Heart Development Flashcards
how do 2 endocardial heart tubes come together?
lateral folding causes them to come together ventrally and fuse
when does separation of the atria and ventricles begin to occur?
4th week
describe folding of the heart tube in the 4th week
the truncus arteriosus and bulbis cordis fold ventrally and caudally and to the right, while the primitive atrium/ventricle starts to fold dorsally, cranially and to the left
what is in the cranial end of the heart tube?
aortic arches
what is in the caudal end of the heart tube?
embedded within septum transversum (thick mass of cranial mesenchyme)
6 primitive divisions of the heart tube?
- aortic arches (1)
- truncus arteriosus
- bulbis cordis
- primitive ventricle
- primitive atrium
- sinus venosus
when does the heart begin to contract and circulate?
day 22 and day 24
where is the primitive SA node?
sinus venosus
heart rate of fetus
less than 100 early in development, and increases to 170 by end of 1st trimester, decreases to 100 at birth
what are the common cardinal veins
on each side of the sinus venosus, veins drain head, trunk and limbs of fetus into sinus venosus, becomes superior vena cava
3 main veins of fetal circulation
common cardinal veins, vitelline veins, umbilical veins
what re the vitelline veins?
drain the primitive gut tube into the sinus venosus, moves anteriorly to the yolk sac to anastamose with the vitelline artery, combines with common cardinal veins to make SVC
what makes up the inferior vena cava?
- anterior and posterior cardinal veins
- subcardinal veins
- supracardinal veins
**slides say right vitelline vein
what are umbilical veins?
oxygen rich blood from the trophoblast, dumps into the sinus venosus
what do the posterior cardinal veins do posteriorly?
anastamose together and form iliac veins
what do anterior cardinal and common cardinal veins on the left side give rise to?
brachiocephalic vein and left subclavian vein
what is the fate of umbilical vein and vitelline vein on the LEFT side?
degenerate
what gives rise to the SVC?
vitelline vein on right side, common cardinal vein on the right side
where does the venous inflow shift during development?
to the right
steps of sinus venosus development
- left horn decreases in size and becomes the coronary sinus
- right horn enlarges and receives venous drainage from all of embryo via newly formed superior and inferior vena cavae
- sinoatrial orifice shifts to the right and empties into the right atrium - right sinus horn incorporated into the right posterior wall of primitive atrium
what does the left sinus horn become?
coronary sinus
what does the right sinus horn become?
superior and inferior vena cavae
what does the right sinus horn develop into?
- incorporates into the right posterior wall of primitive atrium
- forms smooth walled portion of adult right atrium (sinus venarum)
what does the right half of the sinuatrial valve form?
- crista terminalis
- valve of the inferior vena cava
- valve of the coronary sinus
what does the original right atrium contain
pectinate muscles and right auricle
steps of development of the left atrium
- trunk of pulmonary venous system is incorporated into the posterior wall of the left atrium
- single pulmonary vein grows out from the left atrium to the lungs
- as left atrium expands, more and more of pulmonary vein and its branches become incorporated into its wall
- incorporated part of pulmonary veins forms smooth walled portion of left atrium
- left auricle is the remains of the primordial left atrium - rough wall
what is the left auricle
remains of primordial left atrium, has more rough wall (pectinate) (left atrium has less pectinate than right)
what are the atrioventricular canals made from?
endocardial cushions
how are the atria divided?
- septum primum grows down from the atrial roof toward the endocardial cushions (foramen primum is the “gap” between future right and left)
- foramen secundum begins to form as septum primum grows down to the endocardial cushions
- foramen primum closes (septum primum is closed) but then foramen secundum opens
- septum secundum (thicker and muscularly) forms from atrial roof incompletely parallel to septum primum - leaves opening FORAMEN OVALE
- septum primum (thin) forms a one way valve through the foramen ovale from IVC directly to the LA
mechanism by which foramen ovale is closed at birth
in the womb, the pressure in the right atrium is higher than the left, due to the lack of pulmonary circulation, so the blood shunts through foramen ovale, opening the valve of septum primum.
when born, the lungs fill with air and increase pressure in the left atrium, causing increased pressure in left. the blood pushes against the septum primum valve and closes it.
what forms the division of the ventricles?
muscular septum and membranous septum
what forms the outflow tract
aorticopulmonary septum
how are the atrioventricular canals formed?
