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The Endocrinology of Mammalian Reproduction
David O. Norris Ph.D., James A. Carr Ph.D., in Vertebrate Endocrinology (Fifth Edition), 2013
A Embryogenesis of Gonads and Their Accessory Ducts
Main characters that are sexual the vagina, womb, and ov
1 The Gonads
The paired gonadal primordia arise through the intermediate mesoderm regarding the embryo that is mammalian a genital ridge on either region of the midline in close relationship utilizing the transitory mesonephric renal regarding the embryo. Numerous derivatives for the mesonephric kidney and its particular duct system are retained since functional portions associated with the adult reproductive system, even though the almost all the mesonephric renal degenerates. A primordium that is gonadal of an exterior cortex produced by peritoneum as well as an internal medulla ( Figures 10-1 and 10-2 ). Germ cells don’t arise inside the gonadal primordium itself but migrate from their web site of beginning within the yolk sac endoderm to either cortex (female) or medulla (male) dependant on the hereditary intercourse ( Figure 10-2 ). The fundamental pattern of germ cellular migration is evolutionarily conserved from good fresh fruit flies to people and needs a complex interplay between (1) guidance signals and extracellular matrix attachment proteins that assure directed migration associated with germs cells to your vaginal ridge mesoderm, and (2) a host of chemical signals associated with positioning associated with germ cells in the gonad and coalescence associated with gonad that is developing. A number of the genes taking part in managing germ that is primordial differentiation, migration, and meiosis are placed in dining Table 10-2.
FIGURE 10-1. Undifferentiated gonad.
Portion of gonad from 25-mm tadpole of Rana pipiens showing cortical (c) and medullary (m) cells divided by a basal lamina (bl = cellar membrane layer). (a) total gonad (upper left); (b) enlargement; (c) further enlargement showing contact between cortical and medullary cells (arrow).
(Reprinted with permission from Merchant-Larios, M., in “The Vertebrate Ovary” (R.E. Jones, Ed. ), Plenum, Nyc, 1978, pp. 47–81. )
FIGURE 10-2. Growth of testis and ovary in humans.
Primordial germ cells migrate from the hindgut to the mesoderm associated with the bipotential gonad. Into the male, the cortical muscle (orange) degenerates and also the medullary muscle develops to the testis cords, which bring about the seminiferous tubules like the Sertoli cells. Mesonephric tubules bring about the intratesticular ducts like the testis that is rete the efferent ducts and vas deferens. The medullary cords degenerate, and the cortical cords (orange) give rise to an ovary in the female. Some mesonephric elements remain when you look at the feminine too. The vasa deferentia are retained in amphibians but fundamentally they degenerate in reptiles, wild wild birds, and animals when the ureters develop to strain the metanephric kidneys (not present in anamniotes).
(adjusted with permission from Paxton, M., “Endocrinology Biological and Medical Perspectives, ” William C. Brown, Dubuque, IA, 1986. )
TABLE 10-2. Some Genes Involved in Primordial Germ Cell (PGC) Induction, Specification, Migration, and Meiosis
|bmp 2/4/8||bone protein that is morphogenic and competence of PGCs|
|prdm1 and prdm14/blimp1 (mouse)||PR domain zinc finger protein 1||needed for PGC specification|
|pou5f1||POU domain course 5, transcription element 1||PGC marker and specification|
|vasa; ddx4||DEAD box group of ATP-dependent RNA helicases||PGC marker and specification|
|nanos3||Nanos homolog 3||Migration, entry into mesoderm|
|dnd1||Dead end homolog 1||Migration, entry into mesoderm|
|kit||Mast/stem mobile development factor receptor (SCFR); proto-oncogene c-kit||Migration, entry into mesoderm|
|dazl||Deleted in azoospermia-like||Meiosis competency|
Initially, the component that is medullary men and women differentiates into primary intercourse cords.