Step 1 - Embryology 2

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


Question Answer
Branchial apparatus (aka pharyngeal apparatus)Composed of branchial clefts, arches, and pouches. - CAP covers outside from inside: Clefts=ectoderm, Arches=mesoderm, Pouches=endoderm
Branchial cleftsderived from ectoderm. Also called branchial grooves.
Branchial archesderived from mesoderm (muscles, arteries) and neural crests (bones, cartilage).
Branchial pouchesderived from endoderm
Branchial Arch 1 innervationderivatives supplied by CN V2 and V3
Branchial Arch 2 innervation derivatives supplied by CN VII
Branchial Arch 3 innervation derivatives supplied by CN IX.
Branchial Arch 4 and 6 innervationderivatives supplied by CNX.


Question Answer
Saying to remember branchial arch innervationsOne man sat chewing (V) Two hands on his face (VII). The third with his pharynx (IX) Swallowed the fourth plate (X). "Speak up, speak up!"Said the sixth in return (X) . "Your cricothyroid makes me want to burn !"
Branchial arch 1 DerivativesCartilage: Meckel’s cartilage, Mandible, Malleus,incus,spheno-Mandibular ligament Muscles: Muscles of Mastications (masseter, temporalis, pterygoids) Mylohyoid, ant belly digastric, tensor tympani, tensor veli palatini, ant 2/3 tongue Nerves: CNV2,V3 Arteries: Maxillary artery (branch of external carotid)
Treacher collins syndrome1st arch neural crest fails to migrate → mandibular hypoplasia, facial abnormalities
Branchial arch 2 DerivativesCartilage: Reicherts cartilage, stapes, styloid process, lesser horn of hyoid, stylohyoid ligament. . Muscles: facial expression, stapedius, stylohyoid, post belly of digastric . . Nerves: CNVII . . Arteries: Stapedial artery, hyoid artery
Branchial arch 3 DerivativesCartilage: greater horn of hyoid . . Muscles: stylopharyngeus Nerves: CNIX Arteries: none
Congenital pharyngo-cutaneous fistulapersistence of cleft and pouch→ fistula between tonsillar area, cleft in lateral neck
Branchial arch 4-6 DerivativesCartilage: thyroid, cricoid, arytenoids, corniculate, cuneiform Muscles: 4th arch: most pharyngeal constrictors, cricothyroid, levator veli palatini 6th: all intrinsic muscles of larynx except cricothyroid Nerves: 4th: CNX(swallowing) 6th: CNX (speaking) Arteries: none
Arches 3 and 4 formposterior 1/3 of tongue; arch 5 makes no major developmental contributions
Branchial cleft derivatives1st cleft develops into external auditory meatus. 2nd through 4th clefts form temporary cervical sinuses, which are obliterated by proliferation of 2nd arch mesenchyme. Persistent cervical sinus ~ branchial cleft cyst within lateral neck.


Question Answer
1st branchial pouch dcvelops into middle ear cavity, eustachian tube, mastoid air cell s. - contributes to endoderm - lined structures of ear
2nd branchial pouch develops into epithelial lining of palatine tonsil.
3rd branchial pouch develops in to(dorsal wings) develops into inferior parathyroids., 3rd pouch (ventral wings) develops into thymus. - end up below 4th pouch structures
4th branchial pouch develops into(dorsal wings) develops into superior parathyroids.
Abberant development of 3rd and 4th branchial pouchesDiGeorge syndrome→ T cell deficiency (thymic aplasia) and hypocalcemia (failure of parathyroid)
MEN 2Amutation of germline RET (neural crest cel1s)→ Adrenal medulla (pheochromocytoma), ParathyrOid (tumor): 3rd/4th pharyngeal pouch, Parafollicular cells (medullary thyroid cancer):4th/5th pouch


Question Answer
Ear parts from 1st archMalleus, Incus, Tensor tympani (V3)
Ear parts from 2nd archStapes, Stapedius (VII)
Ear parts from 1st cleftExternal auditory meatus
Ear parts from 1st branchial membraneTympanic membrane
Ear parts from 1st pouchEustachian tube, middle ear, cavity, mastoid air cells
Taste nervesCNVII, IX, X
Tongue pain nervesCNV3, IX, X
Tongue motor nervesCN XII


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Thyroid developmentfrom floor of pharynx descends into neck, connected to tongue by thyroglossal duct, disappears but may persist as pyramidal lobe of thyroid. Foramen cecum most common remnant of thyroglossal duct, Tongue most common site of ectopic thyroid.
Cleft lip/palatefailure of fusion of 1.maxillary and medial nasal processes (lip) 1. Lateral palantine processes, nasal septum, median palantine (palate)
Draw diaphragm embryology, kidney131, 133
Diaphragm is derived from (4)Several Parts Build D 1. Septum traversum→central tendon 2. Pleuroperitoneal folds 3. Body wall 4. Dorsal mesentary of esophagus→ crura
Diaphragm innervationsC345 keeps diaphragm alive
Incomplete diaphragm developmentabdominal contents may herniate into the thorax because of incomplete development→ hypoplasia of thoracic organis due to space compression, scaphoid abdomen, cyanosis


