Embryology of the heart Flashcards
which week does formation of the heart start
week 3
what day does the first contraction of the heart occur
day 22
what are the three layers of the heart and what did they derive from
epicardium - visceral layer of the pericardium and is also derived from the visceral mesoderm
myocardium - derived from the visceral mesoderm overlying the heart tube
endocardium - derived from the heart tube
when does vasculogensis occur and what is it
day 17/18
the endoderm induces some cells of the overlying visceral/splanchnic mesoderm to differentiate into angioblasts
angioblasts differentiale into endothelial cells and form tubes - endocardial tubes
endocardial tubes fuse during when
lateral folding
to form the primitive heart tube
how is the myocardium made and what is its role
the visceral mesoderm surrounding the primitive heart tube differentiates to form the myocardium
the myocardium secretes a thick layer of ECM - cardiac jelly
what is cardiac jelly
gelatinous connective tissue separating the myocardium and heart tube endocardium
what occurs in the caudal and cranial regions
caudal - 3 paired veins drain into the tubular heart of a 4 week embryo via the right and left horn of the sinus venosus
cranial - connects to 2 dorsal aortae
what are the 5 dilation of the heart
what is the direction of blood flow
truncus arteriosus concus arteriosus ventricle atrium sinus venosus blood from from the sinus venosus to the truncus arteriosus
what is the bulbus cordus made from
the truncus arteriosus and conus arteriosus
what day does the heart tube start to fold
day 23
during heart tube folding what is the direction of these sections
bulbus cordus
primitive ventricle
primitive atrium
BC - moves caudally, ventrally and to the right
PV - displaced before moving back to midline
PA - displaces cranially and dorsally
what happens to the remnants of the sinus venosus
largely degenerates in week 5
remains as part of the wall of the right atrium (right horn) and contribute to the venous drainage (left horn) of the heart
what does the left horn of the sinus venosus form in week 5
forms the oblique vein of the left atrium and coronary sinus
what does the right horn of the sinus venosus form in week 5
forms part of the smooth walled part of the right atrium - sinus venarum
why is the heart got both smooth and rough sides
right horn forms smooth part from sinus venosus - sinus venarum
rough part is formed from the primitive atrium and appears rough - trabeculated
what is the border between the traebeculated and the smooth part of the heart called
crista terminalis
what is the majority of the ventricular wall formed from
the primitive ventricle with a small contribution from the conus arteriosus
what does the conus arteriosus from
smooth walls of the left and right ventricle which lead to the aorta and pulmonary trunk
what is the rough part of the ventricle formed from
from the primitive ventricle - trabeculae carnae
how are the pulmonary veins created
left atrial wall from a single pulmonary vein - this branches into left and right which then bifurcate to form 4 pulmonary veins
what is intussusception
in week 5 - the 4 pulmonary veins are incorporated into the wall of the left atrium
what is septation of the primitive atrium
division into left and right atria
begins at the end of week 4 with a crescent shaped outgrowth from the dorsal wall - spetum primum
what is the connection between the left and right sides of the primitive atrium called
foramen primum
describe the process of septation of the primitive atrium
spetum primum extends into the atrium , endothelium lining expands to form the dorsal and ventral endocardial
these fun in the midline to from the AV septum creating channels between the future A and V
what happens in week 6 of septation of the primitive atrium
septum primum has fused with AV spetum
apoptosis occurs in the upper pat of the septum primum to from the foramen secundum
a second crescent shaped projection from the dorsal wall of the atrium septum secundum
describe the process of septation of the primitive ventricle
end of week 4 a muscular part projects from the floor of the primitive ventricle towards endocardial cushions leaving an IV foramen
membranous part that projects inferiorly from the endocardial cushion to close the inter ventricular foramen in week 8
what happens to the truncus arteriosus
divided into two channels by endocardial swellings - conotruncal ridges (swellings)
these fuse to form a spetum (conotruncal septum) and fuses with interventricular septum
why don’t the contruncal swellings fuse in a straight line
spiral round each other so that the right ventricle connects with the pulmonary trunk and the left ventricle to connect with the aorta
what is special about the conotruncal swellings in terms of cells
