![]() ![]() In general, the spermatogenic efficiency of healthy testicular parenchyma in bulls is remarkably consistent (approximately 10–12 × 10 6 spermatozoa per gram daily). The testicular parenchyma is encased in a thick, connective tissue capsule (tunica albuginea), which is, in turn, covered by a thin, serous membrane (tunica vaginalis propria). The mediastinum, an area of connective tissue extending lengthwise in mid-testis, contains blood vessels and tubules of the rete testis. The remainder consists of interstitial tissue (Leydig cells, blood and lymph vessels, and connective tissue). Within the testis, most (70% to 90% by weight) of the parenchyma is composed of seminiferous tubules (Sertoli cells and layers of germ cells). The testes are suspended within the scrotum, a feature that is important for testicular thermoregulation, as discussed subsequently. Proceedings of the 11th Technical Conference on A. Thus, the basic structure of the testis (seminiferous cords and interstitial tissues) remains much the same from early fetal life until the onset of puberty.įig. Although the basic components of a functional male gonad are present at birth, the spermatogonia do not undergo meiosis until the onset of spermatogenesis at puberty. 2 By 3 to 4 months following conception, the testes have generally passed through the inguinal canal and entered the scrotum, which is derived from the urogenital folds. In the bovine, the differentiating gonad may be identified as a testis by 41 days after conception, with testosterone production (from fetal Leydig cells) evident soon thereafter. Subsequent hormonal production induces male sexual differentiation. The latter induces the müllerian ducts to regress. ![]() The early testis produces both testosterone (T from the Leydig cells) and müllerian inhibiting substance (MIS from the Sertoli cells). SRY is activated early in embryogenesis to commit the undifferentiated genital ridge to the testicular pathway. Thus, the Y chromosome must contain the dominant inducer of testis formation the testis determining gene (TDF or SRY). The presence of a Y chromosome results in male development, regardless of the number of X chromosomes present. Subsequent sexual differentiation is decided, in mammals, by the presence or absence of the Y chromosome, with females being XX and males XY. The precursors to the male reproductive tract system (i.e., the wolffian duct system) and the female tract (the müllerian duct system) are both present. Sex determination in mammals occurs in three stages: the establishment of chromosomal sex, the development of primary sex characters (the gonads), and the subsequent development of secondary sex characteristics under the influence of gonadal hormones.ĭuring embryogenesis, the gonad first arises from the mesonephros as undifferentiated tissue, which has the capability to subsequently develop in either male or female form.
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