Embryology Flashcards
What layer do the urinary and internal reproductive organs develop from?
Primarily from intermediate mesoderm
Male and female genital systems are initially similar (indifferent stage). The Y chromosome contains the SRY gene (sex-determining region on Y). What is the protein product of this gene? What does it do?
The protein product of this gene (Testis-Determining Factor; TDF) masculinizes the indifferent genital system
The genital ducts begin in the indifferent stage. These form from intermediate mesoderm. What do these form in men and women?
Mesonephric (Wolffian) ducts (mostly contribute to male ducts)
Paramesonephric (Mullerian) ducts (mostly contribute to female ducts)
What induces mesonephric ducts to differentiate into male genital ducts and glands?
Testosterone
What inhibits paramesonephric ducts from developing into female genital ducts?
Antimüllerian hormone (AMH)
What cells produce AMH?
Sertoli cells
What are the 4 embryonic structures for the male?
MEsonephric Duct
Mesonephric tubiles
Urethra
Paramesonephric duct
What happens to the mesonephric tubules during development?
Become the efferent ductules and appendix of epidydimus
What happens to the mesonephric ducts during development?
Form epidydimus, ductus deferens, ejaculatory duct and seminal vesicle.
What happens to the urethra during development?
gives rise to the prostate and bulbourethral glands
What happens to the paramesonephric duct during development? (In males)
Regresses, except for the appendix of the testes and the prostatic utricle
What are the external structures in the indifferent stage?
Cloacal Folds
Genital (labioscrotal) swellings
What is the cause of hypospadia? What is the result? What mediates the process?
Caused by incomplete fusion of the urethral groove on ventral surface of penis.
Abnormal opening of penile urethra on ventral surface of penis.
Testosterone dependent process.
What is epispadias? What does this often occur with? What do we think causes this?
Is this testosterone dependent?
- Urethral opening is on dorsum of penis.
- Often occurs with exstrophy of the bladder.
- Thought to be due to urethral plate developing more dorsally than normal.
- Testosterone independent.
What is a hydrocele? What are the two types?
- Fluid filled sac around scrotum or spermatic cord caused by excessive serous fluid production.
- Noncommunicating and communicating types.
What is cryptorchidism?
What does this process depend upon?
Consequence?
- Failure of testes to descend into scrotum.
- Testosterone dependent.
- Undescended testes will be infertile due to temperature dysregulation.
What is cryporchidism a high risk factor for?
Testicular cancer
What causes the female body plan to form?
Absence of SRY gene
What is required for normal ovary formation?
Two functional X chromasomes.
What happens to the paramesonephric ducts in female development?
- Cranial ends open into abdominal cavity
- Caudal ends fuse and enter cloaca.
What happens to the mesonephric duct in females?
Regresses
What does the cranial end of paramesonephric duct form?
Uterine tube
What does the Caudal, fused portion of paramesonephric form?
The uterus, cervix, superior vagina
What does the sinovaginal bulb (vaginal plate) form?
Inferior portion of the vagina
What does the sinovaginal bulb form from?
Cloaca. Initially forms a solid tube called the vaginal plate (canalizes by 5th month).
What does urethral endoderm give rise to in females?
Greater vestibule and skene’s glands
What are the external genitalia for females during the indifferent stage?
Cloacal folds
Labioscrotal swellings
What does the genital tubercle form in females?
Clitoris
What do the urethral folds form in females?
Labia Minora
- Erectile tissue (bulbs of vestibule; crus of clitoris)
- The urethral groove remains unfused and will form the vestibule
What do the labioscrotal swellings form in the female?
labia majora
What do most uterine and vaginal defects result from?
Incomplete fusion of the two paramesonephric ducts
What causes uterus acuatus?
very slight lack of fusion of paramesonephric ducts.
What is uterus didelphys? What causes this?
Double uterus with double vagina (uterus didelphys) – complete lack of fusion of paramesonephric ducts and formation of two sinovaginal bulbs.
What is uteris bicornis? What causes it?
partial lack of fusion of paramesonephric ducts leads to two uteri
What is uterus bicornis unicollis? What causes it?
caudal portion of 1 paramesonephric duct fails to form, leading to one connected rudimentary uterine horn, and one unconnected.
What causes uterus unicornis? What is this?
One rudimentary uterine horn forms. complete agenesis of one paramesonephric duct.
What causes vaginal and cervical atresia?
atresia of the sinovaginal bulbs or from a failure of canalization.
What are the three remnants of mesonephric tubules and ducts in females? What is important to remember about them?
- Epoophoron (tubules)
- Paroophoron (tubules and duct)
- Gartner’s duct – remnant of caudal mesonephric duct
- All of the above can become cystic.
Why is a klinefelter male infertile?
Low levels of testosterone
What are the signs of XXY?
Impaired sexual maturation and gynecomastia
What is the XO genotype known as?
Turner Syndrome
What is the cause of turner and klinefelter syndromes?
Nondisjunction during meiosis
What are the signs/symptoms of Turner syndrome?
- Gonadal dysgenesis; streak gonads
- Lack of secondary sex trait development at puberty
- Short-stature, broad chest, short neck; lymphedema of hands and feet
Does a turner female develop ovaries?
No
What is Swyer Syndrome?
46, XY
What is the cause of Swyer syndrome?
Point mutation of SRY gene resulting in defective TDF protein.
What are the signs/symptoms of Swyer syndrome?
Gonadal dysgenesis; streak gonads develop. These gonads can become cancerous; often removed before puberty.
Female external and internal genitalia (except for ovaries)
Amenorrhea
Lack of secondary sex trait development at puberty
What is hermaphroditism?
Presence of male and female gonadal tissue (within same or opposite gonad).
What gonads do hermaphrodites get?
Ovotestes - ovarian and testis tissue found in same gonad.
What is the cause of hermaphroditism? What do we see with external genitalia?
- Cause is most likely a translocation of portion of Y (containing SRY gene) onto X chromosome during meiosis.
- Ambiguous external genitalia.
What is the cause of female pseudohermaphroditism? Do ovaries form? What happens to internal and external genitalia?
Cause: congenital adrenal hyperplasia (excessive production of androgens by adrenal glands).
- Ovaries - yes
- Internal reproductive organs usually female
- Masculinization of external genitalia
What is the genotype in male pseudohermaphroditism? What happens to the testes? External genitalia form as?
- 46, XY
- Testes form (due to normal functioning Y chromosome).
- Insufficient androgen production and AMH (hypogonadism)
- External and internal genitalia normally female
Describe androgen insensitivity syndrome.
- 46, XY
- Testes (due to normal functioning Y chromosome)
- AMH and testosterone production is normal
- Lack of androgen receptors (tissues are not responsive to testosterone)
- Mesonephric ducts degenerate (due to insensitivity to testosterone)
- Paramesonephric ducts degenerate (due to presence of AMH)
- Female external genitalia; including secondary sex traits
- Vagina is short and blind-ending