embryology of the CVS Flashcards
what are the 4 major stages in heart development
primitive heart tube
heart looping
atrial and ventricular septation
outflow tract septation
stage 1 - what happens in the 3rd week of development
lateral plate splanchnic mesoderm forms the circulatory system and other viscera
angiogenic cell islands collect in the lateral plate splanchnic mesoderm, move towards midline and coalesce to form the 2 primitive heart tubes
stage 1 - what is the first major system to function in the embryo and why
cardiovascular system
primordial heart starts to funciton at the beginning of week 4
rapidly growing embryo - nutrition by diffusion isnt enough to satisfy it
stage 1 - creation of cardiogenic field (primitive heart and blood vessels)
blood vessels first appear in the wall of the yolk sac, allantois, connecting stalk and chorion
week 3 - appearance of paired endothelial strands (angioblastic cords) appear in the cardiogenic mesoderm
angioblastic cords canalise to form heart tubes
tubular heart joins blood vessels in other areas to form the primordial CVS
stage 1 - formation of pericardium
cranial folding of embryo - reorientation of heart tube dorsal to pericardial cavity
pericardium derived from intra-embryonic coelom
pariteal layer of serous pericardium and fibrous pericardium are formed from somatic mesoderm
visceral layer of serous pericardium is derived from splanchnic mesoderm
stage 1 - development of the heart tube, which end is which?
cranial end - arterial
caudal end - venous
stage 1 - order of sections in the fused primitive heart tube (top to bottom)
- truncus arteriosus
- bulbus cordis
- ventricle
- atrium
- sinus venosus (right and left horns)
which direction does the fused primitive heart tube fold
up towards the right hand side
if it folds towards the left you get dextrocardia
stage1 - venous and arterial end of the heart tube
sinus venosus - venous end, two hornds, each horn gets venous blood from yolk sac (vitelline vein), placenta (umbilical vein) and body of the embyro (common cardinal vein)
truncus arteriosus - arterial end, continuous cranially with the aortic sac, aortic arches arise from the aortic sac and terminate in the dorsal aorta
stage 2 - formation of cardiac (bulboventricular loop)
bulbus cordis and ventricle grow faster than other regions forming a U shaped bulboventricular loop
abnormal cardiac looping
leads to dextrocardia
heart tube loops to the left side instead of the right, ends up lieing facting the right
most frequnt positional abnormality of the heart
dextrocardia can be associated with situs inversus - transposition of viscera
stage 3 - partitioning of primordial heart
seen around 27th and 37th days of embryonic development
involves 1 or 2 actively growing masses of tissues
- endocardial cushion formaiton - separates RA and RV from LA and LV to form L and R AV canals
- septum formation - separates RA from LA and RV from LV
stage 3 - partitioning of primordial heart, clinical issues
many cardiac malformations are associated with defective formation of endocardial cushion and septum formation e.g. ASD and VSD
stage 3 - partitioning of primitive atrium into LA and RA
- formation of the septum primum, formation of the ostium primum
- the ostium secundum begins to form by apoptosis of the septum primum (breaks down towards the top as it grows down and forms a foramen)
- formation of the septum secundum, formation of the ostium secundum is complete, closure of the ostium primum as the septum primum meets the endocardial cushions (the septum secundum perforates in an oval shape to form the foramen ovale)
- formation of the foramen ovale is complete, one way shunt allowing blood to move from the RA to LA
stage 3 - what happens to the septum primum and secundum when the child is born
they snap together and the fossa ovalis is formed
where does the septum secundum grow in relation to the septum primum
to the right of it
in which septums are the foramens the opening in
foramen secundum is opening in septum primum
foramen ovale is opening in septum secundum
role of foramen ovale before birth
allows most of the blood to pass from RA to LA
prevents the passage of blood in the opposite direction
role of the foramen ovale aften birth
normally closes (increased pressure in LA due to increased pulmonary circulation)
septum primum fuses with septum secundum
fossa ovalis of the adult heart is a remnant of foetal oval foramen
non closure resuluts in PFO (patent foramen ovale) = atrial septal defect (ASD)
baby can be cyanotic at birth
atrial septal defect
common congenital heart anomaly
f>m
common form is PFO
what are the 4 clinically significant types of ASD
foramen secundum defect
endocardial cushion defect wih foramen primum defect
