development of the heart Flashcards
what are the 3 germ layers?
endoderm
mesoderm
ectoderm
what is derived from the endoderm?
gut and associated derived tissues (liver, pancreas and lungs)
what is derived from the mesoderm?
bones, connective tissue, skeletal muscle, urogenital system, cardiovascular system
what is derived from the ectoderm?
skin, CNS, PNS, eyes, internal ear
what does the early heart develop from?
cardiogenic mesoderm (lateral plate) originally lying above the cranial end of the developing neural tube
what are the first stages of forming the primitive heart?
angiogenic cell clusters coalesce forming right and left endocardial tubes
Lateral folding of embryo results in fusing of paired endocardial tubes to form primitive heart tube
what is the truncus arteriosus?
proximal aorta and pulmonary artery
what is the bulbus cordis?
ventricular outflow tracts
right ventricle
what is the primitive ventricle?
left ventricle
what is the primitive atria?
left and right atria
what is the sinus venosus?
smooth part of right atrium and coronary sinus
what is the length of the endocardial tubes limited by and how?
limited in length by the pericardium
tube folds within the pericardium –> puts chambers and vessels into similar alignment to the adult heart
when does the heart tube fold into the pericardium?
between days 23 and 28
what is the first step in separating the atria and ventricles?
septum formation in the atrio-ventricular canal
how does septum formation occur in the atrio-ventricular canal and when?
at 28 days, 2 endocardial cushions appear from the walls of the canal
they grow and fuse together to divide canal into right and left
what is the septum primum?
grows from the top of the atria towards the endocardium cushion
what is the ostium primum?
space between the inferior edge of the septum and the cushion
what is the ostium secundum?
second hole that forms in the septum
when does the ostium primum close?
once the ostium secundum has formed
when does the septum secundum form?
when the septum primum reaches the endocardial cushions
what is the foramen ovale?
the valve from the right atrium to the left atrium that’s formed from the 2 septums that form - allows blood to bypass the pulmonary circulation
why does the foramen ovale stay open before birth?
higher pressure in the RA than the LA so the septum primum is opened and the foramen ovale is open
why does the fossa ovalis close after birth?
higher pressure in the left atrium so the septum primum closes and so does the fossa ovalis
when does probe patent foramen ovale occur?
- occurs when the foramen ovale doesn’t completely close
- hole is big enough to pass a probe through it
how many people does the probe patent foramen ovale occur in?
25% of people
why is a probe patent foramen ovale not very significant?
bc it’s a valve so as long as there’s a higher pressure in the LA then the valve won’t open
are atrial septal defects more common in women or men?
women
what part of the heart is affected in atrial septal defects?
defect in either the septum primum or the septum secundum
why are atrial septal defects serious?
not a valve so blood flows from the left to the right side of the heart
how does ventricular septation occur?
AT 28 days a muscular IVS develops from floor of primordial ventricle and grows to the endocardial cushion
- membranous components grows down from the cushion to the muscular component which is growing upwards and they fuse
what is the most common type of cardiac defect?
ventricular septal defect - 25%
how many VSDs will close spontaneously?
30-50%
how many VSDs are in the membranous septum and how many are in the muscular septum?
90% - membranous septum
10% - muscular septum
how does right sided hypertrophy occur?
• Hole in ventricular septum means blood shunts from the left to the right which causes pulmonary hypertension right sided hypertrophy of the heart
what is the purpose of outflow tract septation?
split up the aorta and the pulmonary artery
how does outflow tract septation occur?
truncoconal swelling form in the truncus arteriosus and grow towards each other in a spiral structure
aorta therefore connects with the left ventricle and the pulmonary trunk with the right ventricle
what is the function of the ductus venosus?
shunts blood from umbilical vein to IVC
what does the foramen ovale become when it’s closed?
fossa ovalis
what is the function of the ductus arteriosus?
shunts blood from pulmonary trunk to ascending aorta (bypassing lungs)
what do the ductus arteriosus and ductus venosus fibrose to become?
ligamentum arteriosus and venosus
what are acyanotic congenital heart diseases?
a group of cardiac diseases with a left to right shunt or left heart abnormality which doesn’t result in cyanosis (blue skin colour) of baby
what proportion of heart diseases does ACL make up?
1/3 of congenital heart disease
name common acyanotic heart lesions
Atrial Septal Defects (ASD), Ventricular Septal Defects (VSD), Patent Ductus Arteriosus (PDA), Coarctation of the aorta
what does a small patent ductus arteriosus increase the risk of?
bacterial endocarditis
what is the treatment for patent ductus arteriosus?
give prostaglandin inhibitors
e.g. ibuprofen
if it doesnt close then surgical closure with a clip is done in infants older than 3 months
what are the types of coarction of the aorta?
- Constriction may be above or below the ductus arteriosus (pre-ductal, post-ductal)
- In pre-ductal types, ductus arteriosus persist allowing blood flow.
- In Post-ductal collateral circulations must be established for proper perfusion of body and legs
what are cyanotic heart lesions?
a group of cardiac diseases that allow deoxygenated blood to bypass the lungs and enter the systemic circulation
body tissue therefore has less oxygen than they require –> baby is cyanosed
give examples of cyanotic congenital heart disease
o Tetralogy of Fallot
o Persistent truncus arteriosus
o Transposition of the great vessels
what are the 4 different defects of the tetralogy of fallot?
1) Ventricular septal defect
2) Overriding aorta – sitting over the top of the VSD so you only have mixed blood going into the aorta
3) Pulmonary stenosis – narrow pulmonary trunk
4) Right ventricular hypertrophy
what is a persistent truncus arteriosus?
when a single artery arises from the heart to supply both the aorta and the pulmonary artery
a large VSD below truncal valve allows mixing of the right and left ventricular blood
what is transposition of the great vessels?
pulmonary trunk leads out of LV and aorta out RV
• Other defects alongside this e.g. ASD or VSD which allow some oxygenated blood to be circulated
what intervention has to occur when a baby is blue?
immediate surgical intervention – catherterisation of fossa ovalis to increase mixing of pulmonary and systemic blood– buy time till infant can be operated on at a later date
