Step 1 - Embryology 1

denniskwinn's version from 2015-04-25 15:59


Question Answer
Sonic hedgehog gene Produced at base of limbs in zone of polarizing activity . Involved in patterning along anterior-posterior axis
Wnt-7 geneProduced at apical ectodermal ridge (thickened ectoderm at distal end of each developing limb). Necessary for proper organization along dorsal-ventral axis.
FGF geneProduced at apical ectodermal ridge. Stimulates mitosis of underlying mesoderm, providing for lengthening of limbs
Homeobox geneInvolved in segmented organization of embryogenesis
Day 0 fetal landmarksFertilization by sperm forming zygote, initiating embryogenesis
Within week 1 fetal landmarkshcG secretion begins after implantation of blastocyst.
Within week 2 fetal landmarksbilaminar disk (epiblast, hypoblast)
within week 3 fetal landmarksGastrulation, primitive streak, notochord and neural plate begin to form


Question Answer
Weeks 3-8 (embryonic period) fetal landmarksNeural tube formed by neuroectoderms and closes by week 4
Week 4 fetal landmarksHeart begins to beat, upper and lower limb buds begin to form.
Week 8 (fetal period) fetal landmarksFetal movement, fetus looks like baby
Week 10 fetal landmarksGenitalia have male/female characteristics
Alar plate (dorsal)Sensory
Basal plate (ventral)Motor
Rule of 2’s for 2nd week2 germ layers (bilaminar disk): epiblast, hypoblast . . 2 cavities: amniotic cavity, yolk sac. . 2 components to placenta: cytotrophoblast, syncytiotrophoblast
Rules of 3’s for 3rd week3 germ layers (gastrula): ectoderm, mesoderm, endoderm
Rule of 4’s for 4th week4 heart chambers, 4 limb buds


Question Answer
Epiblastprecursor to ectoderm - invaginates to form primitive streak - cells from the primitive streak give rise to both intraembryonic mesoderm and ectoderm
Surface ectoderm derivativesAdenohypophysis (from Rathke's pouch); lens of eye; epithelial linings of oral cavity, sensor), organs of ear, retina, and olfactory epithelium; epidermiS; salivary, sweat, and mammary glands.
Craniopharyngiomabenign rathke’s pouch tumor with cholesterol crystals, calcifications
Neuroectoderm derivativesBrain (neurohypophysis, CNS neurons, oligodendrocytes, astrocytcs, ependymal cells, pineal gland), retina, spinal cord. (BCSR - bcs rankings)
Neural crest derivativesParfollicular cells, ANS,Laryngeal cartilage, Aorticopulmonary septum, Chromaffin cells, Enterochromaffin cells, Schwann cells, Celiac ganglion, Arachnoid and pia mater, Melanocytes, Drg, Odontoblasts, Cranial nerves, Skull bones. PALACE SCAM DOCS
Endoderm derivativesGut tube epithelium and derivatives (e.g., lungs, liver, pancreas, thymus, parathyroid, thyroid follicular cells).
Mesoderm derivativesMuscle, bone, connective tissue, serous linings of body, cavities (e.g., peritoneum), spleen (derived from foregut mesentery), cardiovascular structures, lymphatics, blood, urogenital structure;, kidneys, adrenal cortex.


Question Answer
Notochord induces ectoderm to form neuroectoderm (neural plate).
Notochord derivative the nucleus pulposus of the intervertebral disk
Mesodermal defectsVACTERL - Vertebral defects, Anal atresia, Cardiac defects, Tracheo-Esophageal fistula, Renal defects, Limb defects (bone and muscle)
Most susceptible time to TeratogensMost susceptible 3rd-8th weeks, before week 3 all or none effect, week 8: growth and function affected.
Alcohol teratogenic effects Leading cause of birth defects and mental retardation; fetal alcohol syndrome
ACE inhibitors teratogenic effectsRenal damage
Alkylating agent teratogenic effectsAbsence of digits, multiple anomalies
Aminoglycosides teratogenic effectsCNVIII toxicity


