Each month, with the menstrual cycle every woman goes through hormonal changes. The pituitary gland (located in the brain) releases hormones such as follicle stimulating hormone (FSH) and luteinizing hormone (LH). The FSH stimulates a follicle in the ovaries, which then grows and secretes estrogen. The estrogen levels continue increasing and lead to the thickening of the uterine lining (mucosa). The mucosa thickens and fills with blood vessels in preparation for implantation of an embryo. After the mucosa develops, a surge of LH causes ovulation, which is the release of an egg from the ovary into the fallopian tube.
During sexual reproduction, the sperm of the male enters the vagina, passes through the cervix and uterus, and goes to the fallopian tube where it merges with the egg that was released in ovulation. Once the sperm has merges with the egg, the head of the sperm detaches from the tail. The tail will gradually disappear and the head is left with the egg. The head merges genetic information with the egg creating an embryo, which then begins to grow. Note that even in normal fertilization the egg is fertilized and begins growing in the fallopian tube (Pregnancy, 3/10/05).
Once fertilized, the egg moves from the fallopian tube to the uterus. During this movement, which generally takes about 72 hours, secretions from the uterine lining nourish the egg. Once the egg reaches the uterus it implants itself into the uterine mucosa where it will be nourished and grow for the next 9 months.
In the case that the egg never leaves the fallopian tube, or implants in the wrong place such as the ovary, cervix or abdomen, it is considered to be an ectopic pregnancy. The most common place for an ectopic pregnancy is the fallopian tube, occurring 92% of the time. Other locations ectopic pregnancies occur are; on the ovary, on the cervix, and even free floating in the abdomen attached to intestines! However, pregnancies that develop in these locations are very uncommon.
There are many reasons for the egg to get stuck in the fallopian tube. One reason the egg might get stuck is because of scarring due to sexually transmitted diseases (STDs) such as Chlamydia and gonorrhea, known as pelvic inflammatory diseases (PIDs). This scarring is caused when bacteria such as Chlamydia and gonorrhea invade the walls of the tube. White blood cells are produced to destroy the bacteria. During this process inflammation can occur which can cause scar tissue to form and close off the fallopian tube. It can also be due to scars from other, non-pelvic, infections such as a ruptured appendix. These infections cause scarring or blockage of the fallopian tube. This inflammation of the tube is called salpingitis (Mattingly, pg. 367). Other causes of salpingitis include infection after the voluntary termination of pregnancy (abortion) and infection after childbirth, especially with abdominal deliveries (Cesarean Sections).
Some women develop tumors of the uterus, known as benign fibroids. These fibroids can not only cause heavy bleeding during menstrual periods, but also can also distort or constrict the fallopian tube, leading to tubal pregnancy. Fibroids are large muscle growths. Because the uterus is so close to the fallopian tubes even small growths on the uterus can push against the tube, changing its form. Some fibroids grow as big as ten to fifteen centimeters (as large as...