Reproductive Embryology Flashcards
What are the criteria that define human sex?
- Genetic sex - presence/absence of Y chromosome
- Gonadal sex - presence of testes or ovaries
- Phenotypic sex - appearance of external genitalia
What is the karyotype of Klinefelter’s?
47XXY
What is the karyotype of Turner’s?
45XO
What is the sex-determining gene?
sry
Where is the sex-determining gene found?
At the end of the short arm of the Y chromosome
What cell is sry expressed from?
Germinal epithelial cells (that form the columns of the primitive sex chords)
When do the gonads begin to develop?
The 5th week, at which they are at the ‘indifferent’ stage
When do the gonads begin to differentiate?
The 7th week - when the sry gene is expressed. In the presence of sry, the indifferent gonads form the testes. In the absence of sry, the indifferent gonads form the ovaries
When are the primordial germ cells first visible?
During the 3rd week
From where do the PGCs originate?
The yolk sac
By what movement do the PGCs migrate?
Ameboid
By what point is migration of the PGCs complete?
Week 6
Where specifically in the yolk sac do PGCs develop?
At the base of the allantois (which becomes the vitelline duct)
Where do the PGCs migrate to?
The genital/gonadal ridge
What is the period in which the PGCs migrate out of the yolk sac called?
Gastrulation
What are the cells that make up the gonadal ridge?
- Mesenchymal cells (mesonephros)
- Mesothelial cells (germinal epithelial cells)
- PGCs
What is the ‘default’ phenotype (external genitalia)?
Female
What hormones are required for the development of the male external genitalia?
Androgens
What hormone is required for the development of the male reproductive tract?
MIF - Mullerian inhibiting factor (called AMH - anti-Mullerian hormone in the UK)
In what cells are androgens produced in males?
Leydig cells
In what cells are MIF produced in males?
Sertoli cells
What is the fate of mesenchymal cells?
Vasculature; M = leydig cells; F = theca cells
What is the fate of PGCs?
M = spermatogonia; F = oogonia
What is the fate of mesothelial cells?
M = sertoli cells; F = granulosa cells
From what is the male reproductive tract formed?
Wolffian ducts (mesonephric ducts)
From what is the female reproductive tract formed?
Mullerian ducts (paramesonephric ducts)
What is required for the development of the male reproductive tract?
MIF - in the absence of MIF, the Mullerian ducts will persist
From what are the Wolffian/Mullerian ducts formed from?
Intermediate mesoderm
What is the temporary role of the mesonephric ducts between weeks 6 and 10?
Drainage of urine from the mesonephros (mesonephros = a temporary kidney)
At what point does MIF begin to be produced?
Week 8
At what point do androgens begin to be produced?
Week 8
What do the Wolffian ducts form?
Epididymis; prostate; vas deferens
What do the Mullerian ducts form?
Oviducts; uterus; cervix; upper 1/3 of the vagina
At what point of the male/female reproductive tracts develop?
Week 9
At what point do the external genitalia differentiate?
Weeks 9-12. Development is complete by week 12
At what point do the external genitalia (indifferent) begin to develop?
Week 4
From what do the external genitalia begin to develop?
Five mesenchymal swellings, covered with ectoderm, that form around the cloacal membrane
What are these five mesenchymal swellings from which the external genitalia develop?
1x genital tubercle
2x urogenital folds
2x labioscrotal folds
How is the urogenital orifice and the anus formed?
Rupture of cloacal membrane
What is the purpose of the gubernaculum in males?
‘Guiding’ of the testes into the scrotum, attaching to the testes, while they are at the posterior abdominal wall, and the labioscrotal swellings
What does the gubernaculum form in females?
Round ligament of uterus; round ligament of ovary; suspensory ovarian ligaments
In what week do Leydig and Sertoli cell develop?
Week 8
Between what weeks do the testes descend?
Week 28-40
What week, on average, do the testes descend?
Week 32
What conditions can result from a patent processus vaginalis?
- Indirect inguinal hernia
2. Hydrocele
What is a processus vaginalis formed from?
A diverticulum of the peritoneum (forming between weeks 8-12), that herniates ventral to the gubernaculum. It descends into the scrotum at week 28
What does the processus vaginalis form in the scrotum?
Tunica vaginalis
What is gonadal agenesis?
