E - Development Of The CV System Flashcards
When does the CV system start to develop?
4th week gestation
Why does the CV system develop early?
The placenta is eventually unable to meet the nutritional requirements of the growing embryo
How does the formation of the heart begin and when?
Formation of the primitive heart tube at the end of the third week
How does formation of the primitive heart tube begin?
Lateral folding and bringing together of two precursor regions
How is the primitive heart tube positioned after lateral folding?
Cephalocaudal folding (folding the embryo inwards from head to tail) which places the heart tube in the future thorax
How is the heart tube initially held?
In the pericardial cavity by a membrane which eventually degenerates to allow for future growth
From superior to inferior - the six regions of the primitive heart tube
Aortic roots (most superior), Truncus ateriosus, bulbus cordis, ventricle, atrium, sinus venosus (most inferior)
(Aunt theresa bakes very acidic shortcake)
When does the heart tube begin to loop?
23rd day of gestation
How does the bulbus cordis move in looping?
Ventrally, caudally and to the right (Forward, down, right)
How does the primitive ventricle move in looping?
Dorsally, cranially and to the left (backwards, up and left)
What is responsible for blood flow to the heart tube in the 4th week?
Sinus venosus - receives blood from the left and right sinus horns
Eventually, venous return in the sinus venosous of the primitive heart tube…
Shifts to the right side of the tube, causing the left sinus horn to recede and form the coronary sinus. The enlarged right sinus horn is absorbed by the growing right atrium and forms part of the inferior vena cava
Venous return in left atrium of primitive heart tube development
The four pulmonary veins are incorporated into the left atrium, forming the smooth inflow portion and the oblique pericardial sinus
The early arterial system…
Begins as a bilaterally symmetrical assortment of arched vessels which undergo extensive modelling to create the major arteries which exit the heart
Derivative of first aortic arch
Maxillary, hyoid and stapedial arteries
Derivative of second aortic arch
Contributes also to maxillary, hyoid and stapedial arteries
Derivatives of third aortic arch
Forms the common carotid artery and part of the proximal internal carotid artery (PICA3)
4th arch in CV development
Right arch - right subclavian artery. Left arch - part of the arch of the aorta (RSAA4)
Derivatives of aortic 5th arch
Never forms, or forms and regresses
Derivatives of aortic 6th arch in CV development
Right arch - right pulmonary artery. Left arch - left pulmonary artery and ductus arteriosus (6PA)
Each of the aortic arches…
Have a corresponding nerve during development, the most important being the recurrent laryngeal nerve
Right recurrent laryngeal nerve development
Initially hooks around 6th right aortic arch. The distal part of the 6th right aortic arch disappears, so the RRLN moves up to hook the 4th aortic subclavian artery
Left recurrent laryngeal nerve arch development
Hooks around the 6th left aortic arch. As the distal part of the left 6th aortic arch persists as the ductus arteriosum, so the nerve remains
Why is the left recurrent laryngeal nerve clinically relevant?
Susceptible to pathology such as compression by an aortic aneurysm
