Fa Embrology

Front 1

Sonic hedgehog gene

Back 1

Produced at base of limbs in zone of polarizing activity. Involved in patterning along anterior-posterior axis

Front 2

Wnt-7 gene

Back 2

Produced at apical ectodermal ridge (thickened ectoderm at distal end of each developing limb). Necessary for proper organization along dorsal-ventral axis

Front 3

FGF gene

Back 3

Produced at apical ectodermal ridge. Stimulates mitosis of underlying mesoderm, providing for lengthening of limbs (also functions with VEGF as an angiogenesis stimulator)

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Homeobox gene

Back 4

Involved in segmental organization

Front 5

HoxA-13

Back 5

Gene involved in hand-foot-genital syndrome (clindactyly, short thumbs, small feet, short great toes, urinary tract abnormalities). Duplication of reproductive tract in females, hypospadias in males

Front 6

FETAL LANDMARKS: day 0

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Fertilization by sperm forming zygote, initiating embryogenesis

Front 7

FETAL LANDMARKS: within week 1

Back 7

hCG secretion begins after implantation of blastocyst.

Front 8

FETAL LANDMARKS: within week 2

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Bilaminar disk (epiblast, hypoblast)

Front 9

FETAL LANDMARKS: within week 3

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Gastrulation! Primitive streak, notochord, and neural plate begin to form

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FETAL LANDMARKS: weeks 3-8 [embryonic period]

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Neural tube formed by neuroectoderm and closes by week 4. Organogenesis. EXTREMELY susceptible to teratogens

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FETAL LANDMARKS: week 4

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Heart begins to beat; upper and lower limb buds begin to form

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FETAL LANDMARKS: week 8, fetal period

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Fetal movement, fetus looks like a baby

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FETAL LANDMARKS: week 10

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Genitalia have male/female characteristics

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Alar plate (dorsal)

Back 14

Sensory development (like spinal cord)

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Basal plate (ventral)

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Motor development (like spinal cord)

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Rule of twos for 2nd week

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2 germ layers (bilaminar disk: hypoblast+epiblast); 2 cavities (amniotic cavity, yolk sac); 2 components to placenta: cytotrophoblast, syncytiotrophoblast

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Rule of threes for 3rd week

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3 germ layers (gastrula): ectoderm, mesoderm, endoderm. The epiblast (precursor to ectoderm) invaginates to form the primitive streak. Cells from the primitive streak give rise to both intraembryonic mesoderm and endoderm

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Rule of fours for 4th weeks

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4 hear chambers, 4 limb buds grow

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Three parts of ectoderm

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(1) Surface ectoderm; (2) Neuroectoderm; (3) Neural crest

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Surface ectoderm

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Adenohypophysis (from Rathke's pouch); lens of eye; epithelial linings of oral cavity, sensory organs of ear, retina, and olfactory epithelium; epidermis; salivary, sweat, and mammary glands

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Craniopharyngioma

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Benign surface ectoderm derived tumor of Rathke's pouch with cholesterol crystals, calcifications

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Neuroectoderm

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Brain (neurohypophysis, CNS neurons, oligodendrocytes, astrocytes, ependymal cells, pineal gland), retina, spinal cord. THINK CNS + BRAIN!

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Neural crest

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ANS, dorsal root ganglia, cranial nerves, celiac ganglion, melanocytes, chromaffin cells of adrenal medulla, enterochromaffin cellls, parafollicular (C) cells of the thyroid, Schwann cells, pia and arachnoid meninges, bones of skull, odontoblasts, laryngeal cartilage, aorticopulmonary septum

Front 24

Endoderm

Back 24

Gut tube epithelium and derivatives (lungs, liver, pancreas, thymus, parathyroid, thyroid follicular cells)

Front 25

Mesoderm

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Muscle, bone, connective tissue, serous linings of body cavities (peritoneum), spleen (foregut mesentery), cardiovascular structures, lymphatics, blood, urogenital structures, kidneys, adrenal cortex

