Apoptosis can occur by change in hormone levels in the ovarian cycle. When there is no feilization of the ovum, the endometrial cells die because :
**Core Concept**
Apoptosis, or programmed cell death, is a physiological process that occurs in the endometrium during the menstrual cycle. It is a key mechanism for shedding the endometrial lining when there is no fertilization of the ovum, preventing excessive bleeding and maintaining uterine health.
**Why the Correct Answer is Right**
The increase in progesterone levels after ovulation prepares the endometrium for implantation of the fertilized ovum. However, when there is no fertilization, the progesterone levels drop, leading to a decrease in the production of the anti-apoptotic protein, Bcl-2. This decrease allows the pro-apoptotic proteins, such as Bax and Bad, to dominate, promoting apoptosis in the endometrial cells. The decrease in progesterone also leads to an increase in the production of the pro-apoptotic cytokine, TNF-alpha, which further contributes to the initiation of apoptosis.
**Why Each Wrong Option is Incorrect**
**Option A:** This option is incorrect because the primary mechanism of apoptosis in the endometrium is not due to a decrease in estrogen levels, but rather a decrease in progesterone levels.
**Option B:** This option is incorrect because the endometrial cells do not die due to an increase in prostaglandins. While prostaglandins do play a role in the menstrual cycle, they are not directly responsible for the apoptosis of endometrial cells.
**Option C:** This option is incorrect because the endometrial cells do not die due to an increase in the production of collagenase. While collagenase is involved in the breakdown of the extracellular matrix during menstruation, it is not the primary mechanism of apoptosis in the endometrium.
**Clinical Pearl / High-Yield Fact**
The menstrual cycle is a classic example of the balance between cell growth and cell death, and the regulation of apoptosis is a key mechanism for maintaining uterine health.
**Correct Answer: A. Decrease in progesterone levels.**