Question Answer
Cocaine teratogenic effectsAbnormal fetal development and fetal addiction, placental abruption
Diethylstilbestrol (DES) teratogenic effectsVaginal clear cell carcinoma
Folate antagonist teratogenic effectsNeural tube defects
Iodide (lack or excess) teratogenic effectsCongenital goiter or hypothyroidism
Lithium teratogenic effectsEbstein’s anomaly (atrialized right ventricle)
Maternal diabetes teratogenic effectsCaudal regression syndrome (anal atresia to sirenomelia)
Smoking (nicotine, CO) teratogenic effectsPreterm labor, placental problems, IUGR, ADHD


Question Answer
Tetracycline teratogenic effectsDiscolored teeth
Thalidomide teratogenic effectsLimb defects
Valproate teratogenic effectsInhibition of intestinal folate absorption
Vitamin A (excess) teratogenic effectsExtremely high risk for spontaneous abortions and birth defects (cleft palate, cardiac abnormalities)
Warfarin teratogenic effectsBone deformities, fetal hemorrhage, abortion
X-rays, anticonvulsants teratogenic effectsMultiple anomalies
Fetal alcohol syndromeLeadlllg causc of congenital malformations in the US. Newborns of mothers who consumed significant amounts of alcohol during pregnancy have increased incidence of congenital abnormalities, including pre- and postnatal development retardation, microcephaly, holoprosencephaly, facial abnormalities, limb dislocation and heart and lung fistulas. Mechanism may include inhibition of cell migration.


Question Answer
Monozygotic twins1 zygote splits evenly to develop 2 amniotic sacs with a single common chorion and placenta. 2. Conjoined twins have 1 chorion, 1 amniotic sac
Dizygotic twins2 placentas - 1. Monozygotes that split early development 2 placentas (separate/fused), chorions, and amniotic sacs 2. Dizygotes develop individual placentas, chorions, and amniotic sacs
Cytotrophoblastinner layer of chorionic villi, Cyto makes cells
Syncytiotrophoblastouter layer of chorionic villi; secretes hCG (structurally similar to LH; stimulates corpus luteum to secrete progesterone during first trimester)
Maternal component of placentaDecidua basalis - derived from the endometrium - Maternal blood in lacunae.
Umbilical arteries1. return deoxygenated blood from fetal internal iliac arteries to placenta 2. Single umbilical artery is associated with congenital and chromosomal anomalies 3. Derived from allantois


Question Answer
Umbilical vein1. Supplies oxygenated blood from placenta to fetus 2. Derived from allantois
Urachal ductin the 3rd week the yolk sac forms allantois which extends into urogenital sinus. Allantois becomes urachus a duct b/w bladder and yolk sac
Urachal duct abnormalitiesfailure to obliterate: 1. Patent urachus - urine discharge from umbilicus 2. Vesicourachal diverticulum - outpouching of bladder
Viteline ductconnects yolk sac to midgut lumen - obliterates in 7th week
Viteline duct fistulameconium discharge from umbilicus (s.a Meckel’s)


Question Answer
Truncus arteriosus (TA) gives rise toAscending aorta and pulmonary trunk
Bulbus cordis gives rise toRight ventricle and smooth parts (outflow tract) of left and right ventricle
Primitive ventricle gives rise toPortion of the left ventricle
Primitive atria gives rise toTrabeculated left and right atrium
Left horn of sinus venosus (SV) gives rise toCoronary sinus
Right horn of Sinus venosus gives rise toSmooth part of right atrium
Right common cardinal vein and right anterior cardinal vein gives rise toSVC


