Cardio Devo Flashcards
Where are Cardiac Precursors located?
Where are the specification and migration signals from?
Splanchnic Mesoderm
Anterior Endoderm
What is acardia and its cause?
Lack of heart formation due to mutation in Nkx2.5 (Tinman)
What do precursor cells in the heart field express?
Nkx2.5
Where is the endocardial heart tube located?
Bilaterally adjacent to foregut
How is the ventral heart formed? How are the heart primordia united?
Heart initially is cranial to the brain but folding in the cranial-caudal plane pulls the heart down to be ventral and inferior to head
Folding in the transverse plane unites the heart primordia in the midline
What is ectopia cordis? What causes it?
Heart is outside of body
Anterior thoracic wall fails to close properly
What is the pentalogy of cantrell?
- Ectopia cordis
- Ventricular septal defect
- Sternal cleft
- Diaphragmatic hernia
- Omphalocele
These all common to a body wall closure defect
What is important to know about the classical concept of heart tube formation?
It’s wrong.
What does the primitive heart tube become? What neighbors the primitive heart tube? Do the primitive heart segments become the mature chambers?
Primitive left ventricle
The arterial and venous poles which result in the other primitive heart segments
Do the primitive heart segments become the mature chambers? ⇒ No
Where is the secondary heart field located? What does it originate from? What is the master gene for it? What is its purprose?
Medial and dorsal to the primary heart field
Originates from splanchnic mesoderm
Isl-2 is master gene
Allows for elongation of the Primiitive heart ventricle, outflow region, primordial atrium, AV canal, sinus venosus
What are the layers of the primitive heart tube? What is the external fourth layer?
From inside to outside:
Endocardium
Cardiac jelly - ECM of GAGs and glycoproteins
Myocardium
Proepicardilal organ coming from coelomic epithelium and
What do cardiogenic precursors become?
- Mesoderm:
- Endocardial Endothelial cell which also form Cushion cells
- Atrial myocyte
- Ventricular myocyte which also forms Purkinje Fibers
- Neural Crest: Aortic Smooth Muscle Neuron
- Proepicardium:
- Coronary smooth muscle
- Endothelial cell
- Fibroblast
Where does venous inflow enter? What are the major veins, what do they drain, and is the blood oxygenated?
Venous inflow enters sinus venosus
Umbilical veins - Placental blood, O2 rich
Vitelline veins - Gut blood, O2 poor
Common cardinal veins - Blood from head and trunk, O2 poor
Where does arterial outflow start? Where does the aortic sac flow to?
Arterial outflow from primitive RV
- Aortic sac - Pharyngeal arch arteries
What is the first step in chamber formation and partitioning?
Cardiac looping
When does the primitive heart tube begin to loop? Which direction does it loop toward? Where is the apex of the loop located?
Looping begins soon after heart tube formation
Loops typically to right
Apex of loop located between primitive and right ventricle
What does right torsion help result in? What happens to the chambers during looping?
Right torsion helps form the inner and outer curvatures
During looping atria and ventricle chambers expand due to ballooning
What is dextrocardia? What is the cause of this? What is it typically associated with?
Right-sided mirror image heart
Turns left due to a cilia abnormality which doesn’t force the heart to twist to the left
Associated with situs inversus (all of abdominal organs flipped), 5-10% have other cardiac abnormalities (TGA)
What are changes resulting from early phase looping and torsion?
- Proper anatomical relationships between segments
- Outflow and inflow regions brought together
- Outflow region forms and elongates into proximal and distal regions
- Distal outflow region continuous with aortic sac
What changes result from late phase looping and torsion?
Caudal and cranial limbs contact at AV canal level via bending at inner curvature
Proximal portion of the outflow region is “wedged” into the AV canal (due to twisting/torsion)
What is the timeline of heart beating?
Begins to beat at 21-22 days: Initially back and forth flow
Flow becomes unidirectional by day 26
2 separate streams leave the heart by day 28
Timeline of development of right atrium
Definitive right atrium forms from primitive right atrium and parts of sinus venosus
Day 22 - Right horn of SV connects to right side of primitive atrium, left horn to left side of atrum
Day 24 - A common SV opens into atrium via the sinoatrial opening, sinoatrial opening flanked by right and left valves
Weeks 5-8: SV is absorbed into the right atrium and venous connections to the SV are lost or remodeled
- Left (proximal) and right umbilical and left vitelline vein atrophy
- Left SV becomes a tributary of the right SV
- Anastomosis forms between the left and right anterior cardial veins
Where do each of these come from?
- Coronary Sinus
- Crista Terminalis
- Valve of the IVC
- Valve of CS
- Smooth Area of RA
- . IVC terminal portion
- SVC
- Auricle
- Left horn of SV
- Rt valve of SV
- Rt valve of SV
- Rt valve of SV
- Absorption of SV, primarily the Rt. Horn
- Rt Vitelline Vein
- Rt Common Cardinal and Proximal Anterior Cardinal Vein
- Primordial Atrium
What is the formation of the definitive left atrium?
