9. Heart Development Flashcards
Where does hematopoiesis begin?
Yolk sac (extra-embryonic splanchnic mesoderm):
begins Day 17
-form early RBC and macrophages, blood islands & early BVs
By day 23, what structure do early hematopoietic cells populate?
Liver
What is the significance of the aortic-gonadal-mesonephric (AGM) region?
Where definitive hematopoietic stem cells are programmed in liver (appear around day 27)
-eventually will seed the liver (day 30) to give rise to proper RBC and WBC
After the liver programs proper RBC and WBC, what structures do these cells populate?
Lymph organs & Bone marrow
Is intraembryonic vasculogenesis coupled with hematopoiesis?
what is vasculogenesis
No
= development of new vessels directly from mesenchyme
With intraembryonic vasculogenesis, what do some of the splanchnopleuric mesoderm differentiate into?
Endothelial precursor cells (aka angioblasts)
starting at day 18
What is the function of angioblasts?
1) Continue to proliferate as EPC
2) Angiogenesis: make new blood vessels
3) Intussusception: splitting of blood vessels
4) Recruitment of new mesodermal cells into walls of existing vessels
What are angiomas?
what are the types
Abnormal blood vessels and lymphatic capillary growth via vasculogenesis
- capillary hemangioma: excess growth of small cap network
- cavernous hemangioma: excess froth of venous sinuses
- hemangiomas: benign tumors mostly made of endothelial cells
what is the cardiac crest?
part of 1st heart field
= cardiogenic precursor cells that differentiate & organize into 2 endocardial tubes that have splanchnic mesoderm on the sides–> tubes = pericardiomyocytes
Which structures do angiogenic clusters give rise to?
clusters found in lateral plate splanchnic layer mesoderm
form 2 endocardial tubes –> which converge during lateral body folding to form one tube
From where does the primitive tubular heart dangle from?
Dorsal mesocardium
develops much of epicardium
Why does the dorsal mesocardium eventually have to rupture?
To allow the heart to loop into S shape
What happens to the remnants of dorsal mesocardium?
Forms the proepicardial organ
-epicardium that covers simple tubular heart
What is the sinus venosus?
Where the inflow of primitive blood confluence
fluid into RA
What does the primitive ventricle give rise to?
Left Ventricle
What does the outflow tract give rise to?
Right Ventricle
What happens to the atrium when cardiac looping begins?
Moves cranially and dorsally
What is the function of the conus arteriosus?
Proximal outflow of both ventricles
-Is divided so blood from LV and RV go out different vessels
What is the function of truncus arteriosus?
Distal outflow tract
become Aorta & Pulmonary Trunk
Describe the why the second heart field is initially inhibited
Initially inhibited due to its proximity to notochord
After body folding, it is farther away and can start proliferating by adding cells to both ends of the primitive heart tube
-drives cardiac looping
What is the role of neural crest cells in terms of cardiac looping?
-Regulates FGF 8 and drives growth of cells in primitive heart
= important role in regulating cardiac looping
Maintains cardiogenic mesoderm proliferation and proper myocardial cell specification within the second heart field
What is ventricular inversion?
Reverse cardiac looping –> right-sided left ventricle
What is heterotaxia & what are the two types?
Any abnormal left-right development of either some or all organs
Situs inversus: total reversal
Situs ambiguous: partial reversal (visceroatrial heteroataxia)
What is visceroatrial heterotaxia?
- heart and GI tract are asymmetrically arranged from one another
- right-sided heart with normal GI tract
- left-sided heart with right-sided GI tract *
*Causes problems with inflow and outflow tract development and can be life threatening
What are the branches of the sinus horns?
Umbilical Vein
Vitelline Vein
Common Cardinal Vein
How do the right and left atria begin to form?
expansion of the atrium–> shift of the left sinus venosus and left horn
–> causes a net shift in the amount of blood returning to the right side of the common atrium
What does the left sinus horn eventually become?
Coronary sinus
What does the right vitelline vein become?
Inferior Vena Cava
What does the right common cardinal vein become?
Superior Vena Cava
Where is the smooth part of the right atrium wall from?
Sinus venosum
Where is the rough part of the right atrium wall from?
Primitive atrium
What does differential growth form?
Muscular interventricular septum: separates ventricles
Muscular Atrial septum: separates atria
What does endocardial cushion tissue do?
Induce formation of mesenchymal cells to close off openings
-produce AV septum
How do endocardial cushion tissues work?
Myocardium produces ECM that sucks up water, causing it to swell.
Endocardium is pushed into lumen and the cells start to delaminate, filling in the lumen.
Where are endocardial cushion tissues found?
Between atria and ventricles
Between ventricles and outflow tract
What is a persistent AV canal?