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Notochord

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Induces ectoderm to form neuroectoderm (neural plate). Its postnatal derivative is the nucleus pulposus of the intervertebral disk

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Mesodermal defects

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VACTERL: Vertebral defects, Anal atresia, Cardiac defects, TE fistula, Renal defects, Limb defects

Front 28

ACE inhibitors

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Cause renal damage

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Alcohol

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Leading cause of birth defects and MR; fetal alcohol syndrome

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Alkylating agents

Back 30

Absence of digits, multiple anomalies

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Aminoglycosides

Back 31

CN VIII toxicity

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Cocaine

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Abnormal fetal development and fetal addicition; placental abruption

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Diethylstilbestrol (DES)

Back 33

Vaginal clear cell adenoma

Front 34

Folate antagonists

Back 34

Neural tube defects

Front 35

Iodide (lack or excess)

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Congenital goiter or hypothyroidism

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Lithium

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Ebstein's anomaly (atrialized right ventricle)

Front 37

Maternal DM

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Caudal regression syndrome (anal atresia to sirenomelia)

Front 38

Tetracyclines

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Discolored teeth

Front 39

Thalidomide

Back 39

Limb defects ('flipper limbs')

Front 40

Valproate

Back 40

Inhibition of intestinal folate absorption

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Vitamin A

Back 41

Extrememly high risk for SAB and birth defects (cleft palate, cardiac abnormalities)

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Warfarin

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Bone deformities, fetal hemorrhage, abortion

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XR, anticonvulsants

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Multiple anomalies

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Fetal Alcohol Syndrome

Back 44

Leading cause of congenital malformations in the US. Newborns of mothers who consumed significant amounts of alcohol during pregnancy have an increased incidence of congenital abnormalities, including pre-and post-natal development retardation, microcephaly, holoprosencephaly, facial abnormalities, limb dislocation, and heart and lung fistulas. Mechanism may include inhibition of cell migration

Front 45

Twin development: dichorionic, diamnotic placenta

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Days 1-3; Monozygotes that split early develop 2 placentas, chorions, and amniotic sacs. Dizygotes develop individual placentas, chorions, and amniotic sacs when two fertilized eggs are implanted in uterus ~same time

Front 46

Twin development: monochorionic, diamnotic placenta

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Days 4-6; Monozygotes that split evenly to develop 2 amniotic sacs with a single common chorion and placenta

Front 47

Twin development: monochorionic, monoamnotic placenta

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Days 8-13; Risk of conjoined twins if occurs in days 13-15.

Front 48

Fetal component of placenta

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Cytotrophoblast = inner layer of chorionic villi. CYTO makes CELLS; Syncytiotrophoblast = Outer layer of chorionic villi; secretes hCG, which stimulates corpus luteum to secrete progesterone during first trimester

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Maternal component of placenta

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Decidua basalis. Derived from endometrium. Maternal blood in lacunae

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Umbilical cord

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1 vein supplying oxygenated blood to fetus; 2 arteries returning deoxygenated blood from placenta to fetus. Umbilical veins and arteries are derived from ALLANTOIS.

Front 51

Urachal duct abnormalities

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3rd week: yolk sac forms allantois, which extends into urogenital sinus. Allantois becomes urachus, a duct between bladder and yolk sac

Front 52

Failure of urachus to obliterate

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(1) Patent urachus = urine discharge from umbilicus; (2) Vesicourachal diverticulum = outpouching of bladder

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Vitelline duct abnormalities

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(1) 7th week - obliteration of vitelline duct (omphalomesenteric duct), which connects yolk sac to midgut lumen; (2) Vitelline fistula - failure of duct to close --> meconium discharge from umbilicus

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Meckel's diverticulum

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Partial closure of vitelline duct, with patent portion attached to ileum. May have ectopic fastric mucosa --> melena and RUQ pain

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Truncus arteriosus

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Gives rise to ascending aorta and pulmonary trunk

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Bulbus cordis

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Gives rise to RV and smooth parts (outflow tract) of left and right ventricle

