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).
What is the thesbian valve?
Valve of the coronary sinus
What is the Eustachian valve?
Valve of the inferior vena cava
For septation of the atrium, what do we need to form?
1. Septum primum
2. Septum secundum
What are the foramen of the septum primum called?
- Foramen primum (ostium primum)
- Foramen secundum (ostium primum)
What is the foramen in septum secundum?
Foramen ovale (ostium ovale)
How does septation of the atrium occur?
- Septum primum will grow down and fuse with the endocardial (AV) cushions.
- Apoptosis beings to occur on the septum primum, forming the foramen secundum (ostium secundum)
- When fusion occurs, the foramen primum (ostium primum) goes away.
- At day 40, septum secundum (which overlaps the septum primum) fuses with the endocardial cushion, forming the foramen ovale (ostium ovale).
- Blood can now enter the R atrium–> shunt through the foramen ovale (ostium ovale) of the septum secundum–> foramen secundum (ostium secundum) of our septum primum–> L atrium
—–thus, this forms a R–> L atrial shunt. ——
What is the shunt between the R and L atrium?
foramen primum.
The formation of what ensures shunting?
Foramen secundum
After septation of atrium is complete, what do we have?
A definitive separation of the atria.
The septum secundum does not fully close, leaving a patent foramen ovale.
During embryonic and fetal life, blood enters the R atrium–> L atrium via what?
Foramen ovale
Foramen secundum (ostium secundum)
What prevents blood from L atrium–> R atrium?
Pressure
Eventually, the foramen ovale will become what?
Fossa ovalis
Fossa ovalis is derived from what?
Septum primum
Tissue around the fossa ovale is derived from what?
Septum secundum
What seperates the ventricles?
Interventricular septum
Has a membranous part and a muscular part
Interventricular septum is made of ___________, which becomes _______.
Splanchnic mesoderm, which becomes muscle.
Septation of the ventricle
- Interventricular septum attempts to migrate to the endocardial cusion.
- Muscular portion does not meet, forming the interventricular foramen.
Septation of the bulbus cordis and truncus arteriosus.
- NC cells associated with the 3, 4, 6 pharyngeal arches migrate to the truncus arteriosus and bulbus cordis (conus cordis), dividing the outflow tract.
- NC cells form bulbar (conotruncal ridges) and truncal ridges
- Spiral 180 degrees.
- Bulbar and truncal ridges migrate to the midline and form–> aorticopulmonary septum, which divides bulbus cordis and truncus arteriosus into ascending aorta and pulmonary trunk.
- Aorticopulmonary septum fuses with the endocardial cushion
- Bulbus cordis on the R side of ventricle –> conus arteriousis
Bulbus cordis on L side–> aortic vestibule.
Once the musclar portion of the interventricular septum is formed, there is still a hole near the endocardium cusion where it did not fuse, what covers the hole?
Membranous interventricular septum made from endocardial cushion and neural crest cells from our left and right bulbar ridges.
Once the right and left bulbar ridges fuse to the [endocardium cushions], the interventricular foramen disappears and forms what?
Membranous part of the interventricular septum
What are the most common birth defects and why?
Defects in the membranous part of the interventricular septum, due to neural crest cells.
What does the membranous interventricular divide?
L and R ventricle
—-also—-
R atrium from the L ventricle
How do we get formation of our cusps for our valves?
As the ridges are fusing, we get formation of dorsal valve swellings, which are derived from mesenchyme (NC and mesoderm).
Heart has been beating since day 22. How do the valves form?
Blood is forced through the developing valves and when at rest, blood drops down, hitting the ventral and dorsal swelling, eroding, forming strong CT and the cusps!
What occurs to the baby when there is no shunt or a L–>R shunt?
Acyanotic bb.
What occurs to the baby when there is a R–> L shunt?
cyanotic bb
occurs affter bb is born
What occurs if there is NO shunt?
1. Abnormality of the aortic arches
2. Coarctation of the aorta
Describe fetal circulation.
- Blood fromes in R atrium –> L atrium.
- L atrium–> L ventricle–> aorta.
- Blood is sent to the head via the common carotid and subclavian and body.
What about the lungs?
However, the blood in the R ventricle is not as oxygenated and the lungs do not need much O2, so when it sends blood to the lungs via the R ventricle, ductus arteriousus will shunt it from the pulmonary trunk– > aorta.
The blood we deliver has medium oxygen content.
Once baby is born (neonatal life)
What is a acyanotic shunt?
L–>R shunt.
Oxygenated blood is shunted to right.
Body is still receiving enough O2.
Once baby is born (neonatal life)
What is a cyanotic shunt?
R shunt –> left shunt
O2 poor is mixing with O2 rich.
Dilutes and bb becomes cyonatic (blue)
if the ductus arteriosus if still prevelant after birth (connects pulmonary trunk to aorta) what will happen?
(PATENT DUCTUS ARTERIOSUS)
L–R shunt
Acyonatic.
