30. Development of the Genital System Flashcards

1
Q

What is the general timeline for development of the genital system?

A

Weeks 1-6 = indifferent embryos

Week 7 = sexual differentiation begins

Week 12 = female and male genitalia can be recognized

Week 20 = phenotypic differentiation complete

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2
Q

Primordial germ cells within the indifferent gonad are thought to arise from _____ cells that end up in the yolk sac wall after gastrulation and body wall folding. They migrate up the _____ ____ to enter the genital ridge around week ____

A

Epiblast; dorsal mesentery; 5

[they are NOT of endodermal origin]

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3
Q

Around week 6 the primordial germ cells in the indifferent gonad complete their migration to the genital ridge. There are somatic support cells there, which differentiate into _____ cells in males, or ______ cells in females

A

Sertoli; follicle

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4
Q

What are the 2 genital ducts that develop around week 6-7 of development?

A

Mesonephric ducts (Wolffian)

Paramesonephric ducts (Mullerian)

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5
Q

Both mesonephric and paramesonephric ducts form in _____ _____ of the urogenital ridge

A

Intermediate mesoderm

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6
Q

Fate of mesonephric ducts in males vs. females

A

Males: epididymis, vas deferens, seminal vesicle, ejaculatory duct

Females: degenerates

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7
Q

Fate of paramesonephric ducts in males vs. females

A

Males: degenerates (appendix of testis, prostatic utricle)

Females: Fallopian tube (oviduct), uterus, upper vagina

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8
Q

Sexual dimorphism is dependent on the ____ chromosome but also autosomes

The ____ gene is the sex-determining region on the above chromosome, it determines gonad type, which determines duct and genitalia development

A

Y; SRY

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9
Q

In the absence of SRY gene, development is ________. There are also other genes that positively drive this development

A

Female

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10
Q

The SRY gene is also called _______; it is present on the Y chromosome and is active from 41-52 days. It s expressed in _______ cells and upregulates testis specific genes.

A

TDF (testis determining factor); somatic support (pre-sertoli)

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11
Q

______ cells surround primordial germ cells in males to organize seminiferous tubules. A subset of intertubular cells differentiate into ________ cells, which are recruited by the cell type mentioned above

A

Sertoli; fetal Leydig

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12
Q

Sertoli cells express SRY gene, which gives off _______ signal and ________ hormone leading to the regression of _____ ducts between weeks 8-10

A

Sox9; Anti-Mullerian (aka Mullerian Inhibitory Substance); Mullerian/paramesonephric

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13
Q

Although the mullerian ducts regress between weeks 8-10 in males, they leave behind what 2 small tissue remnants?

A

Appendix testis

Prostatic utricle

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14
Q

Leydig-derived testosterone drives the mesonephric tubules and ducts to form what 4 major structures in males?

A

Efferent ductules
Epididymis
Vas deferens
Seminal vesicles

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15
Q

Full degeneration of paramesonephric ducts in males is typically complete by what week of development?

A

Week 9

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16
Q

What 2 hormones are secreted by sertoli cells driving male differentiation?

A

AMH —> regression of paramesonephric ducts

Androgen binding factor (binds its receptor on sertoli cells at puberty) —> spermatogonia differentiate into spermatozoa

17
Q

There are 2 populations of Leydig cells — fetal and adult. The fetal leydig cells are important for male differentiation. They secrete ______ at weeks 8-12, driven by ____ of the placenta, leading to differentiation of the mesonephric duct into the ductus deferens, epididymis, and seminal vesicles. They also secrete _________, which changes testosterone to DHT

A

Testosterone; HCG; 5-alpha-reductase

18
Q

DHT is required for:

_________ development into the penis

________ development into the scrotum

_______ development into the prostate

A

Genital tubercle

Genital swellings

Urethral epithelium

19
Q

What hormones are secreted by adult Leydig cells that encourage male differentiation?

A

Androgens — lead to initiation of spermatogenesis, masculinization of brain, male sexual behavior

20
Q

When do fetal leydig cells regress?

A

Fetal or early post-natal life

21
Q

The seminal vesicle buds from the ______ duct, which is composed of _______ of the urogenital ridge

A

Mesonephric; intermediate mesoderm

22
Q

The prostate gland buds from the ______ of the urogenital sinus in the region of the pelvic urethra; this occurs around week ____

A

Endoderm; 10

23
Q

The bulbourethral glands also develop as ______ buds

A

Endodermal

24
Q

The fetus begins with indifferent genitalia, including a ______ ____ which is a remnant of the ruptured cloacal membrane — opening a phallic portion of the urogenital sinus to the exterior, forming an ________-lined plate.

The _______ ____ consists of the remnants of cloacal membrane at the ventral end of the urogenital plate and adjacent ______ ______, which is an ectodermal-covered mesodermal swelling at the ventral and cranial ends of phallic portion of the urogenital plate

A

Urogenital plate; endodermally

Glans plate; genital tubercle

25
Q

The genital tubercle is an _______-covered ________ swelling at the ventral and cranial end of phallic portion of urogenital plate

A

Ectodermal; mesodermal

26
Q

The tip of the urorectal septum seen at the exterior is known as the __________

A

Perineal body

27
Q

The testis start up around ______, and are attached and pulled inferiorly by the _______, eventually anchoring them in the scrotum

A

T10; gubernaculum

28
Q

What is the most common urethral birth defect in males after cryptorchidism?

A

Hypospadias

29
Q

Epispadias is associated with what other GU birth defect?

A

Exstrophy of the bladder

30
Q

In the absence of SRY, development is female. What are 2 other major pro-female genes?

A

Wnt-4 — initially suppresses SOX-9 expression

FOXL2 — continually suppresses SOX-9, maintaining female gonad (suppresses Sertoli and Leydig differentiation)

31
Q

In females, somatic cells differentiate into ____ cells and primordial germ cells differentiate into _____, which later differentiate into ____

A

Follicle; oogonia; oocytes

32
Q

______ cells surround oocytes. Since there are no Sertoli cells, no ____ hormone is secreted so the _____ ducts are retained. There are also no Leydig cells, so the _____ duct system is lost

A

Follicle; AMH; paramesonephric; mesonephric

33
Q

The uterus forms around week ____-____ from fusion of inferior _______ ______

A

9-10; paramesonephric ducts

34
Q

The unfused superior portion of the paramesonephric ducts forms the ______ in females

A

Oviducts

35
Q

_______ = double uterus

A

Didelphys

[due to absence of fusion of inferior paramesonephric ducts during development — leading ot double uterus, double vagina, bicornate uterus, septated uterus, unicornate uterus, cervical atresia, etc.]

36
Q

The vaginal plate is eventually canalized during development. The upper vagina is derived from _____, while the lower vagina is derived from _____

A

Mesoderm; endoderm

37
Q

________ = condition characterized by failure of normal vaginal plate development or failed canalization

A

Vaginal agenesis

38
Q

Female external genitalia development starts out the same as in males, with the phallic segment of the urogenital sinus forming the urogenital plate, glans plate, and genital tubercle. What happens to these structures in the absence of testosterone or DHT?

A

No lengthening of genital tubercle occurs; no fusion of labioscrotal swellings

Labioscrotal swellings —-> labia majora

Urogenital folds —> labia minora