Development Of The Heart Flashcards
The CVS develops in ….
Middle of 3rd week
GR: CVS has to develop very early
Due to that the rapidly growing embryo can no longer maintain sufficient nutrition and oxygenation of inner parts by simple diffusion.
Mention embryonic origin of CVS & name the process
Mesodermal
Angiogenesis
Mention steps of formation of blood vessels
Mesodermal angiogenic cells form blood islands which acquire lumena and form endothelial channels which become interconnected together, the surrounding mesoderm forms mucular & CT of blood vessels
Mention extra & intra-embryonic vessels & origin of each
E: vitelline vessels around youlk sac, umbilical vessels extend to chorion, originate from extra-embryonic mesoderm
I: 2 dorsal aortae, originate from intra-embryonic splanchnic mesoderm
Primitive blood cells develop from …..
Vitelline & umbilical vessels
Mention Intra-uterine organs of hemopoiesis & those continuing post-natal
Liver, spleen, bone marrow & lymph nodes
Bone marrow & lymph nodes
Mention shape & site of pericardial sac
Carnial part of U-shaped intra-embryonic coelom, between bucco-pharyngeal membrane (caudally) & septum transversum (cranially)
Mention shape & site of cardiogenic plate
Horse-shoe shaped, ventral to pericardial sac
Mention steps of development from cardiogenic plate to single heart tube
Angiogenic cell clusters develop, they acquire lumen and fuse together forming rt & lt endocardial tubes which fuse in cranio-caudal direction.
Mention site of myoepicardial mantle
Between the pericardial sac & endocardial tube
Mention structure separating myoepicardial mantle from heart tube
Cardiac jelly
Mention the origin of each:
- Endocardium
- Myocardium
- Epicardium
- Endocardial heart tube
- Myoepicardial tube
- Visceral layer of pericardial sac
The heart tube & pericardial sac rotate on a transverse axis …. Degrees
180
Describe position of heart tube relative to neighbouring structures following folding
Ventral to foregut
Cranial to septum transversum
Caudal to bucco-pharyngeal membrane
Dorsal to pericardial sac
The endocardial heart tube invades pericardial sac from …. Aspect
Dorsal
Absorption of dorsal mesocardium leads to formation of …..
Transverse sinus of pericardium
Mention dilatations of heart tube in cranio-caudal order
Truncys arteriosus, bulbus cordis, ventricle, atrium, sinus venosus
The first chamber to appear are ……&…. . The last is ….
Bulbus cordis, ventricle
Sinus venosus
….&… are initially outside pericardial sac
Atrium & sinus venosus
Each horn of sinus venosus recieves the following:
- Vitelline vein from yolk sac
- Umbilical vein from placenta
- Common cardinal vein from body wall
A total of ….. arches connect each dorsal aorta with corresponding horn.
Mention fate of 2 dorsal aorta
6
Their caudal parts fuse together forming single dorsal aorta
Mention causes of bending of heart tube
- Elongation of heart tube while its two ends are fixed
- Disproportionate growth of heart tube & pericardial sac
- Disproportionate growth of different parts of heart tube
Steps of bending of heart tube
- Bulbus cordis & ventricle elongate more rapidly with formation of U-shaped bulbo-ventricular loop.
- Cardiac loop becomes S-shaped as the atrium & sinus venosus are dragged inside pericardial sac with approximation of the arterial & venous ends of the loop.
- Blbus cordis shifts to right of ventricle
- The atrium expands transversely amd bulges on either side of bulbus cordis
Heart & pericardium migrate from ….. to ….
3rd - 4th somites
17th - 20th somites
Both valves of sinus venosus fuse together cranially forming …..
Septum spurium
What happens due to the left to right shunt of venous blood?
Right horn progressively enlarges in comparison to the diminishing body and left horn. Sino-atrial orifice moves to right opening into future right atrium
Describe formation of smooth part of right atrium & its name
Sinus venarum
Right horn is incorporated into the right atrium due to wifening of sino-atrial orifice.
Mention fate of tributaries of right horn of sinus venosus
The right commmon cardinal , lower part of SVC
The opening of right vitelline vein, opening of IVC
Right umbilical disappears
Mention fate of tributaries of left horn of sinus venosus
Body & left horn, coronary sinus
Left common cardinal, oblique vein of left atrium
Left umbilical & vitelline veins lose their connections
Mention fate of valve sinus venosus
Upper part of right vv, crista terminalis
Lower part of right vv, valves of IVC & coronary sinus
Left venous valve, inter-atrial septum
Where do endocardial cushions appear? What do they form?
On ventral & dorsal walls of A-V canal
Septum intermedium which divides canal into right & keft parts
Fate of A-V canal
- Ventricular opening develops endothelial proliferation which forms cusps of A-V valves.
- Share in formation of atria
- Membranous part of IV septum
Compare 1, foramen primum & 2, foramen secondum
1, the septum primum grows from roof of atrium towards septum intermedium separated from it by foramen primum.
2, the septum primum ruptures in its center forming foramen secondum
Mention site of septum secobdum & foramen found below it
Right side of septum primum
Foramen ovale
Describe the flow of blood in fetal heart & mechnism to prevent regurge
It passes from right atrium to left atrium via a tortuous S-shaped course through foramen ovale then foramen secondum.
