Need the stem cellThe concept of stem cells Everyday, about 10 11 red blood cells are killed inthe spleen, and need to be replaced. The replacements come from populations of stemcells. A stem cell is a cell that is capable of extensive proliferation,creating more stem cells (self-renewal) as well as moredifferentiated cellular progeny.Hematopoietic stem cell (HSC) is critical in hematopoiesis.Differences in hematopoiesisSites Of Embryonic Hematopoiesis Two Phases:Transient embryonic “primitive” phaseDefinitive “adult” phase Different Phases differ in Sites of blood production Timing of hematopoiesis Type of globin genes in red blood cells Blood islands in the ventral mesoderm near the yolksac. Visceral (splanchnic) lateral platemesoderm nearthe aorta, the aorta-gonad-mesonephros (AGM)region. PlacentaBMP2 & BMP4 are critical in inducing the bloodforming cells.Hematopoiesis in the aorta-gonad-mesonephros(AGM) regionTransition of sources of blood cells to the bonemarrow3-Day chick embryoHematopoietic Stem Cell, HSCThe hematopoietic stem cells colonize the fetal liver, and the stemcells from the liver populate the bone marrow.AortaHSCHSCHSCHSCChemo-attractant proteins for HSC, which are secreted from thebone and spleen and attract into them.
11.25 Anterior-posterior patterning in thechick embryoInitial Cell DifferentiationAt embryonic stage-7, mRNA expressions by in situ hybridizationRetinaldehydedehydrogenase-2Retinoic aciddegradationenzymesGATA4 is first seen inthe precardiac cells.N-cadherin is critical forthe fusion of the twoheart rudiments into onetube.The posterior fate becomes committed by retinoic acidFormation of the chick heart from the splanchniclateral platemesodermFusion of the heart rudiments28 hours29 hoursJoining two tubes togetherform the pericardialcavity, the sac in which theheart is formed.Small cells of pericardialcavity form theendocardium, the bloodvessels.The epithelial cells formthe myocardium, rise to theheart muscle.The un-fused posteriorportion of the endocardiumbecome the openings of thevitelline veins into the heart.Contraction of the truncusarteriosus speed the bloodinto the aorta. Initial heartbeatsHeart Looping: The looping of the chickheart is a complex orchestration of events Pulsations of the chick heart begin while the pairedprimordia are still fusing. The sodium-calcium exchange pump in the muscle cellmembrane. Cardiac cell calcium channels in the pacemakerfunction.
Adult and fetal hemoglobin molecules differ in theirglobin subunitsRedirection of human blood flow before birthBeta-chain binds theregulatory protein unloadingoxygen, but not in gammachain.FetusAffinity for oxygen:Fetal > AdultOxygen can bepassed from motherto fetus.Opening ductus arteriosus causes:Pulmonary artery Aorta ( Placenta)Opening foramen ovale causes:(Placenta ) Right atrium Left atrium Left ventricleRedirection of human blood flow after birthNewborn