Flashcards in Embryology Deck (86)
Defective sonic hedgehog gene?
-gene is involved in patterning along anterior-posterior axis
-defect assoc with holoprosencephaly (forebrain fails to develop into 2 hemispheres; have 1 central eye...)
Defect in FGF gene?
-involved in lengthening of limbs
-defect --> Achondroplasia
Hox genes: -what do they code for? if defective?
-code for DNA-binding transcription factors; involved in segmental organization of embryo in a cranio-caudal direction
-Hox mutations--> appendages in wrong locations (ie extra fused digit between 3rd and 4th fingers)
When is embryo most susceptible to teratogens?
between 3-8 weeks, embryonically (so, 5-10 weeks of pregnancy) = "embryonic period" (b/c this is when organogenesis occurs)
***note: before week 3: all-or-none (miscarriage or nothing)
***after week 8: growth and function are affected
What week, embryologically, does the heart begin to beat?
When is it "embryo"? "fetus"?
-"embryo"--> weeks 3-8
-"fetus"--> at week 8, on
When does hCG secretion begin?
within 1 week after fertilization
What week does the neural tube close?
Neural tube formed by neuroectoderm and closes by week 4 (this is why MUST already be taking folic acid prior to pregnancy, b/c spinal development occurs within the first 4 weeks!)
Adenohypophysis arises from which embryologic derivative/germ layer?
Adenohypophysis = Ant pituitary; arises from Rathke's pouch, from Surface Ectoderm
Neurohypophysis arises from which embryologic germ layer/derivative?
Neural Crest derivatives:
-dorsal root ganglia
-chromaffin cells of adrenal medulla
-parafollicular (C) cells of thyroid
-pia and arachnoid
-bones of skull
-odontoblasts (teeth-->crest toothpaste!)
-aorticopulmonary septum (spiral septum of heart)
Which germ layer does the spleen arise from?
Nucleus pulposus is derived from?
Notochord; Notochord induces ectoderm to differentiate into neuroectoderm and form the neural plate; neural plate gives rise to neural tube and neural crest cells; notochord becomes the nucleus pulposus of the intervertebral disk in adults
Agenesis vs Hypoplasia vs Aplasia
Agenesis: No primordial tissue, so no organ
Hypoplasia: Primordial tissue present, but incomplete organ development
Aplasia: Primordial tissue present, but no organ
Malformation vs Deformation
Malformation: Intrinsic disruption (like a teratogen); occurs during embryonic period (3-8 weeks)
Deformation: extrinsic disruption; occurs after embryonic period (after week 8)
teratogenic effect of aminoglycosides?
CN VIII toxicity (hearing problems)
teratogenic effect of DES (diethylstilbestrol), a synthetic estrogen
Vaginal clear cell adenocarcinoma (in female fetuses, when older)
Ebstein's anomaly (enlarged Right atrium; small Right ventricle) - assoc with which teratogen?
Neural tube defects --> caused by which teratogens?
(Valproate and Carbamazepine decrease folate absorption; so, if pts are taking these drugs during pregnancy, then must take extra folate)
infant with flat nasal bridge, "railroad track" ears, thin upper limb, small palpebral fissures, epicanthal folds, upturned nose, smooth philtrum (space from nose to upper lip)... may be caused by which teratogen?
Alcohol (Fetal Alcohol Syndrome)
Which fetal structure secretes hCG?
Syncytiotrophoblast (outer layer of chorionic villi)
maternal component of the placenta; derived from the endometrium; if absent, get placenta accreta (placenta attaches to myometrium instead of to endometrium; so, no separation of placenta after birth; get massive bleeding after delivery)
How many umbilical artery/ies? Vein/s?
2 umbilical arteries
1 umbilical vein
*both are derived from the allantois
Urachal duct: what is it? what's it formed from? what if duct fails to obliterate?
During 3rd week: yolk sac forms allantois, which extends into urogenital sinus; allantois becomes urachus, which is a duct between bladder and yolk sac (so, connects fetal bladder to maternal system)
*If urachus does not obliterate after birth:
-patent urachus --> urine discharge from umbilicus
-vesicourachal diverticulum --> outpouching of bladder; asymptomatic
urine discharge from umbilicus in neonate: what's the cause/abnormality?
-Failure of urachal duct to obliterate (urachal duct connects fetal bladder to maternal system in utero)
Vitelline duct: What is it? Abnormalities associated with it?
