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Anatomy Section 6 > 9 – Fetal Development of Genital System I > Flashcards

9 – Fetal Development of Genital System I Flashcards

1
Q

What part of the ‘genital’ system comes from the ectoderm?

A

-mammary glands
-hypothalamus, both lobes of pituitary (nervous system)
-penis and clitoris (reproductive tract)

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2
Q

What parts of the ‘genital’ system comes from the mesoderm?

A

-gonads (male and female)
-uterus, cervix, part of vagina
-epididymis, ductus deferens
-accessory sex glands

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3
Q

What parts of the ‘genital’ system comes from the endoderm?

A

-most glands
-portions of vagina and vestibule

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4
Q

What is the initial step in sex determination in mammals?

A

-fertilization by sperm
>+/- Y
-genetic initiation of sex differentiation process can occur in the individual animal

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5
Q

What are the 6 embryological events in the development of the reproductive tract?

A
  1. Migration of primordial germ cells from yolk sac (1st)
  2. Sex cords develop in gonad, paramesonephric ducts develop (1st)
  3. Sex evident from structures (1st)
  4. Development of male ducts and testes (or female ducts and ovaries) (1st and 2nd)
  5. Formation of broad ligament (2nd)
  6. Testicular descent (varies, 2nd to 3rd)
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6
Q

Gamete progenitors: primordial germ cells

A

-a population of epiblast cells are put aside for formation of the germ line
-displaced from embryonic disk to definitive yolk sac and part of the allantois
>active migration via chemotaxis into urogenital and gonadal ridge

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7
Q

Gonadal ridge is also known as:

A

-bipotential gonad
>capable of differentiating along two different paths (ovary and testes)
-forms medial to the embryonic kidneys

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8
Q

What happens when primordial germ cells arrive in the Gonadal ridge?

A

-stimulate cells around them to proliferate causing ridge elongation

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9
Q

What are the 3 origins of gonadal (genital) ridge cells?

A

-local mesenchymal cells (mesoderm)
-coelomic epithelium
-cells from mesonephric tubules

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10
Q

Primitive sex cords:

A

-cells from degenerating mesonephric tubules that then form compact strands of tissues
*incorporate (surround) the primordial germ cells

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11
Q

Paramesonephric ducts:

A

-new pair of ducts that form beside the developing mesonephros
*not committed to a particular sex
**SEXUALLY INDFFERENT STAGE

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12
Q

What is the sex of an animal (male or female) defined as?

A

-ability to produce a particular type of gamete (sperm, oocyte), along with any associated phenotypic traits (ex. external genitalia)

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13
Q

What can the sex of animal be a result of? (3)

A

-sex-determining genes
-hormone-encoding gens
-environment

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14
Q

What is sex determination?

A

-process where an organisms begins the development of ovaries or testes from the embryonic gonad
*genetic (genotypic) sex determination (GSD)
*environmental sex determination (ESD)

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15
Q

Genetic (genotypic) sex determination (GSD):

A

-all mammals, birds, and some other vertebrates and invertebrates
*determined by SEX CHROMOSOMES INHERITED AT TIME OF FERTILIZATION
>mammals: males are heterogametic (XY); females are homogametic (XX)

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16
Q

Environmental sex determination (ESD)

A

-reptiles (crocodiles, turtles, some fish and snakes)
*depends on EXTERNAL FACTORS (ex. temperature)
-sex chromosomes are absent

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17
Q

Sex determining region on Y (SRY) chromosome:

A

-gene encodes SRY protein=testis-determining factor (TDF)
-when produced by primitive sex cords within primitive gonad=male reproductive system is stimulated

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18
Q

Gonadal sex determination:

A

-whether testes or ovaries develop
-gonads produce sex-specific hormones leading to internal genitalia and SECONDARY SEX CHARACTERISTICS and EXTERNAL GENITALIS
*phenotypic sex is now determined

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19
Q

Phenotypic sex determination:

A

-apparent sex of an individual

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20
Q

Developmental sequence of testes: step 1

A

-undifferentiated sex cords begin to align themselves with rete tubules
-5-15 mesonephric tubules will penetrate into primitive gonad but NOT connected with rete tubules

21
Q

Developmental sequence of testes: step 2

A

-rete tubules and mesonephric tubules BECOME INTERCONNECTED PROVIDING CONTINUITY BETWEEN UNDIFFERENTIATED SEX CORDS
*sex cords become epithelial in nature=EPITHELIAL CORDS
-paramesonephric duct serves no function here=degenerates in males
-development of seminiferous cords

22
Q

Primitive sex cords proliferate into SEMINIFEROUS CORDS:

A

-solid tubules containing germ cells
-contain a peripheral layer of 15-20 mesonephric derived cells that become SERTOLI CELLS
>surround a centre core of 4 pre-spermatogonia

23
Q

What do the mesenchymal cells between the seminiferous cords develop into?