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Gastroschisisfailure of latera1 body folds to fuse → extrusion of abdominal contents through abdominal folds.
Omphalocelepersistence of herniation of abdominal contents into umbilIcal cord, covered by peritoneum
Foregut becomespharynx to duodenum
Midgut becomesduodenum to transverse colon
Hindgut becomesdistal transverse colon to rectum
Developmcntal defects of anterior abdominal wall due to failure ofRostral fold closure: sternal defects, Lateral fold closure: omphalocele, gastroschisis , Caudal fold closure: bladder exstrophy
Duodenal atresiafailure to recanalize (trisomy 21 ).
Jejunal, ileal, colonic atresiadue to vascular accident (apple peel atresia).


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6th week GI developmentmidgut herniates through umbilical ring → rapid growth.
10th week GI developemntreturn to abdominal cavity + rotate around SMA.
GI Pathology intestinal obstruction, twisting around SMA (volvulus)
Tracheoesophageal fistula Abnormal connection b/w esophagus and trachea - most common subtype is blind upper esophagus with lower eso connected to trachea, Results in cyanosis, choking and vomiting with feeding, air bubble on CXR and polyhydramnios
Congenital pyloric stenosisHypertrophy of the pylorus causes obstruction. Palpable "olive" mass in epigastric region and non bilious projectIle voming at about 2 weeks of age. Treatment is surgical incision. Occurs in 1/600 live births, often in 1st-born males.
Pancreas embryologyderived from foregut. Ventral pancreatic buds becomes pancreatic head, uncinate process (lower half of head), and main pancreatic duct. Dorsal pancreatic bud becomes everything else (body, tail, isthmus, and accessory pancreatic duct).
Annular pancreasventral pancreatic bud abnormally encircles 2nd part of duodenum; forms a ring of pancreatic tissue that may cause duodenal narrowing. Pancreas divisum-ventral and dorsal parts fail to fuse at 8 weeks.


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Spleenarises from dorsal mesentery (hence is mesodermal) but is supplied by artery of foregut (celiac artery)
Pronephrosdevelops week 4; then degenerates
Mesonephrosfunctions as interim kidney for 1st trimester; later contributes to male genital system
Metanephrospermanent; beginnings first appear during 5th week of gestation, nephrogenesis continues through 32-36 weeks of gestation. - Ureteric bud - derived from caudal end of mesoncphros, gives ureter pelvises, and, through branching, calyces and collecting ducts; fully canalized by 10th week.
Metanephric mcsenchymeureteric bud interacts with this tissue; interaction induces differentiation and formation of glomerululs and renal tubules to distal convoluted tubule
Abberant interaction b/w metanephric mesenchyme and ureteric budmay result in congenital malformations of the kidney
Abberant development of urteric budmay result in several congenital malformations of the lower urinary tract


Question Answer
Uteropelvic junction with kidneylast to canalize - most common site of obstruction (hydronephrosis) in fetus
Potter’s syndrome Bilateral renal agenesis - oligohydramnios - limb deformities, facial deformities, pulmonary hypoplasia, caused by malformations of ureteric bud - babies who can’t Pee in utero develop Potter’s
Horseshoe kidneyInferior poles of both kidneys fuse. As they ascend from pelvis during fetal development, get trapped under inferior mesenteric artery and remain low in the abdomen. Kidncy functions normally. Note: horseshoe kidney (partial fusion) vs. cake kidney (complete fusion).
Female genital embryologyDefault development. Mesonephric duct degenerates and paramesonephric duct develops.
Male genital embryologySRY gene on Y chromosome codes for testis-determining factor. Mullerian inhibiting substance secreted by testes (sertoli cells) suppresses development of paramesonephric ducts. Increased androgens from leydig cells develop mesonephric ducts
Mesonephric ductDevelops into male internal structures (except prostate) - Seminal vesicles, Epididymis, Ejaculatory duct, Ductus deferens . . SEED
Paramesonephric ductDevelops into fallopian tube, uterus and upper 1/2 of vagina (lower 2/3 from urogenital sinus)


Question Answer
Bicornuate uterusResults from incomplete fusion of the paramesonephric ducts, associated with urinary tract abnormalities and infertility
Homologue drawing134
Genital tubercle develops intoGlans penis, corpus cavernosum/spongiosum or Glans clitoris, vestibular bulbs
Urogenital sinus develops intoBulbourethral glands(of cowper), Prostate gland or Greater vestibular glands (of Bartholin), Urethral and paraurethral glands (of skene)
Urogenital folds develop intoVentral shaft of penis (penile urethra) or Labia minora
Labioscrotal swelling develop intoScrotum or Labia majora
HypospadiasAbnormal opening of penile urethra on inferior side - more common than epi -
Epispadiasabnormal opening of penile urethra on dorsal side of penis - exstrophy of the bladder associated with epispadias