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Physiology III Exam 1 > Cardiac Physiology: Heart anatomy and physiology > Flashcards

Cardiac Physiology: Heart anatomy and physiology Flashcards

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1
Q

Describe atrial and ventricular heart muscle.

A

Striated, elongated, grouped in irregular anastomosing columns; 1-2 centrally located nuclei

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2
Q

Name the specialized excitatory and conductive muscle fibers.

A

SA node, AV node, Purkinje fibers Side note: contract weakly and few fibrils

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3
Q

Define syncytium

A

Many acting as one

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4
Q

How can cardiac muscle act as a syncytium?

A

Intercalated discs: low resistance pathways connecting cardiac cells end to end; presence of gap junctions

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5
Q

What is the duration of action potentials in cardiac muscle?

A

.2-.3 sec

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6
Q

Name the channels present in cardiac muscle.

A

Fast Na+ channels, Slow Ca++/Na+ channels, K+ channels

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7
Q

What are the permeability changes of cardiac muscle during an action potential?

A

Na+ sharp increase at onset of depolarization Ca++ increased during the plateau K+ increased during the resting polarized state

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8
Q

Describe membrane physiology and permeability during cardiac depolarization and repolarization

A

Na+ Increase at onset of polarization; Decrease during repolarization Ca++ Increase at onset of depolarization ; Decrease during repolarization K+ Decrease at onset of depolarization ; Increase during repolarization

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9
Q

Tetradotoxin selectively blocks what channels?

A

fast Na+ channels changing a fast response into a slow response

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10
Q

What are 3 considerations to assess passive ion movement across cell?

A

Concentration gradient: high to low Electrical gradient: opposite charge attract, like repel Membrane permeability: dependent on presence and state of ion channels

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11
Q

When considering concentration gradient vs electrical gradient, what will an ion do?

A

Seek its Nernst equilibrium potential; gradient favors ion movement in one direction is offset by electrical gradient

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12
Q

During resting membrane potential (Er) what is the sate of the ion channels?

A

Fast Na+ and slow Ca++/Na+ are closed, K+ are open

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13
Q

The negative membrane potential is maintained by what?

A

Na+/K+ pump (3:2)

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14
Q

What binds and inhibits the Na+/K+ pump?

A

Digitalis

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15
Q

What is located in the cardiac cell membrane that exchanges Ca++ from the interior of the cell in return for Na+?

A

Ca++ exchange protein

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16
Q

Why do we have both a Na+/K+ pump and a Ca++ exchange protein?

A

If the Na+/K+ pump is inhibited, function is reduced and more Ca++ accumulates in the cardiac cell increasing contractile strength.

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17
Q

Absolute refractory period

A

Unable to re-stimulate cardiac cell; occurs during the plateau

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18
Q

Relative refractory period

A

Requires a supra-normal stimulus; occurs during repolarization

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19
Q

What protects the ventricles from supra-ventricular arrhythmias?

A

AV node and bundle

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20
Q

What is the normal pacemaker of the heart?

A

SA node

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21
Q

What are the features of the SA node?

A

Self- excitatory in nature, less negative Er, Leaky membrane to Na+/C++ (unstable resting Er), only slow Ca++/Na+ channels operational, no plateau, contracts feebly

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22
Q

What cells are under overdrive suppression by the SA node?

A

Cells of the AV node and Purkinje system

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23
Q

What is overdrive suppression?

A

Driving a self-excitatory cell at a rate faster than its own inherent rate, suppressing its automaticity

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24
Q

What is the mechanism of overdrive suppression?

A

Mechanism may be due to increased activity of the NA+/K+ pump creating more negative Er

