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.
Bicornate uterus
Incomplete fusion of paramesonephric ducts causes 2 uteruses.
Assoc w urinary tract abn and infertility
What does the genital tubercle become?
M: glans penis / F: glans clit
M: corpus cavernosum and spongiosum / F: vestibular bulbs
What does the urogenital sinus become?
M: bulbourethral gland of cowper / F: greater vestibular glands of bartholin
M: prostate gland / F: Urethral and paraurethral glands of skene
What do the urogenital folds become?
M: Ventral shaft of penis (penile urethra)
F: Labia minora
What does the labioscrotal swelling become?
M: scrotum
F: labia majora
Glans penis in F
Glans clitoris
Corpus cavernosum and spongiosum in F
Vestibular bulbs
Bulbourethral glands of cowper in F
Greater vestibular glands of bartholin
Prostate gland in F
urethral and paraurethral glands of skene
Ventral shaft of penis (ventral urethra) in F
Labia minora
Scrotum in F
Labia majora
What is the M and F remnant of the gubernaculum
M: anchors testes w/in scrotum
F: ovarian ligmt and round ligmt of uterus
What is the M and F remnant of the processus vaginalis (evagination of the peritoneum?
M: forms tunica vaginalis
F: obliterated
Klinefelter’s
Male XXY
Testicular atrophy, eunuchoid body shape, tall long extremities, gynecomastia, female hair distribution
May present w devt delay
Presence of inactivated X-chr (barr body)
Common cause of hypogonadism seen in infertility workup.
Hormones of Kleinfelter
Dysgenesis of seminiferous tubules leads to decrsd inhibin, so incrsd FSH
Abn leydig cell fn leads to decreased testosterone, which leads to increased LH, and then to increased estrogen
Turner’s Syndrome
Female 45XO
Short stature (<5ft if untreated), ovarian dysgenesis (streak ovary), shield chest, bicuspid aortic valve, neck webbing (+cystic hygroma), preductal (infantile) coarc of aorta
Most common cause of primary amenorrhea
No barr body
Hormones of Turner’s
Decreased estrogen leads to increased LH and FSH.
Double Y males
Male, XYY
Phenotypically normal, v tall, severe acne
Antisocial bhvr in 1-2%
Normal fertility
Testosterone increased, LH increased
Defective androgen receptor
Normal: Increased LH increases Testosterone.
But here, body doesn’t recognize testosterone do to receptor problem- so it feeds back to elevate LH, which causes even more testosterone production.
Testosterone increased, LH decreased
Testosterone-secreting tumor
Exogenous steroids
Increased testosterone from outside causes neg fdback on Leydig so decreased LH (so Leydig won’t make as much testosterone)
Testosterone decreased, LH increased
Primary hypogonadism
Lots of LH, trying to get Leydig cells to secrete testosterone, but they are hypogonads, so can’t make it.
Testosterone decreased, LH decreased
Hypogonadotropic hypogonadism
LH is low so testosterone is low.
What is pseudohermaphroditism
Disagreement bt phenotypic sex (external genitalia) and gonadal sex (internal genitalia)
Name pt female if ovaries, male if testes.
Female pseudohermaphrodite
XX
Ovaries present, but external genitalia virilized or ambiguous.
Due to excessive and inappropriate exposure to androgenic steroids during early gestation
eg congenital adrenal hyperplasia (21beta hydroxylase def, 17beta hydroxylase def)
eg exog admin of androgens during pregnancy
Male pseudohermaphrodite
XY
Testes present, but external genitalia are female or ambiguous.
Most common form is androgen insensitivity syndrome (aka testicular feminization)
Androgen insensitivity syndrome
46XY
Defect in androgen receptor results in normal-appearing female; female external genitalia w rudimentary vagina (lower 2/3 of vag comes from urogenital sinus, not mullerian, so will have this)
Uterus and uterine tubes generally absent
Presents w no sexual hair
Develops testes (often found in labia majora- removed to prevent malignancy)
Increased testosterone, increased estrogen, increased LH
aka testicular feminization
Causes Male pseudohermaphrodite
True hermaphrodite
46XX or 47XXY
Both ovary and testicular tsu are present, ambiguous genitalia.
V rare
5alpha reductase deficiency
Inability of males to convert testosterone to DHT (more potent form of testosterone)
Ambiguous genitalia until puberty, when increased testosterone causes masculinization/increased growth of external genitalia. Even tho can’t convert it to DHT, have so much testosterone that it doesn’t matter. (Penis at 12)
Internal genitalia are normal.
