Embryology Of The Heart

Question 1

Heart development

Answer 1

▪️starts to form 18-19 days post fertilisation
▪️begins to beat 21-22 days
▪️blood flow can be detected by Doppler ultrasonography during week 4

Question 2

Formation of vascular system

Answer 2

▪️vasculogenesis
-formation of new vascular channels by cell precursors- angioblasts
▪️angiogenesis
-formation of new vessels by budding and branching from pre-existing vessels

Question 3

Development of endocardial heart tubes

Answer 3

-develops near head of embryo (cardiogenic area)
▪️clusters of cells develop cephalic to oropharyngeal membrane (17days)
▪️cells form a plexus of vessels which fuse to form R and L endocardium heart tubes (18)
▪️R and L dorsal aortas develop which are connected by aortic arches- arterioles (18)

Question 4

Development of primitive heart tube

Answer 4

▪️lateral folding of the embryo starts to happen which brings R and L tubes together at the midline where they fuse and become primitive heart tube (22)
▪️still a connection between primitive heart and body through dorsal mesocardium and is surrounded by a pericardial cavity
-dorsal aortas have still yet to fuse at this point

Question 5

Movement of heart tube

Answer 5

▪️due to rapidly growing CNS, the heart tube is forced down through the cervical part of the embryo then into the thoracic region
▪️oropharyngeal membrane is pulled forward above the heart tube due to lateral folding

Question 6

The dorsal mesocardium

Answer 6

▪️eventually disappears due to elongation and folding of the heart tube
▪️creates a space behind the heart - transverse pericardial sinus which connects both sides of the pericardial cavity
▪️heart is suspended in cavity

Question 7

Parts of the heart tube

Answer 7

▪️arterial and venous ends of the tubes are fixed
▪️bulbus cordis- ventricle - atrium- sinus venosus- R and L horn SV
-BC gives rise to infundibulum of aorta and PT
-SV gives rises to SVC, IVC, PV

Question 8

Folding of heart tube

Answer 8

▪️BC and ventricular parts of elongate rapidly- since A and V ends are fixed, the tube begins to bend
▪️firstly a U-shaped bend (bulboventricular loop) than a compound S-shape (A is forced to back of V)
-truncus arteriosus- distal part of BC
-corpus arteriosus/aortic vestibule- proximal part of BC which gets incorporated into RV and LV

Question 9

Partitioning of the heart tube

Answer 9

▪️atrioventricular canal begins to separate A and V (week 4-8)
▪️endocardial cushions form on dorsal and ventral walls of AV canals- eventually move in and fuse (week 5)
-divide AV canal partially into R and L and also A and V partially (AV valves)

Question 10

Partitioning of primordial atrium

Answer 10

▪️runs along with ventricle formation
▪️partially divides into R and L by formation of septum primum- grows downwards from roof towards EC
▪️spaces start to appear where SP hasn’t reached -foramen primum- blood can pass through here
-this starts to disappear as SP fuses with EC
▪️smaller holes appear on SP higher up which come together to form foramen secundum
▪️septum secundum- grows down from wall of RA to the right of SP and eventually overlaps FS
▪️as SP is flexible blood is able to pass between A by pushing past SP
-blood from LA can not travel back through hole as the SP will push onto the SS which is more rigid- acts like a valve- foramen ovale

Question 11

Partitioning of the primordial ventricle

Answer 11

▪️muscular interventricular spetum grows up from the base of the heart towards EC covering the IV foramen and splitting into R and L V
▪️membranous IVS grows down form EC and fuses with MIVS that was growing up
▪️cavitation of V walls forms sponge work of muscular bundles- trabeculae carnae