Sexual Differentiation & Descent of Gonads Lecture Flashcards
When does the adrenal gland/suprarenal gland start developing?
4th wk
Where does the cortex of the adrenal gland come from?
Coelomic mesothelium cells that bilaterally (T6-T12) line the posterior abdominal wall
Where does the medulla of the adrenal gland come from?
Neural crest cells - ultimately forms chromaffin cells (norepinephrine)
In the 5th month, the fetal adrenal cortex is huge (75% androgens & glucocorticoids), but will shrink after birth. It receives _____ stimulation (__) to produce steroid hormones such as __.
Adrenal cortex receives hypothalmo-hypophysial stimulation (ACTH) to produce steroid hormones such as glucocorticoids
The adrenal cortex has 3 layers (steroids): Outermost to innermost
Zona glomerulosa
Zona fasiculata
Zona reticularis
The adrenal ____ has cells that make norepinephrine and epinephrine.
Medulla
Adrenal cortical hyperplasia - overproduction of androgens; could lead to
female pseudo-intersex problems
Male reproductive system
- Testis
- Seminiferous tubules (germ cells &Sertoli cells)
- Leydig cells
- Rete testes
- Epididymis
- Vas deferens
- Urethra
Female reproductive system
Ovary Follicles & germ cells Fallopian tube Uterus Vagina Urethra
Development of the urogential system begins at the start of week __ and ends in the third trimester.
4
Week 4: Forming the gonadal blastema (primitive gonad).
Primordial germ cells in the umbilical vesicle/yolk sac migrated up the ___ of the gut and entered the embryo proper to the medial aspect of the ____ (primitive kidneys).
This forms the ___ - thickened coelomic epithelim.
Formation of the gonadal blastema:
- Primordial germ cells in the yolk sac migrated up the dorsal mesentery.
- Entered embryo proper medial to the mesonephros.
- Formed gonadal ridge.
- Sex cords
The gonadal blastema (indifferent until wk7) are derived from what 3 cell types/sources?
- Coelomic epithelium
- Mesonephric tubules and mesenchyme
- Primitive germ cells
Weeks 4-7 is the
Indifferent stage: external genitalia between male and female are indistinguishable
In ____, the medulla gives rise to medullary cords. In ____, the cortex gives rise to cortical cords.
Testes- medullary cords
Ovaries-cortical cords
What drains the mesonephros? What does it give rise to?
Mesonephric duct
Becomes epididymus in males
In week 7, those primordial germ cells from the yolk sac that entered the embryo proper are now ___.ing
Differentiating such that you can distinguish between a male and female gonad.
Ectopic germ cells
Primitive germ cells don’t go where they’re supposed to go –> can form yolk sac tumor, but don’t form ectopic gonads.
The Y chromosome defines the sex of embryo at feritlization. What does it have that causes morphologic change in week 7?
Testis-determining factor: drives development the primary sex cord that extend into the medulla.
Because females don’t have TDF, they will develop ovaries instead.
Primary sex cord later becomes ___, which house the ____ and __.
Seminiferous tubules, which house the maturing spermatogonia and sertoli cells
Sertoli cells’ 2 functions
- Nurture developing spermatogonia.
- Produces Anti-mullerian hormone (AMH): causes mullerian duct to degenerate
Spermatogonia in the sertoli cells mature into spermatids that then go out the __ and the _.
Leave via tubuli recti and reti testis
Anti-mullerian hormone from Sertoli cells causes…
- Paramesonephric (Mullerian) ducts to degenerate
- ___ cells in the ____ to differentiate into ___, which secrete ___.
Mesenchymal cells in the gonadal ridge to differentiate into Leydig cells, which secrete testosterone & dihydrotestosterone
What causes the seminiferous tubules to canalize, mature, and commence spermatogenesis at puberty?
Testosterone- it also induces other pubertal changes
What causes the indifferent external genitalia in the male to differentiate into a penis and scrotum?
Dihydrotestosterone
Testosterone & dihydrotestosterone both bind androgen receptors.
Ductus deferens is formed from the ____.
Sertoli cells produce __ that suppresses the ____, so that the fallopian tube can’t develop.
Ductus deferens (vas deferens) is formed from the Mesonephric/Wolffian duct
Sertoli cells produce the AMH to suppress the Paramesonephric/Mullerian duct so that the fallopian tube can’t develop.
What maintains the mesonephric duct (Wolffian ducts)? What does this duct give rise to?
LEYDIG CELLS maintain the Wolffian duct. Wolffian duct gives rise to VAS DEFERENS.
Ovaries are not recognizable until week __, when germ cells get incorporated into ___ that break into follicles in the __.
Week10:
Germ cells get incorporated into the cortical cords, which will break into follicles in the cortex.
Remember: When an ovary ovulates, the follicles rupture through the cortex.
Paramesonephric (Mullerian) ducts form bilaterally, lateral to the mesonephros as a longitudinal invagination of ___ ___.
Longitudinal invagination of COELOM EPITHELIUM
In month 7, as the ovary develops, the ___ degenerates and the ovary is suspended by a mesentery, the ___.
Mesonephros degenerates, paramesonephric persists.
Ovary suspended by mesentery, the broad ligament
What does the paramesonephric (Mullerian) duct give rise to?