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Primitive ventricle

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Portion of the left ventricle

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Primitive atria

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Trabeculated left and right atrium

Front 59

Left horn of sinus venosus

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Coronary sinus

Front 60

Right common cardinal vein and right anterior cardinal vein

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SVC

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Truncus arteriosus

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Neural crest migration divides trunk into 2 arteries via fusion and twisting of truncal and bulbar ridges --> ascending aorta and pulmonary trunk. Pathology = TGV and TOF. Malformed in DiGeorge Syndrome = TGV

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Aorticopulmonary Septation

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Neural crest cells migrate into the truncal and bulbar ridges of the truncus arteriosus and bulbus cordis, respective,a nd grow in a SPIRALING FASHION to separate the aorta and pulmonary artery. Failure of this process is responsibe for 3 of the 5 cyanotic heart diseases: TOF, persistent truncus, and TGV

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Fetal erythropoiesis

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Yolk sac (3-8wk) --> Liver (6-30wk) --> Spleen (9-28wk) --> Bone marrow (28wk onward). Young Liver Synthesized Blood (YLSB)

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3 Important Shunts

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(1) Ductus venosus (umbilical vein --> IVC); (2) Foramen ovale (IVC --> aorta) to upper part of body; (3) Ductus arteriosus (SVC --> Pulmonary artery) to lower body of fetus

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Umbilical vein

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Ligamentum teres hepatis

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UmbiLical arteries

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MediaL umbilical ligaments

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Ductus arteriosus

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Ligamentum arteriosum

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Ductus venosus

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Ligamentum venosum

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Foramen ovale

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Fossa ovalis

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AllaNtois

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Urachus, MediaN umbilical ligament

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Notochord

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Nucleus pulposus of intervertebral disk

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Patent urachus

Back 72

Persistent connection between bladder cavity and outside of body via umbilicus; discharge or urine from umbilicus may be noted after birth!

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1st aortic arch

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Part of MAXillary artery (branch of external carotid). 1st arch is MAXimal

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2nd aortic arch

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Stapedial artery and hyoid artery. Second = Stapedial

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3rd aortic arch

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common Carotid artery and proximal part of internal carotid. C = 3rd letter of alphabet

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4th aortic arch

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On left, aortic arch; on right, proximal part of right subclavian artery. 4th arch (4 limbs) = systemic

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6th aortic arch

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Proximal part of pulmonary arteries and (on left only) ductus arteriosus. 6th arch = pulmonary and the pulmonary-tosystemic shunt (ductus arteriosus)

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Prosencephalon

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Telencephalon (hemispheres, lateral ventricles) and diencephalon (thalami, 3rd ventricle)

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Mesencephalon

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Midbrain, aqueduct

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Rhomboencephalon

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Metancephalon (pons, cerebellum, 4th ventricle), and Myencephalon (medulla)

Front 81

Neural tube defects

Back 81

Neuropores fail to FUSE (4th week) --> persistent connection between amniotic cavity and spinal canal. Associated with low folate levels. Elevated AFP in amniotic fluid and maternal serum. Increased AFP and acetylcholinesterase in CSF

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Spina bifida occulta

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Failure of bony spinal canal to close, but no structureal herniation. Usually seen at lower vertebral levels. Dura is intact, tuft of hair often present

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Meningocele

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Meninges herniate through spinal canal defect

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Myelomeningocele

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Both meninges and spinal cord herniate through spinal canal defect

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Anencephaly

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Malformation of anterior end of neural tube; no brain/calvarium, elevated AFP, polyhydramnios (no swallowing center in brain)

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Holoprosencephaly

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No separation of hemispheres across midline; results in cyclopia, associated with Trisomy 13 (Patau syndrome), severe fetal alcohol syndrome, and cleft lip/palate

Front 87

Arnold-Chiari type II malformation

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Cerebellar tonsillar herniation through foramen magnum with aqueductal stenosis and hydrocephaly. Often presents with syringomyelia, thoracolumbar myelomeningocele