Testosterone/estrogen lvls normal
LH normal or increased.
Where are barr bodies found?
In neutrophils- extra drumstick globule on nucleus in 3% of neutrophils.
Shows X-inactivation
Seen in all females
Also in XXY Kleinfelter’s (males).
Not seen in Turner’s (females bc there is no inactivated X chr)
What is the downstream effect of increased LH in males?
LH stim’s leydig cells to make testosterone.
So increased LH will mean increased testosterone.
Cryptorchidism
Undecended testis (one or both)
Lack of spermatogenesis d/t increased body temp
Assoc w high risk of germ cell tumors
Prematurity increases risk of crytorchidism
Rx if before puberty: orchioplexy (bring it into scrotum and suture it there)
SIDS
Usu at 2-4 mo old
Usu when infant is sleeping
Occlude breathing but don’t stir to change their O2 supply.
Maternal risk factors: low SES, age <20, drugs/tobacco during pregnancy
Infant risk factors: low birth weight, female, preemie, prior sibling w SIDS
Prevent: back to sleep, pacifier when sleeping, fan in room
ACA
Lesion causes MMS
medial medullary syndrome:
Triad of 3 things:
1. Dmg to medullary pyramid (and thus corticospinal fibers of pyrimidal tract) –> limb weakness/contralat hemiparesis in lower extremities
2. Dmg to Medial lemniscus - decreased contralat proprioception, vibration, touch
3. Dmg to hypoglossal nerve - ipsilateral musc weakness, so deviation of tongue to ipsilateral side on protrusion
PICA
Lesion causes LMS lateral medullary syndrome aka wallenberg's Contralateral P/T loss Ipsilateral dysphagia Hoarseness, decreased gag reflex Vertigo, diplopia, nystagmus Vom Ipsilateral Horner's Ipsilateral facial P/T loss Trigeminal nucleus (spinal tract and nucleus) loss Ipsilateral ataxia
AICA
Lesion causes LIPS
Lateral Inferior Pontine Synd
Ipsilateral facial paralysis
Ipsilateral loss of cochlear nucleus, vestibular nucleus (nystagmus)
Ipsilateral facial P/T
Ipsilateral dystaxia (MCP, ICP- middle, inf cerebral peduncle)
PCA
Lesion:
Contralateral homonomous hemianopia w macular sparing
Supplies the occipital cortex
MCA
Contralateral face and arm paralysis and sensory loss
Aphasia (dominant sphere)
Left-sided neglect
ACA
Supplies medial surface of the brain, leg/foot area of motor and sensory cortexes
A-Comm
Most common site of circle of Willis aneurysm
Lesions can cause visual defects
P-Comm
Common area of aneurysm
Causes CN III palsy
Lateral striate
Divisions of MCA
Supply Internal Capsule, Caudate, Putamen, Globus Pallidus
“Arteries of stroke”
Infarct of post limb of the IC causes pure motor hemiparesis
Watershed zones
Bt ACA and MCA
Bt PCA and MCA
Dmgd in severe hypotension, leading to upper leg/arm weakness and defects in higher-order visual processing
Basilar artery
Lesion causes “locked-in syndrome”
CN III is usu intact
Stroke of anterior circle of Willis
General sensory and motor dysfn, aphasia
Stroke of posterior circle of willis
Cranial nerve defects (vertigo, visual) Coma Cerebellar deficits (ataxia) Dominant hemisphere- ataxia Non-dom: neglect
Berry aneurysm
Occur at bifurcations of Circle of Willis
Most common site is A-Comm
Rupture (most common complication) leads to hemorrhagic stroke/subarachnoid hemorrhage.
Assoc w: APKD Ehlers-Danlos, Marfans Advanced age HTN Smoking Higher risk in blacks
Charcot-Bouchard microanerysms
Assoc w chronic HTN
affects sml vessles (eg in basal gang, thalamus)
What infarct causes lateral inferior pontine syndrome?
AICA
What infarct affects occipital lobe/vision?
PCA
What infarct causes wallenberg’s syndrome
PICA
aka lateral medullary syndrome
Most common site for berry aneurysm
A-Comm
also P-Comm
Goes to medial part of brain –> Leg, foot
ACA
Supplies Broca’s and Wernicke’s areas
MCA
