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)