Embryology Flashcards
Which layer do the heart and CVS components derive from?
Viscera Mesoderm
Why is the heart one of the first structures to form and function?
Blood flow early on is essential for oxygen and nutrients to get to other structures being developed
How does the heart reach its final position in the thorax?
Lateral folding and cranio-caudal folding occur simultaneously
Where do the beginnings of the gut tube start to develop?
Just adjacent to the heart tube
Which direction does blood flow through the heart tube?
Caudal to cranial end
Sinus venosus to Truncus arteriosus
How many dilatations does the heart tube develop?
Five (Causal to Cranial) Sinus venosus Atrium Ventricle Bulbus cordis Truncus arteriousus
What structures does the sinus venous develop into?
Formed of right and left horns
Right horn forms smooth part of the RA
Left horn shrinks and forms the coronary sinus
What structure does the atrium go on to form?
Trabeculated part of both atria
What structure does the ventricle go on to form?
Trabeculated part of the LV
Which structures does the bulbus cordis go on to form?
Trabeculated part of the RV
Which structures does the trunks arteriosus go on to form?
Aorta
Pulmonary trunk
What happens to a cell as soon as it differentiated to become a heart cell?
It will start to beat, and continue to do so throughout its lifetime
All the cells will beat synchronously
When will the heart begin to loop and fold?
Day 23
In which direction does the atrium move during looping and folding?
Dorsal and cranial
In which direction does the ventricle move during looping and folding?
Displaces left
In which direction does the bulbus cordalis move during looping and folding?
Inferiorly, ventrally to the right
How many septa are there within the heart and how do they develop in relation to each other?
Three main septa Atriaventricular septum Interventricular septum Interatrial septum They develop simultaneously
What are the main steps in the development of the atriaventricular septum?
Atriaventricular canal is divided along its axis by the growth of two partitions from the walls of the adjacent chambers
Endocardial cushions extends and will ultimately fuse into a column, dividing atria and ventricle
What are the main steps in the development of the interventricular septum?
Muscular septum advances across the common ventricle towards the heat base
This leaves a gap (the interventricular foramen)
This is closed over by the formation of a complex spiral septum which forms the aorta and pulmonary artery
What are the main steps in the development of the interatrial septum?
Grows rapidly towards the endocardial cushions, constricting the foramen primum
Before this is completely obliterated, foramen secundum forms, allowing for shunting of blood
Septum scandium developed down like a curtain over the foramen scandium, leaving a small hole (the foramen ovale)
Septum secundum and septum primum together ensure blood only shunts from right to left
Which blood vessels empty into the sinus venosus?
Anterior and posterior cardinal veins
Umbilical veins
Vitelline veins
What is the vasculature like in early development?
Vasculature is doubled
Everything has an identical structure
How does the sinus venosus change during development?
Blood diverts from left sinus horn to right sinus horn (right developed larger)
Right horn becomes vena cave
Left horn becomes coronary sinus, loses its systemic venous drainage and gets its supply solely form the heart
Why are the walls of the left atrium smooth?
As the heart grows, the proximal part of the pulmonary veins from the early stages of development become incorporated into the left atrium
Venous origin = smoothness
How many pairs of aortic arches are there?
Six
Which vessels do aortic arches 1 and 2 give rise to?
Maxillary a.
Stapedial a.
MOSTLY OBLITERATED
Which vessels does aortic arch 5 give rise to?
None
Rudimentary or absent
Which vessels does aortic arch 3 give rise to?
Common carotid aa
First part of ICA
Which vessels does aortic arch 4 give rise to?
Right subclavian a
Part of aortic arch
Which vessels does aortic arch 6 give rise to?
Sprout branches that form pulmonary aa
Ductus arteriosus on the left
Which three venous systems are found in the embryo?
Vitelline veins
Umbilical veins
Cardinal veins
How does the function of the vitelline veins change during development?
Embryo = drain yolk sac Adult = portal venous system draining gut, hepatic sinusoids and veins, hepatic portion of IVC
How does the function of the umbilical veins change during development?
Embryo = drain oxygenated blood from the placenta Adult = right degenerates, left remains as definitive umbilical vein
How does the function of the cardinal veins change during development?
Anterior
Embryo = drain head and neck
Adult = Jugular system and left brachiocephalic vein, SVC
Posterior
Embryo = drains the trunk
Adult = azygous and hemiazygous systems (body wall), gonadal and renal veins, iliac veins, IVC
Describe foetal circulation
Oxygenated blood passes from placenta, through liver to RA, where it is shunted to LA and out to the aorta
Deoxygenated blood also enters RA from SVC
This crosses to the RV (is now slightly more oxygenated due to mixing of blood) and into the pulmonary arteries
Some blood in pulmonary arteries goes to lungs (no oxygenation function), back in pulmonary veins then to aorta
Some blood in pulmonary artery is taken straight to aorta via ductus arteriosus
Blood in aorta for systemic circulation will be slightly deoxygenated
What changes occur in the circulatory system at birth?
Blood supply from the placenta is cut off
Ovale foramen shuts off, so no shunting of blood occurs
Ductus arteriosus shuts off
All blood must now pass through the lungs, which have inflated and can now oxygenate blood
