Choose the correct match w.r.t. menstrual cycle.

Options

A. Follicular phase - Low concentration of estrogen
B. Secretory phase - Low concentration of progesterone
C. Luteal phase - Shedding of endometrial lining
D. Proliferative phase _ Increase in thickness of endometrium lining

Answer

To solve the question regarding the correct match with respect to the menstrual cycle, we will analyze the four phases of the menstrual cycle and the options provided.

### Step-by-Step Solution:

1. **Understand the Menstrual Cycle Phases**:
- The menstrual cycle consists of four main phases:
- Menstrual Phase
- Follicular Phase
- Ovulatory Phase
- Luteal Phase (or Secretory Phase)

2. **Analyze Each Option**:
- **Option 1**: Follicular Phase - Low concentration of estrogen.
- **Analysis**: This is incorrect. During the follicular phase, estrogen levels are high as follicles develop.

- **Option 2**: Secretory Phase - Low concentration of progesterone.
- **Analysis**: This is also incorrect. The secretory phase is characterized by high levels of progesterone, which is essential for maintaining the uterine lining for potential implantation.

- **Option 3**: Luteal Phase leads to shedding of the endometrial lining.
- **Analysis**: This is incorrect as well. Shedding of the endometrial lining occurs during the menstrual phase, not the luteal phase, which is when the lining thickens due to high progesterone levels.

- **Option 4**: Proliferative Phase - Increase in thickness of the endometrial lining.
- **Analysis**: This is correct. The proliferative phase (which overlaps with the follicular phase) involves the thickening of the endometrial lining due to estrogen and progesterone secretion.

3. **Conclusion**:
- After analyzing all options, we find that **Option 4** is the correct match regarding the menstrual cycle.

### Final Answer:
**Option 4**: Proliferative Phase - Increase in thickness of the endometrial lining.

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