Cardiac Embryonic-Fetal Circulation Flashcards
What is the morula?
Unicellular zygote goes through a series of cleavages resulting in a cluster of cells called the morula.
What turns into the blastocyst? What are the 3 components of the blastocyst?
Morula turns into the blastocyst which has 3 components
Outer cell mass (trophoblast)
Inner cell mass (embryoblast)
Central cavity (blastocyst cavity)
What part of the blastocyst forms the embryonic disk?
The embryoblast
What are the two layers of the embryonic disk?
External layer - epiblast
Internal layer - hypoblast
At the blastocyst stage, where are the pericardiac cells located?
Within the epiblast on either side of the primitive streak
How is the intraembryonic mesoderm formed?
Epiblast cells migrate through underneath the primate streak giving rise to the intraembryonic mesoderm… this turns the 2 layer disk into 3 layers
Epiblast
Intraembryonic mesoderm
Hypoblast
At this stage. It’s called gastrula
In the gastrula, what are the 3 layers?
External - ectoderm
Middle - mesoderm
Internal - endoderm
In the gastrula, which layer are the precardiac cells located in? Where do they migrate?
Mesoderm (middle layer). They begin to migrate cephalically
What are 2 challenges that make it very difficult to prevent congenital heart defects?
- The heart starts to develop very early in the pregnancy–often so early that the mother doesn’t know she’s pregnant yet (day 16!)
- No isolated gene defect to fix/prevent
In the gastrula, after the precardiac cells migrate cephalically, where do they establish?
They establish themselves at the cranial end of the embryonic disk which becomes the cariogenic area.
Which germ layer do the cariogenic area cells come from?
Mesoderm
What germ layer does the heart derive from?
Mesoderm
On day 19, folding begins. What does this do to the location of the heart?
The location of the heart goes from the “head” of the disk, to where the chest cavity will be. The cariogenic cells are now ventral to the forebrain and foregut. At this point, the cariogenic cells begin to form 2 endocardial tubes.
When are the endocardial tubes formed?
They are formed after the first fold that brings the cariogenic mesoderm cells from the head of the disk to in front (ventral) of the foregut and the forebrain.
What is the layer that surrounds the heart tubes?
Splanchnic mesoderm
What lines the inside of the heart tubes?
endothelial cells
What significant event in the formation of the heart happens on day 21-22?
The tubes fuse together due to cephalic and lateral folding of the embryo
On what day does the heart begin to beat?
Day 22. After tubes fuse together!
What happens during the pre-loop stage?
Straight heart tube
Atrioventricular sulcus will become the intraventricular septum
The primitive ventricle is the primordial of the trabeculated portion of the LV
The proximal portion of the bulbs cords is the primordial of the trabeculated portion of the RV
Blood flow begins
What is the primordial of the trabeculated portion of the LV?
Primitive Ventricle
What is the primordial of the trabeculated portion of the RV?
Proximal portion of the Bulbous Cordis
When does blood flow begin?
Day 22. Pre-loop stage.
What part of the pre-loop stage heart becomes the intraventricular septum?
Atrioventricular sulcus
What develops into the endocardium?
The inner layer of the heart tube is lined by endothelial lining. This turns into the endocardium of the heart.
What develops into the myocardium and epicardium?
The outer layer of the tube is derived from the mesoderm (epimyocardium) and will go on to develop into myocardium and epicardium.
What is cardiac jelly?
This is a substance between the inner and outer layers of the straight heart tube that plays a role in the looping of the heart as well as septation.
What days are the looping stage?
Day 23-25
At the beginning of the looping stage, things look dimpled and there are more names. Name the components from top to bottom and what they turn into
Truncus (Aortic and pulmonary valves/great vessels) Conus (outflow tract) Bulbs Cordis (RV) Primitive Ventricle (LV) Primitive Atria (Atria) Sinus Venosus (SVC and IVC)
Why does looping of the heart happen?
