The following types of cells are constantly replaced by new cells formed as a result of mitosis

Options

A. Upper layer of the epidermis
B. Cells of the lining of the gut
C. Blood cells
D. All

Answer

To answer the question regarding the types of cells that are constantly replaced by new cells formed as a result of mitosis, we can analyze the different options provided.

### Step-by-Step Solution:

1. **Understanding Mitosis**: Mitosis is a type of cell division that results in two daughter cells that are genetically identical to the parent cell. It plays a crucial role in growth, tissue repair, and cellular replacement.

2. **Identifying Cell Types**:
- **Upper Layer of the Epidermis**: The epidermis is the outermost layer of skin. Cells in this layer are constantly being shed and replaced through mitosis. Therefore, this type of cell is indeed replaced by new cells formed through mitosis.

- **Cells of the Lining of the Gut**: The lining of the gut is also subject to wear and tear due to the digestive process. Cells in this lining are regularly replaced through mitosis to maintain a healthy gut lining. Thus, this type of cell is also replaced by new cells formed through mitosis.

- **Blood Cells**: Blood cells, including red blood cells (RBCs), are produced in the bone marrow and have a limited lifespan. They are continuously replaced through a process that involves mitosis in precursor cells in the bone marrow. Hence, blood cells are also replaced by new cells formed through mitosis.

3. **Conclusion**: All the mentioned types of cells (upper layer of the epidermis, cells of the lining of the gut, and blood cells) are constantly replaced by new cells formed as a result of mitosis.

### Final Answer:
The types of cells that are constantly replaced by new cells formed as a result of mitosis are:
- Upper layer of the epidermis
- Cells of the lining of the gut
- Blood cells