Let’s start with the female genital organs. On the outside is the vulva which is enclosed by two pairs of lips, the outer lips, or labia majora, the inner lips or labia minora. At the top of the vulva the labia minora meet enclose the clitoris, which corresponds to the penis in the male. The clitoris plays no specific role in reproduction but is involved in the female sexual response. The urethra, or entrance to the bladder, and the vagina, or birth canal, opens into the vulva. The vagina is a tube 10 to 15 centimeters long with smooth muscle walls and a lining pink tissue called squamous epithelium. Usually the vaginal walls lie flat against each other but they are capable of great elasticity. The vagina can stretch easily to accommodate the penis during intercourse, and even more so to permit the passage of the baby in childbirth. At the top of the vagina is the cervix, or neck of the uterus. At the time of ovulation, the glands of the cervix supply the mucus that is necessary for the sperms to pass up through the cervix to fertilize the ovum. When it is in the non-pregnant state, the uterus is very small, roughly 5 centimeters wide by 8 centimeters long. During pregnancy, the cervix remains tightly closed while the rest of the uterus grows larger to accommodate the growing fetus, the amniotic sac and the amniotic fluid that surrounds the fetus. During labor, the contractions of the uterus help to open up the cervix to allow the baby to pass through the vagina. The Fallopian tubes are attached to the corners of the uterus and the ova pass down these tubes from the ovaries to the uterine cavity. The process of fertilization takes place in the Fallopian tubes, when one of the sperms penetrates the wall of an ovum.
A man’s primary sex organs are located outside his body. Two sex glands, or testes, are suspended in a protective sac of skin called the scrotum. Each testis contains hundreds of tiny tubes, or tubles, which produce the male reproductive cells, or sperms. On the side of each testis is a tube called the vas deferens, which nourishes and stores the sperm. The sperms are mixed with seminal fluid produced by the seminal vesicles and prostate gland to form the thick, whitish fluid called semen. During sexual excitement, the penis swells with blood and becomes erect, so that it can be inserted into the woman’s vagina. When the man reaches a climax, the muscles at the base of the penis contract and the semen is ejaculated.
For fertilization to occur, however, intercourse must take place near the time of ovulation, which is about halfway through the menstrual cycle (or roughly 14 days before the next period). In the course of ovulation, one o the ovaries releases a ripe egg cell. During intercourse, as many as 500 million sperms may enter the vagina. They have a different cult journey, however, and only a small percentage survive and reach an egg for fertilization, having first travelled from the vagina, into the uterus, and on the Fallopian tubes. Once the egg and sperm cell unite, other sperms cannot penetrate the fertilized egg. The fertilized egg starts to grow during the passage down the Fallopian tube, and when it reaches the uterine cavity it implants itself in the thick uterine lining and continues its development. Each month the lining of the uterus is stimulated by the ovarian hormones to prepare for the fertilized egg.
If for any reason fertilization does not occur, the ripened egg dies after about 24 hours and passes out with the uterine lining in the process known as menstruation. Sperms may live for 72 hours or even longer after ejaculation.