Cervix

The cervix is the lower third portion of the uterus which forms the neck of the uterus that opens into the Vagina . The narrow opening is called the os. The os allows menstrual blood to flow out, and widens during labor to allow the passage of the fetus through the vagina during childbirth. Is is covered by the epithelium which is made of a thin layer of cells. The cells of the epithium are either squamous or columnar. Squamous cells are flat and scaly, while columnar cells appear column-like.
Ectocervix : The portion projecting into the Vagina is referred to as the portio vaginalis or ectocervix. On average, the ectocervix is 3 cm long and 2.5 cm wide. It has a convex, elliptical surface and is divided into anterior and posterior lips.
External os The ectocervix's opening is called the external os. The size and shape of the external os and the ectocervix varies widely with age, hormonal state, and whether the woman has had a vaginal birth. In women who have not had a vaginal birth the external os appears as a small, circular opening. In women who have had a vaginal birth, the ectocervix appears bulkier and the external os appears wider, more slit-like and gaping Endocervical canal The passageway between the external os and the uterine cavity is referred to as the endocervical canal. It varies widely in length and width, along with the cervix overall. Flattened anterior to posterior, the endocervical canal measures 7 to 8 mm at its widest in reproductive-aged women.
Internal os The endocervical canal terminates at the internal os which is the opening of it inside the uterine cavity. Cervical crypts There are pockets in the lining known as cervical crypts. They function to produce cervical fluid.

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