5.2 Embryo Flashcards
Forgut
pharynx to duodenum
celiac artery
Midgut
duodenum to txvrs colon
SMA
Hindgut
distal txvrs colon to rectum
IMA
Devt defects of anterior abd wall
defect of — leads to —
rostral fold closure- sternal defects
lateral fold closure- omphalocele, gastroschisis
caudal fold closure- bladder exstrophy
Gastroschisis
Failure of lateral body folds to fuse –> extrusion of abd contents through abd folds
NOT covered by sac
Defect is lateral to umbilicus, usu on R side
But the “better” one- liver doesn’t protrude, other anomalies in only 10-15%
See incrsd AFP
Rx surgical closure
Omphalocele
persistence of herniation of abd contents into umb cord, covered by peritoneum
IS covered by sac (peritoneum + amnion)
But “worse”- liver is often protruding
Other anomalies v common (50%)- GI, GU, CV, CNS, MS
See elevated AFP lvls
Rx surgical closure
Duodenal atresia
failure to recanalize trisomy 21 (down)
Jejunal, ileal, colonic atresia
due to vascular accident
apple peal atresia
When does normal umbilical herniation occur and regress in utero?
6th week- midgut herniates thru umbilical ring –> rapid growth of midgut (duod to txvrs colon)
10th wk- returns to abd cavity and rotates around SMA
Pathology of normal umb herniation
malrotation of midgut
omphalocele
intestinal atresia or stenosis
vovulus (twisting of gut) +/- incarceration (not enough blood, kinked off)
Tracheoesophageal fistula (TE)
Abn connection bt esophagus and trachea
Most common subtype: blind upper esophagus w lower esophagus connected to trachea.
Results in cyanosis, choking/vom w feeding, air bubble in stomach on CXR, failure to pass NG tube into stomach, pneumonitis, polyhydramnios (bc fetus can’t swallow amniotic fluid)
Congenital pyloric stenosis
Hypertrophy of pylorus causes obstruction
Palpable olive mass in epigastric region and nonbilious (bc no bile since before gall bladder) projectile vom at 2wks old.
Rx surgical incision
Occurs in 1/600 live births, often 1st born males
Will have hypochloremic metabolic alkalosis from the vom. (also hypoK+)
What is marker bt midgut and hindgut?
Splenic flexure (where txvrs colon hits spleen)
What is bladder exstrophy?
Failure of caudal fold closure
Inside of bladder is exposed to outside world
(turned inside out, and outside abd)
If you are alkalotic or acidotic, what will happen to your Cl- and K+ levels
Alkalotic means decreased HCl, so hypochloremic. When you are alkalotic, the H+/K+ countertxptr tries to compensate by dumping H+ into the blood, which means K+ will be brought into cells, at you will be hypokalemic (d/t decreased K+ in blood bc more inside cells)
Acidosis is the opp- too much HCl, so hyperchloremia; plus H+/K+ cotxprt compensates by taking H+ out of blood into cells, which dumps K+ into blood- so hyperkalemia.
In both cases, the hypo/hyperkalemia takes a few weeks of alk/acidosis before it is measurable.
Pancreas embryology
Derived from foregut
Ventral and dorsal pancreatic buds become pancreatic head.
Ventral bud becomes uncinate process (lower half of head) and main pancreatic duct.
Dorsal bud becomes everything else- body, tail, isthmus, accessory pancreatic duct
Annular pancreas
ventral pancreatic bud abnormally encircles 2nd part of duod and forms a ring of pancreatic tsu; can cause duodenal narrowing.
2/3 pts asympt
Sympt onset can occur at any age, dep on severity of duod constriction
Children px of annular pancreas
gastric outlet obstruction- bilious vom (has bile, bc after the GB), feeding intolerance, abd distention
Adult px of annular pancreas
20-50yo
Abd pain, post-prandial fullness and nausea, peptic ulceration, pancreatitis
Rarely, biliary obstruction
Infants w annular pancreas assoc w…
maternal polyhydramnios, Down syndrome esophageal and duodenal atresia imperforate anus Meckel's diverticulum
Pancreas divisum
ventral and dorsal parts fail to fus at 8 weeks
Spleen embryology
arises from dorsal mesentery (it’s mesodermal!) but is supplied by an artery of the foregut, the celiac artery.
Kidney embryology
- Pronephros at week4, then degenerates
- Mesonephros- functions as interim kidney during 1st trimester; later contributes to male genital system
- Metanephros- permanent. starts appearing during 5th wk of gestation, nephrogenesis continues through wks 32-36
Ureteric bud
Derived from caudal end of mesonephros
gives rise to ureter, pelvises, and (by branching) the calyces and collecting ducts
fully canalized by week10
Abberant devt results in congenital malformation of the lower urinary tract
Metanephric mesenchyme
Ureteric bud interacts with this tsu
interaction induces differentiation and formation of glomerulus and renal tubules to DCT
Abberant interaction bt MM and Ureteric bud results in congenital malformation of kidneys
Uteropelvic jn w kidney
Last to canalize, most common site of obstruction (hydronephrosis) in fetus.
Potter’s syndrome
Bilateral renal agenesis Leads to oligohydramnios (little amniotic fluid, bc fetus can't pee), which leads to limb deformities, facial deformities, pulmonary hypoplasia Caused by malformation of ureteric bud POTTER: Pulm hypoplasia Oligohydramnios Twisted skin Twisted face Extremities defects Renal agenesis
Liver diverticulum gives rise to…
Liver
Gall bladder
Bile duct system
Ventral pancreatic bud (!!)
What tsu gives rise to pancreas? To the spleen?
Endoderm - pancreas (from foregut)
Mesoderm - spleen
GI problems in Down Syndrome
Annular pancreas
Duodenal atresia
Horseshoe kidney
Gets stuck under IMA
Inferior poles of both kidneys fuse, ascend during fetal devt but not as high as regular kidneys bc blocked by IMA.
Kidney fn normal
Complete fusion - cake kidney
Female genital embryol
Default devt
Mesonephric duct degenerates and Paramesonephric (Mullerian) duct develops into fallopian tubes, uterus, upper 1/3 of vag
(lower 2/3 of vag is from urogenital sinus, so even if you have Mullerian duct problems can still have a vag)
Male genital embryol
SRY gene on Y chromosome codes for testis-determining factor.
Mullerian inhibiting substance is secreted by Sertoli cells of testis, and suppresses devt of Mullerian (paramespnephric) duct.
Leydig cells secrete increased androgens, leading to devt of mesonephric ducts (wolffian ducts) into seminal vesicles, epididymis, ejaculatory duct, and ductus deferens (everything except prostate).
Default genitals
Female
Mesonephric (wolffian) duct has to be induced to remain.
Otherwise, will get paramesonephric duct and be female.