USMLE_Embryology_Review

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					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:
                                               Third arch
       1. Single tube to four chamber

       2. Atrial and ventricular development
                                                       Fourth arch
       3. Atrial and ventricular septation

       4. Outflow tracts: truncus arteriosus


    Great vessels:

       1. Aortic arches – 3rd, 4th and 6th

       2. Cardinal veins
                                                        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
                                       2
                                               3

                                               1



                                           4
                                                      6
Cardiovascular Embryology
                                          4
 Fetal Circulation:

    1. Umbilical vein
                                          3
                                                  5
    2. Ductus venosus

    3. Inferior vena cava, right atrium
                                                          7
    4. Foramen ovale to left atrium,      2
       left ventricle to aorta

    5. Right ventricle, pulmonary trunk
                                              1
    6. Ductus arteriosus

    7. Aorta
                                              8
    8. Umbilical arteries
Cardiovascular Embryology                                  5

                                                                       4
 Adult Circulation:
                                                               5
                                                       4
    1. Ligamentum teres hepatis
       (umbilical vein - closed)               3

    2. Ligamentum venosum                                          5
       (ductus venosus - closed)                           4

    3. Inferior vena cava, right atrium
                                           2
    4. Right ventricle, pulmonary trunk,
       lungs (ligamentum arteriosum:
       ductus arteriosus - closed)
                                                   1
    5. pulmonary veins to left atrium,
       left ventricle to aorta

    6. Medial umblical ligaments                       6
       (umbilical arteries – closed)
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:


        Telencephalon




           Diencephalon

                  Mesencephalon

                          Metencephalon


                                  Myelencephalon
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:
Branchial Arch and Facial Embryology

  Cranial nerve association:           (1st arch)

                                                    (2nd arch)




                                                          (4th & 6th
                                                           arches)

                                                      (3rd arch)
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:




           Urorectal fistula   Rectovaginal fistula




            Rectal atresia       Imperforate anus
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:



                                 Genital tubercle




                                 Labioscrotal swelling




               Male                                      Female
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      5 weeks   6 weeks
       dermatome from each somite

    3. 4th week: Limb buds form




                                               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
Embryology

  Good Luck on the USMLE!!


  Feel free to contact me with any questions:

  tchampney@med.miami.edu

				
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