Brainscape's Knowledge GenomeTM

Browse over 1 million classes created by top students, professors, publishers, and experts.


See full index

BSMS203 Repro (Theme 2) > 11. Sexual Differentiation: how to make a boy or a girl > Flashcards

11. Sexual Differentiation: how to make a boy or a girl Flashcards

1
Q

What main events make a boy/girl?

A

What makes a boy/girl takes involves 3 main events

(1) Sex determination, during fertilization
(2) Differentiation of gonads, week 5
(3) Differentiation of internal and external genital organs, after week 5

Prevalence of genital abnormalities: 1 in 4500

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
2
Q

Sex determination

A

Sex is determined at fertilisation

Inheritance of X/Y from father

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
3
Q

Gonad origin and differentiation

A

At week 2 primordial germ cells (PGCs) arise from the epiblast

PGCs are pluripotent

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
4
Q

What do the PGCs do?

A

PGC’ migrate to yolk sac stalk to avoid becoming imprinted

Later return, travelling to the genital ridge (next to kidney) and become the indifferent gonad

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
5
Q

What happens at the genital ridge?

A

At genital ridge: XX PGCs replicate at cortex; XY PGCs replicate at the medulla

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
6
Q

Gonad gender decision relies on:

A

Gonad gender decision relies on:

- Genetic switches
- Hormones

Genetic switches:
general transcription factors,
e.g. Wt1, Sf1
- specific promoters of testis development
e.g. Sry, Sox9
specific promoters of ovarian development
e.g. Wnt-4, FoxL2

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
7
Q

General transcription factors

A

Wt1, Sf1

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
8
Q

Specific promoters of testis development

A

Sry, Sox9

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
9
Q

Specific promoters of ovarian development

A

Wnt-4, FoxL2

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
10
Q

Overview of gonad cell line fates

A

urogenital ridge -> bipotential gonad -> future ovary or future testis

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
11
Q

Female gonad cell line fate

A

Female PGCs => oogonia (primary oocytes)
Sex cord cells => granulosa (support and nutrifying the ovum)
Cortex => layer of thecal cells => secrete androgens before those generated by the follicles

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
12
Q

Male gonad cell lines

A

Male PGCs => spermatogonia
Sry influences definition + identity of Sertoli cells => secretion of AMH (Anti-Müllerian Hormone)
AMH supresses female development pathway
AMH induce cells in intermediate mesoderm to become leydig => secrete testosterone

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
13
Q

Kidney development

A

Origin: intermediate mesoderm (as the reproductive organs)

Where: between the somites and lateral plate (each side of the aorta)

3 Stages:
Pronephros - disappears soon after
- Mesonephros - leaves remnants
- Metanephros - becomes kidney

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
14
Q

Internal genital organs

A

Begin differentiation at about week 8, formed from a priori identical primordium structures, i.e. …

… embryos of both sexes possess two sets of paired ducts at the start:

  • paramesonephric a.k.a. Müllerian
  • mesonephric a.k.a. Wolffian
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
15
Q

Internal genital organ fate in female embryos

A

In female embryo: Müllerian duct is kept due to the absence of AMH

Müllerian duct => oviduct
uterus
cervix
upper part of the vagina

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
16
Q

Internal genital organ fate in male embryos

A

In male embryo:

  • AMH causes Müllerian duct regression
  • testosterone promotes Wolffian duct differentiation

Wolffian duct => epididymis
vas deferens
seminal vesicle

17
Q

External genital organs

A

At first embryos of both sexes show an elevated midline swelling – genital tubercle

Tubercle consists:
urethral groove (opening into the urogenital sinus)
- paired urethral folds
paired labioscrotal swellings

18
Q

External genital organs in males

A

Some testosterone is converted into dihydrotestosterone (DHT)
DHT stimulates development of the urethra, prostate and external genitals (scrotum and penis)
Genital tubercle => penis
Fusion of the urethral folds => spongy urethra
Labioscrotal swellings => scrotum

19
Q

External genital organs in females

A 
Absence of DHT
 Genital tubercle => clitoris
 Urethral folds remain open => labia minora
 Labioscrotal swellings => labia majora
 Urethral groove => vestibule
20
Q

