Session 2- embryology Flashcards
which tracts share a common caudal opening
To begin with, the reproductive
tract, urinary tract and GI tract
share a common caudal opening
what is the cloaca
Hindgut ends in a dilated structure
– the cloaca
Closed to the outside by the
cloacal membrane
what is the urogenital ridge
Region of intermediate mesoderm giving rise to both the embryonic kidney and the gonad
• Gonad (indifferent) derived fromintermediate mesoderm plus primordial germ cells
(extragonadal)
what are primordial germ cells
Primordial germ cells
Special population
• “seed” for the next generation
• Allocated shortly after initiation of the current generation
• Arise in the yolk sac and migrate into the retroperitoneum, along the dorsal mesentery
what happens if the male gamete carries the Y chromosome
Male gamete carrying Y chromosome • XY male conceptus • primordial germ cells carry Y chromosome • Expression of SRY genes drives development of male – gonad (testis) – Production of testicular hormones – internal genitalia (male duct system)
what happens if the male gamete carries the X chromosome
Male gamete carrying X chromosome • XX female conceptus • primordial germ cells do not carry Y chromosome • Absence of Y chromosome leads to development of female – gonad (ovary) – internal genitalia (duct system – i.e. tubes & uterus)
What are the names of the ducts that develop in both male and female embryos
• Mesonephric ducts develop in both male and female embryos • Paramesonephric ducts develop in both male and female embryos • Both the mesonephric and paramesonephric ducts end at the urogenital sinus part of the cloaca
what do the mesonephric ducts become in males and females
in males it becomes wolffian ducts - this is because the production of andorgens by the testis supports the development of the mesonephric ducts into wolffian ducts
in females it degenerates as there is not a testes to produce androgens to support the development of the ducts
what do the paramesonephric ducts become in males and females
it degenerates in males
but becomes the mullerian ducts in females
this is because the testis produces mullerian inhibiting hormone which supresses the development of the mullerian ducts in males
the MIH is not produced in females so the ducts degerate
what happens if a XX embryo if exposed to exogenous androgens
wolffians ducts develop because of the androgens
as there are no testis, there will be no MIH so no suppression of the mullerian ducts so the mullerian ducts will also develop
what happens if a XY embryo has androgen insensitivity syndrome (AIS)
the wolffian ducts will not degenerate
as the testis are producing MIH, the mullerian ducts will degenerate
what is the role of the mosenephric duct before it develops into the wolffian ducts
- The mesonephric (Wolffian) duct first acts as the duct for the embryonic kidney
- Drains into the urogenital sinus
- Urogenital sinus will become the urinary bladder
- not needed once the true kidney develops
what happens if testis derived androgens maintain the mesonephric ducts
- wolffian ducts are converted into the vas deferens and epididymis
- Migrates with the testis as it descends
what happens to the paramesonephric duct in the absence of MIH
• Paramesoneprhic ducts (aka Mullerian duct) appear as invaginations of the
epithelium of the urogential ridge
• Caudally: make contact with the cloaca (urogenital sinus)
• Cranially: open into the abdominal cavity
• will develop to form the uterine tubes, uterus, cervix, and the upper one-third of the vagina
what are the basic embryological components of external genitalia in both males and females
– genital tubercle (GT)
– genital folds
– genital swellings
