Cardio Overview Flashcards
(107 cards)
1
Q
What are the 2 main functional systems of the heart?
A
- Pumping system
2, Electrical conduction system
2
Q
What is the function of the AV valves? How is it accomplished?
A
- Prevent backflow of blood from ventricles to atria during systole.
- Chordae tendinae and Papillary muscles
3
Q
What is the function of the semilunar valves?
A
Prevent backflow of blood from
aorta and pulmonary arteries into
ventricles during diastole
4
Q
Which type of valve is subject to more mechanical abrasion?
A
Semilunar valves are Subjected to much greater
mechanical abrasion than AV valves
5
Q
What is a difference between AV and semilunar valves?
A
Semilunar valves exposed to higher pressures, have smaller openings, and have very rapid closure & opening; also they have no chordae tendinae
6
Q
What is the impulse for valve closure and opening?
A
Valves close when a backward pressure gradient pushes blood backwards; valves open when a forward pressure gradient pushes blood forward.
7
Q
Describe the pulmonary circuit
A
- Carries CO2 rich blood to the gas exchange surfaces of lungs
- Returns O2 rich blood back to the heart
8
Q
Describe the systemic circuit
A
- Transports O2 rich blood back to body’s cells
2. Transports CO2 rich blood back to the heart
9
Q
Define sarcomere
A
contracting unit of myofibril which contains actin and myosin proteins
10
Q
What causes the myocardial contraction?
A
Myocardial contraction is a result of coupling of actin and myosin
11
Q
Define tropomyosin
A
Tropomyosin- intertwined with actin and inhibits contraction by hiding the binding receptor sites (Trop I, Trop C, Trop T)
12
Q
What is a unique feature of skeletal muscle?
A
- Intercalated discs- strong union
A. Cell membranes of adj. fibers fuse to form Gap junctions*
B. low resistance bridges for spread of AP, causes a syncytium
13
Q
Define and describe the importance of a synctium
A
A. Syncytium: A multinucleated mass of cytoplasm that is not separated into individual cells.
B. Cardiac muscle syncytium of many heart muscle cells; when one is excited, they all get excited
14
Q
What three channels are associated with a cardiac AP?
A
- Fast Na+ channels
- Slow Ca++ channels
- K+ channels
15
Q
What two channels are open for an extended period of time? Why?
A
Na+ and Ca++ channels remain open for longer period of time to increase contractility in cardiac muscle
16
Q
What is phase 4 of the AP cycle?
A
Resting membrane potential caused by negative K ions on inside of cell
17
Q
What is phase 0 (upstroke) of the AP cycle?
A
rapid depolarization with Na moving to inside membrane
18
Q
What is phase 1 of the AP cycle?
A
closing of Na channels; K is now actively transported out (more - )
19
Q
What is phase 2 of the AP cycle?
A
plateau phase; slow moving Ca channels open and Ca moves in; K channels still open and moving K out
20
Q
What is phase 3 of the AP cycle?
A
repolarization; K moves out; Ca channels close
21
Q
When does the absolute refractory period correspond to the AP cycle?
A
Phase 1-2?
22
Q
What phases are present in the AP at the SA node?
A
0, 3, 4
Phases 1 and 2 do not occur
23
Q
What phases are present for the AP at the ventricular myocardium, bundle of His, and Purkinje fibers?
A
Phase 0, 1, 2, 3, 4
24
Q
What is the sequence of excitation-contraction coupling in skeletal muscle?
A
AP penetrates T-tubules AP acts on sarcoplasmic reticulum to release Ca+ Ca+ diffuse into myofibrils promote sliding filament contraction
25
What controls excitation-contraction coupling in cardiac muscles?
Function of Ca+ ions and T-tubules
26
How are t-tubules in cardiac muscle different than skeletal muscle?
1. T-tubules much larger in cardiac muscle so more Ca+ released and stored
2. Ends of T-tubules open directly to outside cardiac muscle fibers
27
What is the effect of T-tubules that open directly to the outside of cardiac muscles?
