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
