Embryology Flashcards
Where do the urinary and internal repro organs develop from?
intermediate mesoderm
What determines the male development?
The Y chromosome has the SRY gene - the protein product of this gene is TDF which masculiizes the indifferent genital system by causing testes development.
- testes develop and secrete testosterone which results in further masculinzation
What do sertoli cells?
MIF - result in paramesonephric duct’s regression
What do Leydig cells do?
secrete testosterone, which results in formation of DHT
What does testosterone do?
- secreted from Leydig cells
- transforms mesonephric duct and mesonephric tubules into male genitalia ducts and glands
- development of efferent ductules, epidymis, ductus deferens, seminal vesicle and ejaculatory duct
- MASCULINIZES GENITALIA
What does DHT do?
determines hormonal sex
- development of UG sinus/indifferent genitalia to penis, scrotum, prostate gland, prostatic urethra and penile urethra
What is the indifferent stage?
- genital (gonadal) ridges form from intermediate mesoderm
- epithelium (cortex) grows into underlying mesoderm to form primitive sex cords (medulla)
- Primitive germ cells migrate to genital ridges week 4-6. If PGC’s don’t migrate, then gonads will not form
What does TDF do?
TDF induces the indifferent gonad to form testes
- Medulla of primary gonad will form testes (the primitive sex cords will remain as solid tubes until canalization at puberty, where they will form SF tubules, rete testes). Testes start to secrete testosterone at week 8.
- Cortex of primitive gonad will form tunica albuginea
What controls descent of testes?
Testosterone
what is the gubernaculum?
thick ligament that attaches the caudal pole of the testes to the anterior body wall (future site of deep inguinal ring) - aids in descent of gonads
What is the processus vaginalis?
an evagination of peritoneum that passes through the abdominal wall lateral to the site of attachement of the gubernaculum
How do the testes descend?
- the processus vaginalis and gubernaculum (and thus testes and ductus deferens) are pulled through the abdominal wall, forming the inguinal canal
- The proximal portion of the processus vaginalis closes (closes around deep inguinal ring, if not closed can lead to indirect hernia); the distal portion form tunica vaginalis around testes
What is the indifferent stage?
- two duct systems are formed from intermediate mesoderm
1. Mesonephric (Wolffian ducts): mostly contribute to male ducts - form internal genitalia
2. Paramesonephric (Mullerian) ducts: mostly contribute to femal ducts
What does Antimullerian hormone do?
AMH is secreted by sertoli cells
- will inhibit the formation of the paramesonephric ducts, and prevent development of femal genital ducts
What do male mesonephric tubules turn into?
efferent ductules, appendix and epididymis
What do mesonephric ducts turn into?
epididymis, ductus deferens, ejaculatory duct, seminal vesicle
What does urethra in males give rise to?
prostate and bulbourethral glands
What happens with paramesonephric duct in males?
it regresses except for the appendix of the testes and prostatic utricle
What happens with cloacal folds of indifferent stage in males?
The cloacal folds are mesenchymal swellings around the cloacal membrane
- they will divide into urethral and anal folds
- they will anteriorly fuse to form the genital tubercle
- when testosterone and DHT are produced around 12 weeks, they will continue to grow into the penis.
What forms the anus?
anal folds
what forms the glans penis?
genital tubercle
what forms the shaft, root of penis and penile urethra?
urethral folds
- the elongate along with the genital tubercle.
- the urethral groove is an open grove on the ventral penis
- the two urethral folds with fuse to form the penile urethra
- the remaining portion of the urethra (in the glans penis) is formed by ectodermal cells that grow inward.
what froms the scrotum?
Labioscrotal swellings
- scrotal septum forms where the two swellings fuse
hypospadias
- caused by incomplete fusion of the urethral groove on ventral surface of penis.
- abnormal opening of penile urethra on ventrl surface of penis
- DEPENDENT ON TESTOSTERONE
Epispadias
- urethral opening is on dorsum of penis
- often occurs with exstrophy of the bladder
- thought to be due to urethral plate developing more dorsally than normal
TESTOSTERONE DEPENDENT
Congenital indirect inguinal hernia
cause: proximal processus vaginalis remains patent
- intestinal loops pass through the open passageway
- more common in males
Hydrocele
Fluid filled sac around scrotum or spermatic cord
- cause: excessive serous fluid f=production
cryptorchidism
- failure of testes to descend into scrotum
TESTOSTERONE DEPENDENT
undescended testes will be infertile due to temperature dysregulation - one of the biggest risk factors of testicular cancer
what does absence of TDF induce?