High pressure from the aorta will cause blood to go into pulmonary trunk–> lung
O2 rich blood–> O2 poor blood.
Why doesnt our PDA close?
- Low O2
-
Too much Prostaglandin E2 (PGE2), made by the placenta and mediated by
* COX-2*
How can we treat PDA?
Cox-2 inhibitor (because COX-2 makes the PGE2) like ibuprofin and indomethacin
This will cause PDA to close after 72 hours.
What are characteristics of PDA?
Characteristics depend on size of PDA
1. continuous murmur
2. Poor eating,
3. Sweating while crying or eating
4. Tachypnea
5. Increase heart rate.
What is a result of a persistent ductus arteriosus?
The high pressure in aorta goes to the lungs and destroys capillary beds.
How can we detect PDA on X-ray?
- Opaque lungs due to pulmonary edema
- Enlarged heart
Atrial septal defects are more common in: F or M
Females
ASD can occur as secundum ASD (defect in septum secundum) or primum ASD (defect in septum primum. Is this defect cyanotic or acyanotic?
Acyanotic.
L–> R side shunting.
What is secundum ASD?
A. Hole is middle on the interatrial septum.
B. Involves a patent foramen ovale.
C. Excesive cell death during formation of foramen secundum and reabsorption of septum primum
or septum secundum not developing properly.
What causes probe patent foramen ovale in 25% of people?
No direct access from left to right, but can put probe through one atrium to the other.
Incomplete adhesion between foramen ovale and septum secundum
Primum ASD (ostium primum)
The septum primum does not fuse wit the endocardial cushions.
-Often assx with a mitral valve cleft
Ventricular septal defects occur in more male/ females?
Cyanotic/Acyanotic?
Males
Acyanotic
Ventricular septal defects are caused by what embryological defect?
NC cells in the bulbus ridges did not fuse with the endocardium cushion, causnig the membranous part of the interventricular septum not to form.
What can be heard during VSDs?
murmur in left/lower sternal border or left 3-4th intercostal space
Types of AV septal defects
Complete and partial
AV septal defects have complete defects which are characterized by a primum ASD, VSD and a common AV valve.
What is characteristic of a partial AV septal defect?
- Primum ASD
- single AV valve annulus with 2 separate valve orfices (anterior leaflet of mital valve is separated)
What is the embryological basis for the AV septal defect?
Endocardial cushions do not fuse leading to a left to right shunt = acyanotic
common in 20% of people with Downs
What features do you commonly see with atrioventricular septal defects? (3)
1. Atrial septal defect
2. Ventricular septal defect
3. Abnormal valve leaflet
All 3 for complete,
1 & 3 for partial
What defect involves the right atrium –> left ventricle,
left atrium –> right ventricle
right ventricle–>aorta
left ventricle –> pulmonary trunk
AND interventricular septal defect?
Corrected transposition of the Great Vessels
Is corrected transposition of the great vessels defect acyanotic or cyanotic, and what embryological event does this?
Acyanotic because left to right shunt, caused by:
1. Neural crest and improper separation of outflow tract.
2. Reversed rotation of the heart
To tell whether shunt is R–>L or L–R, how can we tell?
Look at pressures.
L has high pressure
R has low pressure: L–>R shunt.
What occurs in the defect: transposition of great vessels?
- Great vessels are from wrong ventricles
- VSD
- PDA
Last two are needed: otherwise will never get oxygenated blood to body
How does transposition of great vessels occur embryologically?
CYANOTIC because oxygenated blood goes to pulmonary trunk
Neural crest cells do not spiral 180 degrees.
Truncus arteriosus
Cyanotic/acyanotic
Truncus arteriosus- [single great vessel + VSD]
-Cyanotic
What is the embryological explanation for truncus arteriosus?
-Neural crest derived
-Absence of bulbar and truncal ridges to form and/or migrate to the midline.
What are the 4 hallmarks of tetralogy of fallot (TOF)?
Cyanotic/ Acyanotic?
Mneumonic: PROV
- Pulmonary stenosis (narrow pulmonary trunk)
- Right ventricular hypertrophy
- Over-riding aorta
- VSD
Cyanotic: R–> L shunt
What is the embryological basis for TOF?
Neural crest derived.
Root cause: septation of outflow tract
Critical pulmonary stenosis
- Cyanotic
-Cusps of the pulmonary trunk are fused/thickened
Why cyanotic–> Decreased pulmonary blood flow.
Critical aortic stenosis
Cyanotic–> decrease in systemic blood flow.
Features: tachypnea, poor feeding, poor perfusion, can lead to hypoplastic L heart syndrome.
What defect includes features of
- Aortic valve stenosis
- Mitral valve stenosis
- Hypoplastic left left ventricle
- Hypoplastic aortic arch
Cyanotic due to NO LEFT VENTRICLE.
PDA and ASD will help with defect so patient does not die
Hypoplastic L heart sydrome
