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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 embryo that is mammalian a vaginal ridge on either part associated with the midline in close relationship with all the transitory mesonephric kidney associated with 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 gonadal primordium comprises of a exterior cortex produced from peritoneum plus a internal medulla ( Figures 10-1 and 10-2 ). Germ cells do not arise in the gonadal primordium itself but migrate from their web web site of beginning into 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 cellular migration is evolutionarily conserved from fresh 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 the germs cells to your vaginal ridge mesoderm, and (2) a host of chemical signals associated with positioning regarding the germ cells in the gonad and coalescence associated with gonad that is developing. A few of the genes involved with managing primordial germ mobile differentiation, migration, and meiosis are listed in dining 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 way of 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, Nyc, 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 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 for instance the rete testis and the efferent ducts and vas deferens. When you look at the feminine, the medullary cords degenerate, therefore the cortical cords (orange) bring about an ovary. Some mesonephric elements remain into the female also. The vasa deferentia are retained in amphibians but fundamentally they degenerate in reptiles, wild birds, and mammals when 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 tissue morphogenic protein Induction and competence of PGCs
prdm1 and prdm14/blimp1 (mouse) PR domain zinc finger protein 1 necessary 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 of this main intercourse cords into seminiferous cords and regression regarding the cortex bring about a testis. Each testis is comprised of seminiferous tubules produced by the main sex cords. The germ cells migrate into the tubules that are seminiferous bring about spermatogonia, and in the end create sperm. The Sertoli or cells that are sustentacular sperm development. Steroidogenic interstitial cells or Leydig cells can be found between your tubules that are seminiferous. These interstitial cells arise from medullary muscle surrounding the main sex cords and be resources of androgens.

In females, the principal sex cords degenerate, and secondary sex cords differentiate through the cortical area. These additional intercourse cords get to be the ovary that is definitive. When you look at the ovary, the germ cells bring about oogonia, which quickly enter meiosis to create main oocytes. The ovaries contain follicles that comprise of 1 or higher levels of follicular cells surrounding a main oocyte.

2 Accessory Ducts

In men, the main percentage of each differentiating testis types a community of tubules, referred to as rete testis, which do not include seminiferous elements. The rete testis kinds a connection between your seminiferous tubules and a surviving part of the primitive mesonephric kidney duct called the wolffian duct, which, intoxicated by testosterone, differentiates to the vas deferens and conducts semen through the testis to your urethra. All of the mesonephric kidney in animals degenerates, except for a few of the mesonephric that is anterior tubules (see Box 10A ). Into the existence of testosterone, this muscle along with a percentage associated with the wolffian duct types two glandular structures, the epididymis together with seminal vesicle ( Figures 10-2 and 10-3 ).

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