Absorption of the pulmonary veins and the primitive
What is the formation of the pulmonary veins?
Initially a single pulmonary vein opens into the left atrium
Connect with pulmonary circulation
Proximal generations formed
- Where is the smooth part of LA derived from?
- Where is the auricle of LA derived from?
- Absorption of PVs
- Primordial Atrium
What other division must occur with common AV canal division to Right and Left AV canals? Why is this necessary?
Separation of atria from ventricles
Division of common AV canal alone would result in right and left AV canals opening into left ventricle
How is common AV canal expanded?
Internal remodeling at the inner curvature of heart resulting from myocardialization: cushion tissue into cardiac muscle
Thinning of the heart wall in this area allows AV canal expannsion to the right during later phase of looping
Where is endocardial cushion tissue located?
What does its formation involve?
Forms in AV canal and outflow region
Involve epithelium to mesenchyme transformation
What causes formation of septum intermedium?
What is the role of looping during this?
Fusion of superior and inferior endocardial cushions forms septum intermedium
Looping and inner curvature remodeling bring the septum intermedium in line with primary atrial septum and muscular IV septum
What is the role of cushion tissue in valve formation?
Forms the rings of the “cardiac skeleton” - Valve bases
Provides structure and prevents electrical conductivity through valves
Also helps form leaflets
- What are the two parts of the IV septum?
- What does the myocardium form?
- What forms the apical trabecular component?
- What is the Primary Interventricular Communication?
- 2 parts: Muscular and membranous
- Myocardium of the ventricles develop trabeculae
- . Ballooning of the ventricle walls
- Space between upper edge of muscular septum & bottom septum intermedium
Does the primary IV communication ever close?
Where does the membranous IV septum form?
Primary IV communication never closes
Membranous IV septum is between the right aortic vestibule and right ventricle ⇒ closing the Secondary Interventricular Communication
What does the division of the primordial atrium require? What is the traditional view of atrial division?
A special septum Initially a septum primum and foramen primum
Septum grows in between to form foramen secundum
Foramen primum is closed and septum secundum develops adjacent to septum primum
Foramen ovale results from septum secundum and is offset from foramen secundum
Two septum come together, septum primum becomes valve of foramen ovale
What is the alternative view of atrial division?
Oval foramen bounded by two folds
No real septum secundum, instead superior interatrial fold
What is the key role of the atrial septum?
Unidirectional flapper valve
Results from offset of the foramen
What do the following outflow tract structures form?
- Proximal outflow region
- Distal outflow region
- Aortic sac
- Ventricular outlets (R&L)
- Pulmonary & Aortic Valves & Pulmonary & Aortic Root
- Pulmonary & Aortic Root
Where are the cushion tissue in the outflow region?
What are these regions named?
Located in both the proximal and distal portions of the outflow region
Either the conotruncal ridges or the bulbar ridges
Proximal outflow region and distal outflow region partitioning
- What is the wall of these regions?
- What are they partitioned by?
- What contributes to this?
- Cardiac muscle
- Bulbar ridges (ECT)
- Neural Crest contribution
How is the aortic sac partitioned?
Divided by a Neural Crest-derived mesenchyme that forms the aorticopulmonary septum
Inferior edges of the aorticopulmonary septum fuse with and extend into superior edges of the proximal outflow region septum
What components fuse together for formation of the membranous IV septum?
Conotruncal septum (dorsal) and endocardial cushion (ventral) fuse together
They fuse with muscular IV septum
What forms the following?
RV:
- Inlet
- Apical trabeculated component
- Outlet
LV:
- Inlet
- Apical trabeculated component
- Outlet
RV:
- Inlet ⇒ AV Canal
- Apical trabeculated component ⇒ Primitive Right Ventricle
- Outlet ⇒ Proximal Outflow Region
LV:
- Inlet ⇒ AV Canal
- Apical trabeculated component ⇒ Primitive Left Ventricle
- Outlet ⇒ Proximal Outflow Region
Pharyngeal Arch Artery Fates
Pair 1
Pair 2
Pair 3
Pair 4
Pair 6
- Mostly degenerates, but contributes to maxillary and external carotid arteries
- Forms the stems of the hyoid and stapedal arteries
*3. Proximal parts - Common Carotids Distal parts - ICAs
*4. Left - Part of aortic arch, Right - Proximal right sublcavian
*6. Left - Proximal part - Proximal left pulmonary artery; Distal part - ductus arteriosus Right - Proximal part - proximal right pulmonary artery Distal part - Degenerates * Highest yield on boards
What are the three shunts of fetal circulation?
- Ductus Venosus - Oxygen rich blood shunted around liver
- Oval foramen - Blood IVC is shunted to the left atrium
- Blood leaving the right ventricle is shunted into the aorta through the ductus arteriosus
What is pulmonary circulation in the fetus?
What are the heart pressures in the fetus?
How does blood return to the placenta?
- Inactive due to high vascular resistance, minimal blood flow
- Right heart pressure > than left
- Blood returns to placenta through umbilical arteries