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25
What is the function of the AV node?
Delays the wave of depolarization from entering the ventricle; allows the atria to contract slightly ahead of the ventricles (.1 sec delay)
26
What takes over as a pacemaker in the absence of SA node?
AV node at a slower rate
27
What is the relationship of heart rate and cycle length?
As heart rate increases, cycle length decreases; inverse proportional
28
Describe systole and diastole at resting
systole \> diastole
29
During systole, perfusion of the myocardium is restricted. Why?
The contracting cardiac muscle compresses the blood vessels- especially in the left ventricle
30
True or false: at a higher HR, the ventricle may not fill adequately.
True
31
Describe Systole.
Isovolumic contraction and ejection
32
Describe Diastole
Isovolumic relaxation, rapid inflow (70-75%), diastasis and atrial systole (25-30%)
33
Describe A to B
Ventricular filling, AV valves open, semilunar valves closed
34
Describe B to C
Isovolumic contraction, AV valves close, semilunar valves closed
35
Describe C to D
Ejection, semilunar valves open, AV valves remain closed
36
Describe D to A
Isovolumic relaxation, semilunar valves close, AV valves remain closed
37
What happens at point A?
AV valves open, ESV
38
What happens at point B?
AV valves close, EDV
39
What happens at point C?
Semilunar valves open
40
What happens at point D?
Semilunar valves close
41
Area enclosed be volume pressure loop is a measure of what?
Work or external work
42
End Diastolic Volume (EDV)
Volume in ventricles at the end of filling
43
End Systolic Volume (ESV)
Volume in ventricles at the end of ejection
44
Stroke Volume
SV=EDV-ESV; volume ejected by ventricles
45
Ejection fraction
percent of EDV ejected (SV/EDV x 100); normal is 50-60%
46
Preload
Stretch on the wall prior to contraction (proportional to the EDV)
47
Afterload
Changing resistance (impedance) that the heart has to pump against as blood is ejected; Changing aortic BP during ejection of blood from LV
48
A wave
Atrial contraction
49
C wave
Ventricular contraction; bulging of AV valves and tugging on atrial muscle
50
V wave
Associated with atrial filling
51
When left ventricle pressure is greater than aortic pressure, what is the state of the aortic valve?
Open; valves open with a forward pressure gradient
52
When aortic pressure is greater than left ventricle pressure, what is the state of the aortic valve?
Closed; valves close with a backward pressure gradient
53
Name the AV valves.
Mitral and Tricuspid
54
What are characteristics of AV valves?
Thin and filmy, chorda tendineae act as check lines to prevent prolapse, papillary muscles increase tension on chordae tendinae
55
Name the semilunar valves.
Aortic and Pulmonic
56
Heart Murmurs associated with systole have which pathologies?
Aortic and pulmonary stenosis, mitral and tricuspid insufficiency
57
Heart murmurs associated with diastole have which pathologies?
Aortic and pulmonary insufficiency, mitral and tricuspid stenosis
58
Heart murmurs with both systole and diastole have which pathologies?
Patent ductus arteriosus, combined vulvar defect
59
What is the Law of Laplace?
At a given operating pressure, as ventricular radius increases developed wall tension also increases Wall tension = (pressure x radius) / 2 Increased tension = increased force of ventricular contraction
60
Define Chronotropic
Anything that affects the heart rate; i.e. caffeine would be a positive
61
Define Dromotropic
Anything that affects conduction velocity
62
Define Inotropic
Anything that affects strength of contraction
63
Describe Frank-Starling Law of the Heart
Within physiological limits, the heart will pump all the blood that returns to it without allowing excessive damming of blood in veins
64
What are mechanisms of Frank - Starling?
Increased venous return causes increased stretch of cardiac muscle fibers: increased cross bridge formation and increased CA++ influx which both increase force of contraction, and increased stretch on SA node which increases HR
65
Describe hetero-metric auto-regulation
Within limits, as cardiac fibers are stretched the force of contraction is increased
66
Describe homeo-metric auto-regulation
Ability to increase strength of contraction independent of a length change; flow induced
67
What is the result of direct stretch on SA node?
Increase Ca++ and/or Na+ permeability which will increase HR
68
What are extrinsic influences of SA node stretch?
Autnomic nervous system, hormonal, ionic and temperature
69
What are the results of sympathetic innervation of the heart?
Increased HR, increased strength of contraction and increased conduction velocity
70
What are the results of parasympathetic innervation of the heart?
Decreased heart rate, decreased strength of contraction, decreased conduction velocity
71
Atropine blocks parasympathetic effects via which receptors and what is the result?
Blocks Beta receptors and muscarinic receptors; HR will increase and strength of contraction will decrease
72
Propanolol block SNS effects on the heart via which receptors?
Beta receptors
73
Stimulation of the left stellate ganglion effects?
Decreased ventricular fibrillation threshold and prolongation of QT interval
74
Stimulation of the right stellate ganglion effects?
Increased ventricular fibrillation threshold
75
Describe the cardio-accelerator reflex
Stretch on right atrial wall induces stretch receptors which in turn send signals to MO to increase outflow to heart; helps prevent damming of blood in heart and central veins
76
Neuro-cardiogenic syncope, a baroreceptor reflex in the ventricles is stimulated by?
Occlusion of circumflex artery (inferior wall infarct) and increase in left ventricle pressure and volume (aortic stenosis)
77
Neuro-cardiogenic syncope (baroreceptor reflex) results in?
Hypotension and bradycardia
78
When does left coronary flow peak?
Onset of diastole
79
When does right coronary flow peak?
Mid systole

Physiology III Exam 1 (3 decks)

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