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Infertility Causes > Woman > Uterus and Cervix Overview - Evaluation - Treatment Options - DiagnosisTHE CERVIX Cervical mucus is produced by a group of cells that line the inside of the cervix known as columnar cells. The cervical mucus is really quite remarkable. During the vast majority of the cycle, it is an extremely effective barrier that prevents anything from entering into the uterus. However, for a few days just prior to ovulation, it changes dramatically. As a result of stimulation by estrogen, which is produced by the cells surrounding the maturing egg, the cervical mucus becomes very clear, almost watery, and probably actually helps rather than hinders the sperm as they try to migrate through on their way to the fallopian tubes. As soon as ovulation occurs and progesterone production begins as a result thereof, the mucus again becomes thick and impenetrable. THE UTERUS The uterus is a remarkable organ. It is comprised primarily of muscle, known as myometrium. When nonpregnant, it is about the size and shape of a small pear, but during pregnancy it can expand to hold a full-term infant. After delivery, it can then contract back down to essentially its original size. The cervix is the part of the uterus that opens into the vagina, and the main part of the uterus is known as the fundus. The cavity of the uterus, which when not pregnant is very small, is lined by a group of cells called the endometrium. It is these cells that undergo the regular monthly changes as a result of the hormones produced by the ovaries. These changes either allow implantation and a pregnancy to occur, or result in a menstrual period. The diagram depicts in schematic fashion the changes that occur in the endometrium on a monthly basis. The first half of the menstrual cycle, the time from the start of the period until ovulation, is known as the proliferative phase because it is during this time that the lining of the uterus is thickening (proliferating). The part of the cycle between ovulation and the next period is known as the secretory phase because the lining is undergoing changes that will allow a pregnancy to implant should one occur. When a period occurs, this tissue is all shed and the whole cycle starts over again.
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