-Vitelline duct = omphalomesenteric duct --> connects yolk sac to midgut lumen
--> obliterated at 7th week
-Vitelline fistula = failure of duct to close; get meconium discharge from umbilicus
-Meckel's diverticulum = partial closure of duct, may have portion attached to ileum; may have ectopic gastric mucosa --> melena and periumbilical pain
meconium discharge from umbilicus: what abnormality caused this?
Vitelline fistula (failure of the vitalline/omphalomesenteric duct to close)
Meckel's diverticulum cause?
Due to partial closure of the Vitelline duct (instead of full closure)
Truncus Arteriosus: What does it give rise to?
Pathologies associated with abnormal formation?
Gives rise to ascending aorta and pulmonary trunk:
-Have neural crest migration --> truncal and bulbar ridges that spiral and fuse to form the aorticopulmonary septum --> ascending aorta and pulmonary trunk
-Transposition of great vessels (failure to spiral)
-TOF (skewed AP septum development)
-Persistent TA (from partial AP septum development)
Bulbus cordis gives rise to:
Right Ventricle and smooth parts (outflow tract) of LV and RV
Left horn of sinus venosus gives rise to:
Right horn of sinus venosus gives rise to:
smooth part of right atrium
Right common cardinal vein and right anterior cardinal vein give rise to:
Where does fetal erythropoiesis occur at different stages?
"Young Liver Synthesizes Blood"
*Yolk sac --> 3-8 weeks
*Liver --> 6-30 weeks
*Spleen --> 9-28 weeks
*Bone marrow --> 28 weeks onward
Which fetal shunt is patent in about 20-30% of normal adults?
Patent Forament Ovale (kept closed b/c LA pressure > RA pressure)
shunts blood from umbilical vein to IVC (bypasses hepatic circulation)
shunts blood entering RA from IVC into LA so that it can be pumped out through the aorta to the head and body
connects pulmonary artery to aortic arch; blood from LV can bypass pulmonary circulation
Foramen Ovale, after it closes (upon baby's first breaths)
What happens when infant takes a breath at birth?
Breath--> decreased resistance in pulmonary vaculature --> pressure in LA > pressure in RA; foramen ovale closes --> increased O2 leads to decreased PG's --> closure of ductus arteriosus
How does deoxygenated blood in fetus go back to mother's circulation?
After circulating, blood goes through internal iliac arteries to Umbilical arteries ---> mother!
Amniotic fluid findings in neural tube defects
increased alpha-fetoprotein and increased Acetylcholinesterase (AChE)
Anencephaly: Findings in amniotic fluid?
-malformation of anterior end of neural tube --> no brain
-increased alpha-fetoprotein in amniotic fluid + polyhydramnios (b/c no swallowing center in brain)
Holoprosencephaly: What is it? What conditions are associated with?
no separation of hemispheres, so may get one central eye (cyclopia), etc...
-Associated with: Patau's syndrome (trisomy 13), severe fetal alcohol syndrome, cleft lip/palate, abnormal sonic hedgehog gene
cerebellar tonsillar herniation through foramen magnus with aqueductal stenosis and hydrocephaly; often presents with syringomyelia
Large posterior fossa, absent cerebellar vermis with cystic enlargement of 4th ventricle; may lead to hydrocephalus and spina bifida
-enlargement of central canal of spinal cord; usually at C8-T1
*loss of pain and temperature sensation in upper extremities with preservation of touch sensation
*associated with Chiari II malformation
Aortic Arch Derivatives:
*1st aortic arch --> Maxillary artery (branch of external carotid)
*2nd aortic arch --> Stapedial artery and Hyoid artery
*3rd aortic arch --> common carotid artery and proximal part of the internal carotid artery
*4th aortic arch --> on left: aortic arch; on right: proximal part of right subclavian artery
*6th aortic arch --> proximal part of pulmonary arteries and (on left only) ductus arteriosus
Derivative of 1st branchial cleft
1st cleft --> external auditory meatus
Branchial Cleft Cysts vs. Thyroglossal Duct Cysts
Branchial Cleft cysts --> within lateral neck; doesn't move with swallowing; d/t persistent cervical sinus
Thyroglossal duct cyst --> in midline of neck; moves with swallowing
1st branchial arch derivatives:
Ms and Ts!
