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Anatomy Exam 2 outline on Embryo

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Boston College
BIOL 1300

ANATOMY EXAM 2: EMBRYONIC PERIOD – WEEKS 3-8 Based on High-Yield Embryology Text INTRO - Lateral body folding of embryo - Craniocaudal folding (head folding) GASTRULATION - Begins with formation of the primitive streak within epiblast - Process that establishes the 3 germ layers: ectoderm, mesoderm, endoderm = trilaminar embryonic disk - Ectoderm  neuroectoderm and neural crest cells - Endoderm  remains intact - Mesoderm  paraxial mesoderm (somites), intermediate mesoderm, lateral mesoderm FETAL CIRCULATION - Three shunts: ductus venosus, ductus arteriosus, foramen ovale - 2 umbilical arteries, 1 umbilical vein (oxy) o L umbilical vein  placenta to fetus  highly oxygenated and nutrient-rich blood  most blood passes hepatic sinusoids via the ductus venosus  enters IVC  R atrium  blood bypasses R ventricle via foramen ovale  enters L atrium  L ventricle  aorta  fetal tissues o Some blood from R atrium anteres R ventricle  R ventricle blood enters pulmonary trunk but most of the blood bypasses lungs through ductus arteriosus  minimal blood goes to lungs for growth and development  blood returned to L ventricle via pulmonary veins o R and L umbilical arteries  fetus to placenta  poorly oxygenated and nutrient-poor blood - Circulatory changes at birth o Decrease in right atrial pressure b/c placental circulation is occluded o Increase in left atrial pressure b/c of increased pulmonary venous return o Changes: closer of R and L umbilical arteries, L umbilical vein, ductus venosus, ductus arteriosus, foramen ovale - Remnants created by closure of fetal circulatory structures Fetal Structure Adult Remnant R and L umbilical arteries Medial umbilical ligaments L umbilical vein Ligamentum teres Ductus venosus Ligamentum venosum Foramen ovale Fossa ovale Ductus arteriosus Ligamentum arteriosum CARDIOVASCULAR SYSTEM - Heart tube formation o Lateral plate mesoderm (cephalic area of embryo) splits into somatic layer and splanchnic layer = formation of pericardial cavity o Precardiac mesoderm distributed to splanchnic layer = heart forming regions that fuse to fomr continuous sheet of mesoderm o Vascular endothelial growth factor induces the sheet to form vascular models that remodel into single endocardial tube = endocardium o Mesodeurm around endocardium forms myocardium o Myocardium secretes ECM proteins = cardiac jelly o Mesoderm migrating into cardiac region from coelomic wall near liver forms epicardium - 5 Heart tube dilatations Embryonic Dilatation Adult Structure Truncus arteirosu Aorta Pulmonary trunk Bulbus cordis Conus arteriosus – smooth part of R ventricle Aortic vestibule – smooth part of L ventricle Primitive ventricle Trabeculated part of R ventricle Trabeculated part of L ventricle Primitive atrium Trabeculated part of R atrium Trabeculated part of L atrium Sinus venosus Sinus venarum – smooth part of R atrium 1 Coronary sinus Oblique vein of left atrium **Smooth part of L atrium formed by pulmonary vein incorporations; jxn of trabeculated and smooth parts of R atrium = crista terminalis - Aorticopulmonary septum formation o Neural crest cells migrate from hindbrain region through pharyngeal arches 3, 4, and 6 o The cells invade truncal and bulbar ridges o The ridges grow and twist around one another in a spiral fashion o Ridges fuse to form AP septum o AP septum divides truncus arteirosus and bulbus cordis into aorta and pulmonary trunk - Atrial septum formation o Septum primum forms in root of primitive atrium and grows towards AV cushions in AV canal o Foramen primum forms between septum primum and AV cushions o Foramen primum closes when septum primum fuses with AV cushions o Foramen secundum forms in center of septum primum o Septum secundum forms to right of septum primum o Foramen ovale = opening between upper and lower limbs of septum secundum – allows blood to be shunted from R to L atrium o Foramen ovale closes right after birth o Later in life, septum primum and septum secundum fuse to complete formation of atrial septum - Atrioventricular (AV) septum formation o Dorsal AV cushion and ventral AV cushion approach and fuse to form AV septum o AV septum partitions AV canal into right AV canal and left AV canal - Interventricular (IV) septum formation o Muscular iV septum develops in midline on floor of primitive ventricle and grows toward fused AV cushions o IV foramen is located between free edge of muscular IV septum and the fused AV cushions o IV foramen is closed by membranous IV septum which forms by proliferation and fusion of tissue from 3 sources: right bulbar ridge, left bulbar ridge, AV cushions - Development of arterial system o Head and neck  Arterial pattern in head and neck develops from 6 pairs of arteries = aortic arches (course through pharyngeal arches)  Aortic arches remodel to produce arterial pattern o Rest of body  Arterial patterns develop from R and L dorsal aortae  R and L dorsal aortae fuse to form dorsal aorta  Dorsal aorta then sprouts posterolateral arteries, lateral arteries, and ventral arteries (vitelline and umbilical) - Development of venous system o Develops from vitelline, umbilical, and cardinal veins that empty into sinus venosus o Veins undergo remodeling due to redirection of venous blood from L side of body to R in order to empty into R atrium Embryonic Structure Adult Structure Aortic arches 1 Part of maxillary artery 2 Part of stapedial artery 3 Part of R and L common carotid arteries R and L internal carotid arteries 4 Part of R subclavian artery Part of aortic arch 5 Regresses in the human 6 Part of R and L pulmonary arteries Ductus arteriosus Dorsal aorta Posterolateral branches Arteries to upper and lower extremities Intercostal, lumbar, and lateral sacral arteries Lateral branches Renal, suprarenal, and gonadal arteries Ventral branches Vitelline arteries Celiac, superior mesenteric, and inferior mesenteric arteries Umbilical arteries Part of internal iliac arteries, superior vesical arteries, medial umbilical ligaments
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