Final answer:
The distal aspect of the uterus extending to the vagina is the cervix, which is about 2.5 cm long and contains a canal connecting the uterus with the vagina.
Step-by-step explanation:
The distal aspect of the uterus extending to the vagina is the cervix. The cervix is also known as the neck of the uterus, and it protrudes downward into the vagina. This region includes a canal that connects the uterine cavity with the lumen of the vagina, allowing for the passage of semen into the uterus as well as the birth of a baby from the uterus during childbirth. The cervix also secretes mucus that changes in consistency during the menstrual cycle, which can either act as a barrier against microorganisms or as a medium to facilitate the entry of sperm around ovulation.
The vagina is a muscular canal about 10 cm long, serving as both the entrance to the reproductive tract and the exit from the uterus during menses and childbirth. The vagina meets the protruding uterine cervix at the superior portion called the fornix, and its walls are composed of an outer fibrous layer, a middle layer of smooth muscle, and an inner mucous membrane with transverse folds known as rugae.