Embryo Flashcards
Cardiac looping
heart beats at week 4
primary heart tube establishes L-R polarity through dynein movement (Kartagener’s = dextrocardia)
Atria formation
Septum primum forms, then detaches at each end to stay in the middle (top hole = foramen secundum, bottom = foramen primum)
Septum secundum first covers most of foramen secundum, then all of foramen primum
Remaining hole of foramen secundum is the foramen ovale (septum primum serves as valve)
Ventricle formation
interventricular foramen is closed by the fusion of muscular septum and aorticopulmonary septum (comes from neural crest!)
Outflow tract
neural crest cells and endocardial cell migrations allow for travel and bulbar ridges that form aorticopulmonary septum
Valve development
- aortic/pulmonary valves: endocardial cushion of outflow tract
- mitral/tricuspid: endocardial cushion of AV canals
Fetal erythropoiesis locations
3-8 wks: yolk sac
6 wks - birth: liver***
10-28 weeks: spleen
18 weeks - birth: bone marrow
Fetal circulations (give 3 shunts)
Ductus venosus: umbilical vein to IVC (bypass portal system)
Foramen ovale: RA to LA (bypass cardiopulmonary system)
Ductus arteriosus: Left PA to descending aorta (bypass lungs)
How can the closure of the DA be manipulated? (accel closure, prevent closure)
Accel closure: indomethacin, NSAIDs (block PGs)
Prevent closure: prostaglandins E1, E2
Notable vessels to ligaments
Allantois - urachus: median umbilical ligament
Notochord: nucleus pulposus
Umbilical arteries: medial umbilical ligaments
Umbilical vein: ligamentum teres hepatis (falciform ligament)
Thyroid diverticulum
primitive pharynx –> descends to neck
(connected to tongue by thyroglossal duct - if duct persists, become pyramidal lobe of thyroid)
most common site of ectopic thyroid tissue: tongue
Thyroglossal duct cyst
Anterior midline neck mass, moves with swallowing
Anterior abdominal wall defects
rostral (head) folds: sternal defects
lateral folds: omphalocele (sealed by peritoneum), gastroschisis
caudal (butt) folds: bladder exstrophy
Duodenal atresia is seen with what genetic condition?
Trisomy 21! Arises due to failure of recanalization. Look for double bubble sign and bilious vomiting (or polyhydramnios)
A vascular accident early in development causes what abdominal abnormality?
Jejunal/ileal/colonic atresia
Can be complete obliteration of intestine
Look for polyhydramnios
Midgut development (ampulla of Vader to proximal 2/3 of transverse colon)
6th week: herniates through umbilical ring
10th week: returns to abdominal cavity, rotates around SMA
Pancreas development
Ventral bud = uncinate process and main duct
encircles duodenum in annular pancreas, can cause obstructive symptoms
Dorsal bud: body, tail, isthmus, accessory duct
Pancreatic divisum: failure of fusion of buds (which normally occurs at 8 weeks), can be a cause of pancreatitis
Notochord function and development
induces overlying ectoderm to become neuroectoderm –> neural plate –> neural tube and neural crest cells
Regional specification of developing brain (3 regions become 5 regions)
Forebrain:
telencephalon: hemispheres/lateral ventricle
diencephalon: thalamus/third ventricle
Midbrain:
mesencephalon: midbrain/aqueduct
Hindbrain:
metencephalon: pons/cerebellum/4th ventricle
myelencephalon: medulla/lower 4th ventricle
CNS/PNS progenitors
neuroectoderm –> CNS, glial cells (ependymal, oligodendroglial, astrocytes)
neural crest –> PNS neurons, Schwann cells
mesoderm –> microglia (come from macrophages!)
Neural tube defects
Failure of cranial neuropore to close: anencephaly
Failure of caudal neuropore to close: spina bifidas
Spina bifida occulta: bones don’t close, no herniation, intact dura (normal AFP)
Meningocele: meninges herniates (can be caused by teratoma)
Myelomeningocele: meninges and neural tissue herniate
Posterior fossa malformations
Chiari Arnold II: herniation of cerebellar tonsils through the foramen magnum, often seen myelomeningocele
Dandy-Walker: agenesis of vermis with cystic enlargement of 4th ventricle, seen with hydrocephalus and spina bifida
Synringomyelia
cystic cavity within spinal cord, leads to damage of anterior commisures and subsequent cape-like distribution of pain/temp loss
Most often occurs at C8-T1
Tongue development
1st/2nd arches: anterior 2/3 (CN V3, CN VII)
3rd/4th arches: posterior 1/3 (CN IX, CN X)
Motor: CN XII (except CN X to palatoglossus)
Renal development
Pronephros: week 4, then degenerates (turns into nothing!)
Mesonephros: interim kidney for 1st trimester (then, contributes to male genitals)
Metanephros: appears in Wk 5, forms permanent kidney
- ureteric bud: caudal (butt) end of metanephros, becomes ureter, pelvises, calyces, CDs
- metanephric mesenchyme: glomerulus through DCT
Ureteropelvic junction = last to canalize, most common site of obstruction (hydronephrosis)
Oligohydramnios/Potter sequence
ADPKD, obstructive uropathy causes decreased amniotic fluid
Compression of fetus –> limb deform, facial anomalies –> compression of chest/lack of fluid in lungs –> pulmonary hypoplasia
Kidney abnormalities:
Horseshoe kidney
Multicystic dysplastic kidney
Duplex collecting system
inferior poles fuse –> trapped under IMA –> kidneys remain low in abdomen (increased risk of obstruction, hydronephrosis, renal stones, infection, etc.)
