Flashcards in Devo Lect 15 - Heart Deck (16)
Timing of circulatory system - why so early?
by stage 13, 28 days, the heart is beating, most other things not developed yet (bones, limbs, nerves); needs nutrients to all the cells and to remove wastes; essential
Earliest blood vessels
Vitelline artery and vein, go into yolk sac; why in humans? no nutrients out there; this is evidence of evolution
Evidence for evolution from development
Yolk sac and its blood vessels; early heart is two chambered like fish; aortic arches like in fish (gills), some in amphibians, fewer in reptiles, one in birds and mammals (aortic arch, rest disappear)
Develops in neck region from part of lateral plate mesoderm; forms at same time as nervous system; endocardial tubes form on either side, migrate together and fuse; myocardium cells around it start to contract (day 20-21); not closed system yet, fluid goes back and forth. 1st functional organ.
Where are myocardium and endocardium derived from?
myocardium and endocardium both from mesoderm
Regions of developing heart
Day 21: bulbis cordis, ventricle, atria; atria bulge, heart bulges and bends; reorients itself (heart looping); Day 35 looks about normal: bulbis cordis became pulmonary artery and aorta, ventricle still one chamber
Reorientation of heart; atria rotate to the anterior end, ventricle moves to posterior end
Forming chambers in heart
Septum primum becomes atrial septum primum and secundum, foramen ovale still there; interventricular septum; both develop between 33 days and the third month
Circulation of blood in fetus
Foramen ovale still open, ductus areriosus is open b/w pulm. art. and aorta; oxygenated blood comes from the placenta via ductus venosus into inf. vena cava; oxygen would be lost in the lungs
Circulation changes after birth
Breathes after birth, lungs and blood vessels expand, pressure drops and blood rushes in from right side of heart; flap of tissue closes foramen ovale (from left side), seals eventually; ductus arteriosus closes due to hormones released due to flow change, smooth muscle squeezes it shut; vessels to placenta degrade
Are we bilaterally symmetrical?
Mostly, but not all parts; early embryo is symmetrical until organs develop eventually; heart, lungs (3 vs 2 bronchi)
Why isn’t symmetry 50/50?
cells in Hensen’s node (in primitive streak) have a few cilia, beat in a certain direction (not random!), move fluid and GFs from R to L; Shh more on L, turn on certain genes (Nodal (GF), turns on Pitx2 (TF)) promotes left sided structures
Situs inversus (totalus)
Rare condition: Organs are switched sides! Often no symptoms.
Since cilia help position cells etc in development, if they are not working, the embryo has 50% chance of developing situs inversus
Study on left-right patterning
Embryos in dish, altered fluid flow across Hensen’s node, Nodal was expressed on the right side. 21/24 times heart developed on the right side