USMLE Review: Embryology. General Embryology Timeline: 1. Week 1: implantation, hCG secretion 2....
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Transcript of USMLE Review: Embryology. General Embryology Timeline: 1. Week 1: implantation, hCG secretion 2....
USMLE Review: Embryology
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)
General Embryology
Timeline:
General Embryology
Teratogens:
1. alcohol (FAS)
2. smoking
3. thalidomide
4. diethylstilbesterol (DES)
5. folic acid / folate
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
Cardiovascular Embryology
Heart:
1. Single tube to four chamber
2. Atrial and ventricular development
3. Atrial and ventricular septation
4. Outflow tracts: truncus arteriosus
Great vessels:
1. Aortic arches – 3rd, 4th and 6th
2. Cardinal veins
Third arch
Fourth arch
Sixth arch
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
Cardiovascular Embryology
Atrial septal defect:
1. Most common congenital anomaly
2. Left to right shunt (↑ pulmonary flow)
3. Maybe asymptomatic until adulthood
LA
RA
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
Cardiovascular Embryology
Tetralogy of Fallot:
1. Ventricular septal defect
2. Pulmonary stenosis
3. Overriding aorta
4. Right ventricular hypertrophy
1
2
3
4
Cardiovascular Embryology
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
1
2
3
4
5
6
7
8
Cardiovascular Embryology
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)
1
2
3
4
4
4
5
5
5
6
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)
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)
Neural Embryology
Development:
Myelencephalon
Metencephalon
Mesencephalon
Diencephalon
Telencephalon
Neural Embryology
Neural tube defects:
Neural Embryology
Anencephaly:
Neural Embryology
Chiari malformation:
Branchial Arch and Facial Embryology
Branchial (Pharyngeal) clefts, arches and pouches:
Branchial Arch and Facial Embryology
Development:
1. Branchial clefts
a. 1st = external auditory meatus
b. no others develop – cysts could remain
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
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)
Branchial Arch and Facial Embryology
Development:
(1st arch)
(2nd arch)
(3rd arch)
(4th & 6th
arches)
Branchial Arch and Facial Embryology
Cranial nerve association:
Branchial Arch and Facial Embryology
Bones and Cartilage:
Branchial Arch and Facial Embryology
Pharyngeal clefts:
Branchial Arch and Facial Embryology
Cervical cysts and fistulas:
Branchial Arch and Facial Embryology
Thyroid and thymus migration:
Branchial Arch and Facial Embryology
Thyroid migration:
Branchial Arch and Facial Embryology
Thyroglossal duct and cysts:
Branchial Arch and Facial Embryology
Tongue development:
Branchial Arch and Facial Embryology
Cleft lips and palate:
Branchial Arch and Facial Embryology
Cleft lip (1:1000) and palate (1:2500):
Incomplete cleft lip Bilateral cleft lip Cleft lip/palate
Cleft palate Facial cleft Midline cleft lip
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)
Gastrointestinal Embryology
Tracheoesophageal fistula:
Gastrointestinal Embryology
Annular pancreas:
1. Ventral pancreas
2. Duodenal stenosis
Gastrointestinal Embryology
Midgut bowel rotation:
1. 180 degrees counterclockwise
2. Around superior mesenteric artery
Gastrointestinal Embryology
Abnormal bowel rotation:
1. A = incomplete bowel rotation
2. B= incorrect clockwise rotation
Gastrointestinal Embryology
Omphalocele:
1. Failure of intestine to return to abdomen
Gastrointestinal Embryology
Bowel atresia and stenosis:
Gastrointestinal Embryology
Vitelline duct:
Gastrointestinal Embryology
Hindgut malformations:
Rectovaginal fistulaUrorectal fistula
Imperforate anusRectal atresia
Urinary Embryology
Kidney development:
1. pronephros: up to 4th week, degenerates
2. mesonephros: interim kidney, contributes to male reproductive
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
Urinary Embryology
Kidney development:
4. urogenital sinus: bladder, urethra
Urinary Embryology
Kidney ascent difficulties:
Pelvic kidney Horseshoe kidney
Urinary Embryology
Double ureters: A, B, D & E
Ectopic ureter: C
Urinary Embryology
Urachal fistula, cycst or sinus:
Urinary Embryology
Bladder exstrophy with or without epispadias:
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
Reproductive Embryology
Male development (mesonephric ducts):
16 weeks 9 months
Reproductive Embryology
Female development (paramesonephric ducts):
8 weeks 9 months
Reproductive Embryology
Adult structures:
Mesonephric ducts Paramesonephric ducts
Reproductive Embryology
Adult homologous structures:
Male Female
Labioscrotal swelling
Genital tubercle
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
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
Musculoskeletal Embryology
Development:
4. Myotomes subdivide to
a. epimere (dorsal ramus)
b. hypomere (ventral ramus)
Musculoskeletal Embryology
Development:
5. Dermatomes
Musculoskeletal Embryology
Syndactyly:
Musculoskeletal Embryology
Amelia:
Musculoskeletal Embryology
Meromelia:
thalidomide
Musculoskeletal Embryology
Cranial sutures:
Musculoskeletal Embryology
Acrocephaly:
premature closure of coronal suture