Chapter 20 - The Heart - REVIEW Flashcards
Define automaticity
automaticity (autorhythmicity) is the ability of cardiac muscle to contract without neural or hormonal stimulation
Which structure of the heart is known as the cardiac pacemaker or the natural pacemaker?
The sinoatrial (SA) node
If the cells of the SA node did not function, how would the heart rate be affected?
the heart would still continue to beat, but at a slower rate. The AV node would act as the pacemaker instead
Why is it important for impulses from the atria to be delayed at the AV node before they pass into the ventricles?
if the impulses from the atria were not delayed at the AV node, they would be conducted through the ventricles so quickly by the bundle branches and Purknije cells that the ventricles would begin contracting immediately. before the atria has finished their contraction.
As a result, the ventricles would not be full of blood as they could be, the the pumping of the heart would not be as efficient, especially during activity
the great cardiac vein drains blood from the heart muscle to the…
right atrium
the autonomic centers for cardiac function are located in….
the cardiac centers of the medulla oblongata
the serous membrane covering the outer surface of the heart is called the….
visceral pericardium
the simple squamous epithelium covering the walls of the heart constitutes the…..
endocardium
the heart lies in the……
mediastinum
Name 2 functions of the cardiac skeleton of the heart
-physically isolates the muscle fibers of the atria from those of the ventricles
-maintains the normal shape of the heart
What role do the chordae tendineae and the papillary muscles play in the normal function of the AV valves?
During ventricular contraction, the tension in the papillary muscles pulls on the chordae tendineae, which keeps the cusps of the AV valves from swinging into the atria. This action prevents backflow or regurgitation of blood into the atrium as the ventricle contracts
Describe the 3 distinct layers that make up the heart wall
- epicardium (visceral pericardium) covers the outer surface of the heart
- myocardium - muscular wall of the heart which forms the atria and ventricles. Contains cardiac muscle tissue and associated connective tissues, blood vessels, and nerves
- endocardium - squamous epithelium that covers the inner surfaces of the heart, including the valves
What are the valves in the heart, and what is the function of each?
atrioventricular (AV) valves
-tricuspid valve - prevents backflow into the right atrium
-biscuspid/mitral valve - prevents backflow into the left atrium
semilunar valves
-aortic valve - prevents backflow into the left ventricle
-pulmonary valve - prevents backflow into the right ventricle
Trace the normal pathway of an electrical impulse through the conducting system of the heart
SA node–> AV node–>AV bundle–>right and left bundle branches–>Purkinje fibers (into the mass of ventricular muscle tissue)
Which is longer — the refractory period of cardiac muscle or skeletal muscle
the refractory period of CARDIAC MUSCLE is longer
if the papillary muscles failed to contract, what would happen?
The AV valves would not close properly
Describe the function of the SA node in the cardiac cycle. How does this function differ from that of the AV node?
The SA node is composed of cells that exhibit rapid prepotential. It is the pacemaker of the heart
The AV node slows down the impulse that signals contraction, because its cells are smaller than those of the conduction pathway
provide the technical terms for heart contraction and relaxation
heart contraction - systole
heart relaxation - diastole
list the phases of the cardiac cycle
- atrial systole
- atrial diastole
- ventricular systole
- ventricular diastole
is the heart always pumping blood when pressure in the left ventricle is rising? explain
no
when pressure in the left ventricle first rises, the heart is contracting but no blood is leaving the heart
during this initial phase of contraction, both the AV and semilunar valves are closed. the increase in pressure is the result of increased tension as the cardiac muscle contracts
when the pressure in the ventricle exceeds the pressure in the aorta, the aortic semilunar valves are forced open and blood is rapidly ejected from the ventricle
What factor could cause an increase in the size of the QRS complex in an electrocardiogram?
this would indicate a larger than normal amount of electrical activity during ventricular depolarization.
The cause could be an enlarged heart because more cardiac muscle is depolarizing and the magnitude of the electrical event would be greater
Define cardiac output
HR*SV
the amount of blood pumped out by the left ventricle per minute
Explain why drinking large amounts of caffeine would increase the heart rate
caffeine has effects on conducting cells and contractile cells that are similar to those of the NE
caffeine acts directly on the conducting system and the contractile cells of the heart, increasing the rate at which they depolarize
if the cardioinhibitory center of the medulla oblongata were damaged, which part of the autonomic nervous system would be affected, and how would the heart be influenced?
this is part of the parasympathetic division of the autonomic nervous system so this would reduce parasympathetic action potentials to the heart.