contain neural crest cells which are sometimes referred to as the 4th germ layer
these migrate laterally and ventrally to produce various structures throughout the body
how does the mothers circulation affect the foetus’
mothers is oxygenating and detoxifying blood therefore foetal circulation shunts blood away from the lungs and liver
describe the path of foetal circulation
oxygenated blood enters through the umbilical vein
most enters the ductus venosus (some enters the liver) to bypass the liver and enter the inferior vena cava
IVC enters the right atrium and most of the blood passes through the foramen ovale to the left atrium, left ventricle and aorta
this is because blood entering the right atrium from the vena cava is poorly oxygenated (from lungs)
what happens to circulation after birth
termination of the umbilical circulation causes the ductus venosus to close and degenerate - ligamentum venosum in adult
the first breath dilates the pulmonary arteries and the foramen ovale is closed by compression of the spetum primum and septum secundum - this is the fossa ovalis in adults
what effect does the first breath have on the ductus venosus
constricts it to form the ligamentum arteriosum in adult
what is dextrocardia
result from abnormal cardiac looping which may be induced via gastrulation in week 3 when laterality is determined
also concerned with abnormal septation of the heart
what is patent ductus arteriosus
normally the ductus arteriosus closes at birth due to increasing oxygen tension
patent - after birth allows shunting of blood from the aorta to the pulmonary artery - increases the workload of the heart which can lead to pulmonary hypertension, V hypertrophy and heart failure
how do you treat patent ductus arteriosus
prostaglandin inhibitors
what are atrial septal defects and how are they caused
failure of the spetum primum and secundum to fun after birth - probe patent foramen ovalen
caused by non overlapping (more commonly due to malfunction in the secundum)
what is probe patent foramen ovale
occurs 1 in 4 people
asymptomatic
usually high pressure in LA pushes the two septum together to shut the valve
if there is high pressure in RA then it may allows shunting from right to left
may lead to stroke or migraine
what is osmium secundum defects
can be caused by excessive apoptosis in spetum primum or by inadequate development of the septum secundum
blood is shunted from left to right and causes hypertrophy of L A/V
what is cor triloculare biventriculare
common atrium
complete absence of atrial spetum
failure of development of the septum primum and secundum
what does premature closure of the foramen ovale do
closure during prenatal life
hypertrophy of the right side of the heart and underdevelopment of the left - death shortly after birth
what is the most common congenital heart defect
ventricular septal defects
what is the result of ventricular septal defects
left to right shunting - pulmonary hypertension, hypertrophy of right ventricle
how do septation defects of the truncus arteriosus occur
abnormal neural crest cells development from the neural tube
what are the three types of defects of the truncus arteriosus
persistent arteriosus, transposition of the great vessels, tetralogy of fallot
what is persistent truncus arteriosus
symptoms and correction
contruncal septum completely absent therefore cannot due with the interventrciular septum
aorta and pulmonary artery receive both types of blood
cyanosis at birth, lethargy, delayed growth
must be corrected surgically or will result in heart failure
what is transposition of the great vessels
conotruncal septum does not form in a spiral but goes straight down and aorta arises from the right ventricle and PA from the LV
this is incompatible with life unless it exists with patent foramen ovale or patent ductus arteriosus
what are the 4 parts of tetralogy of fallot and how often does it occur
pulmonary stenosis
ventricular septal defect
overriding aorta (rightward displacement)
RV hypertrophy caused by higher pressure on the right side
occurs in 1 in 1000 live births
what is coarctation of the aorta
narrowing of the aorta near the ductus arteriosus
idiopathic but maybe due to abnormal migration of cells from the ductus arteriosus
what is preductal coarctation of the aorta
how do you treat it
ductus arteriosus compenstates for the narrowing - remains patent after birth
obliteration of the ductus arteriosus causes rapid decline of infant with hypoperfusion to the lower limb
prostaglandins help keep the ductus arteriosus open
what is post ductal coarctation
more common than pre
during development collateral circulation is established to bypasss narrowing
blood goes through subclavian to internal thoracic arteries to the intercostal arteries to the descending aorta
causes enlargement of internal thoracic and intercostal arteries