- localized proliferations (start to pinch) of tissue along midline of dorsal and ventral walls of the AV canal form endocardial cushions
- dorsal and ventral endocardial cushions grow toward each other and fuse to form left and right AV canals
division of the outflow tract
- bulbar and truncal ridges take spiral course through outflow tract and grow inward toward each other (rotate 180 degrees)
- bulbar and truncal ridges fuse to form aorticopulmonary septum
- aorta and pulmonary trunk formed
how do the semilunar valves develop
swellings in the truncus arteriosus -
pathway of septation of ventricles (mostly muscular)
- end of 4th week, muscular interventricular septum incompletely separates the ventricles (from apex of common ventricle), leaving an interventricular foramen temporarily between ventricles
- then, a thin membranous septum closes the interventricular foramen (arises from endocardial cushion)
pathway of membranous interventricular septum
left and right bulbar ridges migrate inferiorly to fuse with endocardial cushions
what is cavitation of the myocardium
organized degeneration of the inner muscular wall of ventricles, forms trabeculae carneae, atrioventricular valves, papillary muscles, chordae tendinae
what disorders are hypoplastic right heart syndromes?
- patent ductus arteriosus
- hypoplastic right ventricle
- small tricuspid valve
- stenotic/underdeveloped pulmonary valve
- atrial septal defects
*decreased blood flow through right ventricle and pulmonary trunk, so the ductus arteriosus stays open to try and normalize blood flow
what disorders are hypoplastic left heart syndrome?
- hypoplastic ascending aorta
- coarctation of the aorta
- atrial septal defect
- atretic or stenotic mitral valve
- hypoplastic left ventricle
*ductus arteriosus stays open but the blood is deoxygenated so it is inefficient, and the left ventricle tries to pump a lot to compensate for narrowed aorta and small ventricle size.
possible causes of atrial septal malformations
excessive resorption of the septum primum, failure of development of the septum secundum, or complete failure of either to form due to insult to embryo that would delay growth
result of ASM
allows mixing of blood between left and right atria
what is septum primum malformation
the septum primum failed to completely fuse with the endocardial cushion, so a hole is left between the atria - can also cause malformations in AV valves
what malformation is commonly seen in Downs Syndrome?
septum primum malformation
what is the most common malformation?
ventricular septal malformations (high membranous - bc muscular usually resolves itself)
what is muscular septal malformations
more common than membranous, muscular IV septum does not close, but is usually RESOLVED in childhood
what is membranous ventricular septal malformation
failure of fusion of interventricular septum with the endocardial cushion - does NOT correct itself
consequence of ventricular septal malformations
bc of high pressure in left ventricle, even small holes can cause jets of blood from left to right, therefore, increased blood in right ventricle, rigth ventricle hypertrophy
what are truncus arteriosus malformations
failure of spiral septum of truncus arteriosus, affects ascending aorta, pulmonary trunk, and semilunar valves - can be extremely serious or fatal
what is persistent truncus arteriosus
failure of truncus to separate at the beginning of the outflow tract - right at the bifurcation of the common opening, therefore, no separation of blood flows and no aortic or pulmonary valves
what does persistent truncus arteriosus indicate
an automatic ventricular septal malformation because the truncus separation occurs concurrently with ventricular separation
what is the unequal division of truncus
one vessel has a large opening, one has a small opening, usually involves ventricular septal malformation so the right ventricular blood gets into the aorta
consequence of small pulmonary trunk (stenosis)
patent ductus arteriosus to relieve the increased pressure in the trunks d/t small size, therefore, deoxygenated blood in aorta, right ventricle hypertrophy
consequence of small aorta
increased pressure in aorta causes blood to shunt into the pulmonary trunk via patent ductus arteriosus and recirculates oxygenated blood, left ventricle hypertrophy — kind of hypoplastic left heart syndrome
what are the 4 characteristics of Tetralogy of Fallot
- pulmonary stenosis
THEN TO COMPENSATE
- membranous ventricular septal malformation
- overriding aorta
- hypertrophy of right ventricle
(5. may have persistent ductus arteriosus or artial septal malformation to compensate)
what is an overriding aorta
