Page 662 - First Aid for the USMLE Step 1 2020, Thirtieth edition [MedicalBooksVN.com]_Neat

618 SectioN iii RepRoductive ` REPRODUCTIVE—EmbRyOlOgy RepRoductive ` REPRODUCTIVE—EmbRyOlOgy

Umbilical cord Two umbilical arteries return deoxygenated Single umbilical artery (2-vessel cord) is
blood from fetal internal iliac arteries to associated with congenital and chromosomal
placenta A . anomalies.
One umbilical vein supplies oxygenated blood Umbilical arteries and vein are derived from
from placenta to fetus; drains into IVC via allantois.
liver or via ductus venosus.
A
Stomach
Umbilical artery Umbilical artery

Liver bud
Vitelline duct Umbilical
arteries Allantoic duct Umbilical
Allantois Primitive Umbilical vein
intestine Allantoic ducts vein
Amniotic epithelium Wharton jelly Cord lining membrane
Umbilical Hindgut Wharton
ring jelly
Urachus Allantois forms from hindgut and extends into urogenital sinus. Allantois becomes the urachus, a
duct between fetal bladder and umbilicus. Failure of urachus to involute can lead to anomalies
that may increase risk of infection and/or malignancy (eg, adenocarcinoma) if not treated.
Obliterated urachus is represented by the median umbilical ligament after birth, which is covered
by median umbilical fold of the peritoneum.
Patent urachus Total failure of urachus to obliterate Ž urine discharge from umbilicus.
Urachal cyst Partial failure of urachus to obliterate; fluid-filled cavity lined with uroepithelium, between
umbilicus and bladder. Cyst can become infected and present as painful mass below umbilicus.
Vesicourachal Slight failure of urachus to obliterate Ž outpouching of bladder.
diverticulum

Umbilicus

Normal Patent urachus Urachal cyst Vesicourachal diverticulum
Umbilicus
Vitelline duct 7th week—obliteration of vitelline duct (omphalomesenteric duct), which connects yolk sac to
midgut lumen.
Vitelline fistula Vitelline duct fails to close Ž meconium discharge from umbilicus.
Umbilicus
Meckel diverticulum Partial closure of vitelline duct, with patent portion attached to ileum (true diverticulum, white
Patent urachus
Vesicourachal diverticulum
Normal
Urachal cyst
arrow in B ). May be asymptomatic. May have heterotopic gastric and/or pancreatic tissue
Ž melena, hematochezia, abdominal pain.
B Normal Vitelline fistula Meckel diverticulum
Umbilicus

Normal Vitelline fistula Meckel diverticulum

FAS1_2019_15-Repro.indd 618 11/7/19 5:52 PM