Embryo Facts to learn

anterior-posterior axis

dorsal-ventral axis

lengthens limbs

segmental organization

2 germ layers (bilaminar disk)=epiblast, hypoblast

2 cavities: amniotic, yolk sac

2 components to placenta: cytotrophoblast, syncytiotrophoblast

3 germ layers (gastrula): ecto, meso, endo

4 heart chambers (and it starts beating!!)

4 limb buds grow

benign Rathke's pouch tumor (surface ectoderm) with cholesterol crystals and calcifications.

Vertebral defects
Anal atresia
Cardiac defects
Tracheo-esophageal fistula
Renal defects
Limb defects (bone AND muscle)

1 amniotic sac.

monozygotic twins have 2! Note though that monozygotic twins can share an amniotic sac and not be conjoined but there is a risk of conjoined twins happening only when the amniotic sac is shared.

ALCOHOL ALCOHOL ALCOHOL.

Not drinking alcohol is one of the very best things a pregnant woman can do.

syncytiotrophoblast.

outer layer of chorionic villi

It is a duct between the bladder and yolk sac and forms from the allantois

1) patent urachus = urine discharge from umbilicus

2) Vesicourachal diverticulum= outpouching of bladder.

connects yolk sac to midgut lumen... should be obliterated by week 7

Meconium discharge from the umbilicus... there was a FAILURE OF THE VITELLINE DUCT TO CLOSE

Young Liver Synthesizes Blood
1) Yolk sac until 8 weeks
2) Liver 6-30 weeks
3) Spleen 9-28 weeks
4) Bone marrow 28weeks onward

ligamentum teres hepatis

medial umbilical ligaments

ligamentum arteriosum

ligamentum venosum

fossa ovalis

median ubilical ligament-- a urachal cyst or sinus is a remnant too

nucleus pulposus of intervertebral disk

cerebral hemispheres

lateral ventricles are here

thalamus

3rd ventricle is here

midbrain

metencephalon and myelencephalon

pons and cerebellum

4th ventricle

medulla

4th ventricle

AFP!

Would be increased AFP and acetylcholinesterase in the CSF too (wikipedia says in the amniotic fluid too--acetylecholinesterase that is... so who knows just keep it in mind)

failure of bony spinal canal to close, but no structural herniation usually seen at lower vertebral levels. Dura is intact.

enlargement of the central canal of spinal cord.

crossing fibers of spinothalamic tract typically damaged first.

cape-like, bilateral loss of pain and temperature sensation in upper extremities with preservation of touch sensation.

Most common at C8-T1

often presents in pts with arnold-chiari II malformation

1) chewing, 2) facial expression, 3) stylopharyngeus, 4) swallowing, 6) speaking

One man sat chewing,
Two hands on his face.
The third with his pharynx swallowed the fourth plate.
"speak up, speak up!" Said the sixth in return. "Your cricothyroid makes me want to burn!"

1st arch neural crest fails to migrate leads to mandibular hypoplasia, facial abnormalities

persistence of cleft and pouch which leads to fistula between tonsillar area, cleft in lateral neck

(arch 3 issue)

1st cleft

branchial cleft cyst within lateral neck

3rd pouch

4th pouch

anterior 2/3 from the 1st branchial arch innervated by CN V3 (sensation) and taste (CN VII)--remember the CN VII branch that enters the 1st arch

Posterior 1/3 is formed from the 3rd and 4th arches. Innervation is sensation and taste mainly CN IX with the extreme posterior via CN X) Makes sense with the arch derivations.

It originates from the floor of the primitive pharynx and is connected to the tongue by the thyroglossal duct which often disappears but remants may remain as a htyroglossal duct cyst in the midline neck and will move with swallowing!!

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

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

Several Parts Build Diaphragm
Septum Transversum (central tendon)
Pleuroperitoneal folds
Body Wall
Dorsal mesentery of esophagus (crura)

hypoplasia of thoracic organs due to space compression, scaphoid abdomen, cyanosis

Caused by malformation of ureteric bud.

babies who can't PEE in utero get this.

bilateral renal agenesis that leads to oligohydramnios in the amniotic sac thus limb deformities, facial deformities, and pulmonary hypoplasia due to the pressure imposed on the fetus without it's more billowy fluid cushion.

failure to recanalize (trisomy 21)

Failure of lateral body folds to fuse

Extrusion of abdominal contents through abdominal folds

persistance of herniation of abdominal contents into umbilical cord.

Abdominal contents will be covered by peritoneeum

bladder exstrophy

SMA... should go back in cavity at 10 weeks...
If there is a problem with this in any way there could be intestinal obstruction or twisting around SMA (volvulus)

Most common: blind upper esophagus with lower esophagus connected to the trachea.

Clinically: cyanosis, choking and vomiting with feeding, air bubble on CXR and polyhydramnios

cause: hypertrophy of the pylorus causing obstruction

clinical: palpable "olive" sized mass in epigastric region and nonbilious projectile vomiting at around 2 weeks of age.

