USMLE Step 1 Review/Embryology Embryology is the study of
embryonic and fetal development, an understanding of which is
required for the USMLE Step 1. Though embryology is a vast area
of study, the USMLE requires only a very basic understanding;
these can be summarized in a few basic principles about
development and augmented with some details about embryology
relevant to particular disease conditions. Sperm + oocyte →
zygote → proliferation → blastomere → blastocyst → inner cell
mass (embryoblast) + trophoblast differentiation - Inner cell
mass (embryoblast) → - Epiblast → embryo, amnion - Hypoblast →
yolk sac - Trophoblast → syncytiotrophoblast + cytotrophoblast →
placenta Epiblast → endoderm, mesoderm, ectoderm Intestinal
structures outgrow abdominal cavity → forced outside abdominal
cavity → return at ~10 weeks → rotate into final position.
Failure of proper rotation results in malrotation. True
diverticulum of distal ileum, formed by remnant of vitelline
(omphalomesenteric) duct. Gut is formed when trila