sinus venosus defect
common atrium
first 2 types are more common
stage 3 - partitioning of primitive ventricle
muscular ventricular septum forms, opening is called interventricular foramen
bottom of spiral aorticopulmonary septum fuses with muscular ventricular septum to form membranous interventricular septum, closing interventricular foramen
(aorticopulmonary septum divides bulbis cordis and truncus arteriosus into aorta and pulmonary trunk)
growth of endocardial cushions also contributes to membranous portion of interventricular septum
stage 4 - partitioning of bulbus cordis and truncus arteriosus
week 5 of development
aorticopulmonary septum divides BC and TA into aorta and pulmonary trunk
ventricular septal defect
most common type of congenital heart disease - 25% of defects
common in males
can appear in any part of septum
small VSDs close spontaneously (30-50%)
membranous type of VSD is most common
development of the conducting system of the heart
early pacemakers - primitive atrium then sinus venosus
SAN develops during week 5
SAN is located in the RA near the entrance of the SVC in adults
AVN and bundle of his develops from cells of AV canal and sinus venosus
sudden infant death syndrome
cot death
caused by abnormalities of conducting tissue
what does the truncus arteriosus become in adults
aorta
pulmonary trunk
what does the bulbus cordis become in adults
smooth part of RV and LV
what does the primitive ventricle become in adults
trabeculated part of RV and LV
what does the primitive atrium become in adults
trabeculated part of RA and LA
what does the sinus venosus become in adults
smooth part of RA
coronary sinus
oblique vein of LA
aetiology of congenital heart disease
multifactorial
rubella infection in pregnancy (PDA)
maternal alcohol abuse (septal defects)
maternal drug treatment and radiation
gentic - 8%
chromosomal - 2% (Down’s and Turner’s syndrome)
congenital heart disease - VSD and ASD
VSD and ASD account for ~30% of congenital heart disease (VSD 20%, ASD 10%)
girls have ASDs twice as often as boys
VSDs are also slightly more common in females than males
transposition of the great vessels
common cause of cyanotic disease in newborns
associated with ASD and VSD
permit exchange of systemic and pulmonary circulation
causes:
- failure of aorticopulmonary septum to take a spiral course
- defective migration of neural crest cells
e. g. tetralogy of Fallot
Tetralogy of Fallot
made up of 4 cardiac defects:
- pulonary stenosis (obstruction of RV outflow)
- VSD
- dextroposition of aorta (overriding aorta)
- RV hypertrophy
cause: unequal division of the conus due to anterior displacement of aorticopulmonary septum
what are the 2 methods by which blood vessels develop
vasculogenesis - the new formation of a primitive vascular network
angiogenesis - the growth of new vessels from pre-existing blood vessels
formation of aortic sac
extension of TA of primitive heart tube
first arteries to appear in the embryo are R and L primitive aortae
each primitive aorta has a ventral and dorsal part
after the fusion of the 2 endothelial tubes the 2 ventral aortae partially fuse to form aortic sac
aortic branches arise from the aortic sac
development of pharyngeal arch arteries and aortic branches
pharyngeal arches (future neck) develop during week 4-5
each arch recieves its own nerve and artery
pharyngeal arteries communicate with aortic branches (now called aortic arches)
6 aortic arches are formed on each side, all are in communication with the dorsal aortae
where do the aortic arches form from and how many are there
pharyngeal arch arteries join aortic branches to form aortic arches
6 pairs of aortic arches develop from aortic branches and pharyngeal arch arteries
all are not present at the same time
they all terminate in the dorsal aorta
fate of the aortic arches
1 and 2: both disappear early, remnant of arch 1 forms part of the maxillary artery (branch of external carotid)
3: constitues the commencement of the internal carotid artery (is named the carotid arch), same on R and L
4: R - R subclavian, L - distal part of aortic arch
5: either never forms or forms incompletely and then regresses
6: R - proximal part persists as the proximal part of the R pulmonary artery , L - L pulmonary artery and forms the ductus arteriosus, (within 1-3mths the ductus is obliterated and becomes the ligamentum arteriousum)
cause of great arteries anomalies
most defects arise as a result of persistence of aortic arches that normally should regress or regression of arches that normally shouldnt
aberrant R subclavian artery
with regression of the R 4th aortic arch and the R dorsal aorta, the R subclavian a sometimes has an abnormal position on the L side.
