CVS Development of the heart Flashcards
How does the primitive heart tube form?
The cardiogenic field (from which the heart, blood vessels and blood cells develop) is created during gastrulation and lies at the cranial end before folding occurs.
In the 3rd week of development a pair of endocardial tubes develop
Lateral folding creates the heart tube
Cephalocaudal folding brings the tube into the thoracic region
What are the regions of the developing heart?
The primitive heart tube is initially linear, receiving inflow of blood at the caudal end through the SINUS VENOSUS and pumping blood from its cranial end through the AORTIC ROOTS.
The four segments are: (caudal–>cranial)
- primitive atrium
- primitive ventricle
- bulbous cordis
- truncus arteriosus
Describe the looping of the primitive heart tube
There is continued elongation of the heart tube resulting in looping (day 23-28).
The cephalic cranial portion bends ventrally, caudally + to the right (forwards, downwards, right).
The caudal portion bends dorsally, cranially and to the left (backwards, upwards, left).
Looping results in the inflow behind the outflow.
What is the outcome of looping?
The atrium communicates with the ventricle through the atrioventricular canal.
Looping forms the TRANSVERSE PERICARDIAL SINUS (the space between behind the outflow and in front of the inflow.
Describe the development of the atria and the sinus venosus
Sinus venosus: The embryo collects the blood from the body, placenta and yolk sac and it all goes to the sinus venous.
The left and right sinus horns are originally the same size but as venus return shifts to the right the left horn recedes and the right horn is absorbed by the right atria.
The atria: The RA develops from most of the primitive atrium and absorbs the right sinus horn.
The LA develops from a small portion of the primitive atrium and absorbed parts of pulmonary veins. (this forms the OBLIQUE PERICARDIAL SINUS
How are the great vessels developed?
Aortic arches: the early arterial system is a symmetrical system of arched vessels. The arches then undergo remodelling to create the major arteries.
4th arch: Right arch forms the proximal subclavian artery
Left arch forms the aortic arch
6th arch: right arch forms right pulmonary artery
left arch forms left pulmonary artery and DUCTUS ARTERIOSUS
Describe the process of inter-atrial septation
Two endocardial cushions form on the dorsal and ventral sides of the atrioventricular canal
They grow towards each other to divide the heart into right and left channels
The division of the atrium involves formation of two septa with 3 holes:
- septum primum grows towards fused endocardial cushions
- ostium primum is the hole before septum premium fuses with the endocardial cushions
- a second hole, ostium scandium appears in the septum primum
- septum secundum grows, and the hole is called the foramen ovale
Describe the process of inter-ventricular septation
The ventricular septum has:
- Muscular component, forms most of the septum and grows upwards towards the fused endocardial cushions but leaves a hole at the top called the primary interventricular foramen
- Membranous component, fills the gap and closes the primary inter ventricular foramen. It is derived form the spiral septum that separates outflow
How does the foetus receive oxygenated blood?
- the foetal lungs are non functional
- oxygenated blood comes from the mother via the placenta and umbilical vein
- the blood bypasses the lungs and returns to the placenta via umbilical arteries
Give an overview of foetal circulation
Oxy blood from the placenta passes through the Ductus Venosus into the IVC via the umbilical vein
The blood reaches the RA and is shunted from right to left via the foramen ovale, here it is pumped round the body via the aorta.
The ductus arteriosus allows blood to be passed from the pulmonary trunk to the aorta to bypass the fluid filled non functioning lungs.
What are the changes in circulation when the baby is born?
The baby takes its first breath which decreases pressure in the lungs
This results in more blood entering the lungs and more blood returning to LA
The pressure in the LA therefore is higher than the RA causing closure of the foramen ovale
The ductus arteriosus contracts
Placenta removed and dunctus venosus closes
List the fates of the foetal shunts
Foramen ovale –> Fossa ovalis
Ductus arteriosus –> Ligamentum arteriosum
Ductus venosus –> Ligamentum venosum
Umbilical vein –> Ligamentum teres
