The cellular layer that disintegrates and regenerates again and again in human skin is:

Options

A. Endometrium of uterus
B. dermis of skin
C. Cornea of eye
D. Endothelium of blood vessels.

Answer

To solve the question regarding the cellular layer that disintegrates and regenerates in human skin, we need to analyze the options provided:

1. **Endometrium of Uterus**: This layer is involved in the menstrual cycle. It thickens to prepare for a fertilized egg and disintegrates if fertilization does not occur, leading to menstruation. However, it is not part of the skin.

2. **Dermis of Skin**: The dermis is the layer beneath the epidermis and contains connective tissue, hair follicles, and sweat glands. It does not disintegrate and regenerate in the same way as the outer layer of skin.

3. **Cornea of Eye**: The cornea is a transparent layer at the front of the eye. While it can regenerate, it is not related to the skin.

4. **Endothelium of Blood Vessels**: This is the layer of cells lining the blood vessels. It does not disintegrate and regenerate in the context of skin.

Upon reviewing these options, the correct answer is not explicitly listed in the options provided. The cellular layer that disintegrates and regenerates in human skin is actually the **epidermis**, which consists of keratinized cells that continuously shed and renew.

### Step-by-Step Solution:
1. **Identify the Layers of Skin**: Understand the different layers of skin, which include the epidermis (outer layer), dermis (middle layer), and hypodermis (inner layer).
- **Hint**: Remember that the outermost layer of skin is responsible for protection and is constantly renewing itself.

2. **Understand the Function of the Epidermis**: The epidermis is made up of keratinocytes that undergo a process of keratinization. These cells are continuously produced and shed.
- **Hint**: Think about how skin is exposed to the environment and needs to renew itself to maintain barrier function.

3. **Recognize the Process of Disintegration and Regeneration**: The epidermis disintegrates as dead skin cells are shed and regenerates as new cells are formed from the basal layer.
- **Hint**: Consider how often you see skin flakes or how your skin feels after exfoliation.

4. **Conclusion**: The cellular layer that disintegrates and regenerates in human skin is the **epidermis**. The endometrium is not related to skin but is involved in the reproductive system.

### Final Answer:
The cellular layer that disintegrates and regenerates again and again in human skin is the **epidermis**.