Dr. Indran 11 Urogenital System II Flashcards
What are the 4 common features in both male and female systems?
pair of gonads, a system of ducts an external genitalia and accessory glands
Timeline of phenotypic development of the indifferent embryo
Indifferent Gonad and phenotypically indistinguishable embryo: 1- 6 weeks
Beginning of phenotypic sexual differentiation: 7th week
Male/female external genitalia recognition: 12th week
Completion of phenotypic differentiation: Week 20
True or False: In the first stage of gonadal development, it is impossible to distinguish between the male and female gonad:
True, indifferent stage
8.6.1
The gonads begin as _____.
genital ridges
¤A pair of longitudinal ridges derived from intermediate mesoderm and overlying epithelium
¤They i_nitially do not contain any germ cells_
In the fourth week, primordial germ cells begin to migrate from the yolk sac wall to the genital ridges, via the dorsal mesentary of the hindgut:
¤They reach the genital ridges in the sixth week
Explain this image
M: Mesonephros; GR: Genital Ridge; Arrowhead: Mesonephric Duct
8.6.1
Primordial germ cell migration: complete by 6 weeks
8.6.1
Once in the gonads, the germ cells then start to pattern the gonads and their associated ducts
Simultaneously, the epithelium of the genital ridges proliferates and penetrates the intermediate mesoderm to form the primitive sex cords
¨The combination of germ cells and primitive sex cords forms the indifferent gonad:
¤Would develop into the testes or ovaries
Primordial germ cells have i_nductive effect_ on genital ridge, if they fail to reach, the ridges will fail development into ovary or testis
Influence of Primordial Germ Cells on Indifferent Gonad:
Sex Determination
Gonadal sex is determined by the SRY gene
The SRY protein (Sex-determining Region Y protein) or the testis determining factor causes the development of the indifferent gonad into testis
Testis Development
Primitive sex cords proliferate and penetrate deep into the medulla:
Testis cords/ Medullary cords
At hilum, cords break up into a network of cell strands:
Rete testis
In the 4th month, primitive sex cords become horseshoe shaped and the extremities are continuous with rete testis
Testis cords now have primitive germ cells or primordial germ cells and sustentacular cells of Sertoli
______ cells
¨ Derived from genital ridge epithelium
¨ Produce antimüllerian hormone (AMH also called müllerian-inhibiting substance [MIS])
¨ Postnataly, when sperms are formed, serve as nurse cells for sperms
Sertoli
8.6.1
____ cells
¨Derived from mesenchyme of genital ridge
¨ Secrete testosterone
¨ Influences development of genital ducts (mesonephric ducts, tubules, etc.;) an external genitalia (dihydrotestosterone influences external genitalia development)
Interstitial cells (of Leydig):
Testis cords acquire lumen at puberty:
Seminiferous tubules
Join with rete testis
Rete testis opens into ductul efferentes
Development of the ovary stages
Primitive sex cords dissociate into irregular cell clusters:
q Cell clusters reach the medulla and degenerate
q Vascular stroma then replaces the medulla
A second generation of cords (secondary cords or cortical cords) develop from surface epithelium, but remain confined to the cortex:
qSplit into isolated cell clusters
- Surround oogonium (by now the primordial germ cells have become oogonia) with a layer of epithelial cells:
qFollicular cells
Primary oocyte + Follicular cells:
primordial follicle
By 20 weeks, all oogonia have become primary oocytes
Initially both male and female embryos have 2 pairs of genital ducts
Mesonephric duct or Wolffian duct
Paramesonephric duct or Mullerian duct (not in male)
Development of Male Genital Tubules and Ducts
Mesonephric tubules are 2 types:
Epigenital Tubles:
Form efferent ductules
Paragenital Tubules:
Normally degenerate
If remain:
Form paradidymis
Mesonephric ducts caudal to epigenital tubules will form epididymis and vas deferens
Development of Female Genital Ducts and Tubes
Paramesonephric duct is divided into 3 parts:
Cranial Vertical Part: Forms Uterine Tube
Middle Horizontal Part: Forms Uterine Tube
Caudal Fused Vertical Part or Uterovaginal Primordium: Forms Uterus and Upper Vagina
Formation of Uterus and Vagina
Paramesonephric (Mullerian) ducts fuse to form uterus and upper 1/3 of vagina
Lower 2/3 of the vagina from the UROGENITAL SINUS
Induction of the Vagina by the Paramesonephric Ducts
Uterovaginal primordium has inductive effects on urogenital sinus:
- Two solid buds grow out from the pelvic part of urogenital sinus
- Sinovaginal bulbs
Vaginal Development
Upper one third from uterovaginal primordium
Lower two thirds from sinovaginal bulbs
The sinovaginal bulbs, proliferate and form a solid vaginal plate which gets canalized by the 5th month
hymen, thin tissue plate seprates lumen of vagina or urogenital sinus
- 6.1
- 6.1
Uterine Abnormalities
Didelphys (double uterus) anomalies: Occur when there is a complete lack of fusion of the paramesonephric ducts (uterus didelphys bicollis – two uteruses + two cervices)
Bicornuate uterus anomalies Occur when there is partial fusion of the paramesonephric ducts
Septate uterus anomalies Occur when the medial walls of the caudal portion of the paramesonephric ducts partially or completely fail to resorb
External Genitalia Development in Male
Dihydrotestosterone (DHT), causes genital tubercle to elongate: Forms phallus of penis
Phallus growth pulls up urethral folds, urethral groove and phallic part of urogenital sinus
At the end of 3rd month, urethral folds close: Form penile raphe
Urethral groove and phallic part of urogenital sinus form bulbar and spongy urethra
Genital swellings (scrotal swellings) fuse: Form scrotum
Line of fusion of scrotal swellings: Scrotal septum
Development of Glans Penis
8.6.1
epithelial cord
This cord later canalizes and forms:
External urethral meatus
Glandular part of urethra
External Genitalia Development in Female
Genital tubercle: Elongates slightly (no DHT): Forms clitoris
Urethral folds: Do not fuse Develop into labia minora
Genital swellings: Enlarge: Form labia majora
Urogenital groove is open and forms the vestibule
Hypospadia toward ventral side, Epispadias toward dorsum side
Incomplete fusion of the urethral folds:
- Abnormal openings of the urethra occur along the inferior aspect of the penis
Penis curved downward/ventrally:
- Chordee
Episadis: Most often associated with exstrophy of the bladder in which infraumbilical part of ventral abdominal wall fails to develop
Testicular Descent
8.6.1
Frontal View
8.6.1
_______
Processus vaginalis persists
________
Sometimes part of process vaginalis persist and form small cyst
Congenital inguinal hernia:
Cyst of spermatic cord
______
Testis fails to descend
________
Testis fails to descend but lies in normal path of descent
_______
Testis lies outside the normal path of descent
Cryptorchidism:
True Cryptorchidism:
Ectopic testis
Descent of Ovary
Homologs in the Male and Female Urogenital System
