Porth's Essentials of Pathophysiology, 4e

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Disorders of the Male Genitourinary System

C h a p t e r 3 9

Spermatogenic cells

CHART 39-1   Main Actions of Testosterone

Lumen of seminiferous tubule

Testosterone exerts a number of biologic effects in the male (Chart 39-1). In the male embryo, it is essential for appropriate differentiation of the internal and external genitalia, and in the fetus it is necessary for descent of the testes. Testosterone is essential to the development of primary and secondary male sex characteristics dur- ing puberty and for the maintenance of these character- istics during adult life. It causes growth of pubic, chest, and facial hair; it produces changes in the larynx that result in the male bass voice; and it increases the thick- ness of the skin and the activity of the sebaceous glands, predisposing to acne. Most of the actions of testosterone and other andro- gens result from increased protein synthesis in target tissues. Androgens function as anabolic agents in males and females to promote metabolism and musculoskeletal growth. They greatly affect the development of muscle mass during puberty, with boys averaging approximately 50% more of an increase in muscle mass than girls. 1 Spermatogenesis Spermatogenesis, which occurs in the seminiferous tubules of the testes, is the sequence of events that leads to the formation of male germ cells or spermatozoa. The process begins shortly before puberty and continues throughout a man’s life. The seminiferous tubules are composed of two types of cells: Sertoli cells and spermatogenic cells 1–3 (Fig. 39-3A). Sertoli cells are tall columnar cells with extensive cyto- plasmic processes that surround the spermatogenic cells and form tight junctions with other Sertoli cells. Also known as supporting or sustentacular cells , Sertoli cells provide structural organization for the tubules; they sup- ply both physical and nutritional support for the devel- oping germ cells; and their tight junctions prevent the passage of proteins from the interstitial space into the lumen of the seminiferous tubules, thus forming a blood- testis barrier. 2,3 In addition, these cells have been shown to be responsible for the movement of spermatozoa Induces differentiation of the male genital tract during fetal development Induces development of primary and secondary sex characteristics Gonadal function External genitalia and accessory organs Male voice timbre Male skin characteristics Male hair distribution Anabolic effects Promotes protein metabolism Promotes musculoskeletal growth Influences subcutaneous fat distribution Promotes spermatogenesis (in follicle-stimulating hormone [FSH]-primed tubules) and maturation of sperm Stimulates erythropoiesis

Interstitial cells of Leydig

Sertoli cells

A

Spermatogonium

Primary spermatocyte

46

Secondary spermatocyte

23

23

Spermatids

23 23

23 23

Head Middle piece

Tail

Spermatozoa

B

FIGURE 39-3. (A) Cross-section of seminiferous tubule and (B) stages of development of spermatozoa. (46, 23 = number of chromosomes.)

from the base of the tubule toward the lumen and for the release of mature sperm into the lumen. They also phagocytose damaged germ cells and residual bodies formed during the last stage of spermatogenesis. Finally, in response to follicle-stimulating hormone (FSH) or testosterone, the Sertoli cells secrete androgen-binding protein. This substance, which has a high affinity for androgens, provides high concentrations of testosterone to the developing germ cells during spermatogenesis. Spermatogenic cells, the source of spermatozoa, are organized in poorly defined layers of progressive develop- ment between adjacent Sertoli cells. Both spermatogen- esis and oogenesis, its counterpart in the female, involve a unique kind of nuclear division in which the chromo- some number is reduced from 46 to 23 (see Chapter 5).