aorta sits right over the interventricular septum, collecting blood from both ventricles - shifted over toward left, so it gathers left and right ventricular blood thanks to the ventricular defect
what is transposition of the great vessels
septum is straight, not spiral, so right ventricle pumps to aorta and the left ventricle pumps to the pulmonary trunk, so there is no oxygenated blood being circulated to the systemic circulation
adaptations of transposition of great vessels
for survival, a ventricular septal defect or atrial septal defect or patent ductus arteriosus contributes to the mixing of blood - only source of oxygenated blood to the aorta
what is ectopia cordis
failure of sternum to fuse, so heart is outside of the thoracic cavity
what is dextrocardia
reverse rotation, so heart lies on the right side of the thorax - associated with sinus inversus (so there are little problems, but still developmental defects)
what are the aortic malformations
- persistent ductus arteriosus
- coarctation of the aorta
what is persistent ductus arteriosus
ductus arteriosus continues to function, allows pulmonary bypass, increased blood in pulmonary trunk coming from the higher pressured aorta, causing right ventricule hypertrophy and sending oxygenated blood to the lungs again, causes pulmonary hypertension
what is coarctation of the aorta
inexplicable narrowing of aorta near ductus arteriosus
characteristic of coarctation of the aorta
blood pressure to upper extremities increased and blood pressure to lower extremities is minimal (compare brachial pulse to femoral pulse - brachial would be greater, femoral would be almost nonexistent)
what is preductal coarctation of the aorta
narrowing before the ductus arteriosus, so ductus arteriosus persists so it can supply poorly oxygenated blood to lower body
what is postductal coarctation of the aorta
narrowing after ductus arteriosus, which is actually closed and now the ligamentum arteriosum, so blood to abdomen and lower limbs is supplied through anastamoses with intercostal arteries
what does the aortic sac give rise to?
- ascending aorta
- right brachiocephalic trunk
what does the truncus arteriosus give rise to/
- proximal part of ascending aorta
- pulmonary trunk
what does the 3rd aortic arch give rise to?
- left and right common carotid
- left and right internal carotid
what does the 4th aortic arch give rise to?
right arch: part of right subclavian artery
left arch: part of aortic arch
what does the 6th arch give rise to?
right arch: right pulmonary artery
left arch: left pulmonary artery, ductus arteriosus/ligamentum arteriosum
what does the dorsal aorta give rise to?
right side: part of right subclavian artery
left side: arch of aorta and descending aorta
what does the bulbar septum give rise to
interventricular septum inferior to the aorticopulmonary septum, eventually fusing with it
most common VSD
membranous ventricular septal defect
what causes pulmonary trunk stenosis in tetralogy of fallot?
superior malalignment of the subpulmonary infundibulum
what localizes a defect in an AV valve?
systolic murmur at S2
what does transposition of great arteries cause during exam?
murmur at S1
what does aortic stenosis present
murmur at S1
what characterizes VSD during exam?
pansystolic murmur
what malformations are associated with Downs Syndrome
arrhythmias, atrial SD, ventricular SD SEPTUM PRIMUM MALFORMATION
what disorders are associated with diGeorge syndrome aka 22q11 syndrome?
tetralogy of fallot and truncus arteriosus
what disorder is associated with maternal diabetes?
transposition of the great arteries
what disorders are associated with Turners syndrome
coarctation of the aorta
what cells synthesize surfactant in the lungs/
type II alveolar cells
what aortic arches are related to coarctation of the aorta?
3rd, 4th, and 6th aortic arches assist in aortic formation
what infections could lead to patent ductus arteriosus
rubella or other teratogens
where are sinus venosus ASD located?
close to entry of superior vena vava in superior portion of interatrial septum
where are ostium secundum ASDs found
located near fossa ovale, encompass both septum primum and secundum defects
what is ostium primum
less common form ASD, associated with endocardial cushion defects, septum primum fails to fuse with endocardial cushion, results in patent foramen primum.
fate of right horn of sinus venosus
incorporates into the right atrial wall
- one develops into sinus venarum - smooth interior aspect of right atrial wall
- other develops into pulmonary veins
*abnormal septation can lead to inappropriate pulmonary connections
what is the left 6th aortic arch responsible for
both pulmonary arteries and ductus arteriosus
