Question

(i) Explain menstrual phase in the menstrual cycle of human female.

(ii) Why is follicular phase also called proliferative phase ?

(iii) Explain the events that occur in Graafian follicle at the time of ovulation and thereafter.

(iv) Draw a Graafian follicle and label - Antrum and secondary oocyte.

Hint:

Part (i) menstruation after the corpus luteum fails. Part (ii) estrogen makes the endometrium grow. Part (iii) LH surge then corpus luteum.

Answer 1

Step 1: Part (i): the menstrual phase:
The cycle starts with the menstrual phase, which lasts about 3 to 5 days.
If the ovum is not fertilised, the corpus luteum degenerates. The levels of progesterone and estrogen fall.
The endometrium of the uterus breaks down and is shed with blood through the vagina. This flow is called menstruation.

Step 2: Part (ii): why the follicular phase is proliferative:
During the follicular phase the primary follicles in the ovary grow into a mature Graafian follicle.
The growing follicles secrete estrogen. Under its effect the endometrium of the uterus regenerates by cell division, that is, it proliferates.
So the phase is also named the proliferative phase.

Step 3: Part (iii): ovulation and after:
Around day 14, a surge of LH (and FSH) makes the Graafian follicle rupture and release the secondary oocyte. This is ovulation.
The remaining follicular cells turn into the corpus luteum, a temporary gland.
The corpus luteum secretes a large amount of progesterone. It keeps the endometrium ready for implantation.
If there is no fertilisation, the corpus luteum degenerates.

Step 4: Part (iv): diagram (labelled sketch expected):
Draw a large round follicle in the ovary. From the outside to the inside the parts are as follows.
Theca externa and theca interna form the outer layers.
Granulosa cells (membrana granulosa) line the inside.
The fluid-filled cavity is the ANTRUM.
The SECONDARY OOCYTE sits at one side, surrounded by the zona pellucida and a heap of granulosa cells (cumulus oophorus).

Final Answer:
(i) Shedding of the endometrium. (ii) Estrogen makes the endometrium proliferate. (iii) LH surge, ovulation, then corpus luteum forms. (iv) Sketch with antrum and secondary oocyte labelled.