Development Of The Heart Flashcards
Name the regions of the developing heart
The primitive heart tube is linear at first, with blood inflow at the caudal end (sinus venosus) and outflow at the cranial end (aortic roots).
The primitive heart tube is described as having four segments - primitive atrium, primitive ventricle, bulbus cordis, truncus arteriosus.
Describe the formation of the primitive heart tube
The cardiogenic field is created during gastrulation and at first lies at the cranial end before folding occurs.
As development of the CVS begins, a pair of tubes (endocardial tubes) develop in the third week of development. The endocardial tubes are brought together during folding and fuse in the midline to create the primitive heart tube.
Lateral folding creates the heart tube and cephalocaudal folding brings the tube into the thoracic region.
Describe the looping of the primitive heart tube
Looping begins ~day 23 and ends ~day 28.
The cephalic portion loops ventrally, caudally and to the right.
The caudal portion loops does ally, cranially and to the left.
Looping places the inflow behind the outflow and communication between the atria and ventricles via the atrioventricular canal.
Looping of the primitive heart forms the transverse pericardial sinus (the space behind the outflow and in front of the inflow), where a finger can be inserted.
Describe in brief the development of the atria
RA develops mostly from primitive atrium but also absorbs the right horn of the sinus venosus. It receives venous drainage from the body (venae cava) and heart (coronary sinus)
LA develops from a small portion of primitive atrium and absorbs proximal parts of pulmonary veins. It receives oxygenated blood from the lungs.
What is the sinus venosus?
The embryo collects blood from the placenta, yolk sac and the body, this all goes to the sinus venosus.
Describe in brief the development of the sinus venosus
Right and left sinus horns are equal in size.
Venous return shifts to RHS so left sinus horn recedes.
Right sinus horn is absorbed by enlarging right atria.
What is the oblique pericardial sinus and how is it formed?
With the heart in the palm of your hand, your fingers are in a cul-de-sac, known as the oblique pericardial sinus.
It is formed as the left atrium expands and absorbs the pulmonary veins.
Describe in brief the development of the great vessels
Aortic arches - early arterial system is a bilateral system of arched vessels (1,2,3,4,6 - no aortic arch 5 derivative in humans) Arch 4 - right = proximal part of right subclavian artery, left = arch of aorta Arch 6 (pulmonary arch) - right = right pulmonary artery, left = left pulmonary artery and ductus arteriosus, recurrent laryngeal nerve
Describe the process of septation
Endocardial cushions (derived from neural crest cells) develop in the atrioventricular region, dorsally to ventrally. They divide the developing heart into right and left channels by projecting into the canal.
Describe the formation of the inter-atrial septum
Formation of two septa with three holes.
Septum primum grows down towards the fused endocardial cushions.
The ostium primum is a hole present before the septum primum fuses with the endocardial cushions (allows mixing).
The ostium secundum also appears in the septum primum.
A second crescent shaped crescent grows, septum secundum, which has a hole in it called the foramen ovale.
This allows right to left shunt.
The fossa ovalis is the adult remnant of the shunt used in utero to bypass the lungs.
What are the auricles of the heart?
Components derived from the primitive atrium.
Describe the formation of the inter-ventricular septum
Has a muscular and membranous component.
The muscular component forms most of the septum and grows upwards towards the fused endocardial cushions, leaving a small gap called the primary interventricular foramen.
The membranous component of the interventricular septum fills the gap. It is derived from the endocardial cushions/spiral septum that separates the truncus artiosus into the outflow vessels.
Understand the principles of the fetal circulation before birth
The lungs are non functional. The foetus receives oxygenated blood from the mother via the placenta and umbilical veins. It bypasses the liver and goes straight into the IVC via the ductus venosus. The blood reaches the right atrium, where it is shunted to the left atrium through the foramen ovale. It is pumped around the body by the aorta. The ductus arteriosus allows blood to pass from the pulmonary trunk to the aorta, which bypasses the fluid filled, non functioning lungs. Blood is returned via umbilical arteries.
Understand the principles of foetal circulation after birth
When the baby takes its first breath, the pressure in the lungs decreases massively. More blood enters the lungs which causes more blood to enter the left atrium.
When the pressure in the left atrium > pressure in right atrium, the foramen ovale closes.
The ductus arteriosus and venosus shunts also close.
List the fates of foetal shunts
Foramen ovale –> fossa ovalis
Ductus arteriosus –> ligamentum arteriosum
Ductus venosus –> ligamentum venosum
Umbilical vein –> ligamentum teres (hepatitis)
