Blood and Blood Vessels!- Vasculogenesis: vessels arise from blood islands!- endothelium lined cavities fuse to form channels made by angioblasts!- angioblasts (endothelial cells from splanchnic mesoderm) become blood islands!- 1st blood islands: in mesoderm around yolk sac at 3 weeks!- innermost layer--> endothelium, other layers become the tunics (layers) of vessel wall - Angiogenesis: Formation of new vessels by branching from pre-existing vessels!- Endothelial budding Day 16-28: Heart Tube - Small amount of yolk can no longer support growing embryo by diffusion!!- Day 16-18: Progenitor heart cells= Primordial heart migrate --> form the Primary Heart Field (PHF) - Form: atria, L ventricle, and most of R ventricle!- Are in epiblast, right next to cranial end of primitive streak, just above the neural folds --> migrate thru the streak into splanchnic layer of lateral plate mesoderm!- Form a horseshoe = primary heart field - After making PHF, cells are induced to form cardiac myoblasts and blood islands--> islands unite --> form endocardial tubes (from angioblastic cords) in cardiogenic region!!- Day 20-21: Secondary heart field (SHF) generates smooth wall part of R ventricle and R and L outflow tracts= bulbus cordis (to future pulmonary a's)!- in splachnic mesoderm!- laterallity--> spiraling of pulmonary artery and aorta!- regulated by neural crest cells!!- Day 21: Primitive (= primordial) heart tube formed from fusion of endocardial tubes (during body wall folding)!- heart forms from cardiogenic area (splanchnic mesoderm) from angioblastic=cardiogenic cords - Heart tube joins w/vessels --> primordial cardiovascular system!- Fusion occurs cranially to caudally, ventral to foregut!- Heart becomes a cont. expanded tube made of an inner endothelial lining and an outer myocardial layer!- Pericardial coelom: develops around the primitive heart tube --> pericardial cavity!- Dorsal mesocardium suspends the dorsal side of the parietal pericardium --> breaks down to transverse pericardial sinus --> connects both sides of cavity !- Fibrous pericardium formed from pleuropericardial folds!- Epicardium = visceral pericardium is from the proepicardial organ and sinus venosus!- responsible for formation of coronary arties! - Day 22: Primitive heart tube develops into 5 distinct regions and begins to pump! - Caudal pole: receives venous drainage, Cranial pole: begins to pump blood out of 1st aortic arch into dorsal aorta !1) Sinus venosus!a. Receives all the de-O2 blood from the embryo- Umbilical (placenta), vitelline (yolk sac), and common cardinal veins (ant. and post., head and trunk)!b. Will become posterior, smooth part of R atrium!c. Will develop into SA node and coronary sinus, coronary arteries, cardiac veins, and epicardium!d. SA orifice (covering of SV R and L horns) has a R and L valve that form the opening: R valve will become: crista terminalis, valve of IVC, valve of coronary sinus. L valve will become: interatrial septum when it fuses w/septum secundum!2) Primitive atrium!a. Forms the pectinate, anterior part of the R atrium, and both pectinate auricles. Initially forms the L atrium, but will be replaced by ingrowths from the pulm. veins!3) Primitive ventricle a. Trabelculated L ventricle. !4) Bulbus cordis has 3 parts:!a. Trabeculated R ventricle (the rest of the RV is conus cordis)!b. Conus cordis forms the outflow tracts of both ventricles (aortic vestibule and infundibulum)!c. Truncus arteriosus forms the roots and proximal portion of the ascending aorta and the pulmonary trunk. Separates via formation of a spiral septum. The distal portion --> aortic sac! Day 23-28: Heart Folding !- Ends of the heart are fixed in the pericardium, phargyngeal arches, and septume transversum!- When bulbus cordis and ventricle grow extra fast, the heart is forced to bend, loop, and fold (i.e. the folding of the heart tube is dep. on differential rate of growth) !- Primitive ventricle moves ventrally and to the R!- Primitive atrium moves dorsally and to the L!- Trabeculated proximal third of bulbus cordis becomes the primitive R ventricle, prim. ventricle is now trabeculated and called the primitive L ventricle. Bulbis cordic remains smooth-walled for now.!- Conotruncal portion of the heart tube, initially on the R side of the pericardial cavity, shifts to more medial position!- Note: at this point there is no division between atria or ventricles, both atria communicate w/both ventricles, back to this in the formation of the cardiac septum!Day 27-37: Formation of the Cardiac Septa= Endocardial Cusion Development - Endocardial cushions: !- 2 actively growing mesodermal masses of tissues approach each other until they fuse --> dividing the lumen of the atrioventricular canal into 2 separate canals= R and L antriventricular canals - Imp. for assisting in formation of atrial and ventricular septa (membranous portions), antrioventricular canals and valves, aortic and pulmonary channels - Day 28: Formation of the atrial septum - Septum primum!- grows from the roof of the primitive atrium and fuses w/endocardial cusions, but doesn't extend completely to floor, leaving ostium primum to allow incoming blood to form from the primitive R atrium --> primitive L atrium!- Disappears are endocardial cushions grow superiorly!- Ostium secondum: apoptosis caused the 2nd foramen to open cranial to the septum primum, blood flow continues from R--> L!- Septum secundum!- grows adj. to septum primum on the R atrial side from the roof of prim. R atrium to floor, leaving another opening at the edge= Foramen ovale!- valve of foramen ovale is the remnant of septum primum covering the foramen ovale!- w/formation of foramen secundum, the attachment of the foramen primum to the roof of the atria degenerates !- at birth: the septum primum is forced to press against the foramen secundum (foramen ovale) by the increased P in the L atrium. The ostium secundum is sealed by the septum secundum. !- after a couple weeks, cells grow to fuse the foramen primum w/the edges of the foramen ovale!- the membrane covering the foramen ovalein the definitive heart= fossa ovalis! Veins - Fates of cardinal veins!- Anterior cardinal veins --> internal jugular veins!- Anterior cardinal anastomose --> L brachiocephalic!- R common cardinal + anterior cardinal veins develop together --> Superior Vena Cava (SVC) - posterior cardinal veins form more divisions --> will form inferior segments of IVC and azygos v.!- Horns of sinus venosus!- R
View Full Document
Unlocking...