Lecture 5 (Heart Development) Flashcards
What organ is the first to begin functioning?
the heart
By what day are the two heart tubes formed?
Day 20
What happens on day 21 with the endocardial tubes?
they fuse into the primitive heart tube
When does the heart begin to beat?
day 22 (after fushion of heart tubes)
What four major events happen to the primary heart tube from wks 4-8?
- looping/folding
- remodeling
- realignment
- septation
What process brings the two endocardial tubes together so they can fuse?
lateral body folding
On day 23, the heart begins to:
loop
Heart looping is complete by:
Day 28
The septum primum begins forming when the heart looping is complete on day:
28
What endocardial tissues form during week 5?
cushions
Atrioventricular endocardial cushions fuse to form __________ around day _____.
atrioventricular septum
day 42
In week 7, what structure is formed by the septum primum and Secundum?
forman ovale
What happens to the outflow tract of the heart around week 8?
they become fully septated thanks to fusion of outflow tract cushions
ventricular septation is completed by:
joining of outflow tract, atrioventricular, and muscular interventricular septa
Where is the cardiogenic field established?
cranial to neural plate
What forms in the visceral layer of lateral plate mesoderm cranial to developing brain then coalesce?
blood islands
What primitive structure forms as blood islands coalesce in the cardiogenic field?
primitive heart tube - horseshoe-shaped endothelial tube
The cardiogenic field becomes established in week:
3
What master regulator is responsible for heart development?
NKX-2.5
What morphogens are responsible for expression of NKX-2.5 in the cardiogenic field?
upregulation of BMPs
downregulation of WNTs
How many cardiac fields form? What are they called?
2 - primary and secondary
What else is occurring as the body folds to bring the heart tubes together?
midgut remodeling, vitelline duct is constricted, liver and lung buds form
The caudal end of the heart tube is the ______ end
venous
the cranial end of the primitive heart is the _______ end. What sprouts from here?
arterial.
vessels.
The sprouted vessels of the cranial end of the heart become the:
aortic arches.
Which signaling molecules are responsible for lopping and sidedness? What other signals do these repress?
NODAL and LEFTY2 -> PITX2
BMP and WNT are repressed
NKX2.5 leads to the expression of which two signaling molecules?
HAND 1 and HAND2
HAND1 expression leads to development of ->
left ventricle
HAND2 expression leads to development of ->
right ventricle
After looping, the heart is on the _____ side of the body.
left
What is dextrocardia?
when the heart is on the right side of the body instead of the left due to an error in looping
Which ways do the atrial and ventricular regions of the heart grow during looping?
atrial = up and left ventricular = down and right
What days does heart looping occur?
22-24
By day 24 what L and R structures have formed?
sinus horns
What happens to the sinus horns by day 35?
R sinous horn has fused with the atrium
L sinus horn has formed the coronary sinus and oblique vein of left atrium
What is happening in the atria from days 27-37?
septal formation
What has occurred btwn the atria and ventricles by day 33?
they have been separate by the usion of endocardial cushion
By day 37, what separates the right and left atrium?
the septum primum and secundum
What structure is formed by the septum primum and secundum?
the foramen ovale
What is forming in the ventricules around the same time as the foramen ovale? day?
ventricular septum
By what week have the atrioventricular valves formed? What do they form from?
7th week
endocardial cushion
Septation of the outflow tract of the heart is occurring around day:
35.
Heart septation is complete by week:
8
When do neural crest cells migrate to the heart?
3.5-4 weeks
What is the most common type of heart defect? Where do most of them occur?
interventricular septal defects
most occur in muscular portion of the septa, others occur in membranous portion
How does transposition of the great vessels occur? What is considered the cause?
conotruncal cushions dividing the outflow tract fail to rotate 180 degree
neural crest related abnormality
What condition is characterized by four distinct cardiac abnormalities appearing together? What is the believed cause?
tetraology of fallot
neural crest cells
What is responsible for the transition to post natal blood flow?
pressure causing the foramen ovale to close
Mutations in which gene cause ASDs and atrial conduction delays?
NKX2.5
Mutations in what gene can cause Holt-Oram syndrome, preaxial limb defects w/ ASDs, and heart-hand syndromes?
TBX5
How do blood vessels form?
vasculogenesis and angiogenesis
What things form from vasculogenesis?
the heart and major vessels
What things form through angiogenesis?
smaller vessels
What molecules are necessary for vessel formation?
VEGFs
Which aortic arch doesn’t form?
5th
Which aortic arches form first?
the most cranial form and differentiate as the more caudal ones form
which aortic arches from major vessels? List all.
3rd -> carotid system
4th -> right: subclavian, left: arch of the aorta
6th -> pulmonary arteries and ductus arteriosus
