What happens when ventricular pressure drops below the pressure in the aorta and pulmonary trunk during diastole?
The semilunar valves close, preventing backflow into the heart
The electrical impulse initiates ventricular depolarization
The atrioventricular valves close, preventing backflow into the atria
The ventricles contract, forcing blood into the great arteries
The Correct Answer is A
A. The semilunar valves close, preventing backflow into the heart: During ventricular diastole, the ventricles relax and ventricular pressure falls below the pressure in the aorta and pulmonary trunk. This pressure gradient causes the aortic and pulmonary semilunar valves to close, preventing blood from flowing backward into the ventricles.
B. The electrical impulse initiates ventricular depolarization: Ventricular depolarization occurs during the onset of systole, not diastole. It is triggered by the action potential conducted through the bundle branches and Purkinje fibers, leading to contraction. Depolarization does not directly cause semilunar valve closure.
C. The atrioventricular valves close, preventing backflow into the atria: The atrioventricular (tricuspid and mitral) valves close at the beginning of ventricular systole when ventricular pressure exceeds atrial pressure. This prevents regurgitation into the atria and generates the first heart sound (S1), distinct from the semilunar valve closure occurring later in diastole.
D. The ventricles contract, forcing blood into the great arteries: Ventricular contraction occurs during systole when ventricular pressure rises above aortic and pulmonary pressures to open the semilunar valves. Closure of these valves happens during diastole when the ventricles relax, not during active ejection.
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Related Questions
Correct Answer is A
Explanation
A. Sympathetic stimulation releases norepinephrine (NE), which binds to beta-1 receptors, increasing heart rate: Sympathetic nerve fibers release norepinephrine, which binds to beta-1 adrenergic receptors on the sinoatrial node and ventricular myocardium. This increases the rate of depolarization in pacemaker cells, enhancing heart rate (positive chronotropy), and also increases contractility (positive inotropy), preparing the heart for increased cardiac output.
B. Parasympathetic stimulation releases norepinephrine (NE), which binds to beta-1 receptors, increasing heart rate: Parasympathetic fibers do not release norepinephrine; they release acetylcholine. Norepinephrine is specific to sympathetic innervation. Therefore, this description incorrectly attributes sympathetic neurotransmission to parasympathetic activity.
C. Sympathetic stimulation releases norepinephrine (NE), which binds to muscarinic receptors, slowing heart rate: Muscarinic receptors are activated by acetylcholine released from parasympathetic fibers, not by norepinephrine. Sympathetic stimulation increases heart rate, rather than slowing it, through beta-1 receptor activation.
D. Parasympathetic stimulation releases acetylcholine (ACh), which binds to the beta-1 receptors, increasing heart rate: Parasympathetic stimulation releases acetylcholine, but it binds to muscarinic receptors on pacemaker cells, not beta-1 adrenergic receptors. Activation of muscarinic receptors slows the heart rate (negative chronotropy) rather than increasing it.
Correct Answer is F
Explanation
A. Small cardiac vein: The small cardiac vein runs along the right margin of the heart and drains blood from the right atrium and ventricle. It empties into the coronary sinus, facilitating venous return to the right atrium.
B. Coronary sinus: The coronary sinus is a large venous channel on the posterior aspect of the heart. It collects most cardiac venous blood and drains directly into the right atrium, completing coronary circulation.
C. Anterior cardiac vein: The anterior cardiac veins run along the anterior surface of the right ventricle. They bypass the coronary sinus, draining directly into the right atrium, and contribute to the venous return from the right ventricular myocardium.
D. Superior vena cava: The superior vena cava is a major systemic vein that returns deoxygenated blood from the upper body, including the head, neck, and upper limbs, directly into the right atrium of the heart.
E. Middle cardiac vein; The middle cardiac vein runs in the posterior interventricular sulcus, draining the posterior portion of both ventricles. It empties into the coronary sinus, ensuring efficient venous return from the heart’s posterior myocardium.
F. Great cardiac vein: The blood vessel highlighted in the image is the great cardiac vein located on the anterior surface of the heart. The great cardiac vein begins at the apex of the heart and eventually curves around the left side of the heart (within the coronary sulcus) to empty into the coronary sinus on the posterior side. It is the principal vein of the anterior heart.
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