Question Answer
Neural crest migrationdivides truncus arteriosus into 2 arteries via fusion and twisting of truncal and bulbar ridges = ascending aorta and pulmonary trunk
Truncus arteriosus pathologytransposition of great vessels + tetralogy of Fallot
Interventricular septum developmentI. Muscular ventricular septum forms. Opening is called interventricular foramen. 2. Aorticopulmonary septum divides TA into aortic and pulmonary trunks, 3. Aorticopulmonary septum meets and fuses with muscular ventricular septum to form membranous interventricular septum, closing interventricular foramen
Interatrial septum development1. Forament primum narrows as septum primum grows toward endocardial cushions 2. Perforations in septum primum form foramen secundum (foramen primum disappears) 3. Foramen secundum maintains R to L shunt septum secundum begins to grow 3. Secundum contains permanent opening (foramen ovale) 5. Foramen secundum enlarges and upper part of septum primum degenerates 6. Remaining portion of septum primum forms valve of foramen ovale
Fetal erythropoiesis1. Yolk sac (3-8 weeks), 2. Liver (6-30 weeks), 3. Spleen (9-28weeks) 4. Bone marrow (28 week onward)
Shunts in fetal circulation1. Ductus venosus - diverts from umbilical vein into IVC to bypass hepatic circulation 2. Foramen ovale - bypass lungs 3. Ductus arteriosus - pulm artery to lower body of fetus.


Question Answer
O2 sat in umbilical vein80% saturated
Change in infant circulation at birthinfant takes breath and ↓ resistance in pulmonary vasculature causes ↑ left atrial pressure vs right atrial pressure closing the foramen ovale - ↑ in O2 ↓ prostaglandins, causing closure of ductus arteriosus.
How to close PDAindomethacin helps close PDA, prostaglandins keep PDA open
Umbilical vein post natal derivative ligamentum teres hepatis
UmbiLical arteries post natal derivativemedial umbilical ligamcnts
Ductus arteriosus post natal derivativeligamenhlm arteriosum
Ductus venosus post natal derivativeligamentum venosum
Foramen ovale post natal derivativefossa ovalis
Allantois , urachus post natal derivativemedian umbilical ligamenl
Notochord post natal derivative Nucleus pulposus of intervertebral disk


Question Answer
1st Aortic arch derivativepart of maxillary artery (branch of external carotid)
2nd aortic arch derivativeStapedial artery and hyoid artery
3rd Aortic arch derivativecommon Carotid artery and proximal part of internal carotid artery
4th aortic arch derivativeon left, aortic arch; on right, proximal part of right subclavian artery
6th Aortic arch derivativeproximal part of pulmonary arteries and (on left only) ductus arteriosus
Neural tube defectsNeuropores fail to fuse (4th week) → persistent connection between amniotic cavity and spinal canal. Associated with low folic acid intake during pregnancy. Elevated a-fetoprotein (AFP) in amniotic fluid and maternal serum. ↑ AFP + acetylcholinesterase in CSF.


Question Answer
Spina bifida occultafai lure of bony spinal canal to close, but no structural herniation. Usually seen at lower vertebral levels. Dura is intact.
Meningocelemeninges herniate through spinal canal defect.
Myelomeningocelemeninges and spinal cord herniate through spinal canal defect
AnencephalyMalformation of anterior end of neural tube; no brain/calvarium, elevated AFP, polyhydramnios (no swallowing center in brain ).
Holoprosencephaly↓ separation of hemispheres across midline; results in cyclopia; associated with Patau’s syndrome, severe fetal alcohol syndrome, and cleft lip/palate
Arnold-Chiari type II malformationcerebellar tonsillar herniation through foramen magnum with aqueductal stenosis and hydrocephaly. Often presents with syringomyelia, thoraco-lumbar myelomeningocele.
Dandy-walker malformation large posterior fossa; absent cerebellar vermis with cystic enlargement of 4th ventricle. Can lead to hydrocephalus and spina bifida.
SyringomeliaEnlargement of the central canal of spinal cord. Crossing fibers of spinothalamic tract are typically damaged first. "Cape-like," bilateral loss of pain and temperature sensation In upper extremities With preservation of touch sensation - most common C8-T1