The resulting sympathetic dominance would increase the heart rate
how does a drug that increases the length of time required for the repolarization of pacemaker cells affect the heart rate
this would decrease the heart rate because the pacemaker cells would generate fewer action potentials per minute
why is it a potential problem if the heart beats too rapidly?
a heart that beats too rapidly does not have sufficient time to completely fill between beats. thus, when the heart beats too fast, very little blood leaves the ventricles and enters circulation, so tissues suffer damage from inadequate blood supply
what effect would stimulating the acetylcholine receptors of the heart have on cardiac output?
this would slow the heart rate.
this will also lower cardiac output because HR is a factor in the formula for cardiac output
(assuming stroke volume remains the same or less)
what effect would an increase in venous return have on the stroke volume?
stroke volume = amt of blood pumped out by the ventricles per beat
the venous return fills the heart with blood, stretching the heart muscle. According to the Frank-Starling principle, the more the heart muscle is stretched, the more forcefully it will contract.
the more forceful the contraction, the more blood the heart will eject with each beat (stroke volume)
therefore, increased venous return would increase stroke volume (asssuming all other factors are constant)
how would an increase in sympathetic stimulation affect the end-systolic volume?
sympathetic stimulation = faster heart rate
end systolic volume = amt left in ventricles after contraction (systole)
LOWER ESV
joe’s end-systolic volume is 40mL and his end diastolic volume is 125mL.
what is his stroke volume?
SV=EDV-ESV
125-40=85ML
joe’s end-systolic volume is 40mL and his end diastolic volume is 125mL.
what is his stroke volume?
SV=EDV-ESV
125-40=85M
During diastole, a chamber of the heart is….
relaxing and filling with blood
cardiac output is….
the product of heart rate and stroke volume
During the cardiac cycle, the amount of blood ejected from the left ventricle when the semilunar valve opens is the…
stroke volume
What is the cardiac cycle?
What phases and events are needed to complete a cardiac cycle?
the cardiac cycle compromises the events in a complete heartbeat including a contraction/relaxation period for both atria and ventricles
the cycle begins with atria systole as the atria contract and push blood into the relaxed ventricles.
As the atria relax (atrial diastole), the ventricles contract (ventricular systole), forcing blood through the semilunar valves and into the pulmonary trunk and aorta
the ventricles then relax (ventricular diastole). For the rest of the cardiac cycle, both the atria and ventricles are in diastole; passive filling occurs
what 3 factors regulate stroke volume to ensure that the left and right ventricles pump equal amounts of blood?
- Preload (the stretch on the heart before it contracts)
- Contractility (the forcefulness of contraction of involved ventricular muscle fibers)
- Afterload (the pressure that must be exceeded before blood can be ejected from the ventricles)
How do the cells of the conducting system differ from the contractile cells of the heart?
contractile cells do not normally exhibit automaticity
What are the sources and significance of the 4 heart sounds?
S1 - closing of AV valves. “LUBB” marks the start of ventricular contraction
S2 - closing of semilunar valves “DUBB”
marks the start of ventricular diastole
S3 and S4 are quiet
S3=blood flow into the atria
S4=atrial contraction
listening to heart sounds = auscultation
differentiate between stroke volume and cardiac output
how is cardiac output calculated
stroke volume is the volume of blood ejected by a ventricle in a single contraction.
cardiac output is the amount of blood pumped by the left ventricle in 1 min
CO=HR*SV
what factors influence cardiac output
stroke volume and heart rate
what effect does sympathetic stimulation have on the heart?
increases the heart rate and force of contractions
describe the effects of epinephrine, norepinephrine, glucagon, and thyroid hormones on that contractility of the heart
all these hormones have positive inotropic effects which means they increase the strength and contraction of the heart
Vern is suffering from cardiac arrythmias and is brought to the ER. in the ER he begins to exhibit tachycardia and loses consciousness. explain why vern lost consciousness
when cardiac output decreases to a point where not enough blood reaches the brain, loss of consciousness occurs
during tachycardia, there is little time between contractions for the heart to fill with blood again. thus, the heart pumps less blood out
harvey has a heart murmur in his left ventricle that produces a loud “gurgling” sound at the beginning of a systole. which valve is probably faulty?
mitral/bicuspid valve is regurgitating.
When an AV valve fails to close properly, blood flowing back into the atrium produces a murmur.
a murmur at the BEGINNING of a systole indicates an AV valve because this period is when the valve has just closed and the blood in the ventricle is under increasing pressure–thus the likelihood of backflow is the greatest
a sound heard at the END of a systole or even the beginning of a diastole would indicate a semilunar valve (in this case aortic)
Person 1: heart rate 75bpm, stroke volume 60mL
Person 2: heart rate 90bpm
stroke volume 95mL
Which person has a greater venous return?
Which person has the longer ventricular filling time?
longer filling time = person 1
(lower heart rate)
greater venous return= person 2
(higher cardiac output. Starling’s law of the heart: greater CO=greater venous return)
Karen is taking Verapamil, a calcium channel blocker in cardiac muscle cells.
What effect should this medication have on Karen’s stroke volume?
By blocking calcium channels, verapamil will decrease the force of cardiac contraction, which directly lowers Karen’s stroke volume
