Development Of The Reproductive Tracts Flashcards
What needs to differentiate in order o create a reproductive system?
Indifferent gonads, duct systems and external genitalia
What is the cloaca
• The development of the three
systems is closely linked
• To begin with, the reproductive tract, urinary tract and GI tract share a common caudal opening
• Hindgut ends in a dilated structure
– the cloaca
• Closed to the outside by the cloacal membrane
– no mesoderm
What is the urogenital ridge
• Region of intermediate mesoderm giving rise to both the embryonic kidney and the gonad • Gonad (indifferent) derived from intermediate mesoderm plus primordial germ cells (extragonadal) See slide for location
What are the primordial germ cels?
• 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 determines how the undifferentiated parts differentiate
Determine whether to have functional testis or ovary - endocrine function. Hormones produce driven by Y chromosome 0 determines route taken
What happens if the male gamete carries a 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 an 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)
Name the 2 pairs of ducts at the indifferent at age
• Mesonephric (wolffian)ducts develop in both male and female embryos
• Paramesonephric (mullerian) ducts develop in both male and female embryos
• Both the mesonephric and
paramesonephric ducts end at the
urogenital sinus part of the cloaca
What happens to the ducts in a normal male
• Depends on whether there is a functional testis producing androgens
• Diagram B: Normal Male
– Testis producing Mullerian inhibiting hormone
• Suppressing Mullerian (paramesonephric) duct development
– Testis producing androgens
• Supporting Wolffian (mesonephric) duct
What happens to the ducts in a normalfemale
• Depends on whether there is a functional testis • Diagram C: Normal Female
– No testis producing Mullerian inhibiting hormone
• No suppression of Mullerian (paramesonephric) duct development
– No testis producing androgens
• Wolffian (mesonephric) duct degenerates
What happens when exogenous androgens are present in a female
– Exogenous androgen
– Supports Wolffian duct
– But no testis, therefore no MIH
– Therefore Mullerian ducts develop
What happens if receptersfor testosterone arent present in a male
Diagram F – AIS – Receptors for testosterone don’t work – Wolffian ducts don’t survive – But MIH present so Mullerian ducts degenerate
What s the function of the mesonephric duct
- 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
- Surplus to requirement once true kidney develops
What happens to the mesonephric duct once the true kidney develops
• Mesonephric duct is maintained by testis derived androgens • Converted into the vas deferens and epididymis • Migrates with the testis as it descends Not needed in females
Describe the position of the paramesonephric ducts
- 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