Occurs often in 1st born males, 1/600 live births.

ventral pancreatic bud abnormally encircles 2nd part of duodenum; forms a ring of pancreatic tissue that may cause duodenal narrowing.

ventral and dorsal parts fail to fuse at 8 weeks

arises from the dorsal mesentary BUT is supplied by artery of foregut (celiac artery)

uteropelvic junction... it is the last to canalize and so the most likely spot of obstruction causing hydronephrosis in the fetus.

SEED
Seminal vesicles
Epididymis
Ejaculatory Duct
Ductus deferens

Note that the prostate is NOT involved.

incomplete fusion of the paramesonephric ducts.

Associated with UT abnormalities and infertility

abnormal opening of penile urethra on the superior (dorsal) side of the penis.

It is due to faulty positioning of the genital tubercle.


Exstrophy of the bladder is associated with epispadias

(When you have epispadias you hit your EYE when you pee)

Abnormal opening of penile urethra on inferior (ventral) side of penis due to failure of urethral folds to close.

More common than epispadias you fix it to prevent UTIs

glans clitoris

vestibular bulbs

glans penis

corpus cavernosum and spongiosum

Greater vestibular glands of Bartholin

urethral and paraurethral glands of Skene

Bulbourethral glands (of Cowper)

Prostate Gland

labia minora

Ventral shaft of penis (penile urethra)

labia majora

scrotum

ascending aorta and pulmonary trunk

right ventricle and smooth parts (outflow tract) of left and right ventricle

portion of the left ventricle

trabeculated left and right atrium

coronary sinus

smooth part of right atrium

SVC

Neural crest cell migration. They divide the trunk into 2 arteries via fusion and twisting of truncal and bulbar ridges.

Transposition of great vessels and tetralogy of Fallot

part of maxillary artery (which is a branch of the external carotid)

1st arch is MAXimal

Stapedial artery and hyoid artery

Second=Stapedial

common carotid arteries and proximal part of the internal carotid arteries

C is the 3rd letter of the alphabet. 3rd arch = carotid

on left, aortic arch
on right, proximal part of the right subclavian artery

4th arch (4 limbs) = systemic

proximal part of pulmonary arteries and (on left only) ductus arteriosus

6th arch = pulmonary and the pulmonary to systemic shunt (ductus arteriosus)

ectoderm

mesoderm (muscles and arteries)

neural crest cells (bone and cartilage)

endoderm

Clefts=ectoderm
Arches=mesoderm +neural crest
Pouches=endoderm

renal damage

leading cause of birth defects and mental retardation

fetal alcohol syndrome

absence of digits, multiple anomalies

CN VIII toxicity

abnormal fetal development and fetal addition

placental abruption

vaginal clear cell adenocarcinoma

neural tube defects

congenital goiter or hypothyroidism

Ebstein's anomaly (atrialized right ventricle)

caudal regression syndrome (anal atresia to sirenomelia--mermaid syndrome)

preterm labor, placental problems, IUGR, ADHD

discolored teeth

limb defects (flipper limbs)

inhibition of intestinal folate absorption-- neural tube defects

extremely high risk for spontaneous aboritons and birth defects (cleft palate, cardiac abnormalities)

bone deformities, fetal hemorrhage, abortion

multiple anomalies

middle ear cavity, eustachian tube, mastoid air cells

**contributes to the endoderm-lined structions of the ear

epithelial lining of the palatine tonsil

inferior parathyroid

3rd pouch structures end up below 4th pouch structures

thymus

superior parathyroids.

DiGeorge Syndrome: leads to T cell deficiency (thymic aplasia) and hypocalcemia (failure of parathyroid development)

mutation of germline RET (neural crest cells)

As a result you get
pheochromocytoma (adrenal medulla)
parathyroid tumor: 3rd/4th pouch
parafollicular cells that develop medullary thyroid cancer.. also derived from neural crest cells

external auditory meatus

temporary cerivcal sinuses that are obliterated by proliferation of 2nd arch mesenchyme that covers the rest of the clefts.

CN V2 and V3

Maxillary artery

Cartilage: meckel's cartilage, mandible, malleus, incus, sphenomandibular ligament

Muscules: muscles of mastication (temporalis, masseter, lateral and medial pterygoids), mylohyoid, anterior belly of the digastric, tensor tympani, tensor veli palatini, anterior 2/3 of tongue

Cartilage: Reichert's cartilage: stapes, styloid process, lesser horn of hyoid, stylohyoid ligament

Muscles: muslces of facial expression, Stapedium, Stylohyoid, posterior belly of digastric.

CN VII

Stapedial artery, hyoid artery

Cartilage: greater horn of hyoid

Muscles: stylopharyngeus (think of stylopharyngeus innervated by glossopharyngeal nerve)

CN IX

Cartilage: thyroid, cricoid, arytenoids, corniculate, cuneiform

Muscles:
4th arch: most pharyngeal constrictors, cricothyroid, levator veli palatini

6th arch: all intrinsic muscles of larynx except cricothyroid

4th arch: CN X (superior laryngeal branch--SWALLOWING)

6th arch: CN X (recurrent laryngeal branch--SPEAKING)