Cranial segment - fallopian tube, ampulla
Horizontal segment - Intramural part of fallopian tube & fundus of uterus
Caudal segment- fuse to form Y-shaped uterovaginal primordium
Wk 9- The paramesonephric (Mullerian duct) reaches the junction of the urethra and UG-sinus –> begin vagina development.
Where is the superior part and inferior part derived from?
Superior part (upper 1/3) derived from uterovaginal canal (paramesonephric duct)
Inferior part (lower 2/3) is an outgrowth of the urogenital sinus (sinovaginal bulbs)
Vaginal epithelium is from
UG sinus
____ forms a solid plate of cells, the ____, which canalizes to form the vagina and its fornicles.
Sinovaginal bulbs form the vaginal plate that canalizes into the vagina & fornicles.
Incomplete/lack of fusion of the paramesonephric ducts can lead to
Uterus didelphis
Uterus bicornuous
Uterus bicronis unicollis
Uterus didelphis- 2 uteri
Uterus bicornuous- uterus has 2 horns and 1 vagina
Uterus bicronis unicollis - atresia (complete or partial) of one paramesonephric duct, so one fallopian tube isn’t developed.
Double vagina & atresia of the vagina result form problems with ___ formation.
Sinovaginal bulb
In the 3rd week, the genital swellings form by the cloacal membrane.
Labioscrotal folds (lateral)
Urogenital folds (medial)
In the 4th week, the genital swellings unite to form ____, which becomes the __ in the male and the __ in the female.
Genital tubercle
Becomes penis &clitoris
Development of female external genitalia - vestibule of vagina, labia minora, and labia majora
Vestibule of vagina (urethra, vagina, and ducts) come from phallic portion of the UG sinus
Lack of androgens prevents elongation of the genital tubercle into a penis.
Instead, UG folds become labia minora Labioscrotal swellings become labia majora
Development of male external genitalia
Penis
Penile urethra
- DHT induces elongation of the genital tubercle > phallus > penis
- Penis grows, pulling the endoderm UG folds toward the midline/ventrally to form…
- wall of the urethral groove
- Urethral plate
- Canalizes into urethral folds
- Folds fuse into penile urethra
If the urethral folds don’t fuse
Then you don’t get an external urethral orifice on the penis –> hypospadias: urethra opens on the ventral side of the penis.
Glandular hypospadias
Urethra is on ventral surface of glans penis (common)
Penile hypospadias
Uretrha opens on the body of the penis (most common)
Penoscrotal hypospadias
Urethra opens on the base of penis or scrotum with chordee (ventral curvature of penis)
Perineal hypospadias
Associated with chordee, bifid scrotum, cryptochidism
Epispadias- what is it, what causes it, and what are the types
Urethra orifice opens on the dorsal (stomach side) aspect of the penis because the genital tubercle develops more dorsally, so the UG sinus opens dorsally. Can be glandular, penile, or penopubic (associate with extrophy of bladder)
Cause of hypospadius
DHT insufficiency/androgen receptor problems causes failure of the urethral folds to fuse
Indifferent embryo begins phenotypic sexual differentiation during week
7
True intersexuality
46,XX Have both ovarian & testicular tissue; could have separate gonads or ovo-testes
External male pseudo inersexuality
External genitalia are poorly developed due to -Inadequate DHT -Delayed DHT production -Lack of androgen receptors –> testicular feminization/androgen insensitivity syndrome -Mutant androgen receptors (splice variants & point mutations)
Internal Male pseudo intersexuality
normal external genitalia, but internally have a uterus and fallopian tubes (Mullerian duct derivatives) & undescended testis
Testicular feminization/androgen insensitivity syndrome
testes made, but body and external genitalia are female; may have rudimentary vagina & Mullerian duct derivatives
Female pseudo-intersexuality What’s the chromosome? What’s the cause? What are the signs?
46, xx Hypertrophy of clitoris, partial fusion of labia majora (looks like scrotum, Masculinization has broad range Caused by adrenogenital syndrome (
Adrenogenital syndrome (not an LO)
Inborn errors in the steroid hormone synthesis in the adrenal glands. Autosomal recessive traits. Deficient enzymes needed for cortisol synthesis –> decreases ACTH needed for steroid biosynthesis –> instead of cortisol, we get androstenidione. Babies have cliteromegally, fusing of labia majora, pigmented scrotum, enlarged adrenal glands.
Descent of testes into the scrotum
- Testes starts on the posterior abdominal wall attached to a UG mesentery. Ventral part of this mesentery is the gubernaculum testis.
- Gubernaculum passes through anterior abdominal wall and attaches to labioscrotal swelling. Contracts in response to DHT to bring down the testis.
- Processus vaginalis forms as an evagination of peritoneum of coelomic cavity thru ventral abdominal wall; carries with it all the layers of the anterior abdominal wall.
- Processus vaginalis closes off while the testes stays wrapped in layers of abdominal wall.
Difference between congenital inguinal hernia and hydrocele
In a congenital inguinal hernia, the gut herniates thru the patent processus vaginalis into the tunica vaginalis. In a hydrocele, peritoneal fluid passes into the tunica vaginalis.
Cryptorchidism
Undescended testes (75% in inguinal canal, 25% in abdomen) Cause: multifactorial- insufficient DHT Significance: psychological impact, reduced fertility, cancer
Descent of ovaries.
The gubernaculum ovary’s cranial part - ovarian ligament
Caudal part - round ligament of uterus
Gubernaculum passes thru inguinal canal and anchors into labia majora
