USMLE Review: Embryology

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USMLE Review Embryology
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General Embryology
Timeline 1. Week 1 implantation, hCG
secretion 2. Week 2 bilaminar disk
(epiblast / hypoblast) 3. Week 3
gastrulation, notochord, neural plate 4.
Weeks 3 8 (embryonic period) organs form,
neural tube 5. Week 4 heart beats, limb
buds form, neural tube closes 6. Weeks 8
36 (fetal period) looks human, movement,
sexual differentiation, continued neural
development. 7. Respiratory system develops
late (RDS hyaline membrane)
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General Embryology
Timeline
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General Embryology
Teratogens 1. alcohol (FAS) 2.
smoking 3. thalidomide 4.
diethylstilbesterol (DES) 5. folic acid /
folate
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General Embryology
Placental Deveopment 1. fetus chorion
(cytotrophoblast / synctiotrophoblast) 2.
maternal decidua (lacunae with maternal
blood) Umbilical cord 1. one umbilical
vein 2. two umbilical arteries
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Cardiovascular Embryology
Heart 1. Single tube to four chamber
2. Atrial and ventricular development 3.
Atrial and ventricular septation 4. Outflow
tracts truncus arteriosus
Third arch
Fourth arch
Great vessels 1. Aortic arches 3rd, 4th
and 6th 2. Cardinal veins
Sixth arch
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Cardiovascular Embryology
Erythropoieses 1. Yolk sac 3 8 weeks
2. Liver 6 30 weeks 3. Spleen 9 28
weeks 4. Bone marrow 28 weeks
adult 5. Therefore, liver and spleen
can produce blood in disease states
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Cardiovascular Embryology
Atrial septal defect 1. Most common
congenital anomaly 2. Left to right shunt
(? pulmonary flow) 3. Maybe asymptomatic
until adulthood
LA
RA
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Cardiovascular Embryology
Atrioventricular septal defect 1. About ½
of all congenital heart anomalies in infancy
2. Partial atrial defect along with left
atrioventricular valve insufficiency 3.
Complete atrial and ventricular wall defect
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Cardiovascular Embryology
Tetralogy of Fallot 1. Ventricular septal
defect 2. Pulmonary stenosis 3.
Overriding aorta 4. Right ventricular
hypertrophy
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3
1
4
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Cardiovascular Embryology
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Fetal Circulation 1. Umbilical vein
2. Ductus venosus 3. Inferior vena cava,
right atrium 4. Foramen ovale to left
atrium, left ventricle to aorta 5.
Right ventricle, pulmonary trunk 6. Ductus
arteriosus 7. Aorta 8. Umbilical
arteries
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5
7
2
1
8
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Cardiovascular Embryology
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4
Adult Circulation 1. Ligamentum teres
hepatis (umbilical vein - closed)
2. Ligamentum venosum (ductus venosus -
closed) 3. Inferior vena cava, right
atrium 4. Right ventricle, pulmonary
trunk, lungs (ligamentum arteriosum
ductus arteriosus - closed) 5.
pulmonary veins to left atrium, left
ventricle to aorta 6. Medial umblical
ligaments (umbilical arteries closed)
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4
3
5
4
2
1
6
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Neural Embryology
Development 1. Neural tube and neural
crest cells 2. Spinal cord a.
sensory alar plate (posterior / dorsal)
b. motor basal plate (anterior / ventral)
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Neural Embryology
Development 3. Rhombencephalon
(mylencephalon / metencephalon) a.
medulla b. pons / cerebellum
c. 4th ventricle 4. Mesencephalon
midbrain (cerebral aqueduct) 5.
Diencephalon hypothalamus, thalamus, epithalamus
(3rd ventricle) 6. Telencephalon cerebral
hemispheres (lateral ventricles)
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Neural Embryology
Development
Telencephalon
Diencephalon
Mesencephalon
Metencephalon
Myelencephalon
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Neural Embryology
Neural tube defects
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Neural Embryology
Anencephaly
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Neural Embryology
Chiari malformation
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Branchial Arch and Facial Embryology
Branchial (Pharyngeal) clefts, arches and pouches
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Branchial Arch and Facial Embryology
Development 1. Branchial clefts
a. 1st external auditory meatus b.
no others develop cysts could remain
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Branchial Arch and Facial Embryology
Development 2. Branchial arches
a. 1st trigeminal nerve (V) mandible, malleus,
incus b. 2nd facial nerve (VII)
stapes, styloid process, lesser
horn of hyoid c. 3rd
glossopharyngeal nerve (IX)
greater horn of hyoid d. 4th 6th
vagus nerve (X) laryngeal
cartilages
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Branchial Arch and Facial Embryology
Development 3. Branchial pouches
a. 1st middle ear, auditory tube b.
