Embryology Flashcards
what are blood islands
groups of cells that have the capacity to develop into blood cells and bloods vessels
where is the cardiogenic region located
in the splanchic mesoderm at the cranial end
what happens to the endocardial tubes during folding
the pairs of tubes (one at either side of the trilaminar disk) fuse together to form the primitive heart tube
what is the primitive heart tube
a modified blood vessel which contracts to allow the flow of blood
what are the zones that make up the primitive heart tube
aortic roots, truncus arteriosus, bulbus cordis, ventricles, atrium and sinus venosus
why does cardiac looping occur
the primitive heart tube grows and elongates so it runs out of room in the pericardial sac so must fold
what does the right atrium develop from
primitive atrium and the sinus venosus
what does the left atrium develop from
a small amount of the primitive atrium and the pulmonary veins
why are the walls of the left atrium smoother than that of the right
the right atrium is made up of mostly primitive atrium which is trabeculated whereas the pulmonary veins which mostly make up the left is smooth
what happens to the position of the atria during cardia looping
they are pushed up from the most caudal part to toward the head
what does the right 4th arched vessel develop into
the right subclavian artery
what does the left 4th arched vessel develop into
the arch of the aorta
what does right 6th arched vessel develop into
right pulmonary artery
what does the left side of the 6th arched vessel develop into
left pulmonary artery and the ductus arteriosus
what happens to the arched vessels which are of no use
they disappear
what nerve supplies the 6th arched vessel
left recurrent laryngeal nerve
what 3 shunts are found in the fetal heart
ductus venosus, ductus arteriosus and foremen ovale
what does the ductus venosus do
bypasses blood from the liver as it is very metabolically active
what does the ductus arteriosus do
allows blood to flow from the pulmonary trunk into the aorta to bypass the lungs
why must blood bypass the lungs
as blood may damage the developing lungs and also it is not oxygenating the blood as this is done at the placenta
what does the foremen ovale do
allows the passage of blood from the right to left atrium to bypass the right ventricle
what cells develop into the endocardial cushions
neural crest cells
how is the foremen ovale formed
- the septum primum grows from the roof of the primitive atrium towards the endocardial cushion leaving a crescent shaped gap called the ostium primum to allow blood flow
- before the septum primum fully forms, apoptosis occurs to give a hole called the ostium secundum
- the septum secundum forms and apoptosis also occurs to form another hole but lower down
how does the foremen ovale close
at birth the pressure in the LA exceeds that of the RA pushing the septum primum against the septum secundum to close the shunt
what causes the closure of the ductus venosus
the removal of the placenta support
how are the ventricles separated
- a muscle portion forms upwards from the endocardial cushions at the bottom but leaves a small gap called the primary intraventricular foramen
- a membranous portion then forms from connective tissue derived from endocardial cushion
how does septation of the outflow tract occur
endocardial cushions in the truncus arteriosus grow and twist around eachother forming a spiral septum
