Session 1 Embryology of Repro system

• Most of the Repro system is derived from intermediate mesoderm.
• Urogenital ridge differentiates into the nephrogenic cord/ridge that will give rise to the urinary tract and the genital (gonadal) ridge (cord) that will develop into the RS.
• The development of the RS begins with the formation of the genital ridge (cord) in week 4
• Male internal organs/genitalia?

  • Epididymis
  • Vas deferens
  • Testes
  • Seminal vesicles
  • Prostate gland
• Male external organs/genitalia?

  • Penis
  • Scrotum
  • Urethra
• Female internal organs/genitalia?

  • Uterus
  • Cervix
  • Vagina
  • Ovaries
  • Fallopian tube
• Female external organs/genitalia?

  • Labia majora
  • Labia minora
  • Clitoris
• During the 6th week PGCs are incorporated into the gonadal (sex) cords where they will eventually differentiate into oocytes and spermatocytes.
• The paramesonephric (Mullerian) ducts give rise to female genital ducts.
• The mesonephric (Wolffian) ducts give rise to male genital ducts.
• Sexual differentiation is largely influenced by the presence or absence of SRY protein (sex-determining region Y or testis-determining factor (TDF)) encoded by the SRY gene located on Y chromosome.
• Prostatic utricle - remnant of paramesonephric duct
• Gartner's cyst - remnant of mesonephric duct
• Sertoli cells release - Anti-mullerian hormone (AMH) and leydig cells (which secretes testosterone)
• The interaction between Sertoli cells and PGCs plays a key role in development of the male gametes; it inhibits further mitosis of the germ cells and prevent them from entering meiosis.
• the portion of the vas deferens between each seminal vesicle and the urethra is there after called the ejaculatory duct.
• bulbourethral glands is also known as Cowper’s glands
• Gubernaculum in males - descend of testes
• Congenital indirect inguinal hernia - Part of the intestine may descend into the scrotum as a result of the passage between the abdominal cavity and the vaginal process being open (it normally closes in the first year after birth).
• Cryptorchidism - Failure of one or both testes to descend. Risk factor for testicular cancer and subfertility.
• Derivatives of mesonephric ducts? (mesoderm)

  • Vas deferens
  • Epididymis
  • Seminal vesicle
  • Ejaculatory duct
• Derivatives of urogenital sinus in males (endoderm)?

  • urinary bladder
  • Pelvic part - urethra (prostatic and membranous), the prostate and bulbourethral glands
  • phallic part - spongy part of urethra and urethral glands
• Derivatives of paramesonephric duct in females?

  • Cranial part - fallopian tube (uterine tube)
  • Horizontal part - fallopian tube
  • Caudal part - uterus, cervix and upper 1/3 of vagina
• Derivatives of urogenital sinus in females (endodermal)?

  • Vagina (2/3)
  • Urethra
  • Urethral glands, para-urethral and vestibular
  • Vaginal vesibule
• During the 7th week the cloacal membrane is divided by the urorectal septum into a urogenital membrane (ventrally) and an anal membrane (dorsally).
• At the end of the 5th week several cloacal folds form on both sides of the cloacal membrane; they fuse at the anterior end, forming the genital tubercle.

  Lateral to the urethral folds that are formed during week 7, additional pair of prominence are formed, called the genital swelling.
• Differentiation of external genitalia?

  A) penile spongy body

  B) labia minora

  C) penis

  D) clitoris

  E) labia majora

  F) scrotum

  
• Primordial germ cells originate in the ectoderm of the yolk sac.
• PGC's migrate to colonise the primordial gonad - Cortex (future ovary) or Medulla (future testis).
• Function of PGCs after colonizing primordial gonad?

  • Proliferation by mitosis
  • Reshuffles genetically and reduce to haploid by meiosis
  • Cyto-differentiate into mature gametes
• In their arrested state (diplotene) = Primary oocyte

  When primary oocyte is surrounded by granulosa cells = Primordial Follicle
• 3 phases of uterine cycle?

  • Proliferative stage (5-15)
  • Secretory stage (15-28)
  • Menstrual cycle (1-5 /7)
• 3 phases of menstrual/ovarian cycle?

  • Preparatory/follicular phase (1-12) - includes menstruation (1-5)
  • Ovulation (12-15)
  • Luteal/Waiting phase (14-28)
• Selected granulosa cells under hormonal influence accumulate fluid which creates a space between granulosa cells and the oocyte = follicular antrum.
• LH surge triggers rupture and release of ovum.
• Second meiotic division starts at ovulation but is not completed until AFTER fertilisation.
• If conception occurs, once trophoblast has developed, then human gonadotrophic hormone released from the trophoblast maintains the corpus luteum which continues progesterone secretion until 4th month. Thereafter the placenta takes over.
• Fate of corpus luteum if not pregnant?

  • Fills with scar tissue to become corpus albicans
  • Progesterone production reduces, resulting in menstrual bleeding.
• Spermatogenesis: The sequence of events by which spermatogonia are transformed into spermatozoa.
• Spermiogenesis: Transformation of spermatids into mature spermatozoa.