Which type of cells replace columnar cells in the transformation zone?

The transformation zone, located at the junction of the endocervical canal and the vaginal portion of the cervix, is where columnar epithelial cells are replaced by squamous epithelial cells. This change is primarily due to the process of metaplasia, where one cell type transforms into another in response to various stimuli, such as hormonal changes.

In the context of cervical health and biology, squamous cells are prevalent in the cervix, especially in the areas that are exposed to the vaginal environment. This transition from columnar to squamous cells helps protect the underlying tissues from abrasion and infection. Squamous cells are more suited to withstand the trauma of the vaginal canal and also serve as a barrier against potential pathogens.

The other options do not fit this context; for instance, cuboidal cells typically line glands and ducts, columnar cells remain present in the endocervical canal rather than replacing, and reticular cells generally play roles in the immune system and are not involved in the transformation zone of the cervix. Thus, the correct answer highlights the importance of the type of cells that provide adequate protection and resilience in the transitional area of the cervix.