Question

In a human female, menstrual cycle of 28 days is represented by the diagram given below (Phase I: Days 1--5, Phase II: Days 6--13, Phase III: Days 15--28). Select the correct statement related with this diagram.

• A. Primary follicle of ovary matures into Graafian follicle in phase II.
• B. The hormone secreted in large amounts in phase III is also responsible for maintaining pregnancy in human females.
• C. Corpus luteum secretes progesterone in phase I, however it degenerates completely in phase III.
• D. Both (A) and (B).

Hint:

Remember the clear physiological timelines: - Follicular maturation (Primary $\rightarrow$ Graafian) occurs during the Pre-ovulatory/Follicular phase (Phase II). - Progesterone production occurs exclusively post-ovulation in the Luteal phase (Phase III) and is the signature hormone for preserving pregnancy.

Answer 1

The Correct Option is D

Concept: The human menstrual cycle is a tightly regulated complex physiological process spanning an average of 28 days. It consists of multiple synchronous phases occurring in both the ovaries (ovarian cycle) and the uterus (uterine cycle):
• Phase I (Menstrual Phase): Lasts from days 1 to 5, characterized by the shedding of the endometrial lining due to low steroid hormone levels.
• Phase II (Follicular Proliferative Phase): Lasts from days 6 to 13. Under the influence of rising Follicle Stimulating Hormone (FSH), ovarian follicles develop. Concurrently, increasing estrogen levels repair and proliferate the uterine endometrium.
• Phase III (Luteal Secretory Phase): Lasts from days 15 to 28. Following ovulation at day 14 (triggered by an LH surge), the ruptured Graafian follicle transforms into the corpus luteum, which secretes high amounts of progesterone.

Step 1: Analyzing Statement (A).
During Phase II, which is the follicular or proliferative phase, the pituitary gland secretes Follicle Stimulating Hormone (FSH). This hormone stimulates the growth and development of primary follicles in the ovary. A primary follicle matures into a secondary follicle, then a tertiary follicle, and finally a fully mature Graafian follicle by the end of this phase. Therefore, statement (A) is completely true and factually accurate.

Step 2: Analyzing Statement (B).
Phase III corresponds to the luteal or secretory phase. Following ovulation, the remnants of the ruptured Graafian follicle convert into a temporary endocrine structure called the corpus luteum. The corpus luteum secretes large quantities of the steroid hormone progesterone. Progesterone is vital for preparing and maintaining the vascularized, glandular endometrium, making it receptive to a fertilized ovum. It is absolutely essential for the maintenance of pregnancy in human females. Therefore, statement (B) is also true and correct.

Step 3: Analyzing Statement (C).
Statement (C) claims that the corpus luteum secretes progesterone in phase I and degenerates in phase III. This is entirely incorrect. The corpus luteum does not exist during phase I (menstrual phase). It forms during phase III, and it only degenerates (into the corpus albicans) at the very end of phase III if fertilization fails to occur. Therefore, statement (C) is false.

Step 4: Conclusion.
Since both statements (A) and (B) are distinctively correct, option (D) is the correct overarching choice.