Lecture 9: Heart Development Flashcards
Where does hematopoiesis begin?
Yolk sac (extra-embryonic splanchnic mesoderm): Day 17
- source of early RBC and macrophages
- forms blood islands
By day 23, what structure do early hematopoietic cells populate?
Liver
-need to meet immediate need for blood cells
What is the significance of the aortic-gonadal-mesonephric (AGM) region?
Where definitive hematopoietic stem cells are programmed
-eventually will seed the liver 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?
No
With intraembryonic vasculogenesis, what does the splanchnopleuric mesoderm differentiate into?
Endothelial precursor cells (aka angioblasts)
What is the function of angioblasts?
1) Continue to proliferate as EPC
2) Angiogenesis: make new blood vessels from existing ones
3) Intussusception: splitting of blood vessels
4) Recruitment of new mesodermal cells into walls of existing vessels
What are angiomas?
Abnormal blood vessels and lymphatic capillary growth via vasculogenesis
On day 19, the first heart field or cardiac crest forms. What composes this?
EPC clusters from intraembryonic splanchnic mesoderm
Adjacent mesoderm
How does the primitive tubular heart form?
Two endocardial tubes are formed from EPC. Due to body folding, they are fused to make a single tubular heart with myocardium and endocardium.
From where does the primitive tubular heart dangle from?
Dorsal mesocardium
Why does the dorsal mesocardium eventually have to rupture?
To allow the heart to loop
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
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
What does the truncus arteriosus eventually become?
Aorta
Pulmonary Artery
Describe the second heart field.
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
-Maintains cardiogenic mesoderm proliferation and proper
myocardial cell specification within the second heart field
-Plays important role in regulating cardiac looping
What is ventricular inversion?
Reverse cardiac looping –> right-sided left ventricle
What is heterotaxia?
Any abnormal left-right development of either some or all
organs
What is visceroatrial heterotaxia?
Condition whereby the 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?
With the expansion of the atrium, there is a shift of the left sinus venosus and left horn since it is much more pronounced on the left side.
This 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
What happens to the right sinus horn and remaining parts of the veins in the right sinus horn?
Incorporated into posterior wall of right atrium
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 due?
Induce formation of mesenchymal cells to close off openings.
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 superior and inferior cushions to fuse, resulting in all four chambers of the heart to talk to each other
Describe septum primum and secundum.
1) Septum primum is near the AV septum and has a 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.
What is another structure that allows oxygenated blood to bypass lungs and pulmonary trunk to enter systemic circulation?
Ductus arteriosus
How does the right atrium eventually pump blood into the lungs?
After birth, the pressure in the left side of the heart greatly increases while the pressure in right side of the heart decreases.
It is easier for the right side to pump to lungs. Eventually, foramen ovale should close off w/in three months of the birth.
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
What is cyanosis?
Low levels of oxygen saturation in blood that can result 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 right ventricle due to insufficient shifting of AV septum or issues with cardiac looping
-cyanotic
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 tract is not divided between the two ventricles
- mixing of oxygenated and de-oxygenated blood
- will have VSD
- cyanotic
Describe tetralogy of fallout.
Unequal division of pulmonary trunk and aorta
- Will have VSD
- Pulmonary infundibular stenosis
- Overriding aorta
- Pulmonary artery is very small causing right ventricle to hypertrophy
- 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 conotruncal ridges
- cyanotic
Describe pulmonary valvular atresia.
Semilunar valves are fused leading to right ventricle hypoplasia. Foramen ovale is the only way for blood to reach left side of heart.
-if there is VSD, mixing of blood can give patient chance to live
Describe aortic valvular stenosis.
Heart’s aortic valve narrows
-hypertrophy of LV that can lead to cardiac failure and pulmonary hypertension
Describe aortic valvular atresia.
Congenital absence of the normal valvular opening from the left ventricle of the heart into the aorta
Describe bicuspid aortic valve.
Aortic valve that only has two leaflets instead of three
- can cause regurgitation of blood back into heart
- lead to LV hypertrophy
- can cause stenosis of aortic valve
Describe tricuspid atresia.
Tricuspid heart valve is missing or abnormally developed, leading to improper blood flow between right atrium and right ventricle.
Describe a hypoplastic left ventricle.
Underdeveloped left side of heart along with abnormal bicuspid and aortic valves
-right ventricle is doing all the work
