CHAPTER 28LECTURE OUTLINEI. INTRODUCTIONA. Sexual reproduction is a process in which organisms produce offspring by means of germ cells called gametes. B. The organs of reproduction are grouped as gonads (produce gametes and secrete hormones), ducts (transport, receive, and store gametes), and accessory sex glands (produce materials thatsupport gametes).C. Gynecology is the specialized branch of medicine concerned with the diagnosis and treatmentof diseases of the female reproductive system. Urology is the study of the urinary system but also includes diagnosis and treatment of diseases and disorders of the male reproductive system. Andrology is the study of only male reproductive diseases.II. MALE REPRODUCTIVE SYSTEMA. The male structures of reproduction include the testes, a system of ducts (ductus epididymis, ductus deferens, ejaculatory duct, urethra), accessory sex glands (seminal vesicles, prostate gland, bulbourethral glands), and several supporting structures, including the penis (Figure 28.1).B. Scrotum1. The scrotum is a cutaneous outpouching of the abdomen that supports the testes; internally, a vertical septum divides it into two sacs, each containing a single testis (Figures 28.2).2. The reproduction and survival of spermatozoa require a temperature that is lower than normal core body temperature. The temperature of the testes is regulated by the cremaster muscle, which elevates them and brings them closer to the pelvic cavity or relaxes, causing the testes to move farther from the pelvic cavity.C. Testes1. The testes, or testicles, are paired oval-shaped glands (gonads) in the scrotum (Figure28.3).2. The testes develop high on the embryo’s posterior abdominal wall and usually begin their descent into the scrotum through the inguinal canals during the latter half of the seventh month of fetal development.3. The testes contain seminiferous tubules (in which sperm cells are made) (figure 28.4).4. Embedded among the spermatogenic cells in the tubules are large Sertoli cells or sustentacular cells (Figure 28.4).a. The tight junctions of these cells form the blood-testis barrier that prevents an immune response against the surface antigens on the spermatogenic cells.b. The sustentacular cells also nourish spermatocytes, spermatids, and spermatozoa; mediate the effects of testosterone and follicle stimulating hormone on spermatogenesis; phagocytose excess spermatids cytoplasm as development proceeds; control movements of spermatogenic cells and the release of spermatozoa into the lumen of the seminiferous tubule; and secretefluid for sperm transport and the hormone inhibin.c. The Leydig cells or interstitial endocrinocytes found in the spaces between adjacent seminiferous tubules secrete testosterone (Figure 28.4).5. Failure of the testes to descend is called cryptorchidism, involving one or both testes.(Clinical Connection)6. Spermatogenesis is the process by which the seminiferous tubules of the testes produce haploid sperm.a. It begins in the diploid spermatogia (stem cells). They undergo mitosis to reserve future stem cells and to develop cells (2n primary spermatocytes) for sperm production (Figure 28.5).b. The diploid primary spermatocytes undergo meiosis I forming haploid secondary spermatocytes.c. Meiosis II results in the formation of the haploid spermatids. The spermatids are connected by cytoplasmic bridges.d. The final stage of spermatogenesis is spermiogenesis which is the maturationof the spermatids into sperm.e. The release of a sperm from its connection to a Sertoli cell is known as spermiation.7. Sperma. Mature sperm consist of a head, midpiece, and tail (Figure 28.6). They are produced at the rate of about 300 million per day and, once ejaculated, have alife expectancy of 48 hours within the female reproductive tract. Their function is to fertilize a secondary oocyte.D. Hormonal Control of the testes1. At puberty, gonadotropin releasing hormone stimulates anterior pituitary secretion offollicle-stimulating hormone (FSH) and luteinizing hormone (LH). FHS initiates spermatogenesis, and LH assists spermatogenesis and stimulates production of testosterone. Figure 28.7 summarizes the hormonal relationships of the hypothalamus, pituitary gland, and testes.2. Testosterone controls the growth, development, functioning, and maintenance of sex organs; stimulates bone growth, protein anabolism, and sperm maturation; and stimulates development of male secondary sex characteristics. Negative feedback systems regulate testosterone production (Figure 28.8).3. Inhibin is produced by sustentacular (Sertoli) cells. Inhibition of FSH by inhibin helps to regulate the rate of spermatogenesis.III. Reproductive System Ducts in MalesA. The duct system of the testes includes the seminiferous tubules, straight tubules, and rete testis.B. Epididymis1. The epididymis is a comma-shaped organ that lies along the posterior border of the testis (Figure 28.3).2. Sperm are transported out of the testes through the efferent ducts in the epididymis which empty into a single tube called the ductus epididymis.3. The ductus epididymis is lined by stereocilia and is the site of sperm maturation and storage; sperm may remain in storage here for at least a month, after which they are either expelled or degenerated and reabsorbed.C. Ductus Deferens1. The ductus (vas) deferens, or seminal duct, stores sperm and propels them toward theurethra during ejaculation (Figures 28.3 and 28.9).D. Spermatic cord1. The spermatic cord is a supporting structure of the male reproductive system, consisting of the ductus deferens, the testicular artery, autonomic nerves, veins that drain the testes, lymphatic vessels, and the cremaster muscle (Figure 28.2).2. The principle method of sterilization of males is a vasectomy in which both ductus deferens are cut and tied. .This results in no sperm entering the ejaculate(Clinical Connection)E. Ejaculatory ducts1. The ejaculatory ducts are formed by the union of the ducts from the seminal vesicles and ducti deferens; their function is to eject spermatozoa into the prostatic urethra (Figure 28.9).F. Urethra1. The male urethra is the shared terminal duct of the reproductive and urinary systems which serves as a passageway for semen and urine. The male urethra is subdivided into three portions: prostatic, membranous, and spongy (cavernous) (Figures 28.1).G. Accessory Sex Glands1. The seminal vesicles secrete an alkaline, viscous fluid that contains fructose,