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Structure and Function of the Male Reproductive System

The male reproductive system is composed of the primary sex organs, the testes,  and a variety of accessory organs that function in the transportation and maintenance of sperm cells (see Figure 18.1). The testes play the major role in production of functional sperm cells, and also secrete the major male sex hormone, testosterone. We will first examine the testes, and then consider the contributions of the accessory organs.

The Reproductive System

A testis (internal view)


differentiate into primary spermatocytes, each of which undergoes meiosis (refer to the part on meiosis later in this chapter) to produce four haploid spermatids (immature sperm cells). Other cells located in the tubules, the Sertoli cells, function to nourish the developing sperm cells during this time. It is interesting to note that sperm production begins during adolescence, and continues throughout a male’s entire life! Spermatids begin to mature while still in the testis, and the process continues as they move to the epididymis.
  • Epididymis: The epididymis is a coiled tube that lies just above each testis. Here sperm complete their differentiation, acquiring a distinctive shape and the ability to move. A mature sperm cell consists of a head, which contains the nucleus with the chromosomes; the body, which harbors mitochondria for energy production; and a tail, which allows the sperm to “swim”.
  • Vas deferens: Each epididymis is connected to a tube called the vas deferens (plural: vasa deferentia), in which many sperm are stored and transported. The vasa deferentia enter the abdominal cavity where they merge and join the duct of the seminal vesicles. The seminal vesicles secrete a viscous fluid containing fructose (an energy source for the sperm) and hormones that will stimulate the female system when the sperm are deposited. The sperm then travel through the prostate gland, which secretes an alkaline fluid into the semen  to enhance sperm motility. Ultimately, the sperm enter the urethra. The sperm, immersed in semen, exit the body through the urethra, a tube which runs the length of the penis, the male organ of sexual intercourse. (Recall that urine also exits the body through the urethra; in males, the reproductive and urinary systems are intimately connected. Special precautions exist that prevent the conduction of both semen and urine at the same time.)

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