Opening and closing of the heart valves is caused by
Breathing
Gravity
valves contracting and relaxing
osmotic gradients
pressure gradients
The Correct Answer is E
A. Breathing: Thoracic pressure changes during inspiration and expiration can influence venous return to the heart. However, these pressure fluctuations are not the direct mechanical force that operates the cardiac valves. Valve function is localized to the hemodynamics occurring within the cardiac chambers themselves.
B. Gravity: While gravity affects blood distribution in the upright position, it is not the mechanism responsible for the rapid snapping open and shut of heart valves. The heart must generate significant internal forces to overcome gravitational pull and ensure forward flow. Valves rely on active fluid dynamics rather than passive positioning.
C. valves contracting and relaxing: Heart valves are passive structures composed of endocardium and connective tissue that do not possess muscular tissue. They do not have the physiological ability to contract or relax on their own like myocardium. They move strictly in response to the movement and pressure of the blood.
D. osmotic gradients: Osmotic gradients govern the movement of water across semipermeable membranes in the capillaries. They have no mechanical role in the movement of large anatomical structures like the atrioventricular or semilunar valves. Valve operation is a macro-mechanical process driven by hydrostatic force, not molecular osmosis.
E. pressure gradients: The opening and closing of heart valves are driven by differences in fluid pressure on either side of the valve. When pressure in a proximal chamber exceeds that of a distal chamber, the valve is pushed open. Conversely, backpressure from a distal chamber forces the valve leaflets to seal shut.
Nursing Test Bank
Naxlex Comprehensive Predictor Exams
Related Questions
Correct Answer is D
Explanation
A. oblique fissure: This is the anatomical groove that separates the superior and inferior lobes of the left lung. While it is a prominent surface feature, it does not represent the specific indentation created by the heart. It facilitates the sliding of lung lobes during the respiratory cycle.
B. hilum: The hilum is the triangular depression on the medial surface of the lung where primary bronchi and pulmonary vessels enter and exit. It serves as the "root" of the lung rather than a space-occupying indentation for the heart. It is located posterior to the cardiac impression.
C. apex: The apex is the superior, blunt tip of the lung that projects above the level of the first rib into the neck. It is located far above the anatomical position of the mediastinal heart. It does not interface with the cardiac apex or ventricular mass.
D. cardiac notch: This is a distinct medial indentation on the anterior border of the superior lobe of the left lung. It accommodates the lateral projection of the heart's apex within the thoracic cavity. This anatomical feature explains why the left lung is smaller than the right lung.
E. base: The base is the broad, concave inferior surface of the lung that rests upon the convex surface of the diaphragm. While the heart sits superior to the central tendon of the diaphragm, it does not indent the diaphragmatic base. The base primarily conforms to the abdominal dome.
Correct Answer is ["A","C"]
Explanation
A. Sinoatrial (SA) node: This structure is located in the right atrium near the opening of the superior vena cava. It initiates the electrical impulse that starts each heartbeat. Because it has the highest intrinsic firing rate (about 60–100 beats per minute), it determines the heart’s rhythm and is therefore called the pacemaker of the heart.
B. Atrioventricular (AV) node: The AV node is located in the lower part of the right atrium near the interatrial septum. Its main function is to delay the electrical impulse coming from the atria before passing it to the ventricles. This delay allows the ventricles time to fill with blood before they contract. It can act as a backup pacemaker, but its intrinsic rate is slower (40–60 bpm), so it is not the primary pacemaker.
C. Atrioventricular (AV) bundle (Bundle of His): This structure carries the impulse from the AV node into the interventricular septum. It is the only normal electrical connection between the atria and ventricles. It conducts impulses but does not normally initiate them, so it is not the pacemaker.
D. Bundle branches: These pathways run down the right and left sides of the interventricular septum. They rapidly conduct electrical impulses toward the apex of the heart. Their role is conduction, not impulse generation, so they are not pacemakers.
E. Purkinje fibers spread throughout the ventricular myocardium. They distribute the impulse to ventricular muscle cells, causing coordinated ventricular contraction. Although they have an intrinsic firing ability, it is very slow (20–40 bpm) and only takes over if higher pacemakers fail. Therefore, they are not the normal pacemaker.
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