This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: None, Subject name: Gynaecology & Obstetrics
Ectocervix is predominantly lined by which of the following type of epithelium? 
Select and explain. 
A. Cuboidal epithelium, B. Mucin secreting columnar epithelium, C. Pseudostratified columnar epithelium, D. Nonkeratinized stratified squamous epithelium
D: Nonkeratinized stratified squamous epithelium
Answer: D: Nonkeratinized stratified squamous epithelium 
Explanation: The poion of the cervix exterior to the external os is called ectocervix. It is lined predominantly by nonkeratinized stratified squamous epithelium. The endocervical canal is covered by a single layer of mucin-secreting columnar epithelium. During pregnancy mucus produced by the endocervical epithelium becomes thick and forms a mucus plug within the endocervical canal. During pregnancy, the endocervical epithelium moves out and onto the ectocervix during enlargement of the cervix. Ref: Cunningham F.G., Leveno K.J., Bloom S.L., Hauth J.C., Rouse D.J., Spong C.Y. (2010). Chapter 2. Maternal Anatomy.