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AVS 222 > Embryogenesis and Sexual Differentiation > Flashcards

Embryogenesis and Sexual Differentiation Flashcards

1
Q

differentiation

A

Process by which a primitive group of unspecialized cells

develop a functional and specialized group of cells that provide a common function

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2
Q

how many germ layers does differentiation involve

A

3

Ectoderm, mesoderm, endoderm

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3
Q

embryonic tissue

A

forms all adult tissues and organs

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4
Q

Ectoderm

A

forms exterior tissues

  • skin, hair, sweat glands
  • mammary glands
  • hypothalamus. anterior/posterior pituitary
  • part of the reproductive tract (male and female)
  • vestible/outer vagina
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5
Q

mesoderm

A

forms structural tissue

  • Muscle, skeletal system, blood vessels
  • Reproductive system
    a. gonads, uterus, cervix, part of vagina, accessory sex glands
  • Renal system (urinary system)
  • Skeletal system
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6
Q

endoderm (nothing to do w/ reproductive tract)

A

form internal organs

  • digestive system, liver and lungs
  • majority of glands
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7
Q

genetic differentiation

A
  1. An individual’s sex is genetically determined by the presence of a Y chromosome
  2. Genetic differentiation takes place at fertilization when a sperm delivers either an X
    (female) or Y (male) chromosome to the oocyte
  3. SRY gene: Sex determination gene located on the Y chromosome
    i. Causes the undifferentiated gonad to develop into the testis
  4. SRY gene controls the expression of Testis Determining Factor (TDF), which is
    secreted by the sex cords.
  5. TDF controls the pathway towards either male or female development.
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8
Q

SRY gene

A
  • sex determination gene located on the Y chromosome

- controls the expression of Testis Determining Factor (TDR), which is secreted by the sex cords

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9
Q

gonadal differentiation

A
  1. Development of primordial germ cells in the yolk sac (first 15% of gestation)
  2. Migration of primordial germ cells from the yolk sac into the genital ridge
  3. Genital ridge gives rise to undifferentiated/bipotential gonad
  4. Genital ridge with stimulation of sex cords give rise to renal system
  5. Development of the urinary system
  6. Development reproductive tract
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10
Q

urinary system

A

pronephros
mesonephros
metanephros

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11
Q

pronephros

A

primitive kidney

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12
Q

mesonephros

A

closely associated with the undifferentiated gonad

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13
Q

metanephros

A

becomes the functional kidney

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14
Q

reproductive tract

A

mesonepheric ducts
paramesonepheric ducts

REMEMBER! BOTH the mesonephric and paramesonephric ducts are present at the
SAME TIME, called the SEXUALLY INDIFFERENT STAGE. The undifferentiated gonads
thus need a signal to differentiate into either female or male gonads.

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15
Q

mesonepheric ducts

A

Wolffian Ducts; MALE reproductive tract

efferent ducts, epididymis, vas deferens

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16
Q

paramesonepheric ducts

A

Müllerian Ducts; FEMALE reproductive tract

oviducts, uterus, cervix, vagina

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17
Q

Male Gonadal Differentiation

A

I. Presence of Y chromosome/ SRY gene

II. Presence of Testis Determining Factor (TDF)

III. Development of undifferentiated gonad to testes and Sertoli cells

IV. Secretion of Anti-Müllerian Hormone (AMH) by sertoli cells

V. Degeneration of Müllerian ducts (paramesonephric) and development of Wolffian ducts
(mesonephric)

VI. Differentiation of interstitial Leydig cells

VII. Secretion of testosterone from Leydig cells and development of male reproductive duct
system

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18
Q

Female Gonadal Differentiation

A 
I. No Y chromosome/ Absence of SRY gene

II. No Testis Determining Factor (TDF)

III. Development of ovaries

IV. No Sertoli cells

V. Absence of Anti-Müllerian Hormone (AMH)
VI. 
VII. Regression of Wolffian ducts and differentiation of Müllerian ducts
VIII. 
IX. Development of female reproductive duct system
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19
Q

Hypothalamic/Brain differentiation

A

Pre-knowledge: The hypothalamic GnRH surge center is necessary for initiation of the estrous cycle
and follicular ovulation in the female

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20
Q

male hypothalamic differentiation (defeminization of the brain)

A

Pre-knowledge: Hypothalamic GnRH surge center is necessary for initiation of the estrous cycle and
follicular ovulation in the female
I. Testosterone from the fetal testis crosses the blood-brain barrier and reaches the brain

