Lecture 5+6 Flashcards
What does the heart develop from?
cardiogenic mesoderm
3rd week of development
formation of the heart tubes (angioblastic cords/endothelial strands)
heart tubes will fuse to form the tubular heart
Epicardium, myocardium, and endocardium development
Epi: from mesothelial cells arising from the external surface of the sinus venosus
myo: from myoblasts from the first heart field
endo: from the primitive heart tube
Transverse pericardial sinus
communicates between both sides of the pericardial cavity
formed from the degeneration of the central part of the dorsal mesocardium
in adult: posterior to aorta and pulmonary trunk, anterior to SVC
Subdivisions of the tubular heart?
- truncus arteriosus
- bulbous cordis
- primitive ventricle
- primitive atrium
- sinus venosus (receives paired veins)
Cardiac looping
days 23-28
Bulbus cordis and ventricle grow faster than other regions causing it to bend on itself
Dextrocardia and situs inverus
dextrocardia:
The L-loop positions the apex to the right instead of the left (D-loop, normal)
situs inverus:
major organs are reversed
Fate of the primitive atrium
becomes the right and left auricle
internal surface has a rough, trabeculated appearance
Fate of the left and right horns of the sinus venosus
left horn - mostly obliterates
remnants: the coronary sinus and the oblique vein of the LA
right horn - seen as the sinus venarum
smooth-walled part of RA
fate of the primitive ventricle
Trabeculated part of the wall of the right and left ventricles
Fate of the bulbous cordis
Majorly contribute to form outflow tracts of the right and left ventricles
- Right – conus arteriosus (infundibulum)
- Left – Aortic vestibule
Fate of the truncus arteriosus
left = ascending aorta
right = pulmonary trunk
End of the 4th week
partitioning of the AV canal:
AV endocardial cushions develop from the cardiac jelly and neural crest cells
the endocardial cushions grow towards each other and fuse (forms AV valves)
Formation of the right atrium and left atrium
Right atrium:
The right horn of the sinus venosus and the primitive atrium enlarge. The primitive atrium absorbs the right horn, thus forming the RA. Later becomes the sinus venarum.
Left atrium:
Primordial pulmonary veins forms the left atrium. These veins are incorporated into the walls of the LA.
Forms the oblique pericardial sinus which is an area of pericardium between the pulmonary veins
arterial partitioning (end of 4th week)
The septum primum grows from the roof of the atrium towards the endocardial cushions
foramen primum - space between inferior edge of septum primum and endocardial cushions.
The growth of the septum primum closes the foramen primum
foramen secundum: appear in septum primum
septum secundum grows downward, eventually overlapping foramen secundum
The opening between the free edges septum secundum and septum primum is called foramen ovale
Ostium secundum defect (atrial defect)
In the area of the fossa ovale
disrupted or absent septa
defects of both septa primum and secundum
usually leads to an patent/open foramen ovale
Endocardial cushion defect with a foramen primum defect (atrial defect)
septum primum - not fused with endocardial cushions
patent foramen primum defect
Sinus venosus defect (atrial defect)
located in the sinus venarum
Defect:
• incomplete resorption of the right horn of sinus venosus into the right atrium
•abnormal development of the septum secundum
• or a combination of these factors
Common atrium (ASD)
Prevalent in patients with ostium primum, ostium secundum and sinus venosus defects
Complete absence of interatrial septum
Partitioning of the common ventricle
Muscular interventricular septum develops first from myocytes from the primitive ventricle.
IV foramen allows for the communication between the right and left ventricles
Week 5
The bulbar ridges and truncal ridges will fuse to form the aorticopulmonary septum
this septum divides the truncus arteriosus and bulbous cordis into the pulmonary trunk and ascending aorta
The two types of VSD’s
Muscular:
No muscular septum results in a common ventricle
occurs anywhere throughout the septum (in isolation or “swiss cheese”)
membraneous: Most common
No membranous septum - incomplete closure of the IV foramen
What cardiac structures are derived from neural crest cells
- endocardial cushions
- bulbar ridges
- truncal ridges
- spiral septum
- membranous interventricular septum
- semilunar valves
- AV valves
- pharyngeal arches
What does increasing the resting muscle fiber length do?
increases the force of contraction (length-tension relationship)
this is done by increasing the preload such as blood volume
How can one increase the amount of force from a given length with no change in preload
Norepinephrine (NE) (beta-1 activation)
increases contractility (+ inotropic effect)
greater tension
increase Vmax
How do calcium blockers impact contractility
decreased contractility (- inotropic effect)
less tension
decrease Vmax