1. Contact with extracellular fluid
2. Quantity of Ca+ in T-tubules dependent on amount Ca+ in ECF*
3. Unlike skeletal muscle, contraction of cardiac m. is dependent on the entry of Ca++ from ECF
28
Where is Ca+ stored?
*Ca+ for skeletal and cardiac muscle contraction are stored in SR; contraction is not affected by ECF Ca+ levels in skeletal muscle
29
When is Ca+ involved in the AP cycle?
Phase 2- plateau phase
30
What does Ca do to cause E-C coupling?
1. Inward Ca++ flow causes release of Ca++ from SR (increase intracellular Ca++)
2. Ca++ binds to troponin C, tropomysin moves out of its blocking position, allowing actin and myosin to form cross-bridges
31
What happens when cross bridges are formed?
Actin and myosin filaments slide past each other resulting in cardiac muscle contraction
32
How does cardiac contraction end?
Contraction ends when Ca++ ATPase helps reuptake of Ca++ into the SR, reducing intracellular Ca++
33
Define Cardiac absolute refractory period
Interval of time during which normal cardiac impulse cannot re-excite an already excited area of cardiac muscle
34
Define Cardiac relative refractory period
Interval of time which cardiac myocyte can be excited with greater than nl AP
35
What does the long refractory period cause in cardiac muscle?
Due to long refractory period, cardiac m. cannot be tetanized like skeletal m. can
36
Define automaticity
Capable of spontaneous depolarization
| “self-excitation”
37
What cells have automaticity properties?
SA node, AV node, bundle of His, Purkinje fibers
38
What is the normal pacemaker node of the heart? What is its rate of impulse?
SA node
| Generates impulses 60-100 times/min
39
What is the pathway of conduction from the SA node?
Impulses generated at SA nodeatrial pathwaysAV nodebundle of His (branches)Purkinje sysventricular muscle
40
What is the function of the Bachmann's bundle?
Tracts from SA node extending to LA
41
What is the function of the internodal tracts?
Tracts that transmit impulses through RA
42
What is the function of the AV node?
1. Responsible for delaying impulses that reach it to allow the ventricles to complete their filling as the atria contract
2. Allows the cardiac muscle to stretch to its fullest for peak CO
43
What is the function of the Bundle of HIs?
1. Tract of tissue extending into ventricles next to interventricular septum
2. Responsible for rapid conduction through ventricles
3. Divides into R & L bundle branches
44
What doe the left bundle split into?
L anterior fasciculus & L posterior fasciculus
45
What is the function of the purkinje fibers?
1. Carries impulses from bundles to ventricular myocardium
| 2. Conduct AP very quickly
46
What carries impulses to the papillary muscles?
Moderator band delivers impulses directly to the papillary muscles; therefore papillary muscles contract earlier than the ventricle
47
Define ectopic pacemaker
pacemaker cells in other areas can fire spontaneously if the above system malfunctions
48
What is the rate of impulse from junctional/AV node pacemakers?
40-60 bpm
49
What is the rate of impulse from purkinje fibers?
30 bpm
50
Define reentry events
Impulses can cause depolarization during the later phase of repolarization of previous impulse
51
Define retrograde conduction and its effects
1. Impulses that begin below AV node can be transmitted backward towards atria
2. Atria & ventricles can beat out of synch
52
What are the 2 main phases of the cardiac cycle?
Ventricular systole and ventricular diastole
53
what does the electrical signal at the myocyte trigger?
Once electrical signal at myocyte, depolarization begins: Ca++ is released into myocyte triggering the actin-myosin interaction
54
What physiological changes cause S1?
Pressure builds up in LV and RV, the mitral and tricuspid valves close causing S1 (beginning of systole)
55
Define isovolumetric contraction phase
1. Time btw the closure of mitral and tricuspid valves and opening of aortic and pulmonic valves is called isovolumetric contraction*phase (all valves closed)
2. *contraction occurring but blood is not being ejected across semilunar valves yet
56
What causes the opening of the aortic and pulmonic vavles?
