HIGH YIELD EMBRYOLOGY
Gastrulation
Notochord
Sirenomelia
Sacrococcygeal teratoma
Alpha-fetoprotein
Spina bifida occulta
EARLY EMBRYOLOGY
– substance affecting migration, proliferation or interaction of cells, causes congenital
anomalies
– pruning of the sperm glycocalyx; permits the sperm-oocyte interaction
– implantation occurs outside of the uterine cavity; can occur in the uterine tubes or in
the pelvic cavity
– implantation occurs near the cervix; provides a high risk of bleeding
– placenta becomes detached
– abnormal adherence of the chorionic villi to the myometrium
– villi penetrate the full thickness of the myometrium
– results when there is no embryo or embryo dies and the chorionic villi fail to
vascularize; “uterine enlargements greater than expected for gestational age”; can
give rise to choriocarcinomas or persistent trophoblastic disease
– fertilization of empty oocyte (contains only paternal chromosomes); produces high
levels of hCG
– derives from a poorly developed embryo; always triploid and produce hCG
– arises from multiple ovulations (high levels of FSH)
– arise from splitting of a single zygote
– secreted by syncytiotrophoblast
– secreted by corpus luteum for five months, then by placenta; contraceptive “pill” and
RU-486 are anti-progesterones
– process where the epiblast gives rise to mesoderm, endoderm and ectoderm
– derives from both endoderm and mesoderm; forms the nucleus pulposus
– caudal dysgenesis from inadequate mesoderm; lower limb defects
– persistence of primitive streak, forms multi-tissue tumor
– liver glycoprotein; leaks into amniotic fluid with neural tube or ventral wall defects
– incomplete neural arch, patch of hair over defect
Poland anomaly
Congenital torticollis
Amelia
Meromelia
Congenital clubfoot
MUSCULOSKELETAL
– congenital absence of the pectoralis major
– contracture/shortening of the sternocleidomastoid
– absence of limb
– absence of part of a limb
– any defect involving the talus
Teratogen
Capacitation
Ectopic pregnancy
Placenta previa
Placental abruption
Placenta accreta
Placenta percreta
Hydatidiform moles
Complete moles
Partial moles
Dizygotic (fraternal) twins
Monozygotic (identical) twins
Human chorionic gonadotrophin (hCG)
Progesterone
Splanchnic mesoderm
Pleuropericardial membranes
Tetralogy of Fallot
Dextrocardia
Undivided truncus arteriosus
Patent ductus arteriosus
Atrial septal defect
Ventricular septal defect
Transposition of the great vessels
Veins:
CARDIOVASCULAR
– forms the primitive hear tube; beats on day 22
– form the pericardium and pleura (somatic parts)
– a combination of four heart defects:
1. pulmonary stenosis
2. right ventricular hypertrophy
3. over-riding aorta
4. ventricular septal defect
– left sided heart
– neural crest defect where the bulbar regions fail to form
– common defect associated with rubella and pregnancies occurring in high altitudes;
more common in females
– patent foramen ovale, common, can involve defect in septum primum or septum
secundum
– common; involves the membranous part of the interventricular septum
– most common cause of cyanosis in newborn
Vitelline – left disappears, right forms portal system
Umbilical – right disappears, left drains placenta (becomes ligamentum teres hepatis)
Cardinal:
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Ductus venosus
Early development
Tracheoesophageal Fistulas
VACTERL Association
Early development
Notochord
Neural tube
Neural crest
Spina bifida occulta
Spina bifida cystica
Anencephaly
Arnold-Chiari malformation
Hydrocephalus
Mental retardation
Tethered cord syndrome
Craniopharyngiomas
Schizencephaly
Craniopharyngiomas
Congenital hydrocephalus
Arnold-Chiari malformation
Cranium bifidum
Omphalocele
Umbilical hernia
Congenital pyloric stenosis
Subcardinal – drains kidneys
Sacrocardinal – common iliac
Supracardinal – drains body wall (azygos veins)
– between left umbilical and right vitelline veins; forms ligamentum venosum
RESPIRATORY
– begins in the 4th week; derived from the gut tube; lungs become viable during the 24 th
gestational week due to secretion of surfactant; formation of most alveoli occurs
between birth and the 8th year
– abnormal connections between esophagus and airway, usually involves a proximal
esophagus that ends in a blind pouch and a distal esophagus that connects to the
