The internal reproductive anatomy in the female body includes a few different organs. It is important to understand the different parts of the reproductive system and how they relate to each other. The outermost part of the internal reproductive system is the vagina. This is the only organ of the reproductive system which one can access without special instruments, usually only available to a doctor. At the top of the vagina lies the uterus. The uterus is divided into two parts: the cervix which is a passageway between 2.5 and 4 cm long that connects the vagina to the uterus, and the main part of the uterus, called the corpus. The uterus is a hollow organ which can expand during pregnancy to hold a baby. A channel through the cervix allows for sperm to enter the uterus, and menstrual blood to exit.
At the top of the uterus are two fallopian tubes. These tubes connect the uterus to the ovaries, where the eggs are housed. The ovaries contain follicles of eggs, and hormones to regulate the reproductive cycles. Conception generally occurs in the fallopian tubes, and the fertilized egg then travels through the fallopian tubes to the uterus where they implant in the wall of the uterus.
A typical menstrual cycle is as follows. With the onset of a period, follicle stimulating hormones are released from the brain that stimulate a number of eggs in the ovaries to start growing. This hormone also triggers a rise in estrogen. As the estrogen level rises, it sends a message to turn of the follicle stimulating hormones coming from the brain, to limit the number of eggs which will grow, thus conserving eggs for future cycles and pregnancies.
After a few days, one follicle in one ovary becomes dominant, and suppresses all the other follicles that are actively growing eggs. The dominant follicle continues maturing, and producing estrogen. Toward the end of this part of the cycle, the uterine lining begins building up in preparation for a pregnancy.
After about 14 days, the ovulation stage begins. This is the midpoint of the menstrual cycle. During this stage the following occurs. The rise in estrogen from the maturing follicle triggers the brain to release more hormones, which in turn cause the follicle to release the now-mature egg. The egg falls into the fallopian tubes. During this time, the woman’s body increases both the amount and thickness of mucus produced by the cervix. This serves to capture sperm, and move it toward the egg for fertilization.
The next stage of the menstrual cycle is called the luteal stage. During this time a fertilized egg has the chance to pass out of the fallopian tubes and implant in the uterus. If the egg was not fertilized, it passes through the uterus, and out of the body. No longer needed to support a pregnancy, the uterine lining breaks down and sheds as a period, and the cycle begins anew.