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
When does septation of the heart begin?
When endocardial cushions in the atrioventricular region expand to divide the heart
What does the development of the primitive atrium involve?
Formation of two septa and three holes
First step of atrial septation
Septum primum forms and extends downwards towards the fused endothelial cushions to split the atrium into two.
Second step of atrial septation
A second septum called the septum secundum grows with a hole known as the foramen ovale. The foramen ovale in the septum secundum and the ostium secundum in the septum primium allow for the presence of a right and left shunt in the growing heart
In the development of the atria (holes)
There is always a hole in the septum to allow for communication between the right and left atria - allows for blood to be shunted to the left side of the heart (bypasses the developing lungs)
The interventicular septum of the ventricles has two components…
One muscular and one membranous
The muscular portion of the interventricular septum…
Grows up from the ventricle floor to the fused endocardial cushions, but a small gap called the primary interventricular foramen remains - filled with the membranous portion made from connective tissue
What are circulatory shunts for during gestation?
Required for blood to bypass liver and developing lungs
Through what shunts does blood bypass the lungs in gestation?
The foramen ovale (primarily) in the atrial septum and if not through there, the ductus ateriosus in the pulmonary trunks
Through what shunt does blood bypass the liver in gestation and why?
Ductus venous, ensures enough oxygen gets to the developing brain
How does the foramen ovale shunt close after CV maturation?
Intake of air increases pressure within the left atrium. As blood cannot move from the right to left atrium (higher pressure in left atrium), this closes the shunt
How does the ductus arteriosus shunt close after CV maturation?
Muscular wall contracts to close after birth via a process called bradykinin
Adult remnant of Forman ovale
Fossa ovalis
Adult remnant of the ductus arteriosus
Ligamentum arteriosum
Adult remnant of the ductus venosus
Ligamentum venosum
Adult remnant of the umbilical vein
Ligamentum teres (hepatis)
What is tetralogy of fallot?
A congenital heart defect with four abnormalities
The four abnormalities in tetralogy of fallot (VORP)
- Ventricular Septal Defect - failure of the interventricular septum to fully close
- Overriding Aorta (aorta is connected to both right and left ventricles
- Right ventricular hypertrophy - right ventricle is more muscular than the left
- Pulmonary stenosis - narrowing of the right ventricular outflow tract
How is tetralogy of fallot discovered?
Echocardiography
How is tetralogy of fallot treated and what happens if not?
Surgery - pulmonary valve is widened and the ventricular septal defect is repaired. If not treated, right ventricular hypertrophy gets worse - leads to heart failure
