Revision: Embryology Flashcards
formation of primitive heart tube
cardiogenic field, where heart, blood vessels and cells arise from, is created in gastrulation and begins in the cranial end of the embryo before folding starts
as development of CVS starts, a pair of endocardial tubes develop in the 3rd week
Folding: lateral folding brings these two together to form the heart tube (diagram)
-cephalocaudal folding brings the tube into thethoracic region
regions of primitive heart tube
originally recieves blood at sinus venosus (caudal) before pumping blood out of the aortic roots (cephalic)
consists of: sinus venosus, primitive atrium, primitve ventricle, bulbus cordis, truncus arteriosus, aortic roots
looping of heart tube and result
continued elongation leads to bending between days 23-28
Cephalic/cranial part: caudally, ventrally, to the right
Caudal part: cranially, dorsally, to the left
Afterwards, the atrium communicates w/ vent.s via a/v canal, a constriction between the two, the first division between the chambers
Forms tranverse pericardial sinus, a space behind the outflow and in front of the inflow, where a finger can be inserted
describe fate of sinus venosus
receives blood from yolk sac, placenta and body
at first the r and l horns are equal in size -> venous return then shifts to the RHS -> l/horn recedes -> enlarging RA absorbs r/ sinus horn
describe development of atria
RA: from most of the prim. atrium and r/horn of sin. ven.
LA: from small amount of prim. atrium, absorbs prox. part of pulmonary veins
-as the LA expands and absorbs the pulmonary veins, the oblique pericardial sinus is formed - with the heart in the palm of your hand, your fingers are in a cul-de-sac - the OPS
development of the aortic arches
early system is a bilateral symmetrical system of arched vessels -> undergo extensive remodelling -> major arteries
-NB no. 5 has no derivative in humans and either incompletely forms or never forms at all
4th arch: l -> arch of aorta, r -> prox. part of r/ subclavian
6th arch: the recurrent laryngeal nerve forks underneath here, l -> l/pulmonary artery and ductus arteriosus, r -> r/pulmonary artery
first stage in septation
development of endocardial cushions on back and front of a/v canal -> grow towards each other -> divides heart to r/ and l/ sides
atrial septation
formation of 2 septa w/ 3 holes:
Septa: Septum primum: grows down towards endocardial cushions
-Septum secundum: crescent shaped 2nd septum
Holes: ostium primum: hole beofre SP fuses w/ endocardial cushions
- ostium secundum: before ost. prim. closes, 2nd hole appears in sep. prim. by apoptosis
- foramen ovale: hole inside septum secundum
ventricular septation
formed of a muscular and membranous portion:
- muscular: forms most of septum, grows upwards towards fused endocardial cushions leaving a hole at the top, the primary interventricular foramen
- membranous: fills gap of primary interventricular foramen, derived from spiral septum that grows to separate the truncus arteriosus into outflow valves
foetal circulation principles, outline, fate
Lungs are obv. non functional in a foetus and it is important that they do not receive too much blood as they can be damaged
Foetus: receives blood from mother via placenta -> umbilical veins, which bypasses the lungs, blood returns to the placenta via umbilical arteries
-changes in circulation must occur immediately at birth, shunts are required to make this happen
Diagram: IVC=inf. ven cava
ignore written part about DA
after birth: baby takes breath -> massively dec. press in lungs -> more blood enters lungs -> more blood enters LA -> press. in LA>RA -> foramen ovale shuts, DA contracts, placental support removed so DV shuts
fates of foetal shunts
forman ovale -> fossa ovales
ductus arteriosus -> ligamentum arteriosum (mediated by bradykinin)
ductus venosus -> ligamentum venosum
umbilical vein -> ligamentum teres hepatitis