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Dandy-Walker malformation

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Large posterior fossa; absent cerebellar vermis with cystic enlargement of 4th ventricle. Can lead to spina bifida and hydrocephalus

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Syringomyelia

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Enlargement of central canal of spinal cord. Crossing fibers of spinothalamic tract are typically damaged first. 'Cape-like' distribution of bilateral loss of pain and temperature sensation in upper extremities with preservation of touch sensation. Often presents with Arnold-Chiari II malformation. Most common at C8-T1

Front 90

Branchial cleft, arches, pouches

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CLEFTS: ectoderm. ARCHES: mesoderm (muscles, arteries) and neural crests (bones, cartilage). POUCHES: endoderm. [CAP covers outside from inside]

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Branchial arch 1

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Supplied by CN V2 and V3

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Branchial arch 1

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Supplied by CN VII

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Branchial arch 1

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Supplied by CN IX

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Branchial arch 4 and 6

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Supplied by CN X

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How to think of arches:

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Chewing (1); Facial expression (2); Stylopharyngeus (3); Swallowing (4); Speaking (6)

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First branchial arch: cartilage

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Meckel's cartilage, Mandible, Malleus, incus, sphenoMandibular ligament

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First branchial arch: muscles

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Muscles of Mastication (temporalis, Masseter, later and Medial pterygoids), Mylohyoid, anterior belly of digastric, tensor tympani, tensor veli palatini, anterior 2/3 of tongue

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First branchial arch: nerves

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CN V2 and V3

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First branchial arch: arteries

Back 99

Maxillary artery (a branch of external carotid); 1st = MAXimal

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First branchial arch: abnormalities

Back 100

Treacher-Collins Syndrome: 1st arch neural crest cells fail to migrate --> mandibular hypoplasia, facial abnormalities. Autosomal Dominant inheritance. Micrognathia, downslanting eyes, conductive hearing loss, malformed/absent ears, underdeveloped zygomatic arch

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Second branchial arch: cartilage

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Reichert's cartilages, STAPES, Stylohyoid process, lesser horn of hyoid, Stylohyoid ligament

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Second branchial arch: muscles

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Muscles of facial expression, Stapedius, Stylohyoid, posterior belly of digastric

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Second branchial arch: nerves

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CN VII

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Second branchial arch: arteries

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Stapedial artery and hyoid artery. Second = Stapedial

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Third branchial arch: cartilage

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Greater horn of hyoid

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Third branchial arch: muscles

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Stylopharyngeus (think of styloPHARYNGEUS, innervated by glossoPHARYNGEAL nerve)

Front 107

Third branchial arch: nerves

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CN IX

Front 108

Third branchial arch: abnormalities

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Congenital pharyngeocutaneous fistula; persistence of cleft and pouch --> fistula between tonsillar area, cleft in lateral neck

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4th and 6th branchial arches: cartilage

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Cartilages: thyroid, cricoid, arytenoids, corniculate, cuneiform

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4th and 6th branchial arches: muscles

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4th arch: most pharyngeal constrictors, cricothyroid, levator veli palatini; 6th arch: all intrinsic muscles of larynx except cricothyroid

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4th and 6th branchial arches: nerves

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4th arch: CN X (superior laryngeal branch - swallowing); 6th arch: CN X (recurrent laryngeal branch - speaking)

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4th and 6th branchial arches: abnormalities

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Arches 3 and 4 form posterior 1/3 of tongue.

