Final answer:
The birth canal is formed by the vagina, which is an elastic muscular canal accommodating the baby during delivery, and the cervix, which dilates to allow the baby to pass through from the uterus into the vagina.
Step-by-step explanation:
The birth canal is formed by the vagina and cervix, which are integral structures of the female reproductive system responsible for facilitating childbirth. The vagina is an elastic, muscular canal, approximately 10 cm long, that serves as the entrance to the reproductive tract and exit from the uterus during childbirth, making it a critical part of the birth canal.
During delivery, the cervix also plays a vital role by dilating and allowing the baby to pass from the uterus into the vagina. The vagina's flexible walls, lined with mucous membranes known as the rugae, expand during childbirth to accommodate the baby, with the cervix opening up to 10 cm to let the baby pass through. The vagina's mucous secretions, which are produced by Bartholin's glands and lesser vestibular glands, help maintain moisture in the area.