- indifferent gonad to form the ovary
- sex cords in medulla degenerate
- second generation of cortical sex cords form from the epithelium; these form the follicular cells around the oogonia
- Cortex forms ovary; medullar regresses
what does female gubernaculum form?
forms the ovarian ligament and round ligament of the uterus
what will processus vaginalis form in female?
very small, obliterates before birth
female mesonephric duct?
mostly regresses
female paramesonephric duct?
mostly contributes to female ducts
- cranial end opens into abdominal cavity to form tubes
- caudal end fuse and enters cloaca to form body of uterus
What does absence of AMH result in?
no testosterone production.
- allows paramesonephric ducts to differentiate into female genital ducts.
- mesonephric ducts degenerate in absence of testosterone
what forms the uterine tube
cranial end of paramesonephric duct
what forms the uterus, cervix, superior vagina?
caudal fused portion of the paramesonephric ducts
what forms the inferior portion of the vagina?
sinovaginal bulb (vaginal plate)
- forms from the urogenital portion of the cloaca - induced by the paramesonephric ducts.
- initally forms a solid tube called the vaginal plate which canalizes by 5th months
- forms the hymen
- urethral endoderm will give rise to greater vestibular and skene’s gland
what forms the clitoris?
genital tubercle
what forms labia minora
urethral folds
- urethral groove remains unfused and will form the vestibule
what forms labia majora
labioscrotal swellings.
uterus arcuatus
slight lack of fusion of paramesonephric ducts: slight indentation seen at fundus of uterus
uterus didelphys
double uterus with double vagina
- complete lack of fusion of paramesonephric ducts and formation of two sinovaginal bulbs
- most extreme!
uterus bicornis (bicollis)
partial lack of fusion of paramesonephric ducts
- see two uteruses, but one vagina
uterus unicornis
complete agenesis of one paramesonephric duct
vaginal and cervical atresia
atresia of the sinovaginal bulbs or failure of canalization
remanants of mesonephric tubules and ducts?
- epoophoron (tubules)
- paroophoron (tubules and duct)
- gartner’s duct: remant of caudal mesonephric duct
- ** all of the above can become cystic
klinefelter syndrome
cause: nondisjunction during meiosis
47, XXY; male
- infertile due to low levels of testosterone; aspermatogenesis
- impaired sexual maturation
- gynecomastia
- external genitalia is male; but at puberty don’t develop secondary male characteristics
- high levels of estrogen results in more female secondary sex characteristics.
Turner syndrome
45 XO
cause: nondisjunction during meiosis
- ovaries don’t form, testes don’t form
- gonadal dysgensis occurs and there is streak gonads (persistent genital ridge)
- lack of secondary sex characteristics at puberty
- short stature, broad chest, short neck, lymphadema of hands and feet
Swyer syndrome
46 XY
Cause: point mutation of SRY gene results in defective TDF production
- gonadal dysgenesis occurs and streak gonads develop. Thes gonads can become cancerous and are often removed before puberty
- female external and internal genitalia (except for ovaries)
- amenorrhea
- lack of secondary sex trait characteristics because no ovaries = no estrogen
True hermaphroditism
extremely rare!
- presence of male and femal gonadal tissue
“ovatestes” - ovarian and testes tissue found in same gonad
- most have 46, XX
- cause is due to translocation of portion of Y containing SRY gene onto X
- ambiguous external genitalia
female psuedohermaphroditism
46, XX –> has ovaries
- external genitalia is opposite of genotype
cause: congenital adrenal hyperplasia (excessive production of androgens by adrenal glands) - internal reproductive organs are female
- masculinization of external genitalia due to hyperactive corted secreteing testosterone which causes vaginal plate to regress and enlarged clitoris that looks like a penis
male psudohermaphroditism
46, XY
- phenotypically female
- testes form due to normal functioning Y chromosome
- insufficient androgen production and AMH results in hypogonadism
- external and internally genitalia is female
androgen insenstitivy syndrome
46 XY
- has testes due to normal functioning Y chromosome
- AMH and testosterone production is normal
- lack androgen receptors on the tissues - they tissues are not responsive to testosterone
- mesonephric duct degernerates due to insensitivity to testosterone
- paramesonephric duct degenerates as well because of AMH
- have female external genitalia; including secondary sex traits
- vagina is short and blind-ending
- no internal genitalia besides undescended testicles