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The 5th branchial arch

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Makes no major developmental contributions

Front 114

Branchial cleft derivatives

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1st 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

Front 115

Branchial pouch derivatives: 1st pouch

Back 115

Develops into middle ear cavity, eustacian tube, mastoid air cells. Contributes to endoderm-lined structures of ear

Front 116

Branchial pouch derivatives: 2nd pouch

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Epithelial linging of palantine fossa

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Branchial pouch derivatives: 3rd pouch (dorsal wings)

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Develops into inferior parathyroids

Front 118

Branchial pouch derivatives: 3rd pouch (ventral wings)

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Develops into thymus

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Branchial pouch derivatives: 4th pouch (dorsal wings)

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Develops into superior parathyroids

Front 120

Ear development

Back 120

1st arch: malleus/incus, tensor tyMpani (V3); 2nd arch: stapes, stapedius (VII); 1st cleft: external auditory meatus; 1st branchial membrane: tympanic membrane; 1st pouch: Eustachian tube, middle ear cavity, mastoid ear cells

Front 121

Tongue development

Back 121

1st branchial arch forms anterior 2/3 (thus sensation via V3, taste via VII); 3rd and 4th arches form posterior 1/3 (sensation and taste mainly via CN IX, extreme posterior via CN X); Motor innervation is via CN XII. Muscles of tongue are derived from occipital myotomes

Front 122

Thyroid development

Back 122

Thyroid diverticulum arises from floor of primitive pharynx, descends into neck. Connected to tongue via thyroglossal duct, which normally disappears but many persist as pyramidal lobe of thyroid. Foramen cecum is normal remnant of thyroglossal duct. Most common ectopic thyroid tissue site is the tongue.

Front 123

Thyroglossal duct cyst

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MIDLINE in the neck and will move with swallowing (vs. persistent cervical sinus leading to branchial cleft cyst in lateral neck)

Front 124

Cleft lip

Back 124

Failure of fusion of the maxillary and medial nasal processes (formation of primary palate)

Front 125

Cleft palate

Back 125

Failure of fusion of the lateral palatine processes, the nasal septum, and/or the median palatine process (formation of secondary palate)

Front 126

Diaphragm embryology

Back 126

Diaphragm is derived from (1) Septum transversum --> central tendon; (2) Pleuroperitoneal folds; (3) Body wall; (4) Dorsal mesentery of esophagus --> crura (Several Parts Build Diaphragm = SPBD). The diaphargm descends during development, but maintains innervation from above - C3, C4, C5 keeps the diaphargm alive

Front 127

Failure of pleuroperitoneal folds to develop

Back 127

Abdominal contents may herniate into the thorax. Hypoplasia of the thoracic organs due to space compression, scaphoid abdomen, cyanosis

Front 128

GI Embrology

Back 128

(1) FOREGUT: pharynx to duodenum; (2) MIDGUT: duodenum to transverse colon; (3) HINDGUT: distal transverse colon to rectum

Front 129

Developmental defects of anterior abdominal wall

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(1) Rostral fold closure: sternal defects; (2) Lateral fold closure: omphalocele, gastroschisis; (3) Caudal fold closure: Bladder exstrophy (can lead to adenocarcinoma of bladder)

Front 130

Duodenal atresia

Back 130

Failure to recanalize (trisomy 21 association)

Front 131

Jejunal, ileal, colonic atresia

Back 131

Due to vascular accident (apple peel atresia)

Front 132

GI Embrology

Back 132

Midgut herniates through umbilical ring in 6th week --> rapid growth; Returns to abdominal cavity + rotates around SMA in 10th week. Defects in rotation may cause intestinal obstruction, twisting around SMA (volvulus)

Front 133

Gastroschisis

Back 133

Failure of lateral body folds to fuse --> extrusion of abdominal contents though abdominal folds

Front 134

Omphalocele

Back 134

Persistence of herniation of abdominal contents into umbilical cord, covered by peritoneum. Associated with Beckwith-Wiedemann

Front 135

TE fistula

Back 135

Abnormal connection between esophagus and trachea. MC subtype is blind upper esophagus with lower esophagus connected to trachea. Results in cyanosis, choking, and vomiting with feeding, air bubble on CXR, and polyhydramnios

Front 136

Congenital pyloric stenosis

Back 136

Hypertrophy of pylorus causes obstruction. Palpable olive mass in epigastric region and nonbilious projectile vomiting at 2 weeks of age. Treatment is surgical incision. Occurs 1/600 liver births, often 1st born males. Throught to be caused by deficiency of NO synthase (similar to achalasia)

