The lower tapering third of the uterus (womb). Its lower, blunt part projects into the vagina; its upper part communicates with the body of the uterus through a slight constriction (the isthmus). The vaginal part is firm in the non-pregnant uterus, and relatively soft in the pregnant uterus. A small opening at the lower end of the cervix (the external os) allows communication between the uterine cavity and the vagina.
The cervix (from Latin "neck") is the lower, narrow portion of the uterus where it joins with the top end of the vagina. It is occasionally called "cervix uteri", or "neck of the uterus".
Anatomy
Ectocervix
The portion projecting into the vagina is referred to as the portio vaginalis or ectocervix.
External Os
The ectocervix's opening is called the external os.
Endocervical canal
The passageway between the external os and the uterine cavity is referred to as the endocervical canal.
Internal Os
The endocervical canal terminates at the internal os which is the opening of the cervix inside the uterine cavity.
Cervical crypts
There are pockets in the lining of the cervix known as cervical crypts. They function to produce cervical fluid.
Cervical mucus
After menstruation ends, the external os is blocked by a thick acidic mucus that prevents infection. The mucus thins and its pH increases several days prior to ovulation, allowing spermatazoa to pass through the cervix to the fallopian tubes where they wait for an ovum to be released. Although most oral contraceptives work primarily by preventing ovulation, their effectiveness is increased because they prevent the cervical mucus from thinning, therefore blocking spermatazoa from entering the female reproductive tract. During pregnancy the cervix is completely blocked by a special antibacterial mucosal plug which prevents infection, somewhat similar to its state during the infertile portion of the menstrual cycle. The mucus plug comes out as the cervix dilates in labor or shortly before.
Cervical position
After menstruation and directly under the influence of estrogen, the cervix undergoes a series of changes in position and texture. However, as a woman approaches ovulation, the cervix becomes soft and mushy, and rises and opens in response to the high levels of estrogen present at ovulation.
Functionality
During menstruation the cervix stretches open slightly to allow the endometrium to be shed.
During childbirth, contractions of the uterus will dilate the cervix up to 10 cm in diameter to allow the child to pass through.
During orgasm, the cervix convulses and the external os dilates.
Cervical cancer
In humans the cervix is associated with cervical cancer, a particular form of cancer which is detectable by cytological study of epithelial cells removed from the cervix in a process known as the pap smear.
Lymphatic drainage
The lymphatic drainage of the cervix is along the uterine arteries and cardinal ligaments to the parametrial, external iliac vein, internal iliac vein, and obturator and presacral lymph nodes.
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