In a young female of reproductive age with regular menstrual cycles of 28 days ovulation occurs around 14th day of periods. When is first polar body extruded.
**Core Concept**
Ovulation in a 28-day menstrual cycle occurs around the 14th day, marking the release of a mature ovum from the dominant follicle in the ovary. This process involves meiotic division of the oocyte, resulting in the extrusion of a first polar body and the release of the secondary oocyte.
**Why the Correct Answer is Right**
During meiotic division I, the primary oocyte undergoes an unequal division, producing a larger secondary oocyte and a smaller first polar body. This process typically occurs 24-26 hours after the onset of ovulation. The first polar body contains most of the cytoplasm and 19-20 chromosomes, while the secondary oocyte retains the remaining cytoplasm and 19 chromosomes. The extrusion of the first polar body is a crucial step in the maturation of the oocyte, allowing it to undergo further meiotic division and potentially fertilization.
**Why Each Wrong Option is Incorrect**
* **Option A:** This option does not provide a specific time for first polar body extrusion, making it an incorrect choice.
* **Option B:** This option is not supported by scientific evidence, as the first polar body is extruded before the secondary oocyte is released.
* **Option D:** This option does not specify a time frame for first polar body extrusion, making it an incorrect choice.
**Clinical Pearl / High-Yield Fact**
The timing of ovulation and first polar body extrusion is crucial for fertility and conception. Understanding the menstrual cycle and ovulation can help women with irregular cycles or fertility issues.
**Correct Answer: C. 24-26 hours after ovulation.**