters the ventricle from the atrium causing increase in ventricular volume
- Pressure increases in atrium and ventricle
23
Q
What are the 3 sections of an ECG?
A
- P wave
- QRS complex
- T wave
24
Q
What is the P wave associated with?
A
Atrial depolarisation causing atrial contraction
25
What is the QRS wave associated with?
Ventricular depolarisation causing ventricular contraction
26
What is the T wave associated with?
Ventricular repolarisation i.e. relaxation and fall in ventricular pressure
27
What is the QT interval?
Time between start of ventricular depolarisation and the end of ventricular repolarisation
28
How do you calculate cardiac output?
Heart rate x stroke volume
29
What is the approximate value of cardiac output at rest?
5L per minute
30
What is stroke volume?
Volume of blood ejected per heartbeat
31
What is the approximate value of stroke volume at rest?
70ml
32
How do you calculate stroke volume?
- End diastolic volume - end systolic volume
- (Volume of ventricle before contraction - volume after blood has been ejected)
33
What is the approximate value of End Diastolic Volume (EDV)?
120ml
34
What is the approximate value of End Systolic Volume (ESV)?
50ml
35
What is the ejection fraction?
Percentage of blood that the ventricle pumps out with each contraction
36
How do you calculate ejection fraction?
Stroke volume/EDV
37
What value should the ejection fraction be in healthy individuals?
At least 55%
38
What is the structure of cardiac muscle? (3)
- Cardiomyocytes are made up of myofibrils
- Myofibrils contain sarcomeres (contractile units)
- Myocytes are connected by intercalated disks forming a syncytium
39
What is the purpose of intercalated discs in cardiac muscle?
Allows electrical activity to spread between muscle cells via gap junctions
40
What are the 2 components of intercalated discs?
- Desmosomes (mechanical)
- Gap junctions (electrical)
41
What is a sarcomere? (2)
- Structural unit of muscle with a striped appearance
- Distance between 2 Z lines
42
What are the 2 major proteins within a sarcomere?
- Actin (thin)
- Myosin (thick)
43
What is the M line?
The middle of the sarcomere
44
What are the 2 sources of Ca2+ needed for cardiac muscle contraction?
- Depolarisation causes Ca2+ influx from the ECF via L-type Ca2+ channels in the plasma membrane
- Release of Ca2+ stores via ryanodine receptor type 2 on the sarcoplasmic reticulum (calcium induced calcium release)
45
What is the alternative name for L-type Ca2+ channels?
Cav1.2
46
Which source of Ca2+ is the most important for cardiac muscle contraction?
Ryanodine receptors (RYR2) as they are open for longer
47
Which protein on the sarcoplasmic reticulum helps with cardiac relaxation?
SERCA2a
47
What does SERCA2a do? (2)
- ATPase
- Pumps Ca2+ back into the sarcoplasmic reticulum in exchange for 2 H+ during cardiac muscle relaxation
48
Which proteins on the plasma membrane help with cardiac relaxation? (2)
- PMCA
- NCX1
49
What does PMCA do?
- ATPase
- Pumps Ca2+ out of the cell in exchange for H+ during cardiac muscle relaxation
50
What does NCX1 do? (2)
- Pumps 3 Na+ into the cell in exchange for Ca2+
- Relies on the Na+ gradient set up by the Na+/K+ ATPase in the plasma membrane which pumps 3 Na+ out of the cell and 2K+ in
51
Which protein on the mitochondrial membrane helps with cardiac relaxation?
MiCa
52
What does MiCa do?
Channel which opens to allow Ca2+ to enter the mitochondria
53
Where in the cardiac myocyte is SERCA2?
Sarcoplasmic reticulum membrane
54
Where in the cardiac myocyte is PMCA?
Plasma membrane
55
Where in the cardiac myocyte is NCX1?
Plasma membrane
56
Where in the cardiac myocyte is MiCa?
Mitochondrial membrane
57
Where is Ca2+ transported to allow cardiac muscle relaxation? (3)
- Across the plasma membrane
- Into the sarcoplasmic reticulum
- Into the mitochondria
58
What is passive tension?
Tension generated at set sarcomere length in the absence of stimulation (stretch)
59
Which 2 proteins are important in generating passive tension?
- Titin
- Desmin
60
Where is titin in the sarcomere?
Embedded in the Z line and connects to the myosin
61
How is titin important in passive tension?
Cardiac muscle has shorter titin than skeletal muscle meaning that cardiac muscle has greater passive tension
62
Where is desmin in the sarcomere?
- Found in the Z lines
- Links sarcomeres together
63
What is active tension?
The tension generated on top of passive tension by stimulation of the muscle
64
What is the optimum sarcomere length?
The length of the sarcomere where there is the maximum overlap between the actin and myosin filaments - max no. cross bridges
65
What is Starling's law?
- The strength of contraction depends on the sarcomere length
- i.e. larger length = greater contraction
66
What kind of tension is generated in diastole?
Passive tension
67
What kind of tension is generated in systole?
Active tension
68
According to Starling's law, what happens to ventricular contraction if venous return increases? (2)
- More blood in the ventricles during diastole causes greater stretching of the sarcomeres which generates a greater passive tension
- Greater length of sarcomeres causes greater force of contraction during systole which generates a greater active tension
69
What does the velocity of shortening depend upon?
- Arterial pressure (afterload/force that must be overcome to eject the blood) and initial level of stretch in the muscle (pre-load)
- Low arterial pressure = high velocity of shortening
70
What is ventricular contraction like when there is a large ventricular volume and a low arterial pressure?
Strong and fast
71
What is ventricular contraction like when there is a large ventricular volume and a high arterial pressure?
Strong and slow
72
What is ventricular contraction like when there is a low ventricular volume and a low arterial pressure?
Weak and fast
73
What is ventricular contraction like when there is a low ventricular volume and a high arterial pressure?
Weak and slow
74
What are inotropic agents?
Things which can change contractility
75
What are chronotropic agents?
Things which can change rate of contraction
76
What is the Bowditch staircase phenomenon and why does it happen? (3)
- An increase in heart rate gives an increase in tension over time due to increased Ca2+ availability
- NCX action is reversed during depolarisation so pumps Na+ out and Ca2+ in
- Heart rate stimulates SERCA2 which takes more Ca2+ into the sarcoplasmic reticulum rather than it being expelled into ECF
77
End of myocyte contraction coupling flipped
Heart electrophysiology next
