notes27 - 27. The Reproductive System This is the only...

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1 27. The Reproductive System This is the only system not required for the life of the individual. Rather, it is required for the continued existence of the species. The reproductive system in an individual produces, stores, nourishes, and transports either male or female gametes . The female reproductive system is also responsible for protecting, supporting, and nourishing a developing fetus. The reproductive system includes the following components: A. Gonads are organs that produce gametes and reproductive hormones. B. Accessory reproductive organs include (1) ducts that provide passages for transport of the gametes, (2) various glands that secrete fluids required by the reproductive system, and (3) perineal structures that are important during copulation. (Perineal structures are also referred to as the external genitalia .) I will probably not review the information in the paragraph that follows. However, you should be familiar with this information to better understand the concepts of Chapter 27. All cells in your body, except gametes, have two copies of all your genes. These cells are called somatic cells , and they may be referred to as diploid (or 2n ) to indicate the presence of two copies of the genes. Each gamete has only one copy of your genes, and gametes may be referred to as haploid (or 1n ) to indicate the presence of only a single copy of each gene. In order for a new individual to form, two 1n gametes must fuse to form a 2n zygote , a process called fertilization . The zygote then divides by mitosis to form an embryo, which may eventually grow into an adult human. Gametes are produced from 2n cells via the process of meiosis , which reduces the amount of genetic material by half (2n ÷ 1n). I. Anatomy of the Male Reproductive System The basic structures of the male reproductive system are shown in Fig. 27.1. The male gonads are the testes . The male duct system begins with the epididymis , which leads to the ductus (or vas ) deferens , the ejaculatory duct , and finally the urethra . Accessory glands include the seminal vesicles , the prostate gland , and the bulbourethral glands . Perineal structures include the scrotum and the penis . The scrotum During early development, testes form inside the body near the kidneys. Prior to birth, the testes typically descend into the scrotum. The scrotum is a sac made of a layer of skin and an underlying layer of tissue called the superficial fascia (Fig. 27.2). Bands of skeletal muscle, called the cremaster muscle , lie deep to the dermis of the scrotum. Contraction of the cremaster muscle pulls the testis close to the body wall. Contraction or relaxation allows regulation of temperature of the testes, which should be about 1ºC cooler than core body temperature for normal sperm development. Spermatic cords
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notes27 - 27. The Reproductive System This is the only...

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