The preceding paragraphs have described the manner in which sperm are produced. Now look at the entire pathway a sperm must travel to fertilize an ovum.

a. With each ejaculation, the testes release up to 400 million sperm. The goal is for one sperm cell to meet and fertilize one ovum.

b. When a male ejaculates, sperm are ejected from the pocket of the testes through a series of ducts (the epididymis ducts, the ductus deferens, and the ejaculatory ducts).

c. Seminal fluid, pouring into the ducts from the prostate gland and the bulbourethral glands, flushes the sperm through the urethra and out of the tip of the penis.

d. Before fertilization can take place, the sperm must be deposited in the vaginal vault, pass through the tiny opening of the cervix, swim through the uterus, and reach the fallopian tubes.

Editor’s Note: While sperm are capable of swimming short (microscopic) distances, this is no longer believed to be the primary mechanism by which sperm reach the egg. The uterus has rhythmic contractions around the time of ovulation which propel sperm from the cervix up through the uterine cavity and out into the fallopian tube. The swimming action of sperm is still thought to play a role, but only at the very end of the process, when the sperm are within microscopic distances of the egg.

(1) Only the strongest sperm cells survive. Most sperm are destroyed immediately by the acidic fluids that cleanse the vagina. Only a few thousand sperm reach the cervix, and fewer still reach the fallopian tubes.

(2) Normally, the cervix is blocked by a hard wall of mucus which prevents bacteria from entering the uterus. For a few days each month (near the time of ovulation), this thick cervical mucus changes into a fluid stream that sperm can penetrate.

(3) Those sperm that pass through the cervix have about 48 hours in which to reach and fertilize an ovum before they (the sperm) die. Sperm cells can travel this distance in a few minutes.

e. The difficulty of this journey helps ensure that only the most healthy sperm cells reach the fertilization point. Sometimes a poor quality sperm and ovum do unite. Most of these fertilized ova stop developing and are lost spontaneously. The woman losing such an ovum does not even realize that she has been pregnant.

NOTE: Erection of the penis and ejaculation of semen are necessary for the placement of sperm in the female reproductive tract. Semen, also called seminal fluid, is a mixture of sperm and secretions from the seminal vesicle, the prostate gland, and the bulbourethral glands.