Flashcards in Embyology Deck (66)
What is the triple test? When should it be performed?
Triple test: AFP, hCG, estriol
Should be performed btw weeks 16-18
What is AFP?
Alpha-fetoprotein is synthesized by fetal liver, GI tract, and yolk sac (early gestation only). Maternal serum AFP levels increase with gestational age.
What is the most common cause of elevated AFP? What are some other causes?
Most common: dating error aka underestimation of gestational age--> confirm by fetal u/s
Other causes: neural tube defects, anterior abdominal wall defects (omphalocele, gastroschisis), multiple gestation.
What is estriol? What are decreased levels of estriol suggestive of?
Estriol levels: placental and fetal function, both are necessary for synthesis.
Decreased estriol suggest placental insufficiency or IUGR
What is hCG? What are increased levels of hCG associated with?
Human chorionic gonadotropin is synthesized by trophoblastic tissue.
Increased levels associated with multiple gestation, hydatidiform mole, choriocarcinoma.
Cranial nerve and bone/cartilage derivatives of pharyngeal (branchial) arch 1
CN V (trigeminal)
Mandible, maxilla, zygoma, incus, malleus
Muscles: muscles of mastication (masseter, temporalis, etc)
Cranial nerve and bone/cartilage derivatives of pharyngeal arch 2
CN VII (facial nerve)
Stapes, styloid process, lesser horn of hyoid
Muscles: muscles of facial expression
Cranial nerve and bone/cartilage derivatives of pharyngeal arch 3
CN IX (glossopharyngeal)
Greater horn of hyoid
Cranial nerve and bone/cartilage derivatives of pharyngeal arch 4 and 6
Laryngeal cartilages: cricoid, thyroid cartilages
Dysfunction= laryngeal and pharyngeal paralysis and autonomic dysfunction (eg, esophageal motility, gastric acid secretion, heart rate variability)
What are pharyngeal arches?
Developing embryo has 6 pharyngeal (branchial) arches. All but 5th arch contribute to adult structures. Mesoderm forms muscular and vascular elements, neural crest cells form bony/cartilaginous structures. Each arch gives rise to specific CN.
What is Treacher-Collins syndrome (TCS)?
Genetic disorder (usually AD) resulting in abnormal development of 1st and 2nd pharyngeal arches. Mutation affects production of "treacle" a protein integral to normal neural crest migration. Resulting craniofacial abnormalities: mandibular and zygomatic bone hypoplasia, microtia (underdeveloped pinna), downward slanting palpebral fissures, lower eyelid colobomas. Typically require extensive craniofacial surgery in childhood due to airway compromise and feeding difficulty.
What is the pathophysiology behind duodenal atresia?
Failure of recanalization at 8-10 weeks gestation. Sx. bilious or nonbilious emesis. Double-bubble sign on x-ray. Associated with Down syndrome.
What is the pathophysiology behind jejunum/ileum/proximal colon (midgut) atresia?
Vascular injury/occlusion in utero. Diminished intestinal perfusion leads to ischemia of segment of bowel with subsequent narrowing (stenosis) or obliteration (atresia) of lumen. Sx. Bilious emesis and abdominal distension. Associated with gastroschisis.
What is "apple-peel" or "Christmas tree" atresia?
If SMA occluded in utero, the area of intestinal necrosis is large leading to a proximal segment that ends in a blind pouch followed by an area of absent small bowel and associated dorsal mesentery. Finally, distal segment of ileum assumes spiral configuration around an ileocolic vessel.
Failure of NC cells to migrate into the distal colonic wall. Submucosal and myenteric plexi do not develop and distal colon becomes nonfunctional. Infant has intestinal obstruction, abdominal distention, and failure to pass meconium.
How does neural system form?
During 3rd week of life ectoderm on dorsal surface of embryo thickens to form neural plate. Neural plate deepens in the center to create the neural groove that is bound on both sides by neural folds. The folds fuse to create a neural tube with openings at the ends called neuropores. Anterior and posterior neuropores close during 4th week of fetal life. Failure to close leads to neural tube defects. Folic acid supplementation early in pregnancy significantly decreases risk of these defects.
What is fetal alcohol syndrome?
Most common cause of mental retardation. Caused by alcohol consumption during pregnancy. Associated with cardiac defects (VSD), brain defects (microcephaly, holoprosencephaly) and abnormal facies (short palpebral fissures and smooth/long philtrum).
How does smoking during pregnancy affect infant?
Can cause fetal hypoxia, IUGR, low birth weight, premature delivery. Not associated with NTDs.
What are the embryologic derivatives of surface ectoderm?
Rathke's pouch (anterior pituitary); lens, cornea; inner ear sensory organs; olfactory epithelium; nasal/oral epithelial linings; epidermis; salivary, sweat/mammary glands
What are the embryologic derivatives of neural tube?
Brain, spinal cord, posterior pituitary, pineal gland, retina
What are the embryologic derivatives of neural crest cells?
Autonomic, sensory, celiac ganglia (PNS); Schwann cells; pia mater, arachnoid mater; aorticopulmonary septum, endocardial cushions; branchial arches (bones and cartilage); skull bones; melanocytes; chromaffin cells of adrenal medulla; thyroid parafollicular C cells
MOTEL PASS: Melanocytes, Odontoblasts, Tracheal cartilage, Enterochromaffin cells, Laryngeal cartilage, Parafollicular cells of thyroid, Adrenal medulla, Schwann cells, Spiral membrane
What are the embryologic derivatives of mesoderm?
Muscles (skeletal, cardiac, smooth), connective tissues, bone and cartilage, serosa linings, CV system, blood, lymphatic system, spleen, internal genitalia, kidney and ureters, adrenal cortex
What are the embryologic derivatives of endoderm?
GI tract, liver, pancreas, lungs, thymus, parathyroids, thyroid follicular cells, middle ear, bladder and urethra
What is gastrulation and when does it occur?
1. 3 primary germ layers are formed during week 3 of embryogenesis during gastrulation.
2. Initiated by formation of primitive streak, a thickening of epiblast cell layer that appears at caudal end of embryo and grows cranially.
3. Epiblast cells undergo epithelial-to-mesenchymal transition, causing them to lose cell-cell adhesion properties.
4. Allows them to migrate downward through the primitive streak to form the mesoderm and endoderm layers.
5. Remainder of epiblast layer forms ectoderm.
What is the notochord and how does it form?
The notochord becomes the nucleus pulposus of the intervertebral disk in adults. 2 days after gastrulation begins, some epiblast cells migrate cranially through primitive node to form a midline cellular cord, the notochord, which induces the overlying ectoderm to differentiate into neuroectoderm and form the neural plate.
What is a true diverticulum?
Contains all layers of GI tract (mucosa, submucosa, muscularis, serosa) i.e. Meckel's diverticulum, appendix.
What is a pseudodiverticulum?
A false diverticulum. Only contains mucosa and submucosa layers as the diverticulum herniates through defects in the muscularis. ie. Zenker's diverticulum, colonic diverticula
What is a Meckel's diverticulum?
Remnant of the omphalomesenteric (vitelline) duct that previously connected lumen of midgut to yolk sac and normally obliterates during 7th week of fetal life. In Meckel's diverticulum there is partial failure of this duct to obliterate.
What is the rule of 2s?
2% of population, 2 feet from ileocecal valve, 2 inches long, 2% symptomatic, males 2x more likely to have one.