The flap-valvular action of remaining lower part of septum primum closes foramen ovale preventing regurge.
What is the result if absorption if proximal part of pulmonary venous system
The four pulmonary veins open directly in the left atrium
Mention sources of right atrium
The right half of primitive
The absorbed right horn of sinus venosus
The upper part of right atrio-ventricular canal
Mention sources of left atrium
The left half of primitive atrium, absorbed pulmonary veins, upper part of left atrio-ventricular canal.
Fate of lower part of bulbus cordis
Incorporated with common ventricle forming bulbo-ventricular chamber. It forms rough inflowing parts of both ventricles.
Describe development if proximal part of smooth part of bulbus cordis
Divided by proximal bulbar septum to ventral (infundibulum of Rt ventricle) & dorsal (vestibule of Lt ventricle).
The septum shares in IV septum.
Describe development if distal part of smooth part of bulbus cordis
Divided by dorsal bulbar septum into dorsal (aortic orifice) & ventral (pulmonary orifice)
Each orifice develops 3 valves (aortic, 2A & 1P,,pulmonary 2P & 1A) at the beginning, then with rotation the semilunar valves assume their normal anatomical position. They are also hollowed forming cusps.
Mention origin of muscular part of the IV septum
Initially result of dilatation of both ventricles & fusion of opposing walls.
Later, active cellular proliferation
Mention origin of membranous part of IV septum
- The septum intermedium (mainly dorsal cushion)
2. The proximal bulbar septum
What structures result from spongework cavitation of myocardium
Trabeculae carneae, papillary muscles, chordae tendinae
Name the septum dividing ascending aorta & pulmonary trunk
Spiral aortico-pulmonary septum
GR: The valves are situated at the beginning of ascending aorta & pulmonary trunk
Because the lower border of the spiral septum fuses with distal bulbar septum.
GR: The two great vessels are ensheathed by a single coat of serous pericardium
Because the pulmonary trunk and ascending aorta are developed from the same tube.
GR; Helical arrangement of the two great vessels
Because of the spirality of the septum separating them
Mention methods of formation of cardiac septa
Cell proliferation
Non-growing ridge between 2 expanding chambers (never divides lumen)
All cardiac septa develop in the ……, except ….. develops in …..
4th week
Aortico-pulmonary septum
5th week
Frequency of CHD is …..
They occur due to …..
6-8/1000 births
Genetic or environmental causes
Mention cardiac anomalies of position
Dextricardia
Ectopia cordis
Describe dextricardia & its cause
Right sided heart, alone or in situs inversus totalis.
Due to bending of heart to the right & not to the left
Describe ectopia cordis & its cause
Heart protrudes through a median gap in chest, due to faulty development of the sternum.
Mention variants of site of atrial septum defect and its C/P
A hole in middle of inter-atrial septum (site of fossa ovalis)
A hole in lower part of interatrial septum (fossa primum defect) +/- persistent A-V canal
A hole in upper part of interatrial septum
Trilocular biventricular heart
C/P cyanosis due to right-to-left shunt
Causes of interatrial defect according to site
Middle:
1. Underdeveloped septum secondum
2. Excessive resorption of septum primum
3. Failure of fusion of septa (probe-patent fossa ovalis) founf in 25% of normal hearts
Lower: failure of endocardial cushions to grow and fill fossa primum +/- failure of cushions to grow together.
Upper: due to failure of absorption of sinus venosus & failure of incorporation of the venosus valve to the septum
Common atrium: failure of formation of both septa
Mention types of atrial septal defects (4)
- Patent foramen ovale
- Endocardial cushion ASD
- Sinus venous ASD
- Common atrium
Mention the VSDs their cause & description
Membranous VSD, persistence in IV foramen, due to failure of formation of membranous part (Roger’s disease)
Muscular VSD, a hole or mutiple holes (swiss cheese VSD) in muscypular septum due to excessive cavitation
Common ventrucle, due to failure of formation of both septa
Mention defects if truncus arteriosus
- Persistent truncus arteriosus
- Tramsposition of geart vessels
- Congenital stenosis or atresia of pulmonary or aortic orifice
- Fallot’s tetralogy
Mention description & cause of pesistent truncus arteriosus
One vessel recieves blood from both ventricles & distributes it to pulmonary & systemic circulations
Due to failure of formation aortico-pulmonary septum
Mention description & cause of transposition of great vessels
The aorta from rt v & pulmonary trunck from lt v
Due to formation of non-spiral pulmonary septum
Mention cause of stenosis or atresia of aortic or pulmonary orifice
Unequal division of truncus arteriosus
Write a short note on Fallot’s tetralogy
- Pulmonary stenosis
- Hypertrophy if Rt ventricle
- Membranous VSD
- Overriding of aorta on pulmonary septum
Caused by unequal division of truncus arteriosus with very narrow pulmonary trunk & its valve & very wide aorta & its valve, rt ventricular hypertrophy is 2ry to pulmonary stenosis.
The most common congenital heart defect is …..
VSD
… is common in males,….is common in females
VSD, ASD
…… is the most common cause of neonatal cyanosis
Fallot’s tetralogy
