Heart Embryo Flashcards
What, heart related, occurs in the third week?
Circulatory system and the heart begin to form.
When does actual circulation begin?
Week 4
When does the heart begin to beat?
Week 4 (day 22)
What type of tissue is the heart derived from?
- Splanchnic mesoderm (gives rise to all aspects of the heart)
- Mesenchyme (neural crest cells)
- Angioblastic tissue (gives rise to blood vessels)
What type of tissue are heart fields derived from?
What part of the embryo are they established in?
- Splanchnic mesoderm
-Cranial end of the embryo
- What do our primary heart fields develop into?
- What tissue is our primary heart field developed from?
1. L/R atria and left ventricle
2. Mesoderm from the primitive streak
-
- What does our secondary heart fields develop into?
- What tissue does our secondary heart fields develop from?
1. R ventricle
2. Outflow tracts (bulbus cordis–> aorta & truncus arterious–> pulmonary trunk)
3. Part of the atria (venous pole)
-Comes from mesoderm derived frm the pharyngeal arches
What makes up our outflow tracts?
- Bulbus cordis–> aorta
- Truncus arteriosis –> pulmonary trunk
In what region does heart folding begin and in what plane?
- Cranial region
- Median/longitudinal folding and goes down with the septum transversum into the thorax.
What forms our pericardial cavity?
Intraembryonic coelum
What is another name for heart tubes/ primary heart fields?
Cardiogenic cords
What tissue is the pericardial coelum and cardiogenic cord derived from?
Splanchnic mesoderm
The heart is derived from _______________.
What about the endocardium, myocardium and epicardium?
Splanchnic mesoderm.
Also splanchnic mesoderm
How is our heart primordia formed?
- During lateral/horizontal holding, 2 endocardial heart tubes (made up endocardium) approach each other and fuse.
What is mesentary?
Mesentary is our dorsal mesocardium.
Mesentary is a double layer of splanchnic mesoderm that provides a route for BV, lymphatics and nerves to reach its organs.
What is our dorsal mesocardium?
Dorsal mesocardium is mesentary.
It suspends the heart into the thorax and allows it to connect to the posterior body wall.
What does our dorsal mesocardium become?
Why is what it makes important?
Transverse pericardial sinus.
-Clinically usefull because it separates our outflow tracts from venous flow. If we put our fingers here, they are under the aorta & pulmonary trunk. They can be clamped during CABG.
In the formation of our heart, how do neural crest cells contribute?
NEURAL CREST CELLS SEPARATE OUR OUTFLOW TRACTS
- Neural crest cells from myelencephalon (medulla)
- [migrate] –> pharyngeal arches 3, 4 and 6
- [help form]–> truncus arteriousus & articopulmonary septa (septa that divides our aorta and pulmonary trunk).
THUS: NEURAL CREST CELLS SEPARATE
What regulates the neural cells used to help form our truncus arteriosus and aorticopulmonary septa?
1. Retanoic acid (vitamin a)
2. Hox genes
3. Nf-1
4. Pax3
How does retanoic acid regulate NC cells?
Too much RA (vitamin A) disrupts the migration of NC cells.
-Example: too much can result in cardiac deficits. Acutane during pregnancy is bad 4 you.
As we have said; during horizontal (lateral) folding, two endocardial tubes fuse to form our primitive heart tube at day 21.
Describe the primitive heart tube that is formed and how blood travels.
The primitive heart tube (HOLLOW) is divided into 5 segements (from superior to inferior).
1. Truncus arteriosus
2. Bulbus cordis
3. Ventricle
4. Atrium
5. Sinus venosus (where embryological veins deliver blood)
Blood travels from structure 5-1.
Describe heart formation
- Day 21- two endocardial tubes fuse to form our primitive heart tube.
- Day 23- RIGHT folding of the heart occurs.
To do so, the bulbus cordis and the ventricles proliferate quickly, causing the heart to bend on itself and form a bulboventricular loop that bends to the right.
- As this occurs, the atria and SV rotate superior and posterior (they come to lie dorsally).
We want _____ handed folded looping to occur.
RIGHT
If our heart folds to the left, what is this called?
Dextrocardia
What is dextrocardia?
Left folding of our heart, causing it to be a mirror image of what it should be.
If Dextrocardia occurs by itself–> congintal abnormalities.
However, if it occurs with situs inversus (all abdominal contents are mirrored)–> No problems.
Dextrocardia in isolation: sx or asymptomatic
Sx.
BAD
Dextrocardia + situs inversus: sx or assxy
Assxy.
BEcause all of our internal organs will be mirror images.
How do we test for dextrocardia?
If heart sounds are NOT on the left side–> dextrocardia.
What occurs on day 35?
Truncus arteriosus will lead to the aortic sac.
Aortic arch arters come off of the sac and give rise to the vessels.
Arches then enter our dorsal aorta.
What occurs after heart folding and when?
Septation events- septate the hollow tube we created.
Begins at mid 4th week- week 8.
Do septation events occur at different times?
No. All At DA SaMe DaMn Tyme
Septation event number 1: formation of our atrioventricular canals (separation the atria and ventricle).
What are endocardial cushions?
ALSO CALLED AV CUSHIONS
Endocardial cushions derived from mesodermal growth from the dorsal and ventral walls.
Septation event number 1: formation of our atrioventricular canals (separation the atria and ventricle).
How does this occur?
- At week 5, mesenchyme will invade the mesodermal growths on the dorsal and ventral wall.
- Endocardial cusions fuse together
- 90 degree turn
RESULT: Right and left atrioventricular canal, which separates the atria and the ventricle.
The formation of our endocardial (AV) cushions depends on what?
Retanoic acid.
If retanoid signaling is fucked up–> AV canal defect
What kind of muscle is our primitive heart tube?
Pectinate muscle
Anything that is smooth muscle in the atria originates from what?
Sinus venosus.
What does our sinus venosus give rise to?
- Left horn of sinus venosus–> coronary sinus
- Right horn of the sinus venosus –> incorperaets into the atrium wall to form
A. Sinus venarum
B. Orifices (opening) for the superior and inferior vena cava veins
C. Orifice (opening) of the coronary sinus.
What is the process by where the sinus venosus makes the openings of the superior/inferior vena cava veins and coronary sinus?
Intussecption?
What happens when the R horn of the sinus venosus undergoes intussception?
Bend itself and form a sinuatrial orifice is formed. On either side, L and R sinuatrial (venous) valves will be present.
After the sinuatrial orifice is formed, what happens to the left and right sinuatrial (venous) valve?
The valves are going to fuse cranially and caudally.
- Cranially, the will both fuse with septum spurium.
- The right venous (sinuatrial) valve will fuse cranially–> crista terminalis
- Fuse cadually–> valve of the coronary sinus (thesbian valve) and most of the valve of the inferior vena cava (eustachian valve).