3 - Embryology of the Reproductive System Flashcards
What are the steps to making a reproductive system?
- Primarily from intermediate mesoderm
- At the hindgut in the posterior abdominal wall there is the cloaca and this forms the urogenital sinus for urinary and reproductive
What is the gonads embryological origin?
- Intermediate mesoderm plus extragonadal primordial germ cells
- Primordial germ cells come from yolk sac after gastrulation , and when map of body done they migrate intro retroperitoneum along dorsal mesentry to gonad to be future ova or sperm
Why might you end up with a teratoma in the abdomen?
Migration of primordial germ cells during embryological development went AWOL
How does the gonad differentiate?
If SRY gene then seminiferous tubules form. If not no tubules develope and primordial germ cells remain as primordial follicles to developed into oocytes at puberty
How does the internal genitalia form if the conceptus is XY?
- Germ cells carrying Y chromosome and SRY gene and testicular hormones start
- Testis produce MIH to stop mullerian duct forming
- Testes produce androgen to support Wolffian duct to form epididymis and vas def
- Duct fuses with gonad (testes) so continuous and not open to peritoneum
How does the internal genitalia form if the conceptus is XX?
- No MIH so paramesonephric stays
- No androgens so mesonephric degenerates
- Duct is separate to gonad so gap in peritoneum. Duct forms uterus and uterine tubes
What are some genetic issues that could arise on embryological formation of the internal genitalia?
- Female could have exogenous androgen so Wolfian stays, no MIH so Mullerian also stays
- Male may have AIS where receptors for testosterone don’t work. Have MIH still so both ducts degenerate
Both have gonads (ovary and testes) but nothing else
Apart from male genitalia what else does the mesonephric duct form?
Embryonic kidney draining into urogenital sinus
Even though the vagina is internal genitalia it is not all formed by the paramesonephric duct, what is it’s other embryological origin?
- Upper 1/3: paramesonephric duct
- Lower 2/3: endoderm
What is the structure of the undifferentiated external genitalia?
- Genital tubercle
- Genital folds
- Genital swellings
How does the external male genitalia form?
- Testes presence of dihydrotestosterone
- Penis: elongation of GT and elongation/fusion of genital folds. GT is glans.
- Scrotum: fusion of genital swellings
How does the external female genitalia form?
- No testes so vulva
- No fusion of folds or swellings so labias form
- Tubercle becomes clitoris
- Urethra opens into vestibule
How do the testes descend from the posterior abdominal wall?
- Gubernaculum from inferior gonad to scrotal fols
- As cavity gets larger and volume increases descent starts
- Bit of peritoneum pinched off and follows behind called processus vaginalis, then should break off
How do the ovaries descend from the posterior abdominal wall?
Stays in pelvis due to barrier of developing uterus. Gubernaculum becomes round ligament.
If a baby has a malascended teste what should you do?
Check path the testes make to get to scrotum and surgically correct
Draw a flow diagram to show how male and female internal genitalia forms.
Draw a flow diagram to show how male and female external genitalia forms.
A baby is born with genotype XY, testicular development and normal secretion of testosterone and MIH. However, fetal genitalis is insensitive to testosterone or DHT, what will be the consequences of this?
Androgen Insensitivity Syndrome
- Female genitalia
- Both ducts regress
- Testes but no vas def
- Woman with maldescended testes, 2/3 vagina then 1/3 blind ended as comes from duct
A baby is born having a genotype XX but has excessive secretions of androgens from the adrenal glands due to congenital adrenal hyperplasia, what is the consequences of this?
- Both ducts stay so female and male internal genitalia
- Female to male spectrum external genitalia depending on how many androgens released (e.g may just be enlarged clitoris)
What is the embryologial origin of each part of the vagina?
- Lower two thirds from external genitalia
- Upper third from paramesonephric duct