trachea
– combination of defects that arise from exposure to high levels of
estrogens/progesterones during the embryonic period (weeks 3 – 9)
NERVOUS SYSTEM
– notochord induces formation of neural plate which gives rise to neural crest and
neural tube
– persists as the nucleus pulposus of the intervertebral disc
– alar plate is dorsal (sensory); basal plate is ventral (motor)
– gives rise to all ganglia, Schwann cells, meninges, suprarenal medulla, melanocytes,
cartilage, bone and blood vessels of the head
– involves only vertebral arch, small tuft of hair over the lesion
– incomplete closure of the neural tube caudally (caudal neuropore on day 27); can be
detected by alpha-fetoprotein and includes a sac containing CSF
 meningocele – sac includes meninges and CSF
 meningomyelocele – includes nervous tissue
– result when the anterior neuropore fails to close (day 25); forebrain is poorly
developed
– cerebellum herniates through the foramen magnum; seen in conjunction with spina
bifida cystica accompanied by hydrocephalus
– most often due to stenosis of the cerebral aqueduct secondary to a fetal viral infection
– most commonly caused by maternal alcohol abuse
– conus and filum are abnormally fixed, lower limb and bladder control problems
– arise from remnants of Rathke’s pouch, associated with diabetes insipidus and visual
deficits
– large clefts in cerebral hemispheres continuous with lateral ventricles
– arise from remnants of Rathke’s pouch, associated with diabetes insipidus and visual
deficits
– congenital constriction of the cerebral aqueduct
– herniation of the cerebellum through an enlarged foramen magnum; associated with
spina bifida cystica
– skull defect that permits structures to herniate:
 Meningocele – only meninges
 Meningoencephalocele – meninges and brain
 Meningohydroencephalocele – meninges, brain and ventricle
GASTROINTESTINAL
– occurs when the intestines do not return to the abdominal cavity following normal
herniation; the guts are covered by the amniotic sac
– guts protrude outside of the abdominal cavity but covered with skin and connective
tissue
– characterized by projectile vomiting in a newborn
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Atresia
Meckel’s diverticulum
Hirschsprung’s disease
Imperforate anus
Vitelline Fistula
– interruption of the gastrointestinal tract; at esophagus vomit contains uncurdled milk;
at gastric region the vomit contains curdled milk; at the duodenum the vomit contains
bile
– a remnant of the vitelline stalk and yolk sac, exists as an outward projection of the
distal ilium about one meter form the ileocecal junction that can contains gastric or
pancreatic tissue; found in about 2% of the population
– occurs when the hindgut fails to be invaded by migrating neural crest cells, results in
hypomobility, constipation and congenital megacolon
– the anal membrane does not regress
– connection between the midgut and umbilicus
UROGENITAL
Derivatives of the genital ducts:
Horseshoe Kidney
Bifid ureter
Epispadias
Hypospadias
Turner’s syndrome
Klinefelter’s syndrome
External Genitalia:
Gonads
Hydrocele
Urachal Fistula
male – high level of testosterone stimulates development of the mesonephric duct;
Mullerian inhibiting factor prevents development of paramesonephric ducts
female – low level of testosterone prevents development of mesonephric ducts and no
Mullerian inhibiting factor permits development of the paramesonephric ducts
Mesonephric ducts:
male: epididymis, ductus deferens, seminal vesicle and ejaculatory duct
female: epoophoron, paroophoron, Gartner’s duct
Paramesonephric duct:
male: appendix of testes and prostatic utricle
female: uterine tube, uterus and superior part of vagina
– occurs when the inferior poles of the kidneys contact each other before ascent; the
kidneys fuse and ascent to the lumbar region is prevented by the inferior mesenteric
artery
– involves the ureteric bud
– rare; seen with exstrophy of the bladder
– common; opening on the ventral aspect of the penis; results from a failure of urethral
folds to completely meet
– 45 XO; infantile female genitalia, ovarian streaks and webbed neck
– 47 XXY; common (1/500); gynecomastia, infertile males
– after week 9 the genitalia can be distinguished as male or female!
