Primary Sexual Traits

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, uterus, and ov

1 The Gonads

The paired gonadal primordia arise through the intermediate mesoderm associated with embryo that is mammalian a vaginal ridge on either region of the midline in close relationship with all the transitory mesonephric kidney of this embryo. Many derivatives associated with the mesonephric renal and its own duct system are retained since functional portions of this adult reproductive system, even though almost all the mesonephric renal degenerates. A primordium that is gonadal of a 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 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 fundamental pattern of germ mobile migration is evolutionarily conserved from good fresh good fresh 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 involved with positioning for the germ cells inside the gonad and coalescence for the gonad that is developing. A number of the genes involved with managing primordial germ mobile differentiation, migration, and meiosis are listed in 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 by way of a basal lamina (bl = cellar membrane). (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 in to the mesoderm of this gonad that is bipotential. 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 for instance 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 stay within the female also. The vasa deferentia are retained in amphibians but fundamentally they degenerate in reptiles, wild birds, and animals when the ureters develop to strain the metanephric kidneys (not found in anamniotes).

(Adapted 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 factor 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 cellular development element receptor (SCFR); proto-oncogene c-kit Migration, entry into mesoderm
dazl Deleted in azoospermia-like Meiosis competency

Initially, the medullary component in men and women differentiates into primary intercourse cords. Differentiation associated with main intercourse cords into seminiferous cords and regression regarding the cortex end in a testis. Each testis is comprised of seminiferous tubules based on the sex that is primary. The germ cells migrate into the tubules that are seminiferous bring about spermatogonia, and finally produce sperm. The Sertoli or sustentacular cells help sperm development. Steroidogenic interstitial cells or Leydig cells can be found amongst the tubules that are seminiferous. These interstitial cells arise from medullary muscle surrounding the sex that is primary and start to become resources of androgens.

In females, the principal sex cords degenerate, and additional sex cords differentiate from the region that is cortical. These additional intercourse cords end up being the definitive ovary. Within the ovary, the germ cells bring about oogonia, which quickly enter meiosis to create main oocytes. The ovaries contain follicles that comprise of just one or higher levels of follicular cells surrounding an oocyte that is primary.

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 rete testis types 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 semen through the testis towards the urethra. A lot of the mesonephric renal in animals degenerates, apart from a few of the mesonephric that is anterior tubules (see Box 10A ). Within the existence of testosterone, this muscle as well as a percentage of this wolffian duct types two glandular structures, the epididymis additionally the seminal vesicle ( Figures 10-2 and 10-3 ).

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