As a result of a failure of formation or migration of PGCs. The gonads do not develop, but the internal reproductive tract and external genitalia follow the female (default) pathway.
What is true hermaphroditism?
An individual has one testicle, one ovary, and external genitalia that is either of:
- Both genders
- Male only
- Female only
- Ambiguous (most commonly)
What is male pseudohermaphroditism?
Male karyotype and gonads (i.e. testes MUST be present), but phenotype is female or undervirilized (under-masculinised) male
What is female pseudohermaphroditism?
Female karyotype and gonads (i.e. ovaries MUST be present), but phenotype is male or overvirilized (over-mascalinised) female
What is another name for male pseudohermaphroditism?
Complete androgen insensitivity syndrome
From what does the scrotum develop from?
Fusion of the labioscrotal swellings
From what does the shaft of the penis develop from?
Fusion of the urogenital folds
From what is the internal spermatic fascia formed?
Transversalis fascia
From what is the cremasteric fascia formed?
Internal oblique
From what is the external spermatic fascia?
Aponeurosis of external oblique
What forms the foreskin?
A breakdown of the ectoderm over the glans
What is the name of the procedure performed to surgically fix the testes within the scrotum?
Orchidopexy
What are hypospadias?
Ectopic positioning of the urethral meatus on the inferior side of the penis
What % of men with cryptorchidism also have hypospadias?
10%
What are hypospadias caused by?
Failure of the urogenital folds to close
What are epispadias?
Ectopic positioning of the urethral meatus on the superior side of the penis
What condition is associated with epispadias?
Bladder exstrophy
At what meiotic stage are oocytes at birth?
Prophase I
How many oocytes is a female born with?
2 million
How many oocytes does a female have at the beginning of puberty?
300 000
What are epispadias caused by?
Malpositioning of the glans penis
From what is the lower third of the vagina formed from?
Two outgrowths of the urogenital sinus wall - the sinovaginal bulbs. The ascending sinovaginal bulbs fuse with the descending paramesonephric (Mullerian) system, creating the vaginal plate. The vaginal plate canalizes with only the thin covering of the hymen remaining
What are the greater and lesser vestibular glands?
Bartholin and Skene glands release mucus into the vestibule of vagina. They are endodermal outgrowths of the urogenital sinus, and are located on the urogenital diaphragm
What is the clitoris formed from?
Genital tubercle
What is the labia minora formed from?
Partial fusion of the urogenital folds
What is the labia major formed from?
Partial fusion of the labioscrotal swellings
From what is the broad ligament formed from?
A fold of coelomic (or body cavity) epithelium and mesenchyme that is pulled into position when the Mullerian ducts descend through the pelvis
What is the most common congenital abnormality of great development?
Accessory nipples
From what are accessory nipples formed?
When portions of the mammary ridge do not regress
What do mammary glands develop from?
Apocrine sweat glands
What are the remnants of the Wolffian ducts in females?
Epoopheron; paraoopheron; Gartner’s cysts
What are the remnants of the Mullerian ducts in males?
Appendix testes; urtecuris prostaticus
What are the remnants of the Wolffian ducts in females?
Epoophoron; paraoophoron; Gartner’s cysts
What is ovarian hypoplasia?
Underdevelopment of the ovaries
In whom is ovarian hypoplasia seen?
Turner’s syndrome
Ovaries subject to ovarian hypoplasia may be referred to as…?
Streak ovaries
What induces the development of the female mammary gland? And when does this occur?
The presence of oestrogen. It occurs at puberty - embryologically, breast development is identical in males and females
How do breasts develop embryologically?
Week 4 = mammary ridge develops - thickening of the ectoderm from inguinal region to the axilla
Weeks 4-6 = regression of mammary ridge, except at the pectoral region
Week 6 = mammary buds form
Weeks 6-birth = placental hormones (e.g. lactogen) result in lactiferous duct branching. Mesenchyme develops into fat + connective tissue. Nipple formed from a depression in the skin
What causes a double uterus?
When there is no fusion of the Mullerian ducts
What causes a bicornuate uterus?
Incomplete fusion of the Mullerian ducts
What causes a unicornuate uterus?
Failure of one of the Mullerian ducts to develop
What causes a septate uterus?
Incomplete resorption of the uterine septum formed when the Mullerian ducts first form
