In the human female reproductive cycle, which statement correctly describes the uterine cycle when fertilization occurs and the corpus luteum must be maintained?

Introduction / Context:
The uterine or menstrual cycle involves cyclic changes in the endometrium under the influence of ovarian hormones. It includes menstrual, proliferative, and secretory phases. When fertilization and implantation occur, special hormonal signals are needed to maintain the endometrium and the corpus luteum. This question asks which statement about the uterine cycle is correct, especially in the context of fertilization and hormone support.

Given Data / Assumptions:

• The uterine cycle has three main phases: menstrual, proliferative, and secretory.
• Hormone levels of estrogen and progesterone change during these phases.
• The corpus luteum secretes progesterone and supports the endometrium after ovulation.
• The options describe hormone levels in various phases and a statement about fertilization and corpus luteum maintenance.

Concept / Approach:
During the proliferative phase, estrogen released from developing follicles stimulates regeneration and thickening of the endometrium. Progesterone is low at this time. After ovulation, during the secretory phase, the corpus luteum secretes large amounts of progesterone along with some estrogen, making progesterone the dominant hormone. If fertilization and implantation occur, the developing embryo secretes human chorionic gonadotropin (hCG), which maintains the corpus luteum so that it continues to produce progesterone and support the endometrium. The menstrual phase typically lasts about three to five days in a textbook 28 day cycle, not up to day 8. Thus, the only fully correct statement is the one about embryonic hormone maintaining the corpus luteum.

Step-by-Step Solution:
Step 1: Evaluate statement A. The secretory phase is dominated by progesterone from the corpus luteum, with moderate estrogen levels. Estrogen is not at its highest in this phase, so this statement is incorrect. Step 2: Evaluate statement B. During the proliferative phase, estrogen, not progesterone, rises as follicles develop. Progesterone begins to rise mainly after ovulation in the luteal or secretory phase. Therefore, this statement is also incorrect. Step 3: Evaluate statement C. After fertilization, the developing embryo secretes hCG, which maintains the corpus luteum and thus progesterone production. This correctly describes the hormonal support of early pregnancy. Step 4: Evaluate statement D. In a standard 28 day cycle, the menstrual phase usually lasts around day 1 to day 3 or 5, not to day 8. Thus, this statement is inaccurate. Step 5: Conclude that statement C is the only accurate description among the options.

Verification / Alternative check:
Gynecology and physiology texts describe that if pregnancy occurs, hCG secreted by the developing embryo (and later by the placenta) preserves the corpus luteum for several weeks. Charts of hormone levels in the menstrual cycle show a rise in estrogen during the proliferative phase, followed by a combined elevation of progesterone and estrogen in the secretory phase. Clinical tests for pregnancy often detect hCG in blood or urine, reinforcing the idea that an embryonic hormone maintains the corpus luteum. These facts confirm that statement C is correct.

Why Other Options Are Wrong:
Option A: The secretory phase is characterized by high progesterone, not maximal estrogen levels. Estrogen peaks just before ovulation during the late proliferative phase.
Option B: Progesterone does not significantly rise during the proliferative phase. That phase is dominated by estrogen from growing follicles.
Option D: Although cycle lengths vary, the textbook menstrual phase is shorter than eight days and typically ranges from three to five days.

Common Pitfalls:
Students often mix up the timing of hormone peaks, confusing estrogen and progesterone dominated phases. Another common error is misremembering the duration of the menstrual phase. Additionally, some learners forget the role of embryonic hCG in pregnancy maintenance and mistakenly assume the corpus luteum persists automatically. Always connect hormonal changes to specific phases to avoid these confusions.

Final Answer:
The correct statement is that if fertilization occurs, the corpus luteum is maintained by a hormone secreted by the developing embryo, namely human chorionic gonadotropin.