2nd palatine tonsil c. 3rd
thymus, inferior parathyroids
d. 4th superior
parathyroids, ultimobranchial body
(parafollicular cells)
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Branchial Arch and Facial Embryology
Development
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Branchial Arch and Facial Embryology
Cranial nerve association
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Branchial Arch and Facial Embryology
Bones and Cartilage
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Branchial Arch and Facial Embryology
Pharyngeal clefts
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Branchial Arch and Facial Embryology
Cervical cysts and fistulas
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Branchial Arch and Facial Embryology
Thyroid and thymus migration
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Branchial Arch and Facial Embryology
Thyroid migration
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Branchial Arch and Facial Embryology
Thyroglossal duct and cysts
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Branchial Arch and Facial Embryology
Tongue development
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Branchial Arch and Facial Embryology
Cleft lips and palate
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Branchial Arch and Facial Embryology
Cleft lip (11000) and palate (12500)
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Gastrointestinal Embryology
Bowel development 1. Foregut esophagus,
stomach (celiac artery) 2. Midgut
duodenum, small intestine, 2/3rds of
large intestine (superior mesenteric artery)
3. Hindgut 1/3 large intestine, sigmoid colon,
rectum (inferior mesenteric artery)
GI organs 1. Pancreas (celiac superior
mesenteric artery) 2. Liver (celiac artery)
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Gastrointestinal Embryology
Tracheoesophageal fistula
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Gastrointestinal Embryology
Annular pancreas 1. Ventral pancreas
2. Duodenal stenosis
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Gastrointestinal Embryology
Midgut bowel rotation 1. 180 degrees
counterclockwise 2. Around superior
mesenteric artery
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Gastrointestinal Embryology
Abnormal bowel rotation 1. A incomplete
bowel rotation 2. B incorrect clockwise
rotation
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Gastrointestinal Embryology
Omphalocele 1. Failure of intestine to
return to abdomen
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Gastrointestinal Embryology
Bowel atresia and stenosis
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Gastrointestinal Embryology
Vitelline duct
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Gastrointestinal Embryology
Hindgut malformations
Urorectal fistula
Rectovaginal fistula
Imperforate anus
Rectal atresia
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Urinary Embryology
Kidney development 1. pronephros up to
4th week, degenerates 2. mesonephros
interim kidney, contributes to male reproductive
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Urinary Embryology
Kidney development 3. metenephros
permanent kidney a. ureteric bud
outgrowth from mesonephros forms
collecting system of kidney (collecting ducts
through ureter) b.
metanephric blastema forms
glomerulus through distal
convoluted tubule
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Urinary Embryology
Kidney development 4. urogenital sinus
bladder, urethra
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Urinary Embryology
Kidney ascent difficulties
Horseshoe kidney
Pelvic kidney
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Urinary Embryology
Double ureters A, B, D E Ectopic ureter C
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Urinary Embryology
Urachal fistula, cycst or sinus
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Urinary Embryology
Bladder exstrophy with or without epispadias
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Reproductive Embryology
Male and female development 1.
Paramesonephric duct is the default (female)
2. Mesonephric duct must be stimulated to remain
(male) a. SRY gene testis
determining factor b. Mullerian
inhibitory factor suppresses paramesonephric
c. Androgens stimulate mesonephric
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Reproductive Embryology
Male development (mesonephric ducts)
16 weeks
9 months
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Reproductive Embryology
Female development (paramesonephric ducts)
8 weeks
9 months
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Reproductive Embryology
Adult structures
Mesonephric ducts
Paramesonephric ducts
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Reproductive Embryology
Adult homologous structures
Genital tubercle
Labioscrotal swelling
Female
Male
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Musculoskeletal Embryology
Development 1. Somites develop for each
spinal nerve level 2. Sclerotome, myotome
and dermatome from each somite 3. 4th week
Limb buds form
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Musculoskeletal Embryology
Development 1. Somites develop for
each spinal nerve level 2. Sclerotome,
myotome and dermatome from each somite
3. 4th week Limb buds form
5 weeks
6 weeks
7 weeks
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Musculoskeletal Embryology
Development 4. Myotomes subdivide to
a. epimere (dorsal ramus) b.
hypomere (ventral ramus)
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Musculoskeletal Embryology
Development 5. Dermatomes
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Musculoskeletal Embryology
Syndactyly
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Musculoskeletal Embryology
Amelia
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Musculoskeletal Embryology
Meromelia thalidomide
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Musculoskeletal Embryology
Cranial sutures
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Musculoskeletal Embryology
Acrocephaly premature closure of
coronal suture
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Embryology
Good Luck on the USMLE!! Feel free to contact
me with any questions tchampney_at_med.miami.edu