Cartilage: Meckel's; Mandible, Malleus, Mandibular ligament
Muscles of Mastication: Temporalis, Masseter, lateral and Medial pterygoids, Mylohyoid, Tensor Tympani, Tensor veli palatini, ant Two-Thirds of Tongue
Nerves: CN V2 and V3 (Mandibular and Maxillary of Trigeminal)
2nd branchial arch derivatives:
Cartilage: Stapes, Styloid process, Stylohyoid ligament, etc
Muscles: Stapedius, Styloyoid, etc
Nerve: CN VII (Seven! for Smiles!)
3rd branchial arch derivatives:
Cartilage: greater horn of hyoid
Nerve: glossopharyngeal (CN IX)
4th-6th branchial arch derivatives:
Neck and Voice box!
*4th arch --> muscles include cricothyroid muscle; nerve: superior laryngeal branch of CN X
*6th arch --> all intrinsic muscles of larynx EXCEPT cricothyroid; nerve: recurrent laryngeal branch (CN X)
1st branchial pouch derivatives:
middle ear cavity, eustachian tube, mastoid air cells
2nd branchial pouch derivatives
3rd branchial pouch derivatives:
dorsal wings --> inferior parathyroids
ventral wings --> thymus
4th branchial pouch derivatives:
Most common ectopic thyroid tissue site?
normal remnant of thyroglossal duct
Failure of fusion of the maxillary and medial nasal processes
Failure of fusion of the lateral palatine processes, the nasal septum, and/or the median palatine processes
Which artery supplies the foregut? midgut? hindgut?
Celiac Artery --> foregut
SMA --> midgut
IMA --> hindgut
pharynx to duodenum; supplied by celiac artery
duodeum to transverse colon (splenic flexure/watershed area); supplied by SMA
distal transverse colon (splenic flexure/watershed area) to rectum; supplied by IMA
extrusion of abdominal contents through abdominal folds; not covered by peritoneum (increased AFP in amniotic fluid)
persistence of herniation of abdominal contents into umbilical cord; covered by peritoneum (Increased AFP in amniotic fluid)
infant with cyanosis, choking/vomiting with feeding, air bubble in stomach on CXR, polyhydramnios (in utero), can't pass NG tube into stomach, pneumonitis
Tracheoesophageal fistula (polyhydramnios, b/c fetus can't swallow amniotic fluid, b/c blind esophagus, etc...)
infant about 2 weeks old with: palpable "olive" mass in epigastric region and non-bilious projectile vomiting
Congenital pyloric stenosis (most common condition requiring surgery during first month of life)
What germ layer does the pancreas arise from?
Ventral pancreatic bud becomes? Dorsal pancreatic bud becomes?
*Ventral pancreatic bud --> pancreatic head, uncinate process, and main pancreatic duct
*Dorsal pancreatic bud --> becomes everything else
Ventral pancreatic bud abnormally encircles 2nd part of duodenum; forms ring of pancreatic tissue that may cause duodenal narrowing
bilateral renal agenesis --> oligohydramnios --> limb deformities, facial deformities, pulmonary hyperplasia
*caused by malformation of ureteric bud
Fusion of inferior poles of both kidneys; get trapped under INFERIOR MESENTERIC ARTERY and thus remain low in the abdomen
*kidneys function normally
*assoc. with Turner's syndrome
Mesonephric duct develops into:
Mesonephric duct = Wolffian duct (development is stimulated by androgen secretion from Leydig cells)
*Develops into male internal structures (except prostate!): "SEED"
Paramesonephric duct develops into:
Paramesonephric duct = Mullerian duct; develops into female internal structures:
-upper 1/3rd of vagina (Lower 2/3rds of vagina develop from urogenital sinus)
Cause of bicornuate uterus?
Incomplete fusion of paramesonephric ducts
Female equivalent of glans penis?
female equivalent of corpus cavernosum and spongiosum?
female equivalent of bulbourethral glands?
greater vestibular glands (of Bartholin)
female equivalent of prostate gland?
Urethral and paraurethral glands (of Skene)
female equivalent of of ventral shaft of penis (penile urethra)?
female equivalent of scrotum?
Female and Male remnants of Gubernaculum?
Female: ovarian ligament + round ligament of uterus
Male: fibrous tissue that anchors testes within scrotum