Organogenesis Vocabulary

horseshoe shaped distribution of angiogenic/cardiogenic cells migrating from the lateral mesoderm at the cranial end of the unfolded embryo (third week)

differentiated angiogenic cells which unite to form 2 endothelial lined tubes on either side of the midline

fusion of the 2 endothelial tubes during embryonic folding to form a single heart tube made up of 5 regions: aortic roots, bulbus cordis, primitive ventricle, primitive atrium and sinus venosus

rostral most end of the heart tube which remains rostral throughout development and develops into the aorta

part of heart tube that will go on to form most of the right ventricle - moves inferiorly, anteriorly and to the right during heart looping

part of the heart tube between the bulbus cordis and primitive atrium which will go on to form the left ventricle by moving to the left of the bulbus cordis which forms most of the right ventricle

part of the heart tube between the primitive ventricle and sinus venosus which goes on to form the right and left atria by moving superiorly and posteriorly to end up posterior to the bulbus cordis and primitive ventricle areas

caudal most part of the heart tube which goes on to form the superior vena cava by moving posteriorly and superiorly together with the primitive atria; left sinus horn forms connections with the umbilical vein

folding of the heart tube during the fourth week to form the atrioventricular structure of the heart

internal opening between primitive ventricle and primitive atrium

outflow tract from primitive ventricle formed from the rostral part of bulbus cordis, will eventually form the aorta and pulmonary trunk

ventral and dorsal outgrowths from the atrioventricular canal between the primitive ventricle and atrium after heart folding which will fuse to separate the right and left atrioventricular canals forming the "fused" endocardial cushions

downgrowth from the roof of the primitive common atrium towards the fused endocardial cushions at the end of the fourth week (thin, membraneous tissue)

closing gap between the septum primum and endocardial cushions connecting the RA and LA allowing shunting of blood away from pulmonary circulation

hole that forms through septum primum by apoptosis as ostium primum closes

second downgrowth from roof of RA towards the endocardial cushions which forms the borders of the foramen ovale (thick and muscular tissue compared to septum primum); finishes growing at end of 6th week

result of the degeneration of the upper part of septum primum and ostium secundum leaving only the lower part of septum primum which covers the foramen ovale

thinned oval part of the interatrial septum formed by the fusion of the septum primum (valve of foramen ovale) with the septum secundum due to pressure changes

failure of the interatrial septum to fully form due to excessive resorption or absence of one or both septa

muscular outgrowth from floor of common ventricle up towards endocardial cushions which almost completely separates the ventricles bar the very upper part which is the interventricular foramen

opening between muscular ventricular septum and fused endocardial cushions

outgrowth of thin tissue from endocardial cushion which fuses to the muscular interventricular septum to completely separate the ventricles

failure of either of the components of the interventricular septum to develop properly

two ridges of tissue that appear on the sides of the truncus arteriosus which grow towards each other and make a spiral shaped septum called the aorticopulmonary septum

outgrowths of the conotruncal ridges to form the barriers between the aorta and pulmonary trunk in the truncus arteriosus

when the aorticopulmonary septum connects in such a way that the aorta is continuous with the right ventricle and the pulmonary trunk is continuous with the left ventricle

migration of dense mesenchymal tissue of the endocardial cushion and walls of atria downwards to form atrioventricular valves while myocardium migrates up to form papillary muscle

blockage of outflow tract from right ventricle to pulmonary trunk which is only compatible with life in the presence of ventricular septal defect allowing deoxygenated blood in the right side of the heart to be recycled through the aorta (with some being shunted to the lungs via the ductus arteriosus

3-8 weeks period of greatest sensitivity

gene defects, chromosomal defects, maternal infections, maternal disease, constraint, drugs/chemical exposure BUT MOSTLY UNKNOWN/MULTIFACTORIAL

• Embryonic - lung buds form bronchioles
• Pseudoglandular - terminal bronchioles, undifferentiated cuboidal epithelium
• Canalicular - respiratory bronchioles, vasculature, epithelial differentiation
• Saccular - terminal sacs, primitive alveoli, type II pneumocytes
• Alveolar - vascular and epithelial proliferation, septation and maturation of alveoli

ventral outpouching at week 4 of cranial endoderm (primitive foregut) which branches into LR lung buds and then further to bronchopulmonary segments

formation of terminal bronchioles from lung buds which have cuboidal undifferentiated epithelium (weeks 5-16, well into second trimester)

Branching and differentiation of each terminal bronchiole into two or more respiratory bronchioles, with formation of vasculature and epithelial differentiation to squamous, during weeks 16-25 (most of second trimester)

formation of terminal sacs with thin squamous type I epithelium and penetration of capillary endothelial cells to form primitive alveoli; differentiation into type II pneumocytes from week 28-

from week 32 and into childhood, there is maturation of alveoli by proliferation of vasculature and type I epithelium causing septation and increased SA as well as increasing numbers of type II pneumocytes

opening of esophagus into trachea increasing risk of aspiration to the lung

esophagus is blind ended pouch from the mouth which must be immediately modified to allow for feeding

infant respiratory distress syndrome occurring particularly in premature babies whose lungs have yet to reach maturity required - low volume/surface area and high surface tension due to lack of surfactant

amphipathic lipoprotein produced by type II pneumocytes from week 28 onwards which reduces surface tension between alveolar membranes to increase overall lung compliance; this reduces the pressure difference required to expand the lungs during inspiration (decreases work of breathing)

CRAACS: compliance low, residual volume low, alveolar collapse, airway closure, capillary leak, shunting

all derived from mesoderm (intraembryonic coelem): septum transversum, pleuroperitoneal membranes, mesoderm of body wall, esophageal mesenchyme

cranial-most end of intraembryonic coelom continuous with amnion (derived from mesoderm)

cranial intraembryonic coelom formed from embryonic folding of mesoderm which extends towards the anterior septum transversum to close off the pericardioperitoneal canal

closing gap between septum transversum and pleuroperitoneal membranes

defect in barrier between thoracic and abdominal viscera causing abdominal GIT to herniate through to thorax preventing normal development of lungs