Continued pressure build up
57
When does systole begin?
Systole begins when the aortic and pulmonic valves open and blood begins to flow across them
58
Define stroke volume
The volume of blood ejected w/ each cycle is the Stroke Volume (SV)
59
When do the aortic and pulmonic valves close? What does this correspond to?
1. Once pressure in aorta and pulm artery begin to exceed pressures in the LV and RV, respectively, the aortic and pulmonic valves will close
2. This is S2 (aortic first, pulmonic second), beginning of diastole.
60
Define isovolumetric relaxation phase
Ventricle continues to relax w/o further changes in volume until pressure falls below LA and RA pressures which is called isovolumetric relaxation phase
61
What physiological changes are occurring in ventricular systole?
AV valves shut, and LA and RA are filling w/ blood and their pressures rising
62
What happens when LA and RA pressures > LV and RV pressures?
the AV valves open and the first rapid filling phase begins, if heard is S3, can be nl in up to age 40
63
What is S4?
Second rapid filling phase of diastole is S4 and if heard is abnormal
usually due to LV hypertrophy
64
How much blood flows directly from atria to ventricle? How much is pumped through atrial contraction?
1. About 80% of blood flows directly through atria to ventricles before atria contract
2. Atrial contraction causes an additional 20% filling of ventricles during last 1/3 of diastole (atrial kick)
65
When is diastole filling time decreased?
1. Diastole filling time is decreased due to increased HR (exercise) or when heart disease impairs ventricular filling
If it were not for the atria pumps during the above scenario, the CO would fall
66
Define the concept of primer pump and why it's important
Therefore, atria act as primer pumps for ventricles. Heart can operate satisfactorily under nl resting conditions without extra 20% blood flow. As a result, when atria fail to function, difference is not noticed until a person exercises; then they develop heart failure.
67
What heart sound is assoc. with closing of AV valves?
S1
68
What heart sound is assoc. with closing of semilunar valves?
S2
69
What heart sound is assoc. with rapid ventricular filling in first 1/3 of diastole?
S3
70
What heart sound is assoc. with rapid ventricular filling in last 1/3 of diastole?
S4
71
What is the SV value in an average heart? WHat is the equation for SV?
1. 70 cc
| 2. SV = End Diastolic Volume - End Systolic Volume
72
Define EDV
volume in the ventricle during diastole (mitral valve closed)
Approx 120 ml
73
Define ESV
Remaining volume in the ventricle after systole (aortic valve closed)
Approx 40-50 ml
40% of EDV at rest
74
Define SV
1. In a nl heart, it is same volume of blood as ejected into the aorta during each systole
2. Approx 70 ml (60% of EDV at rest )
3. SV= EDV-ESV
75
Define Ejection fraction (EF)
1. Fraction of blood ejected by ventricle relative to its filled volume (EDV)
2. Normal approx 55-65%
3. EF= SV/EDV
76
What does an echocardiogram measure?
Ejection fraction
77
Define CO
1. Amount of blood pumped by each ventricle in one minute
2. CO = HR x SV
3. 5000ml/min (5L/min)=75 b/min x 70 ml
78
What affects CO?
