Unlike smooth and skeletal muscle, cardiac muscle tissue is capable of
The Correct Answer is {"dropdown-group-1":"D"}
A. Distension: Cardiac muscle tissue is capable of stretching to accommodate varying volumes of blood, a property shared with smooth muscle (in blood vessels and hollow organs) and skeletal muscle to some extent. Distension alone does not distinguish cardiac muscle from other muscle types.
B. Relaxation: Relaxation is a fundamental property of all muscle types, including skeletal, smooth, and cardiac muscle. After contraction, all these muscles return to their resting length to allow subsequent filling or preparation for the next contraction.
C. Contracting: Contraction is a universal property of all muscle types. Skeletal, smooth, and cardiac muscles all contract via actin–myosin cross-bridge cycling in response to appropriate stimuli.
D. Autorhythmicity: Cardiac muscle is unique in its ability to generate spontaneous action potentials without external nervous stimulation. Specialized pacemaker cells within the sinoatrial node initiate rhythmic depolarization, allowing the heart to maintain a coordinated and continuous heartbeat. This intrinsic automaticity is distinct from skeletal and smooth muscle, which require neural or hormonal stimuli to contract.
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Correct Answer is {"dropdown-group-1":"B"}
Explanation
A. Aortic: The aortic valve is a semilunar valve located between the left ventricle and the aorta. It opens during ventricular systole to allow blood ejection into the systemic circulation and closes during diastole to prevent backflow. Its closure produces the S2 heart sound, not S1.
B. Atrioventricular: The atrioventricular (AV) valves, comprising the tricuspid and mitral (bicuspid) valves, are located between the atria and ventricles. During ventricular contraction (systole), these valves close to prevent backflow into the atria. The closure of the AV valves generates the first heart sound (S1), commonly described as "lub," marking the onset of systole.
C. Semilunar: The semilunar valves, including the aortic and pulmonary valves, prevent backflow from the arteries into the ventricles. Their closure occurs at the end of ventricular systole and produces the second heart sound (S2), which is distinct from the "lub" of S1.
D. Pulmonary: The pulmonary valve is another semilunar valve located between the right ventricle and the pulmonary artery. It opens during right ventricular systole and closes during diastole. Its closure contributes to the S2 heart sound rather than S1.
Correct Answer is F
Explanation
Correct answer: F.
A. Trabeculae carneae: These are irregular, muscular ridges lining the inner walls of the ventricles. They prevent suction during contraction, aid in ventricular contraction efficiency, and contribute to overall cardiac structural integrity.
B. Pulmonary semilunar valve: This valve is located between the right ventricle and pulmonary artery. It prevents backflow of blood into the ventricle during diastole and ensures unidirectional pulmonary circulation toward the lungs.
C. Papillary muscles: Papillary muscles are conical projections of ventricular myocardium that anchor chordae tendineae. During ventricular contraction, they contract to prevent inversion or prolapse of atrioventricular valves, ensuring proper unidirectional blood flow.
D. Pectinate muscles: Pectinate muscles are comb-like muscular ridges in the atrial walls, particularly prominent in the right atrium. They enhance atrial contraction, increasing blood flow into the ventricles efficiently during systole.
E. Chordae tendineae: These are thin, fibrous cords connecting atrioventricular valve leaflets to papillary muscles. They prevent valve prolapse during ventricular contraction, maintaining proper closure and unidirectional blood flow from atria to ventricles.
F. Right atrium: It is located on the superior right side of the heart and receives deoxygenated blood from the superior vena cava, inferior vena cava, and coronary sinus. It forms the right border of the heart. Physiologically, the right atrium functions as a receiving chamber that collects systemic venous blood and delivers it through the tricuspid valve into the right ventricle during atrial contraction.
G. Bicuspid valve: Also called the mitral valve, it is located between the left atrium and left ventricle. It prevents backflow into the atrium during ventricular contraction, ensuring efficient systemic circulation.
H. Fossa ovalis: This is a depression in the interatrial septum, the remnant of the fetal foramen ovale. It allowed blood to bypass the fetal lungs and normally closes after birth.
I. Left ventricle: The left ventricle pumps oxygenated blood into the aorta under high pressure. Its thick muscular wall enables strong contractions necessary to sustain systemic circulation throughout the body.
J. Interventricular septum: This thick muscular wall separates the left and right ventricles. It prevents mixing of oxygenated and deoxygenated blood and contributes to the contractile force of ventricular systole.
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