Question

(a) Explain the menstrual phase in a human female. State the levels of ovarian and pituitary hormones during this phase.
(b) Why is the follicular phase in the menstrual cycle also referred to as a proliferative phase? Explain.
(c) Explain the events that occur in a Graafian follicle at the time of ovulation and thereafter.
(d) Draw a Graafian follicle and label antrum and secondary oocyte.

Answer 1

Hint: The menstrual cycle is a reproductive cycle that takes place in the females of primates such as monkeys, apes, and humans. Menstruation (monthly discharge of blood) starts at puberty around (11-12 years old) and continues up to old age (45-50 years old).

Complete Step by Step Answer:
The menstrual cycle is a cycle that repeats after a time interval of 28-29 days. It consists of the following phases i.e. menstrual phase, follicular phase, ovulatory phase, and luteal phase which come one after another.
(a)The beginning of the menstrual phase is defined by the breakdown of the endometrial lining of the uterus and its blood vessels, which then flows out in the form of liquid from the vagina. This phase lasts for 3-5 days. Both ovarian and pituitary levels are low in this phase. Low levels of ovarian hormones stimulate the production of pituitary hormones for the next phase.
(b) Follicular phase comes after the menstrual phase. In this phase, the primary follicles in the ovary develop to become a Graafian follicle. This phase is also known as the proliferative phase as the endometrium of the uterus regenerates itself with lining through proliferation.
(c) During the middle of the cycle (14th day) both FSH and LH attain a peak level. This rapid secretion of LH is known as LH surge which causes the rupture of the Graafian follicle and the ovum is released (ovulation). After this, the remains of the Graafian follicle develop into a structure called corpus luteum which releases progesterone and its function is to maintain the lining of the endometrium.

Note:
- The antrum is a fluid-filled cavity which is a characteristic of the tertiary follicle.
- The corpus luteum degenerates in the absence of pregnancy thus causing the breakdown of the lining of the uterus.