Development of the Urogenital System Part 2 Flashcards

1
Q

When is the sex of an embryo determined

A
  • At the time of fertilization
  • The genetic sex of the embryo depends on whether an X or Y-bearing sperm fertilizes an X-bearing oocyte
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2
Q

Why is the initial genital period referred to as the indifferent stage of sexual development?

A
  • Because at the beginning, the early genital systems in the two sexes are similar as we cannot differentiate between a a male and a female
  • The appearance of the two gonads are indifferent up until the 7th week
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3
Q

The gonad are derived from what?

A

3 sources:
- the mesothelium, lining the posterior abdominal wall
- the underlying mesenchyme
- Primordial germ cells

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4
Q

Describe the point of indifferent gonads

A
  • There are cortexes and medullas in the gonads of both males and females
  • In embryos with an XX chromosome, the cortex differentiates to an ovary and the medulla regresses
  • In embryos with an XY chromosomes, the medulla differentiates into a testis and the cortex regresses
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5
Q

Explain the migration of the primordial germ cells

A
  • Originally, these cells are found among endodermal cells of the yolk sac in the caudal region of trilaminar disc in the 4th week.
  • Then the cells migrate along the dorsal mesentery of the hindgut to the gonadal ridges which is complete in week 6
  • The cells enter the underlying mesenchyme to incorporate into the gonadal cord
  • The migration is regulated by BMP4, stella and fragilis
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6
Q

What determines the sex of an embryo

A
  • The sex-determining region on the Y chromosome gene (SRY) expresses the testis-determining factor (TDF) that allows for testicular differentiation
  • The absence of the Y chromosome results in the formation of an ovary due to the lack of the SRY gene
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7
Q

describe the development of the testes from the indifferent gonad

A
  • In the presence of TDF
  • The gonadal cords become the seminiferous tubules by the involvement of Sox9 ad FGF9 that allow the mesonephric ducts to integrate to the gonadal ridge
  • The mesonephric ducts/tubules are incorporated into the rete testes and tubuli as they branch and fuse together
  • A thick tunica albuginea grows and no cortical cords form (meant for females)
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8
Q

What does the walls of the seminiferous tubules include

A
  • Sperm from the primordial germ cells
  • Sertoli cells from the surface mesothelium
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9
Q

Where are leydig cells found and what is their function

A
  • Leydig cells lie in between the seminiferous tubules
  • They secrete testosterone in the 8th week to influence the development of indifferent ducts and external genitalia
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10
Q

describe the development of the ovary from the indifferent gonad

A
  • In the absence of TDF
  • The gonadal cords degenerate and the cortical cords form which incorporates primordial germ cells
  • The primordial germ cells form clusters = follicular cells and oogonia that divide to produce primary oocytes
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11
Q

Explain the genetic signals between a male and a female

A
  • An embryo has the SRY and Wnt4 gene
  • In males, the SRY gene will produce Sox9 which will inhibit Wnt4
  • In females, Wnt4 will produce Dax1 (and other genes) which will inhibit Sox9
  • Sox9 will upregulate SF1 with other genes that help develop the testes
  • SF1 develops sertoli cells and leydig cells
  • Dax1, TafII and other genes help develop the ovaries
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12
Q

What is the function of Sertoli cells

A
  • Sertoli cells produce the antimullerian hormone and mullerian inhibiting factor
  • These two hormones inhibit the development of the paramesonephric (or Mullerian) duct which develops the uterine tube
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13
Q

What is the function of Leydig cells

A
  • These cells produce testosterone which acts on the mesonephric tubules/ducts to develop the epididymus, vas deferens and seminal vesicle
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14
Q

explain the development of the genital ducts

A
  • the mesonephric and paramesonephric ducts run parallel from each other and fuse on the cranial end to form the uterovaginal primordium which gives rise to the uterus
  • In males, the mesonephric ducts are developed into genital ducts and the reproductive organs when the testes releases testosterone
  • A hormone is also produced by the sertoli cells to prevent the paramesonephric ducts from developing
  • In females, because there’s no testosterone, the paramesonephric ducts develop uterine tubes and the mesonephric ducts regress
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15
Q

describe the development of external genitalia in males

A
  • The indifferent external genitalia develops in the 4th week
  • because of the presence of testosterone, the external genitalia masculinizes
  • the phallus becomes the penis
  • the urogenital folds fuse to form the urethra
  • the labioscrotal swellings fuse to form the scrotum
  • the corpora cavernous a and spongiosum develop the mesoderm for the penis
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16
Q

What does the indifferent external genitalia include

A
  • the genital tubercle → phallus
  • the labioscrotal swellings
  • The urogenital folds
17
Q

describe the development of external genitalia in females

A
  • the last of testosterone causes the phallus becomes the clitoris
  • the urogenital folds become the labia minora
  • the labioscrotal swellings becomes the labia majora