12th Class Biology Sample Paper Biology - Sample Paper-15

  • question_answer During menstrual cycle, uterus also shows cyclical changes.


    Menstrual cycle is the reproductive cycle in female primates. The cycle of events starting from one menstruation till the next one is called menstrual cycle. It consists of following four phases in which following changes occur in uterus.
    (i) Menstrual phase The endometrial lining of the uterus breaks down due to the deficiency of progesterone and is sloughed off. It occurs in the absence of fertilisation and uterus starts to prepare itself for the next cycle.
    (ii) Follicular phase The endometrium of uterus regenerates through proliferation. It is necessary for the implantation of fertilised egg.
    (iii) Ovulatory phase This phase ismainly concernedwith the ovulation. Endometrium thickens.
    (iv) Luteal phase The corpus luteum secretes large amounts of progesterone essential to maintain endometrium. It is necessary for the implantation and other events of pregnancy. In the absence of fertilisation, it is sloughed off.

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