Front 137

Pancreas embrology

Back 137

Derived from foregut. Ventral pancreatic bud becomes pancreatic head, uncinante process, and main pancreatic duct. Dorsal bud becomes everything else (body, tail, isthmus, accessory duct)

Front 138

Annular pancreas

Back 138

Due to abnormal migration of ventral pancreatic bud as it encircles the 2nd part of duodenum forming a ring of tissue that may cause duodenal narrowing

Front 139

Pancreas divisum

Back 139

Ventral and dorsal parts of pancreas fail to fuse at 8 weeks

Front 140

Spleen

Back 140

Arises from dorsal mesentery (hence is mesodernmal, but is supplied by artery of forefut (celiac artery)

Front 141

Kidney embrology

Back 141

Pronephros --> degenerates at week 4; Mesonephros --> functions as interim kidney for first trimester; later contributes to male genital system; Metanephros --> permanent, beginnings first sppear during 5th week gestation, nephrogenesis continues through 32-36 weeks gestation

Front 142

Ureteric bud

Back 142

Derived from mesonephros; gives rise to ureter, pelvises, and through branching, calyces and collecting ducts; fully canalized by 10th week

Front 143

Metanephric mesenchyme

Back 143

Ureteric bud interacts with this tissue, inducing differentiation and formation of glomeruli and renal tubules to distal convoluted tubule

Front 144

Uteropelvic junction obstruction

Back 144

MC site of obstruction because it is the last to canalize. MCC of fetal hydronephrosis

Front 145

Potter's syndrome

Back 145

Bilateral renal agenesis --> OLIGOHYDRAMNIOS, limb deformities, facial deformities, pulmonary hypoplasia; caused by malformation of ureteric bud

Front 146

Horseshoe kidney

Back 146

Inferior poles of both kidneys fuse; as they ascend from pelvis during development, horseshoe kidneys get stuck under the IMA and remain low in abdomen. Kidney functions are normal.

Front 147

Female genital embryology

Back 147

Default development: mesonephric duct degenerates and paramesonephric duct develops

Front 148

Male genital embryology

Back 148

SRY gene on Y codes for testis-determining factor. Mullerian inhibiting substance secreted by testes (Sertoli cells) suppresses development of paramesonephric ducts. Increased androgens (Leydig cells) --> development of mesonephric ducts

Front 149

Mesonephric (wolffian) duct

Back 149

Develops into male internal structures (except prostate) - seminal vesicles, epididymis, ejaculatory duct, and ductus deferens

Front 150

Paramesonephric (mullerian) duct

Back 150

Develops into fallopian tube, uterus, and upper 1/3 of vagina (lower 2/3 from urogenital sinus)

Front 151

Bicornuate uterus

Back 151

Reuslts from incomplete fusion of paramesonephric ducts. Associated with urinary tract abnormalities and infertility. Associated with Hand-Foot-Genital syndrome (Homeobox gene mutation HoxA-13)

Front 152

Genital tubercle

Back 152

MALES: glans penis, corpus cavernosum/spongiosum; FEMALES: glans clitoris, vestibular bulbs

Front 153

Urogenital sinus

Back 153

MALES: bulbourethral glands of Cowper, prostate gland; FEMALES: greater vestibular glands of Bartolin, urethral and paraurethal glands of Skene

Front 154

Urogenital folds

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MALES: ventral shaft of penis (penile urethra); FEMA:ES labia minora

Front 155

Labioscrotal folds

Back 155

MALES: scrotum; FEMALES: labia majora

Front 156

Hypospadia

Back 156

Abnormal opening of penile urethra on inferior (ventral) side of penis due to FAILURE OF URETHRAL FOLDS to close

Front 157

Epispadias

Back 157

Abnormal opening of the penile urethra on superior (dorsal) side of penis due to FAULTY POSITION OF GENITAL TUBERCLE