Chapter 24. Animal Reproduction and Development
24.3. Human Reproductive Anatomy and Gametogenesis
charles-molnar and jane-gair
Learning Objectives
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. When testosterone is absent, the tissues develop into female sexual tissues. Primitive gonads become testes or ovaries. 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 Figure 24.8 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.
Which of the following statements about the male reproductive system is false?
- The vas deferens carries sperm from the testes to the penis.
- Sperm mature in seminiferous tubules in the testes.
- Both the prostate and the bulbourethral glands produce components of the semen.
- The prostate gland is located in the testes.
Sperm mature in seminiferous tubules that are coiled inside the testes, as illustrated in Figure 24.8. 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 deve