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By the end of this section, you will be able to:
  • Describe human male and female reproductive anatomies
  • Discuss the human sexual response
  • Describe spermatogenesis and oogenesis and discuss their differences and similarities

As animals became more complex, specific organs and organ systems developed to support specific functions for the organism. The reproductive structures that evolved in land animals allow males and females to mate, fertilize internally, and support the growth and development of offspring.

Human reproductive anatomy

The reproductive tissues of male and female humans develop similarly in utero until a low level of the hormone testosterone is released from male gonads. Testosterone causes the undeveloped tissues to differentiate into male sexual organs. When testosterone is absent, the tissues develop into female sexual tissues. Primitive gonads become testes or ovaries. Tissues that produce a penis in males produce a clitoris in females. The tissue that will become the scrotum in a male becomes the labia in a female; that is, they are homologous structures.

Male reproductive anatomy

In the male reproductive system, the scrotum    houses the testicles or testes (singular: testis), including providing passage for blood vessels, nerves, and muscles related to testicular function. The testes    are a pair of male reproductive organs that produce sperm and some reproductive hormones. Each testis is approximately 2.5 by 3.8 cm (1.5 by 1 in) in size and divided into wedge-shaped lobules by connective tissue called septa. Coiled in each wedge are seminiferous tubules that produce sperm.

Sperm are immobile at body temperature; therefore, the scrotum and penis are external to the body, as illustrated in [link] so that a proper temperature is maintained for motility. In land mammals, the pair of testes must be suspended outside the body at about 2 ° C lower than body temperature to produce viable sperm. Infertility can occur in land mammals when the testes do not descend through the abdominal cavity during fetal development.

Art connection

Illustration shows a cross section of the penis and testes. The penis widens at the end, into the glans, which is surrounded by the foreskin. The urethra is an opening that runs through the middle of the penis to the bladder. The tissue surrounding the urethra is the Corpus spongiosum, and above the Corpus spongiosum is the Corpus cavernosum. The testes, located immediately behind the penis, are covered by the scrotum. Seminiferous tubules are located in the testes. The epididymis partly surrounds the sac containing the seminiferous tubules. The Vas deferens is a tube connecting the seminiferous tubules to the ejaculatory duct, which begins in the prostate gland. The prostate gland is located behind and below the bladder. The seminal vesicle, located above the prostate, also connects to the seminal vesicle. The bulbourethral gland connects to the ejaculatory duct where the ejaculatory duct enters the penis.
The reproductive structures of the human male are shown.

Which of the following statements about the male reproductive system is false?

  1. The vas deferens carries sperm from the testes to the penis.
  2. Sperm mature in seminiferous tubules in the testes.
  3. Both the prostate and the bulbourethral glands produce components of the semen.
  4. The prostate gland is located in the testes.

Sperm mature in seminiferous tubules that are coiled inside the testes, as illustrated in [link] . The walls of the seminiferous tubules are made up of the developing sperm cells, with the least developed sperm at the periphery of the tubule and the fully developed sperm in the lumen. The sperm cells are mixed with “nursemaid” cells called Sertoli cells which protect the germ cells and promote their development. Other cells mixed in the wall of the tubules are the interstitial cells of Leydig. These cells produce high levels of testosterone once the male reaches adolescence.

When the sperm have developed flagella and are nearly mature, they leave the testicles and enter the epididymis, shown in [link] . This structure resembles a comma and lies along the top and posterior portion of the testes; it is the site of sperm maturation. The sperm leave the epididymis and enter the vas deferens (or ductus deferens), which carries the sperm, behind the bladder, and forms the ejaculatory duct with the duct from the seminal vesicles. During a vasectomy, a section of the vas deferens is removed, preventing sperm from being passed out of the body during ejaculation and preventing fertilization.

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Source:  OpenStax, University of georgia biology. OpenStax CNX. Dec 09, 2013 Download for free at https://legacy.cnx.org/content/col11585/1.6
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