Abnormalities

A 
Chromosomal
Hermaphroditism
Gonadal dysfunction
Tract abnormalities
Gonadal descent
External genitalia
21
Q

Turner’s syndrome

A

Chromosomal
Monosomy, XO

1:2500 females (does not affect males)

99% non-viable embryos

Survivors fail to sexually mature at puberty

Exhibit several physical abnormalities (next slide)

Diagnosis confirmed through amniocentesis

22
Q

Klinefelter’s syndrome

A

Chromosomal
47, XXY

1:600-1000 male births (does not affect females)

Birth appear normal (undetected)

Become infertile

Exhibit some features associated with female development (e.g. gynecomastia)

Diagnosis confirmed through amniocentesis

23
Q

Hermaphroditism

A

Named after the offspring of the Greek gods Hermes and Aphrodite

True hermaphrodite

Female pseudohermaphrodite

Male pseudohermaphrodite

(note: these colloquial terms are used for your understanding only and not actually used in the medical profession)

24
Q

True hermaphrodites

A

Extremely rare

Born with both ovarian and testicular tissue (ovotestis)

46XX (SRY+), 45X (SRY+) and 45X

Possible cause e.g. two ova fertilized by two sperm that fuse to form a tetragametic chimera

External genitals may be ambiguous,
or appear to be female or male

25
Q

Female pseudohermaphrodite

A

46, XX with virilization (due to androgens)

Internal sex organs are normal, inc. ovaries

External appearance and genitals: male

Features: fusion of labia; enlarged clitoris

Possible cause: exposure to male hormones prior to birth (e.g. from congenital virilizing adrenal hyperplasia)

26
Q

Male pseudohermaphrodite

A

46, XY with undervirilization

External genitals: incompletely formed, ambiguous or clearly female

Some features: blind-ending vagina, absence of breast development, primary amenorrhea

Testis: normal, malformed or absent

Main causes:
defective androgen synthesis
defective androgen action (e.g. receptor disorder)

27
Q

Androgen insensitivity syndrome

A

A.k.a. testicular feminization

Affects 1:20000-64000 male births

(Male) hormones are normal

Disfunctional receptor to these hormones

28
Q

Leydig cell hypoplasia

A

Leydig cells do not secrete testosterone

Possible reason: body insensitive to LH

External genitalia normally female/slightly ambiguous

No female internal genitalia
(uterus) develops

29
Q

Gonadal dysfunction

A

e.g. XY gonadal dysgenesis, a.k.a. Swyer’s Syndrome

Associated with XY karyotype

Cause: alteration to Sry gene

External appearance: female (no menstruation)

No functional gonads (no testicular differentiation)

Gonad may develop into malignancy

30
Q

Tract abnormalities

A

Some examples:

Uterine: e.g. unicornuate uterus

Vagina: e.g. agenesis

Ductus Deferens: unilateral or bilateral absence, failure of mesonephric duct to differentiate

31
Q

Gonadal descent

A

More apparent and common in males (cryptorchidism) than on females (undescended ovaries)

Cryptorchidism:
may be unilateral/bilateral
occurs 30% premature; 3-4% term males
descent may take place during year 1

Undescended ovaries:
quite rare
detected in clinical fertility assessment

32
Q

External genitalia

A

The most common: male hypospadia

1:125 live male births
Failure of male urogenital folds to fuse
Outcome: proximally displaced urethral meatus

33
Q

The brain and behaviour

A

What also makes us a boy or girl: sexual behaviour

Research from mutants revealed that the brain acquires its ‘gender identity’ not from the influence of sex hormones…
… but instead from gene expression, given the correlation between inactivation of genes from the X chromosome and predisposition to transexualism

In mouse embryos, 51 genes are expressed differently between male and female brain prior to advent of sex hormones (RT-PCR)
These genes are active before gonads even develop, let along differentiate, about week 2 of development

Money, J: ‘Gender identity is one’s own categorization of one’s individuality… as experienced in self awareness of one’s own mental processes and own’s actual behaviour’
This breakthrough can potentially help surgeons to decide which gender to opt in cases of genital malformation or of transexualism

BSMS203 Repro (Theme 2) (26 decks)

Brainscape helps you reach your goals faster, through stronger study habits.
© 2024 Bold Learning Solutions. Terms and Conditions