Session 2 - Early development of the heart Flashcards
What is the cardiogenic field?
-An undifferentiated area within an embryo from which the heart, vessels and blood cells arise from
What happens to the cardiogenic field to produce the primitive heart tube?
-Pair of endocardial tubes form in the cardiogenic field by week 3 -Lateral folding of the embryo results in fusion of the endocardial tubes at the midline, forming the primitive heart tube
Where is the primitive heart tube after lateral folding?
-Initially suspended in the pericardial cavity by a membrane, membrane breaks down and primitive heart tube is free within the cavity
What is the effect of cephalocaudal folding on the heart tube?
-Relocates the primitive heart tube, within the pericardial cavity, to the correct anatomical location
At what point in the pregnancy does the primitive heart tube form?
-Approx. day 25
Describe the primitive heart tube initially
-Linear pulsatile sturcture consisting of sinus venosus, primitive atrium, primitive ventricle, bulbus cordis, truncus arteriosus and aortic roots
Where, initially, is the inflow of the primitive heart tube?
-At the caudal end -> sinus venosus
Where, initially, is the outflow of the primitive heart tube?
-At the cranial end -> throughout the aortic roots
In what direction is bloodflow through the primitive heart tube?
-From caudal to cranial
Why does the primitive heart tube need to develop from its original linear structure?
-The linear structure is sufficient to supply the embryo at first, but as the embryo develops, the primitive heart tube needs to change to meet demand
Why is looping a key developmental event?
-Ensures septation of chambers and outflow tract -Development of transverse sinus -Optimises space for growth
What is looping of the primitive heart tube?
-Continued elongation of the primitive heart tube results in the tube bending and folding upon itself -The primitive ventricle pushes ventrally, caudally and right -The primitive atrium pushes dorsally, cranially and left
When does looping occur?
-Approximately day 23-day 28
What does looping achieve?
-Primordium of right ventricle closest to its outflow -Primordium of LV closest to its inflow -Atrium dorsal to bulbis cordis (inflow dorsal to outflow) -Both inflow and outflow are cranial
What does the development of the transverse sinus ensure?
-The great arteries are in front of the great veins
What is the atrioventricular canal?
-A constriction between the primitive atrium and the primitive ventricle which is the first division between the two zones
What is the purpose of the atrioventricular canal?
-Allows communication between the atria and ventricles -Contributes to the asymmetrical development of the heart, allowing the ventricles to enlarge more than the atria
When is the oblique sinus formed?
-During formation of the left atrium when the LA absorbs the pulmonary veins and expands
What happens to the sinus venosus during atrial development?
-As venous return shifts to the right side of the heart, the left horn of sinus venosus recedes and the right atrium absorbs the right sinus horn
Where does the right atria develop from?
-Most of the primitive atrium and the right sinus horn
Where does the left atrium develop from?
-A small portion of the primitive atrium but mostly from pulmonary veins
Describe development of the left atrium
-LA sprouts pulmonary veins which branches into 4 veins -LA absorbs the proximal portions of these branches and expands to form complete LA
Name the shunts in the feotal system
-Ductus arteriosus -Ductus venosus -Foramen ovale
What is the function of ductus arteriosus?
-Shunt blood from the pulmonary trunk to aorta in order to bypass the lungs
What is the function of ductus venosus?
-A shunt from umbilical vein to inferior vena cava to bypass the liver, as it is the first organ to be reached, and it is a very demanding one which would use all the oxygen and nutrients
What is the function of foramen ovale?
-A shunt from the RA to the LA in order to bypass the right heart as it is not needed
Why is there a ductus arteriosus if the right heart is bypassed?
-Because a small amount of blood does pass into the right ventricle in order to support its development and the development of the lungs
Why does blood pass through the ductus arteriosus instead of continuing to the lungs?
-The resistance in the lungs is very high as they are collapsed, so flows through DA where pressure is lower
What are the aortic arches?
-A bilateral system of arched vessels, connected to the primitive heart, which undergo extensive remodelling to create the major arteries leaving the heart
What are the derivatives of the 4th aortic arch?
-Right -> right subclavian artery -Left -> arch of aorta
What are the derivatives of the 6th aortic arch?
-R-> Right pulmonary artery -L->Left pulmonary artery and ductus arteriosus
Which arch does the recurrent laryngeal nerve correspond to?
-6th
What is the function of the recurrent laryngeal nerve?
-Innervate the intrinsic muscles of the larynx
Where do the left and right recurrent laryngeal nerve loop?
-Left loops around aorta as it is hooked around the ductus arteriosus -Right loops around the right subclavian artery due to remodelling of the arches
