Which of the following is responsible for the 'lub-dub' sound of the heart?
A. Opening of heart valves
B. Closing of heart valves
C. Contraction of ventricles
D. Blood flow turbulence
Answer: Option B
Solution (By JKSSB Mock Tests)
The first heart sound 'lub' is caused by the closure of the atrioventricular valves (mitral and tricuspid) at the beginning of ventricular systole. The second sound 'dub' is due to closure of semilunar valves (aortic and pulmonary) at the end of systole. Abnormal sounds (murmurs) indicate valve defects. This is due to turbulence, but the sound specifically is produced by valve closure.
Explanation:
Robert Hooke, in 1665, observed thin slices of cork under a compound microscope and saw box-like structures he named 'cells'. Leeuwenhoek observed live cells, Brown discovered the nucleus, Virchow proposed cells arise from cells.
Explanation:
Fertilization typically occurs in the ampulla, the widest region of the fallopian tube, where the sperm meets the secondary oocyte. The zygote then travels to the uterus for implantation. The ovary releases the egg, the uterus supports embryo development, the cervix is the lower portion opening into the vagina.
Explanation:
The right ventricle pumps deoxygenated blood through the pulmonary artery to the lungs for oxygenation. The pulmonary artery is the only artery carrying deoxygenated blood. Pulmonary veins carry oxygenated blood from lungs to the left atrium. The left atrium receives oxygenated blood, not deoxygenated. The right atrium receives deoxygenated blood from the body. Thus, C is correct.
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