To supply blood to the R arm this forces the R subclavian a to cross the midline behind the trachea and oesophagus, which may constrict these organs
usually has no clinical symptoms
double aortic arch
occurs with the non-regression of the R aortic arch
i.e. abnormal R aortic arch in addition to the normal L aortic arch
forms a vascular ring around the trachea and oesophagus
usually causes difficulty breathing and swallowing
patent ductus arteriosus (PDA)
more frequent in females
common anomaly associated with maternal rubella infection - early pregnancy
cause - failure of muscular wall to contract, respiratory distress syndrome (low o2), lack of surfactant in the lungs
early symptoms are uncommon but in the 1st year of life include increased work of breathing and poor weight gain
uncorrected PDA may lead to congestive heart failure with increasing age
coarctation of the aorta
aorta is narrowed, normally in the area where the ductus arteriosus inserts
coarctations are most common in the aortic arch
can proximal to ductus arteriosus (preductal) or distal to it (postductal)
90% of cases coarctation occurs opposite the ductus arteriosus
theories of cause:
- incorporation of muscle tissue of DA into arch of aorta, when DA contracts after birth, part of the arch also constricts
- genetic/environmental
embryonic circulation
vitelline = yolk sac
umbilical = placental
cardinal = rest of the body
fate of vitelline arteries
embryo - supply the yolk sac
adult - represented by arteries to the foregut, midgut and hindgut
fate of umbilical arteries
before birth - paired branches of the dorsal aorta to placenta
after birth - proximal portion persists as internal iliac and superior vesical branches to urinary bladder
embryonic venous system
vitelline veins - blood from yolk sac to sinus venosus
umbilical veins - originate from placenta, oxygenated blood to the embryo
cardinal veins - draining the body of embryo
fate of cardinal veins
main venous drainage system of the embryo
form vena caval system by anastamosis among the veins
carry the blood from the head and lower body into the heart
venous system abnormalities
- result of not regressing as they should
double IVC at the lumbar level arising from persistence of the L sacrocardinal vein
absent IVC - lower half of the body is drained by the azygos vein which enters the SVC. The hepatic veins enters the heart the the site of the IVC
Left SVC - normally only have R one
double SVC
development of the lymphatic system
develops at end of week 6 around main veins
6 1y lymph sacs develop at the end of embryonic period
lymphatic vessels will join the lymph sacs later
foetal circulation shunts
- ductus venosus - shunts L umbilical vein blood flow directly to IVC, allows oxy blood from placenta to bypass the liver
- oval foramen - allows blood to enter LA from RA, bypasses lungs
- ductus arteriosus - allows blood that still escapes to RV to bypass the lungs
neonatal circulation changes after birth - closure of shunts and umbilical arteries
ductus venosus becomes ligamentum venosum of the liver
oval foramen closes after birth by tissue proliferation and adhesion of septal structures - fossa ovalis
ductus arteriosus obliterates to form ligamentum arteriosum
umbilical ateries ligamentous - medial umbilical ligament s