abnormal interaction between ureteric bud and metanephric mesenchyme –> nonfunctional kidney of cysts and connective tissue
Bifurcation of ureteric bud creates Y-shaped bifid ureter. Assoc w/ vesciureteral reflux and/or ureteral obstruction (increased risk of UTIs)
Genes involved in early development (Shh, Wnt-7, FGF, Hox)
Shh - anterior-posterior patterning, ZPA
Wnt-7 - dorsal-ventral patterning, apical ectodermal ridge
FGF - stimulates mitosis of mesoderm, limb lengthening
Hox - segmental organization, transcription factors
Early development (give events by week)
Wk 1: implantation of blastocyst, secretion of bHCG
Wk 2: bilaminar disc
Wk 3: trimlaminar disc (three germ layers)
Wk 4: neural tube closure, heart beats
Wk 4-8: organogenesis, susceptible to teratogens!
Wk 6: heart visible
Wk 10: sex-distinguishable genitalia
Ectoderm derivatives (surface ectoderm, neuroectoderm, neural crest)
Surface ectoderm: epidermis, oral cavity, ears, nose, glands (parotid, sweat, mammary), *cranipharyngioma
Neuroectoderm: Brain, spinal cord, optic nerve, posterior pituitary
Neural crest: PNS, melanocytes, adrenal medulla (chromaffin), skull, **aorticopulmonary system
Mesoderm derivatives
Muscle, bone, connective tissue, CV structures, lymph, blood,
VACTERL: Vertebral defects, Anal atresia, Cardiac defects, Tracheo-Esophageal fistula, Renal defects, Limb defects
Endoderm derivatives
Gut tube epithelium, urethra (from urogenital sinus), lungs, liver, GB, pancreas, eustachian tube, parathyroid
Notable teratogens, give their effects
Aminoglycosides Lithium Phenytoin Tetracyclines Warfarin
Aminoglycosides - Cn VIII toxicity
Lithium - Ebstein anomaly (atrialized R ventricle, disp of tricuspid)
Phenytoin - fetal hydantoin (cleft palate, cardiac defects, fingernail hypoplasia)
Tetracyclines - discolored teeth
Warfarin - bone deformities, fetal hemorrhage, abortion
Twinning
0-4 days: Di/di
4-8 days: Mono/di
8-12 days: Mono/mono
>13 days: conjoined
Dizygotic (80%) - 2 eggs fertilized separately, di/di
Placental cells
Fetal: syncytiotrophoblasts - decreased MHC-1 reduces chance of attack by maternal immune system
Maternal: decidua basalis - endometrium derivative, maternal blood flows in lacunae
Umbilical cord anatomy
1 vein (blood from mom to fetus)
2 arteries (1 from each internal iliac of fetus to mom)
Surrounded by Wharton jelly
Derived from allantois
Urachus
Yolk sac becomes allantois becomes urachus (duct from fetal bladder to yolk sac)
Patent urachus = failure to obliterate, urine discharge from umbilicus
Urachal cyst = partial failure to obliterate, fluid-filled cavity lined with uroepithelium (infection, adenocarcinoma)
Vesicourachal diverticulum = slight failure of urachus to obliterate, leads to outpouching of bladder
Vitelline duct
Goes from midgut lumen to yolk sac
Vitelline fistula = meconium discharge from umbilius
Meckel diverticulum = partial closure, leads to patent portion with gastric/pancreatic tissue
Aortic arches (develop into arterial system)
1st = maxillary artery 2nd = stapedial artery, hyoid artery 3rd = common carotid, proximal internal carotid 4th = aortic arch (left), R subclavian (right) 6th = pulmonary arteries, ductus arteriosus (left)
Branchial clefts (ectoderm!)
1st: EAM
2nd-4th = temporary cervical sinuses
persistent cervical sinus become branchial cleft cyst!
Branchial arches
1st (mandibular) = muscles of mastication, CN V2/V3 (Treacher Collins = mandibular hypoplasia)
2nd (pharyngeal) = stapes, styloid, CN VII
3rd = stylopharyngeus, CN IX
4th-6th = cartilages of neck (thyroid, cricoid, etc.), CN X, CN X
Branchial pouches (endoderm!)
1st = middle ear, eustachian tube 2nd = tonsils 3rd = inferior parathyroid, thymus (end up below 4th pouch structures) 4th = superior parathyroid
DiGeorge: abnormal 3rd and 4th
MEN 2A: germline RET mutation (neural crest cells) –> medullary thyroid, pheochromocytoma (adrenal medulla) 4th pouch, parathyroid 3rd/4th pouches
Genital embryology
Female: mesonephric duct degenerates, paramesonephric (Mullerian ) –> internal structures
Male: SRY = MIF, leads to suppression of paramesonephrics, Leydig (testosterone) stimulates mesonephric (Wolffian) to internal structures
Low MIF/No Sertoli = both male/female internal, only male external
5a-reductase def (no DHT) = male internal, ambiguous external
Male/female homologs (male = DHT, female = estrogen)
tubercle –> glans (penis, clitoris)
urogenital sinus –> Cowper/prostate or Bartholin/Skene glands
urogenital folds –> ventral shaft or labia minora
labioscrotal swelling –> scrotum or labia majora
Spadias
Hypo = ventral opening, failure of urethral folds to fuse Epi = faulty positioning of genital tubercle (exstrophy of bladder)
Descent of ovaries and testes
Gubernaculum (band of fibrous tissue) = anchors testes in scrotum, also forms ovarian ligament + round ligament
Processus vaginalis = forms tunica vaginalis, obliterated in females
