Understanding spermatogenesis is a prerequisite for treatment

Abstract

Throughout spermatogenesis multiplication, maturation and differentiation of germ cells results in the formation of the male gamete. The understanding of spermatogenesis needs detailed informations about the organization of the germinal epithelium, the structure and function of different types of germ cells, endocrine and paracrine cells and mechanisms, intratesticular and extratesticular regulation of spermatogenesis. Normal germ cells must be discriminated from malformed, apoptotic and degenerating germ cells and tumor cells. Identification of the border line between normal and disturbed spermatogenesis substantiate the diagnosis of impaired male fertility. The profound knowledge of the complicate process of spermatogenesis and all cells or cell systems involved with is the prerequisite to develop concepts for therapy of male infertility or to handle germ cells in the management of assisted reproduction.

Figure 1

(A) Cross-section of the human testis. Drawing of a paraffin section. × 2.5. (B) Arrangement of the seminiferous tubules in the human testis and of the excurrent ductular system of the epididymis. Semi-schematic drawing. (C) Cross section of a seminiferous tubule of a fertile man 32 years of age. Drawing of a semithin section. × 300.

Figure 2

(A) Sector of the germinal epithelium in the seminiferous tubule. Drawing on the basis of a semithin section. × 900 (B) Sertoli cells divide the germinal epithelium in a basal and adluminal compartment. Arrows indicate the transport of substances only to the basal compartment, via the Sertoli cell into the adluminal compartment, via the Sertoli cell into the lumen.

Figure 3

(A) The storage of lipid droplets of different size and composition in the Sertoli cells correlates to the age of the man. The Sertoli cell represent a "biological clock" of the testis. (B) Seminiferous tubule with marked clones of germ cells. Drawing on the basis of a semithin section. × 300

Figure 4

(A) Section of the germinal epithelium with multilayered spermatogonia. 52 years old infertile patient with arrest of spermatogenesis at the stage of spermatogonia. Drawing on the basis of a semithin section. × 600 (B) Arrest of spermatogenesis at the stage of A pale type-spermatogonia. 37 years old infertile patient with arrest of spermatogenesis at the stage of spermatogonia. Drawing on the basis of a semithin section. × 600 (C) Tumour cells in the basal compartment of the germinal epithelium dislocate a pale type-spermatogonia. 33 years old patient. Drawing on the basis of a semithin section. × 600 (D) Megalospermatocytes do not complete meiosis. 37 years old patient with impaired fertility. Drawing on the basis of a semithin section. × 600 (E) Arrest of spermatogenesis at the stage of primary spermatocytes. 34 years old patient with impaired fertility. Drawing on the basis of a semithin section. × 600 (F) Arrest of spermatogenesis at the stage of immature spermatids. 52 years old patient with impaired fertility. Drawing on the basis of a semithin section. × 600.

Figure 5

(A) Steps of spermatid differentiation: (1) Immature spermatid with round shaped nucleus. The acrosome vesicle is attached to the nucleus, the tail anlage fails contact to the nucleus. (2) The acrosome vesicle is increazed and flattened over the nucleus. The tail contacted the nucleus. (3–8) Acrosome formation, nuclear condensation and development of tail structures take place. The mature spermatid (8) is delivered from the germinal epithelium. Semi-schematic drawing on the basis of electron micrographs. From Ref. [14]. (B) Development of a giant spermatid by confluence of double headed spermatids of a clone. The giant spermatid remains in contact with the Sertoli cell. Drawing on the basis of electron micrographs. From Ref. [9]. (C) Differentiation of acrosomeless spermatozoa. The nuclear condensation and the development of tail structures is not disturbed. The acrosome, however, fails to establish contact to the nucleus of the spermatid and remains in the Sertoli cell cytoplasm. Drawing on the basis of electron micrographs. From Ref. [9].

Figure 6

(A) Development of headless spermatozoa. Only the proximal centriole contacts the basal plate of the nucleus of the spermatid. The distal centriole is separated and develops the headless flagellum. Drawing on the basis of electron micrographs. From Ref. [9]. (B) Loss of the mitochondrial sheath during spermiogenesis. The spermatozoon is immotile. Drawing on the basis of electron micrographs. From Ref. [9]. (C) Development of malformed fagellar structures. Drawing on the basis of electron micrographs. From Ref. [9]. (D) Multiple malformations of spermatids. Drawings on the basis of electron micrographs from testicular specimen of several patients aged 43–85 years. The testes were removed by surgery as an additive treatment of prostatic cancer.

Figure 7

(A) Microvasculature of the intertubular space. Co-cells encase the capillaries, Leydig cells and the seminiferous tubule. Modified from Ref. [20]. (B) The human spermatozoon. (1) Light microscopical aspect, (2) Virtual preparation of the spermatozoon showing the acrosome, the nucleus and nuclear envelopes, the mitochondrial sheath of the main piece of the flagellum, (3–11) Cross sections of the human spermatozoon of different levels indicated in (12) longitudinal section of the human spermatozoon. Semi-schematic drawing on the basis of electron micrographs. From Ref. [14].

Figure 8

Intrinsic regulation of gametogensis. On the left a section of the germinal epithelium with basal lamina propria and below a cluster of Leydig cells surrounding a capillary are outlined. Arrows indicate different influences of secreted hormones and growth factors. On the right the main processes of spermatogenesis are correlated to regulatory processes.