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Flashcards in Lecture 21 & 22 Deck (14):
1

Describe the time-line for development of the genital system.

Gonadal ridge: 5th week

Development of indifferent gonads: before 7 weeks

Ovarian development: 10 weeks

Sexual differentiation: 12 weeks

 

 

2

Describe the development of the gonads and the differentiation into testes and ovaries.

Indifferent Gonadal development:

- Gonadal ridge (medial aspect of mesonephros) at 5 weeks

- primitive sex cords developes from epithelial cords growth into underlying mesenchyme

- primordial germ cells induce the formation of gonads

Differentiation of Gonads:

Female:

- regression of medulla, allows for ovarian development from cortex

- dissociation of primitice germ cells into clustors to form vascular stroma

- surface epithelium proliferates and forms cortical cords

- cortical cords proliferate and split into follicular cells (primordial follicles)

Male:

- regression of cortex and differentiation of medulla allows testicular development

- TDF on SRY gene acts as switch for testis development; induction of condensation and elongatoin of gonadal cords (seminiferous/medullary cords)

- Sertoli cells produce AMH which suppresses female development

- Leydig cells produce testosterone which plays a major role in the development of mesonephric duct and external genitalia

 

3

Describe the descent of the testes into the scrotum and the clinical significance of failure to descend.

2 phases of testicular descent:

1. Transabdominal:

- descent is result of abdominal growth

2. Inguinal

- gubernaculum guided descent under influence of testosterone

- carries ducts and vasculature

- formation of spermatic cord by fascia extensions of abdominal wall

- extension of processus vaginals forms the tunica vaginalis

Clinical Correlation:

1. Congenital Inguinal Hernia:

- patency of processus vaginalis in the inguinal canal

- allows for herniation of intestines

2. Hydrocele:

- processus vaginalis contains fluid before obliterated

- fluid is not reabsorbed

- key characteristic: transillumination

4

Describe defects in testicular descent including cryptorchidism and ectopic testes

Cryptorchidism:

- usually due to pre-mature birth

- testes do not descend into the scortum; unilateral or bilateral

- usually found in inguinal canal

Ectopic Testis:

- lodged in various location after descent through the inguinal canal

5

Describe the development of the male reproductive ducts and associated glands.

- Development of the male genital ducts stimulated by Testosterone in the mesonephric ducts.

- AMH suppresses formation of female ducts

- persistence of mesonephric tubule become efferent ductules which give rise to epididymus

- thickening of mesonephric duct with smooth muscle forms ductus deferens

- outgrowth of caudal end of mesonephric duct forms seminal vesicles

- between duct of gland and urethra forms ejaculatory duct

- endodermal outgrowth of prostatic urethra becomes glandular tissue (prostate), which surrounds the ejaculatory duct

- outgrowth of spongy urethra becomes bulbourethral glands

6

Describe the development of the female reproductive ducts in relation to the paramesonephric ducts, uterovaginal primordium and urogenital sinus.

- Development of female genital ducts from paramesonephric ducts in absence of AMH, and under the influence of estrogen

- caudal paramesonephric ducts fuse in midline to form uterovaginal primordium(UP) -> superior vagina

- UG contacts urogenital sinus (UG) to form sinus tubercle

- sinus tubercle induces endodermal outgrowth to form sinovaginal bulbs

- fusion of sinovaginal bulbs forms vaginal plate which breaks down to form vaginal canal

- invagination of posterior wall of UG forms hymen

- bilateral outgrowths from vagina forms urethral and paraurethral glands

- outgrowth of UG in lower 1/3 of labia majora forms greater vestibular glands

7

Describe the development of birth defects of the female genital tract including a double uterus, a unicornuate uterus, a bicornuate uterus vaginal agenesis and imperforate hymen.

Double Uterus:

- failure of uterovaginal primordium to fuse

Bicornate Uterus:

- incomplete fusion of superior portion of uterovaginal primordium

Unicornate Uterus:

- incomplete development of one of the paramesonephric ducts

Rudimentary Horn:

- failure of parts of one or both paramesonephric ducts to develop

Vaginal Atresia:

- incomplete canalization of vaginal canal

Vaginal Agenesis:

- failure of sinovaginal bulbs to develop and form the vaginal plate

- usually accompanied with the absence of uterus; development of the uterus induces the formation of the sinovaginal bulbs

Imperforate Hymen:

- failure of the vaginal plate to perforate

8

Describe the anatomical location, mechanism and clinical sequences of canal of Nuck hernias.

- Round Ligament passes through the inguinal canal on its way to the labia majora and carries with it the processus vaginalis.

- patency of the processus vaginalis is called Canal of Nuck, in which hernias and hydroceles can occur.

9

Describe the formation and differentiation of the external genitalia of males and females from the urogenital folds and labioscrotal swelling.

Males:

1. genital tubercle: penis

2. urogenital folds: fuse to form ventral surface of penis and spongy urethra

3. phallic portions of UG sinus: most of penile urethra

4. labioscrotal swellings: fuse to form scortum

Females:

1. phallic tubercle: clitoris

2. urogenital folds: labia minora

3. phallic portion of UG sinus: vesitbule of vagina

4. labioscrotal swellings: labia majora

10

Explain the developmental mechanism responsible for the formation of hypospadias and epispadias.

Fusion of the urethral folds beginning posteriorly along the ventral surface of the penis forms the spongy urethra and the penile raphe

Hypospadias:

- failure of urethral folds to unite

- 3 types: glanular (most common; durectly below glans penis), penile (along spongy/penile urethra), and perineal (along scrotal raphe)

Epispadias:

- urethra opens on the dorsal surface of penis

- associated iwth exstrophy of bladder

- inadequate ectodermal-mesenchymal interactions

11

Describe the identification and clinical significance of disorders of sex development (DSD’s)

Ovotesticular DSD (True Hemaphroditism):

- both ovarian and testicular gonads develop

- 46, XX

- ambiguous genitalia

46, XY DSD:

- inadequate production of testosterone and AMH in-utero

46, XX DSD:

- females exposed to excessive amount of androgens

- adrenal hyperplasia

- masculinization of external genitalia; enlarged clitoris, partial fusion of labia majora, persistent UG sinus

AIS:

- female, but 46, XY

- blindly ending of vagina, rudimentary/absent uterus and uterine tubes

- testes present in inguinal canal

12

Describe the consequence of decreased levels of dihydrotestosterone on development of male characteristics.

- genetically 46, XY with testes, but appears female

- undergo masculinzation at puberty and descent fo testes

13

Describe the formation and clinical significance of Gartner duct cysts.

cysts develop from embryologic remnants of the Wolffian (mesonephric) duct.

14

Discuss the level at which the gonads develop and its relationship to referred pain.

Gonads develop at T10, carrying it innervation with it, as it descends. Pain is referred to T10 when gonads injuried.