II. Testosterone is converted to estradiol by aromatase enzyme in the hypothalamus

III. Regression of the hypothalamic GnRH surge center by estradiol

IV. Defeminization of the hypothalamus (no surge center)

21
Q

female hypothalmic differentiation (feminization of the brain)

A

I. Estradiol from fetal ovaries binds with a protein called alpha-fetoprotein (produced by the liver)

II. Alpha-fetoprotein prevents estradiol from crossing blood brain barrier

III. Estradiol cannot affect the hypothalamic surge center

IV. Surge center retained in females

22
Q

three phases of testicular descent

A

Transabdominal: 1. Growth and elongation of the body away from the stationary testes.
Inguinal-Scrotal: 2. Rapid growth of the distal gubernaculum
a. Rapid growth results in the testes being pulled from the region of the tenth
thoracic vertebra to the inguinal ring
Inguinal-Scrotal: 3. Shrinkage of the gubernaculum within the scrotum pulls the testes through the
inguinal ring.
a. Regression continues and gubernaculum situates the testes within the
scrotum.

23
Q

growth and regression of the gubernaculum (descent of testis)

A
  1. Testosterone (from Leydig cells) and insulin like-3 (Insl-3) (also called descendin)
    synthesized by the fetal pancreas needed for gubernacular growth
  2. Intra-abdominal pressure may play a larger role in the movement of the testes out of
    the abdomen and into the scrotum
24
Q

what happens when the testis fail to descend?

A
  1. Cryptorchidism
  2. Hormone production is NOT decreased in cryptorchid males
    a. Will exhibit secondary sex characteristics and normal reproductive behavior
  3. Cryptorchidism is heritable-therefore cull
    a. It is possible to surgically or with pharmaceuticals lower the retained testis;
    however, it is most likely that fertility will be compromised
  4. Descent of testes from the body cavity into the scrotum occurs by:
    a. mid-gestation (bull and ram)
    b. last quarter of gestation (boar)
    c. just before birth/ at birth (stallion)
25
Q

Cryptorchidism

A

Undescended testes or testis (“Crypt” = hidden “Orchid” = testis)

26
Q

bilateral cryptorchidism

A

both testis retained in the body cavity: male is sterile

-increases temperature, decreases sperm (TEMP REGULATION)

27
Q

unilateral cryptorchidism

A

one testis retained: male is fertile-sub-fertile

28
Q

why are bilateral cryptorchids sterile?

A

Temperature regulation: The temperature requirements for normal spermatogenesis is specific. If you increase the temperature of the scrotum and the testes cannot lower to allow for cooling (thermoregulation) spermatogenesis is impaired (increased # of abnormal sperm=decreased fertility)

29
Q

freemartinism: (“free” = sterile “martin” = bovine)

A

 Common blood supply between twins during gestation
 Testosterone and AMH from male fetus influences female fetus
 Paramesonephric ducts in female do not develop correctly
 Results in canalization and a “blind” reproductive tract in the female
 Ovaries do not develop properly and do not secrete estradiol  secrete testosterone instead
 Often see male-like behavior in freemartin heifers

30
Q

why keep freemartin heifers in herd?

A

Normally we should not, but it may useful for detecting estrus in other females due to malelike sexual behaviors!

31
Q

3 parts of sexual differentiation

A

genetic
gonadal
brain

32
Q

oocyte

A

always have x chromosome (haploid- n)

33
Q

sperm

A

x or y (haploid- n)

34
Q

oocyte+sperm

A

becomes diploid (2n)

35
Q

xx

A

female

36
Q

xy

A

male

37
Q

absence of SRY and TDN

A

female

38
Q

TDF

A

stimulates male development

39
Q

GnRH

A

Gonadotropin Releasing Hormone

40
Q

no surge center

A

has to do with blood-brain barrier

41
Q

estradiol is responsible for

A

regression of GnRH surge center

42
Q

recombination of sex chromosomes at fertilization

A

1) chromosomal sex (genotype)

2) Hermaphrodite

43
Q

in females one of the

A

x chromosomes is deactivated

appears as the barr body in somatic cells

44
Q

abnormal

A

aneuploidy

45
Q

XXY

A

Klinefelter’s syndrome

sterile: testicular hypoplasia

46
Q

XO

A

Turners syndrome

sterile: inactive ovaries

47
Q

true hermaphrodite

A

contain combination of ovaries and testis

48
Q

male pseudohermaphrodite

A

has testis but has female external genetalia

lack androgen receptor for sexual development

49
Q

female pseudohermaphrodite

A
  • has incomplete ovaries, masculinized external genetalia
  • male hormone pass into female in twin pregnancy
  • – exchange of blood cells from male to female, stimulates male duct development

AVS 222 (5 decks)

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