Devo Lect 15 - Heart

Question 2

Timing of circulatory system - why so early?

Answer 2

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

Question 3

Earliest blood vessels

Answer 3

Vitelline artery and vein, go into yolk sac; why in humans? no nutrients out there; this is evidence of evolution

Question 4

Evidence for evolution from development

Answer 4

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)

Question 5

Heart development

Answer 5

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.

Question 6

Where are myocardium and endocardium derived from?

Answer 6

myocardium and endocardium both from mesoderm

Question 7

Regions of developing heart

Answer 7

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

Question 8

Heart looping

Answer 8

Reorientation of heart; atria rotate to the anterior end, ventricle moves to posterior end

Question 9

Forming chambers in heart

Answer 9

Septum primum becomes atrial septum primum and secundum, foramen ovale still there; interventricular septum; both develop between 33 days and the third month

Question 10

Circulation of blood in fetus

Answer 10

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

Question 11

Circulation changes after birth

Answer 11

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

Question 12

Are we bilaterally symmetrical?

Answer 12

Mostly, but not all parts; early embryo is symmetrical until organs develop eventually; heart, lungs (3 vs 2 bronchi)

Question 13

Why isn’t symmetry 50/50?

Answer 13

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

Question 14

Situs inversus (totalus)

Answer 14

Rare condition: Organs are switched sides! Often no symptoms.

Question 15

Kartagener syndrome

Answer 15

Since cilia help position cells etc in development, if they are not working, the embryo has 50% chance of developing situs inversus

Question 16

Study on left-right patterning

Answer 16

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

Question 17

Experiment with chicks with left-right symmetry

Answer 17

Inserted a bead of Shh on right side, Nodal expressed on both sides, 50/50 L/R