Question

(e) Which period is said to be period of secretions of glands in endometrium? 
 

Hint:

During the menstrual cycle remember the sequence: menstrual phase (shedding) → proliferative phase (regeneration under estrogen) → ovulation (around day 14) → secretory phase (glandular secretion under progesterone); match ovarian events (follicle growth, ovulation, corpus luteum) with uterine changes for clear answers.

Answer 1

During the secretory phase, the endometrial glands become highly coiled and secrete nutritive fluids under the influence of progesterone produced by the corpus luteum, preparing the lining for possible implantation.
The secretory phase follows ovulation and typically lasts from day 15 to day 28 in a 28-day cycle. This phase is characterized by significant hormonal and structural changes that make the endometrium receptive to a fertilized egg. Key aspects of the secretory phase include:
- Hormonal Changes: After ovulation, the ruptured follicle in the ovary transforms into the corpus luteum, which begins to secrete progesterone. Progesterone plays a critical role in maintaining the thickened endometrial lining, making it more suitable for embryo implantation. Estrogen levels also remain elevated, but progesterone takes the lead during this phase.
- Endometrial Changes: Under the influence of progesterone, the endometrial glands become more coiled and increase in size. The glands begin to secrete a thick, nutritious fluid, providing an ideal environment for a potential embryo. The stroma (the connective tissue in the endometrium) also becomes more edematous (fluid-filled) and more vascular, enhancing the uterine lining's ability to nourish a developing embryo.
- Cervical Mucus: During the secretory phase, cervical mucus becomes thicker and less receptive to sperm, which helps prevent fertilization during this time, as the body shifts focus to possible implantation and pregnancy.
- Implantation Window: The endometrial lining reaches its peak thickness and nutrient content around days 20–24 of the cycle. If fertilization has occurred, the embryo may implant into the lining during this "implantation window." The uterine lining secretes factors that promote successful implantation and early embryonic development.
- Corpus Luteum Function: If pregnancy does not occur, the corpus luteum degenerates, leading to a sharp drop in progesterone levels. This drop triggers the breakdown of the endometrial lining, marking the transition into the menstrual phase and the start of a new cycle. If fertilization and implantation occur, the corpus luteum is maintained by human chorionic gonadotropin (hCG), ensuring continued progesterone secretion to support the pregnancy.
In summary, the secretory phase is crucial for the preparation of the uterine lining to support implantation and early pregnancy. The hormonal and structural changes that take place during this phase are essential for a successful pregnancy to occur if fertilization happens.