Sperm (and the Male Reproductive System)

The male reproductive system consists of three main components:

1. Testicles
2. Epididymis
3. Vas Deferens

1. Testicles (Testes)

   The testicles are paired organs, approximately 1½–2 inches long, located within the scrotum (a multi-layered muscular structure that protects the testes and helps with temperature regulation). The testicles have two very important functions that are essential for normal male fertility:

   1. The production of testosterone and
   2. The production of sperm.

   Sperm only start their development in the testes. From there, they move on to the epididymis, where they mature and are stored.

2. Epididymis

   The epididymis is the long, narrow tube coiled and contained beneath a fibrous sheath. Uncoiled, the epididymis would be approximately 19 feet long. The epididymis sits behind the testis. It is divided into head, body and tail regions. Here, sperm undergo their final development and maturation, and they are stored until they are ejaculated. From the epididymis, sperm proceed into the vas deferens, also known as the spermatic cord.

3. Vas Deferens

   The vas deferens is also a long, tube-like structure that connects the epididymis (where the sperm is stored) to the urethra (the tube that expels sperm). Although the urethra also expels urine, a valve that controls the flow of sperm versus urine. During ejaculation, the sperm flows out of the testicles, through the vas deferens and into the urethra. Seminal fluid is added by the prostate and other glands as the sperm flow outside the body through the penis.

Normal Male Reproduction

The production of sperm is a very complicated process that begins at puberty and lasts, in healthy males, until death. The production of sperm begins in the testicles and is controlled by several hormones. These hormones are regulated by the hypothalamus and the pituitary gland located in the brain.

The hypothalamus regulates the hormonal activity of the pituitary gland by secreting gonadotropin-releasing hormone (GnRH). This hormone controls the production of the gonadotropins, follicle-stimulating hormone (FSH), and luteinizing hormone (LH) from the pituitary. LH triggers the production of testosterone (a hormone needed for sperm production). FSH also triggers hormones that help with sperm production.

From beginning to end, sperm production takes about 72 days. Sperm spend their first 50 days in the testicles and the last 22 to 24 days in the epididymis. It is in the epididymis that sperm mature and gain motility (the ability to swim). During sexual activity, motile sperm are ejaculated into the female reproductive tract and begin their journey through the cervix and uterus to the fallopian tubes, the site of fertilization. There are many pockets (crypts), folds or ‘wrong turns’ along the way that can prevent many of the sperm from reaching their final destination. This is why so many sperm are needed for the fertilization process.