Question

In a human female, the reproductive phase starts on the onset of puberty and ceases around middle age of the female. Study the graph given below regarding menstrual cycle and answer the questions that follow:

(a) Name the hormones and their source organ, which are responsible for menstrual cycle at puberty.    [1]

(b) For successful pregnancy, at what phase of the menstrual cycle an early embryo (upto 3 blastomeres) should be Implanted in the Uterus (IUT) of a human female who has opted for Assisted Reproductive Technology (ART)? Support your answer with a reason.    [1]

(c) Name the hormone and its source organ responsible for the events occurring during proliferative phase of menstrual cycle. Explain the event.    [2]

                                               OR

(c) In a normal human female, why does menstruation only occurs if the released ovum is not fertilised? Explain.    [2]

Answer 1

(a) 

1. Follicle-stimulating hormone (FSH): Pituitary gland
2. Luteinising hormone (LH): Pituitary gland
3. Estrogen: Ovaries (specifically, the developing ovarian follicles)
4. Progesterone: Ovaries (specifically, the corpus luteum)

(b) The early embryo (up to three blastomeres) should be implanted in the uterus (UT) during the luteal phase of the menstrual cycle in order for assisted reproductive technology (ART), such as in vitro fertilisation (IVF), to successfully produce a child.

1. The endometrium, or uterine lining, changes during the luteal phase of the menstrual cycle when progesterone levels are high, preparing it for embryo implantation during assisted reproductive technology (ART) treatments such as in vitro fertilisation (IVF).
2. The hypertrophied and augmented endometrium, coupled with optimum angiogenesis, establishes a perfect milieu for successful embryo implantation and subsequent gestation.
   In implanting the early embryo up to three blastomeres at this phase, the uterus is guaranteed to be receptive, increasing the likelihood of a successful implantation and, eventually, a successful pregnancy. Thus, embryo transfer usually occurs during the luteal phase of the menstrual cycle in ART operations.

(c) The hormone responsible for the events occurring during the proliferative phase of the menstrual cycle is estrogen. Estrogen is predominantly synthesised by the maturing ovarian follicles in the ovaries.

1. Follicular (Proliferative) phase: In this phase, the main follicle develops into Graafian follicles. This induces the regeneration of the endometrium.
2. Estrogens stimulate:
   1. Proliferation of ruptured uterine endometrium and mucous lining of oviduct and vagina.
   2. Development of secondary sexual characters.
   3. Estrogen inhibits the secretion of FSH and stimulates the secretion of LH. It also causes the thickening of the uterine endometrium.

                                               OR

(c) After ovulation, the remains of the Graafian follicle are transformed into the yellow endocrine structure known as the corpus luteum. It produces progesterone. Progesterone hormone facilitates the preservation and preparation of the endometrium for embryo implantation. Menstruation ceases during pregnancy, stopping all menstrual cycle occurrences.
In the absence of fertilisation, the corpus luteum degenerates and transforms into a white mass known as the corpus albicans. Due to its lack of secretory function, the progesterone level in the blood decreases. It indicates the onset of menstruation, marking the beginning of a new cycle.