A

-Leydig (interstitial) cells
*also begin to form connective tissue septa to divide the testis into a number of lobules

24
Q

What happens at puberty to the seminiferous cords?

A

-become tubules (with a lumen)
>there is continuity between rete testis and efferent ducts

25
Q

Developmental sequence of testes: step 3

A

-mesonephric duct develops into epididymis and the ductus deferens
*excurrent extragonadal duct system

26
Q

What is all part of the excurrent extragonadal duct system and what does it do?

A
  1. Efferent ducts
  2. Epididymis
  3. Ductus deferens
    *carry sperm through to the urethra
27
Q

What are the accessory sex glands? (bull, ram, stallion, lab animals)

A

*STEP 4
-prostate
-bulbourethral glands
-seminal vesicles (CATS don’t have)
-ampullae ductus deferentis
*DOGS only have a prostate gland

28
Q

What do the seminal vesicles and ampullae ductus deferentis develop from?

A

-epithelial evaginations from mesonephric duct

29
Q

What do the prostate and bulbourethral glands arise from?

A

-epithelial evagination from the urogenital sinus

30
Q

Testicular descent:

A

-in all domestic species the testes descend into the scrotum
-2 largely different processes
-2 layers of peritoneum covering and descending with the testis

31
Q

Testicular descent requires:

A

-rapid GROWTH and then rapid REGRESSION of ligamentous structure (GUBERNACULUM)
-from body cavity to scrotum

32
Q

2 layers of peritoneum covering and descending with the testis:

A
  1. Visceral vaginal tunic
  2. Parietal vaginal tunic
33
Q

2 stages of testes descent:

A
  1. Transabdominal phase
  2. Inguinal-scrotal phase
34
Q

Transabdominal phase of testes descent:

A

-retroperitoneal testes are attached caudally to the gubernaculum
-gubernaculum grows toward and into scrotal region
-peritoneal cells form a junction with gubernaculum in the inguinal region

35
Q

Inguinal-scrotal phase of testes descent:

A

-gubernaculum moves the testes into the inguinal canal
*rapid growth is dependent on androgens
-once testes in inguinal region they enter inguinal opening as gubernaculum shrinks
*further shrinkage pulls the testes deeper into the scrotum
*each testis becomes surrounded by inner layer of peritoneum (visceral vaginal tunic)

36
Q

Testis, epididymis, and spermatic cord are covered by:

A

-inner visceral vaginal tunic

37
Q

Outer parietal vaginal tunic:

A

-directly adjacent, but not attached to the inner tunic

38
Q

Vaginal cavity:

A

-between the visceral and parietal vaginal tunic
*allows each testis to move freely within scrotum

39
Q

Cryptorchidism (retained testes):

A

-failure of 1 or both testes to descend into the scrotum
*testosterone still produced in both cases
*spermatogenesis does NOT occur
-still intact characteristics (ex. urine making, aggression)
-remains in abdomen or inguinal canal

40
Q

Unilateral cryptorchidism:

A

-1 testes retained
-most typical presentation

41
Q

Bilateral cryptorchidism:

A

-both testes retained
-typically infertile

42
Q

Retained testes should be removed:

A

-can develop tumors
-appears to be heritable
-to avoid intact male behaviours

43
Q

What drives the development of male external genitalia?

A

-androgens
>genital tubercule elongates into the phallus
>UROGENITAL folds form lateral boundaries of the urethral plate

44
Q

What forms between the urogenital folds that form the lateral boundaries of the urethral plate?

A

-urethral groove develops=epithelial cord

45
Q

Penile urethra:

A

-urogenital folds fuse enclosing the urethral groove=tube
-following canalisation it opens at the tip of the penis

46
Q

Urethral plate of tissue does NOT extend to tip of penis:

A

-ECTODERMAL portion invaginates into tip of penis and will fuse with the ENDODERMAL cells lining the penile urethra

47
Q

Hypospadias:

A

-urethra opens on VENTRAL surface rather than the end
-degree of length can vary

48
Q

Epispadias:

A

-urethra opens on DORSAL surface rather than the end

49
Q

Hypospadias (and epispadias) result from:

A

-formation of urethral groove to close in the male
-cause is unknown
>potential inheritable defect in some dog breeds

Anatomy Section 6 (18 decks)

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