9.27.11+-+Embryology+of+the+Urogenital+System

OBJECTIVES: 1. Name the three initial structures formed by condensation of the intermediate mesoderm, and describe what each of these three structures gives rise to in the adult.
 * Pronephros-goes away
 * Mesonephros
 * mesonephric mesenchyme -- salt balance (until week 10) and gonads
 * mesonephric duct -- ureters in both genders, male genital tubes
 * paramesonephric duct -- female genital tubes
 * Metanephros

2. Describe how the ureteric bud and metanephric mesenchyme gives rise to the kidneys and urine-collecting system. Describe how the interaction can sometimes result in two ureters, and how a supernumerary (i.e., an extra) ureter can drain into the vagina or urethra, resulting in incontinence.
 * The metanephric mesenchyme induces formation of a diverticulum from the Mesenephric duct – the ureteric bud – that grows towards and into the metanephros
 * Bilateral branching occurs (similar to that in the lung) and the initial 3-4 bifurcations fuse. If this doesn't happen, you may form 2 ureteric buds. 1 might be below the sphincter or attached to the vaginal wall resulting in incontinence.

3. Describe the ascent of the kidneys from the pelvis into the abdomen, and how this ascent can sometimes be blocked, resulting in developmental abnormalities. Explain what is meant by a "horseshoe" kidney. Explain why supernumerary renal arteries are frequently seen, and how they relate to this ascent of the kidneys.
 * 1) Kidney ascends from the pelvis into the abdomen, and as it ascends, it rotates 90° medially (from the perspective of the embryo)
 * 2) Kidney needs to maintain is blood supply during its ascent


 * Failure to resorb transient renal arteries results in the presence of accessory renal arteries (supernumerary), which may or may not be a problem in the adult.
 * During ascent, the kidneys can get entangled by the gonadal arteries, trapping the kidney in the pelvis region.
 * Horseshoe kidney: caudal portion of kidneys fuse and get snagged by the IMA during ascent

4. Describe the cloaca and how it is divided by the urorectal septum to give rise to the rectum and urogenital sinus. Name the adult structure that arises from the caudal tip of the urorectal septum. Describe how parts of the urogenital sinus gives rise to the median umbilical ligament, the urinary bladder (including the trigone region), and the urethra. Describe how failure of the cranial portion of the urogenital sinus to form properly can result in urachal fistulas, cysts and sinuses, or even extrophy of the bladder.
 * Septation of the Cloaca into the Urogenital Sinus and Anorectum
 * 1) Growth of urorectal septum (splanchnic mesoderm covered with endoderm)
 * 2) Fusion of the urorectal septum with the cloacal membrane to form the perineal body, as well as two chambers -- the anorectal canal and the urogenital sinus.
 * 3) Where the urorectal septum fuses with the cloacal membrane becomes the perineal body of the adult -- a structure that serves as a very important supportive structure.
 * 4) Resorption of the mesonephric duct into wall of the urogenital sinus, giving rise to separate connections of the ureteric buds (i.e., ureter anlage) and the mesonephric duct.
 * median umbilical ligament: tissue that represents the embryonic urachus. The urachus is a remnant of the allantois that drains the bladder of the fetus via the umbilical cord.
 * The urogenital sinus has three regions: alantois, urinary bladder anlagen, urethra/perineum anlagen
 * the trigone region of the bladder is derived from the caudal end of mesonephric duct
 * Urachal fistulas: Urine can flow out of the umbilicus
 * Urachal cyst and sinus: When the urachal lumen incompletely obliterates
 * Extrophy of the bladder: The bladder pushes out due to the failure of the abdominal wall to close during fetal development and results in protrusion of the posterior bladder wall through the lower abdominal wall

5. Describe how the presence or absence of the SRY gene product determines the gender of the individual.
 * SRY gene product is TDF (testes determining factor) a transcription factor that facilitates the production of dihydrotestosterone via 5alpha reductase and the induction of leydig and sertoli cells which produce testosterone and mullerian inhibitory substance

6. Explain what is meant by the "indifferent gonad" and how it forms from the mesonephric mesenchyme. Describe the changes that occur in the indifferent gonad of the male to form the testes. Describe the changes that occur in the female to form the ovary. Describe how the mesonephric duct forms the genital tubes associated with the testes, and how the paramesonephric duct forms the genital tubes associated with the ovary. Specifically, identify those portions of the embryonic genital tubes or urogenital sinus that gives rise to: MALE ductus deferens-Mesonephric duct seminiferous tubules-Primary sex cords + PGCs rete testes-Primary sex cords efferent ductules-Mesonephric duct urethra-middle pelvic portion of the urogenital sinus? ejaculatory ducts- Mesonephric duct prostate-middle pelvic portion of the urogenital sinus? seminal vesicles-Mesonephric duct bulbourethral gland-Mesonephric duct? FEMALE uterine tubes-paramesonephric duct uterus-paramesonephric duct vagina-paramesonephric duct greater vestibular glands? paraurethral glands? urethral glands?


 * Indifferent Gonad: Gonad that can either form the ovaries or the testis.
 * 1) Mesothelium thickens
 * 2) invagination of mesothelium--> primary sex cords
 * 3) mesonephric duct migrates
 * 4) PGC associates with primary sex cord
 * 5) "indifferent gonad"
 * In Males
 * 1) PGC associates with primary sex cords
 * 2) primary sex cords suppress differentiation
 * 3) testosterone keeps sex cords alive
 * In Females
 * 1) primary sex cords die
 * 2) PGC is stranded (I think)
 * 3) Secondary sex cords form epithelium and envelop the PGC

7. Explain how problems associated with fusion of the caudal portions of the paramesonephric tubule can result in abnormalities of the uterus, cervix and vagina. Explain how problems associated with fusion of the ventral raphé of the penis can result in hypospadia.
 * uterus dideiphys with double vagina, uterus arcuatus, uterus bicornis, atresia of cervix, atresia of vagina
 * Hypospadia of penis: abnormally located opening of urethra (somewhere along the ventral raphe)?

8. Describe the location where the primordial germ cells originate, how they migrate into the gonads, and how mis-migration of these cells can result in teratomas.
 * May originate from the yolk stalk. They can differentiate into specific cells depending on the external influences