Determinants of CO are preload, contractility and afterload
79
Define preload
1. Degree the ventricle is distended before systole occurs
| 2. Stretching of muscle fibers in LV during diastole [directly proport. to EDV] : Frank-Starling Law
80
Define afterload
1. Force against which the heart has to pump
2. Or, amount of pressure in LV must work against to pump blood into circulation (during ejection) : Laplace’s Law [CO and afterload have inverse relationship]
81
Define contractility (inotropism)
1. Ability of muscle cells to contract after depolarization
| 2. The greater degree of inotropy, the more forceful the contraction, the higher the ensuing SV
82
Define the Frank Starling principle
1. Greater heart muscle is stretched during filling causes:
A. The greater the force of contraction
B. The greater the quantity of blood pumped into aorta
2. “more in=more out”
3. Incr EDV, Incr SV
83
What is ejection fraction used to measure?
measure for assessment of myocardial function
84
When is ejection fraction increased?
increased with + ionotropic drugs such as dopamine, epi, norepi
85
When is the ejection fraction decreased?
decreased in myocardial ischemia or heart failure
86
What is a Swan-ganz catheter and what is it used for?
1. Pulm artery catheter, multi-lumen
2. Pulmonary capillary wedge pressure (“wedge pressure”) can be measured, which is an indicator of pulm. venous and LA pressure. Can also approximate the left ventricular end-diastolic pressure (LVEDP).
87
When is pulmonary capillary wedge pressure important?
1. PCWP is important in critical care settings, CT surgery
| A. provides a hemodynamic assessment (ie acute heart failure)
88
What are the effects of the sympathetic nervous system on cardiac function?
1. Increases HR
2. Increases contractility force
A. Increases volume of blood pumped
B. Increases ejection pressure
3. With above effects, C.O. is significantly increased
89
What is the mechanism for sympathetic nervous system activation of the heart?
1. Postsynaptic symp. fibers release NE>α1-adrenergic receptors, causing vascular smooth m. contraction,
BP
2. Epi acts on β2-adrenergic receptors causing dilation of vascular smooth muscle
90
What are the effects of the parasympathetic nervous system on cardiac function?
1. Decreases HR
2. Decrease contractility strength by 20 – 30%
3. Overall, above can decrease cardiac output by 50% or more (esp in diseased hearts)
91
What is the mechanism for parasympathetic nervous system activation of the heart?
1. Vagal stimulation primarily to atria
| 2. Postsynaptic parasymp fibers do not innervate vascular smooth muscle
92
What is the effect of hypokalemia on cardiac function?
1. Causes hyperpolarization in myocytes RMP
| 2. Usually causes tachyarrhythmias
93
What is the effect of hypokalemia on an EKG tracing?
U wave, flattened or inverted T waves, ST depression, wide PR interval
94
What is the most common electrolyte abnormality?
Hypokalemia, 20% of inpatients
95
What is the effect of hyperkalemia on an EKG tracing?
Can block conduction of cardiac impulse through AV node
| Tall peaked T waves, widened QRS
96
What is the effect of hyperkalemia on cardiac function?
1. Heart becomes extremely dilated and flaccid
2. Slows heart rate
3. Above certain level of K+ the depolarization inactivates Na+ channels, opens K+ channels, thus the cells become refractory- impairs cardiac conduction which can cause V fib or asystole
97
What effects does hypercalcemia have on heart function?
1. Causes heart to go into spastic contraction
| 2. Direct effect of Ca++ ions exciting contractility process
98
What effects does hypocalcemia have on heart function?
Causes cardiac flaccidity (similar to effect of high K+)
99
What differences are present in SA node APs?
1. No Phase 1 or 2: no sustained plateau
2. Unstable resting membrane potential
3. Depolarization caused by Ca influx (T type)
4. The rate of phase 4 depolarization sets heart rate
100
What does the P wave correspond to?
Atrial depolarization
101
What does the QRS complex correspond to?
Ventricular depolarization and masking of atrial repolarization
102
What does the T wave correspond to?
Ventricular repolarization
103
What does the PQ segment correspond to?
AP is conducted from AV node to bundle of His
104
What is within the ST segment?
Absolute refractory period
105
What occurs during the PQ interval?
The time from initial depolarization of atria to initial depolarization of ventricles. Thus, the time the stimulus is conducted through AV node
106
What does the QT interval represent?
first ventricular depolarization to last ventricular repolarization
107
How are the aortic and pulmonic valves opened?
continued pressure build up