MALE
FEMALE
UG folds
floor of urethra
labia minora
Genital swellings scrotum
labia majora
Genital tubercle penis
clitoris
UG sinus
urethra/prostate urethra/vagina
– develop from epiblast and migrate along the yolk sac and mesentery to the lumbar
region
– fluid in the cavity of the tunica vaginalis from a patent processus vaginalis
– connection from bladder to umbilicus
HEAD AND NECK
Pharyngeal Apparatus
Clefts (Grooves) – four pairs; ectoderm that forms only epithelium
The first cleft gives rise to the external auditory meatus.
The second through fourth clefts typically regress; may form a cervical sinus.
Pouches – four pairs; endoderm that forms only epithelium
The first pouch gives rise to the auditory tube, mastoid antrum and tympanic cavity.
The second pouch forms the palatine tonsil.
The third pouch gives rise to the thymus and inferior parathyroid gland.
The fourth pouch gives rise to the superior parathyroid
Pharyngeal Arches – There are five pharyngeal arches; mesoderm forms skeletal muscle; neural crest grows into each arch and
forms all connective tissue (cartilage, bone and blood vessels)
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Derivatives of the Pharyngeal Arches
First
Second
CN
V3
Nerve
CN VII
muscles of mastication,
anterior belly of
digastric, mylohyoid,
tensor tympani and
Muscles
tensor veli palatini
maxillary
Artery
malleus and incus
Cartilage
facial
muscles,
stapedius,
posterior
belly of
digastric and
stylohyoid
hyoid and
stapedial
Third
Fourth
Sixth
CN IX
CN X
CN X
stylopharyngeus muscles of palate, muscles of larynx,
pharynx and
inferior
cricothyroid
constrictor,
cricopharyngeus
and superior
portion of
esophagus
common and
internal carotid
left: portion of
arch; right: part
one of subclavian
Pulmonary trunk
(left - ductus
arteriosus)
stapes, styloid greater horn and laryngeal cartilage laryngeal cartilage
process,
inferior portion of
lesser horn
body of hyoid
and superior
portion of
body of hyoid
Torticollis – This is a condition characterized by a shortening of the sternocleidomastoid muscle and results in an elevation of the
chin to the opposite side; can be caused by damage to the muscle, spinal accessory nerve or can be congenital.
Cysts of the Neck
Lateral cervical cysts (branchial fistula) – arises from the second through fourth pharyngeal clefts
Midline cysts – most often arise from a remnant of the thyroglossal duct (thyroglossal duct cysts)
Cleft Lip – Results from failure of the maxillary prominence to join the medial nasal prominences to form the intermaxillary segment
(primary palate derives from intermaxillary segment)
Cleft Palate
Anterior cleft – anterior to incisive foramen; lateral palatine process fails to fuse with primary palate
Posterior cleft – occurs through the 2 palate where lateral palatine process don’t fuse or meet nasal septum
Complete cleft – involves both the primary and secondary palate
Situs inversus
Diaphragm
Congenital diaphragmatic hernia
Stem villi
Intervillous space
umbilical arteries
umbilical veins
urachus
foramen ovale
ductus arteriosus
ductus venosus
MISCELLANEOUS
– reversal of organs; can involve all organs or just single organs (heart – dextrocardia)
– develops from the septum transversum, pleuroperitoneal membranes, paraxial
mesoderm and dorsal mesentery of the esophagus
– results from a failure of the pleuroperitoneal fold to close the pericardioperitoneal
canal; most common on the left side
– form from trophoblast and somatic layer of extraembryonic mesoderm
– contains maternal blood
CHANGES AT BIRTH
paired medial umbilical ligaments
round ligament of liver
median umbilical ligament
fossa ovalis
ligamentum arteriosum
ligamentum venosum
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