Primary Sexual Traits

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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 ducts that are accessory

Main characters that are sexual the vagina, womb, and ov

1 The Gonads

The paired gonadal primordia arise through the intermediate mesoderm for the mammalian embryo as a vaginal ridge on either region of the midline in close relationship aided by the transitory mesonephric renal for the embryo. Numerous derivatives associated with mesonephric renal and its own duct system are retained since functional portions for the adult reproductive christian connection system, even though almost all the mesonephric renal degenerates. A gonadal primordium comprises of an exterior cortex produced from peritoneum as well as a inner medulla ( Figures 10-1 and 10-2 ). Germ cells do not arise in the gonadal primordium itself but migrate from their web site of beginning within the yolk sac endoderm to either cortex (female) or medulla (male) based upon the sex that is genetic Figure 10-2 ). The essential 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 for the germs cells into the vaginal ridge mesoderm, and (2) a host of chemical signals involved with positioning for the germ cells in the gonad and coalescence for the developing gonad. A few of the genes involved with managing primordial germ mobile differentiation, migration, and meiosis are placed in dining dining Table 10-2.

FIGURE 10-1. Undifferentiated gonad.

Part of gonad from 25-mm tadpole of Rana pipiens showing cortical (c) and medullary (m) cells divided with a basal lamina (bl = cellar membrane layer). (a) total gonad (upper left); (b) enhancement; (c) further enlargement showing contact between cortical and medullary cells (arrow).

(Reprinted with authorization from Merchant-Larios, M., in “The Vertebrate Ovary” (R.E. Jones, Ed. ), Plenum, Ny, 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 bipotential gonad. The cortical tissue (orange) degenerates and the medullary tissue develops into the testis cords, which give rise to the seminiferous tubules including the Sertoli cells in the male. Mesonephric tubules bring about the intratesticular ducts including the rete testis and 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 stay within the feminine also. The vasa deferentia are retained in amphibians but fundamentally they degenerate in reptiles, wild wild birds, and animals where the ureters develop to strain the metanephric kidneys (not present in anamniotes).

(adjusted with authorization 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

Gene Name Role
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 category 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. Differentiation for the main intercourse cords into seminiferous cords and regression associated with cortex lead to a testis. Each testis is made of seminiferous tubules produced from the sex that is primary. The germ cells migrate into the seminiferous tubules, give rise to spermatogonia, and finally produce semen. The Sertoli or cells that are sustentacular sperm development. Steroidogenic interstitial cells or Leydig cells can be found between the tubules that are seminiferous. These interstitial cells arise from medullary muscle surrounding the main intercourse cords and start to become resources of androgens.

In females, the main sex cords degenerate, and additional sex cords differentiate through the region that is cortical. These additional intercourse cords get to be the ovary that is definitive. The germ cells give rise to oogonia, which soon enter meiosis to form primary oocytes in the ovary. The ovaries have follicles that comprise of just one or maybe more levels of follicular cells surrounding a main oocyte.

2 Accessory Ducts

A network of tubules, known as the rete testis, that do not contain seminiferous elements in males, the central portion of each differentiating testis forms. The testis that is rete a connection amongst the seminiferous tubules and a surviving part of the ancient mesonephric renal duct called the wolffian duct, which, intoxicated by testosterone, differentiates to the vas deferens and conducts sperm through the testis to your urethra. The majority of the mesonephric renal in animals degenerates, apart from a few of the mesonephric that is anterior tubules (see Box 10A ). This tissue together with a portion of the wolffian duct forms two glandular structures, the epididymis and the seminal vesicle ( Figures 10-2 and 10-3 ) in the presence of testosterone.