Read the given passage and answer the following questions:
The oviducts (fallopian tubes), uterus and vagina constitute the female accessory ducts. Each fallopian tube is about 10-12 cm long and extends from the periphery of each ovary to the uterus, the part closer to the ovary is the funnel-shaped infundibulum. The edges of the infundibulum possess finger-like projections called fimbriae, which help in collection of the ovum after ovulation. The infundibulum leads to a wider part of the oviduct called ampulla. The last part of the oviduct, isthmus has a narrow lumen and it joins the uterus. The uterus is single and it is also called womb. The shape of the uterus is like an inverted pear. It is supported by ligaments attached to the pelvic wall. The uterus opens into vagina through a narrow cervix. The cavity of the cervix is called cervical canal which alongwith vagina forms the birth canal. The wall of the uterus has three layers of tissue. The external thin membranous perimetrium, middle thick layer of smooth muscle, myometrium and inner glandular layer called endometrium that lines the uterine cavity. The endometrium undergoes cyclical changes during menstrual cycle while the myometrium exhibits strong contraction during delivery of the baby.
Statement I: In the absence of fertilisation, the corpus luteum degenerates, which causes thickening of the endometrium.
Statement II: The endometrium maintained by the corpus luteum is necessary for implantation of the fertilised ovum and other events of pregnancy.
In the light of the above statements, choose the correct answer from the options given below:
Answer & explanation
Correct answer: option 2
The correct answer is Option (2) → Only Statement II is correct.
Statement I: In the absence of fertilisation, the corpus luteum degenerates, which causes thickening of the endometrium. — False. The first part is right. But when the corpus luteum degenerates, progesterone falls and the endometrium breaks down (disintegrates). This is menstruation, which marks a new cycle. The endometrium thickens in the proliferative phase, before ovulation.
Statement II: The endometrium maintained by the corpus luteum is necessary for implantation of the fertilised ovum and other events of pregnancy. — True. The corpus luteum secretes large amounts of progesterone, which maintains the endometrium. Only such an endometrium can receive the embryo and support pregnancy.
NCERT Extract:
Menstrual Cycle – “… The corpus luteum secretes large amounts of progesterone which is essential for maintenance of the endometrium. Such an endometrium is necessary for implantation of the fertilised ovum and other events of pregnancy. During pregnancy all events of the menstrual cycle stop and there is no menstruation. In the absence of fertilisation, the corpus luteum degenerates. This causes disintegration of the endometrium leading to menstruation, marking a new cycle.”