Failure of the AV septum (superior and inferior cushions) to fuse
-all 4 chambers communicate
=abnormal or agenesis of AV valves
= pul HTN, exercise intolerance, SOB, cardiac congestion, increased risk of endocarditis
-*linked with Downs syndrome
Describe septum primum and secundum
1) Septum primum - near AV septum - hole, ostium primum.
2) Ostium primum is replaced by foramen secundum, which is much higher up.
3) . Eventually, septum secundum will overlap foramen secundum and has its own hole - foramen ovale.
What is the purpose of all the holes (e.g. osteum primum, foramen secundum, foramen ovale)?
Oxygenated blood from umbilical vein can bypass the lungs and pulmonary trunk and enter systemic circulation (blood from RA to LA)
What is another structure that allows oxygenated blood to bypass lungs and pulmonary trunk to enter systemic circulation?
Ductus arteriosus
What can cause some atrial septal defects?
1) Too much resorption of septum primum that cannot be covered by septum secundum
2) Absence of septum secundum
3) Ostium primum never covered from due to failure of up-growth of AV cushion tissue from AV septum
W >M
What is cyanosis?
Low levels of oxygen saturation in blood from mixing of oxygen-rich and oxygen-poor blood
can lead to blue skin
How does the AV canal shift?
Myocardialization: outer myocardial wall is thinned and replaced by cushion cells
What can happen after the AV canal shifts?
Separation of right and left ventricle
What is double outlet right syndrome?
Both aorta and pulmonary artery exit via RV bc insufficient shifting of AV septum or issues with cardiac looping –>cyanotic
breathlessness, murmur, poor weight gain
What structures does neural crest cells contribute to?
Aortic-pulmonary septum
Semilunar valve
Describe ventricular septal defects.
Improper closure of ventricular septum
- starts acyanotic (left to right shunt)
- right ventricle hypertrophies due to increased workload
- becomes cyanotic after birth (right to left shunt)
Describe persistent truncus arteriosus.
Outflow tracts not divided btn the two ventricles bc conal truncal ridges dont form
- mixing of oxygenated and de-oxygenated blood
- will have VSD
- cyanotic
Describe tetralogy of fallout.
Unequal division of pulmonary trunk and aorta
- VSD
- Pulmonary infundibular stenosis
- Overriding aorta
- RV hypertrophy (bc pul A very small)
-cyanotic
Describe transposition of great vessels.
Pulmonary artery is connected to left ventricle while aorta is connected to right ventricle
- due to improper spiraling of conal truncal ridges
- cyanotic
Describe pulmonary valvular atresia.
no opening to pul A –> underdevelop RV (hypoplasia)
Foramen ovale only way for blood to reach left side
if there is VSD, mixing of blood can give patient chance to live
Describe aortic valvular stenosis.
Heart’s aortic valve narrows
LV hypertrophy –> cardiac failure & pul HTN
M > F
congenital, pathological, degenerative
Describe aortic valvular atresia.
Congenital absence of aortic valve
- LV hypoplasia
- RV hypertrophy
patent ductus arteriosus & ASD
Describe bicuspid aortic valve.
Aortic valve 2 leaflets instead of 3 –> regurgitation of blood
- initial asymptomatic but can lead to LV hypertrophy
- can cause stenosis of aortic valve (associated w/ development of aortic aneurysm)
- can be inheritable
Describe tricuspid atresia.
Tricuspid valve missing or abnormally developed, –> improper blood flow btn RA & RV
patent foramen ovale, RV hypoplasia, VSD & patent ductus arteriosus
Describe a hypoplastic left ventricle.
Underdeveloped left side of heart along w/ abnormal bicuspid and aortic valves
–>underdeveloped ascending aorta
patent ductus arteriosus & patent foramen ovale (or ASD)
-right ventricle is doing all the work (univentricular)
Which structures do hemangioblasts give rise to?
primitive hematopoietic stem cell and endothelial precursor cells
what is the primary fxn of the hemangioblasts
meet the immediate needs for blood cells
Which vessels are responsible for inflow of blood into the primitive heart?
common cardinal, vitelline, and umbilical veins
how are definitive hematopoietic stem cells programmed
hemogenic endothelial cells in AGM break off from doral aorta and seed liver
-interaction takes place –> program these cells
Which organ is primarily responsible for producing blood cells in development?
liver via hematopoietic precursor cells
which structure gives rise to myocardium
splanchnic mesoderm
which germ layer gives rise to the valves of the heart
endocardium from the intraembryonic splanchnic mesoderm
which germ layer give rise to the conotruncal ridges in outflow tract
endocardial (intraembryonic splanchnic mesoderm)
NCC (ectoderm)