Because, the cardiac tube is growing at a faster longitudinal rate than the rest of the embryo so it starts looping onto itself
During heart folding, do the atria fold in front or behind of the ventricles?
Behind (posteriorly)
What happens if someone has incorrect looping during heart development?
They end up with a heart prone to a lot of defects
The long axis of the atrioventricular canal is initially cephalic to caudal in the straight heart. But with looping, what happens?
The long axis of the atrioventricular canal becomes posterior to anterior
What is double outlet right ventricle?
This is a congenital heart defect where the truncus does not septate with the aorta connected to LV and pulmonary artery connected to the RV. As you can see from the straight heart tube, the truncus is connected only to the RV and then eventually septates into two tubes with one on each ventricle. If this doesn’t happen, you get double outlet right ventricle.
Does double outlet left ventricle exist?
No. This is because the truncus begins on the RV. Problem with the truncus septating will result in all double outlet on the RV but there isn’t any way that you would get the double outlet on the LV because the truncus is on the RV to begin with (in the straight heart)
What days are the early post-loop stage?
Day 26-28
What happens in the early post-loop stage?
Ventricles and atria are now in alignment (after looping stage). This is when early septation begins.
Blood flow in the heart tube occurs through the sinus venosus via 3 sets of veins. What are they?
- Umbilical vein - from placenta (disappears after birth) (oxygenated blood from mother)
- The Vitelline vein - from the yolk sac (nutrients and stuff)
- The Cardinal vein - drains the embryo’s deoxygenated blood back into the sinus venosus
What is the anatomic correlate for the Right umbilical vein?
Disappears
What is the anatomic correlate to the Left umbilical vein?
Distal => ductus venosus
What is the anatomic correlate to the right vitelline vein?
Distal => superior mesenteric artery
Proximal => suprahepatic portion of IVC
Also contributes to hepatic sinusoids
What is the anatomic correlate to the left vitelline vein?
Contributes to the hepatic sinusoids
What is the anatomic correlate to the right cardinal vein?
SVC, brachiocephalic vein, innominate veins
What is the anatomic correlate to the left cardinal vein?
Ligament of marshall
How do the pulmonary veins get established?
It is not entirely known but the theory is that part of the splanchnic plexus forms the pulmonary venous plexus which develops into the pulmonary veins. An endothelial projection from the LA connects to the pulmonary venous plexus and forms a common pulmonary vein. A lumen forms and the common vein branches forming the R and L pulmonary veins.
What congenital defect can happen with pulmonary veins?
If they don’t develop correctly and merge with the LA, surgery is needed right after birth where they find the plexus and merge it to the LA.
When is the post-loop stage?
Days 28-42
When does atrial and ventricular septation happen?
Post-loop stage
When do great arteries form?
Days 35-56
What happens first to create the great arteries?
Septation of the conus
How does septation of the conus happen?
In early post-loop stage, masses appear on the inside wall of the conus. These 2 masses are dextrodorsal and sinistroventral clonal crests. The clonal crests fuse with the ventricular septum caudally.
How does septation of the truncus happen?
4 swellings appear:
Masses appear in the truncus: dextrosuperior and sinistroinferior truncal swellings.
A right intercalated swelling becomes the non coronary aortic cusp.
A left intercalated swelling becomes the anterior pulmonary cusp.
True or False: The septation of conus, truncus, into the aortic sac is spiral
True
Explain the septation of the aortic sac
The aorticopulmonary septum originates as an extra cardiac septum in the aortic sac
How do the separations between conus, truncus, and aortic sac combine?
SVCC continues with SITS
DDCC continues with DSTS
DSTS and SITS join the APS
At the infundibular level, how are the pulmonary and aortic infundibulum oriented?
The pulmonary infundibulum is anterior and to the right of the aortic infundibulum
At the level of the valves, how are the pulmonary and aortic valves oriented?
The pulmonary valve is anterior and to the left of the aortic valve
At the level of the great arteries, how are the pulmonary artery and aorta oriented?
The pulmonary artery is posterior and to the left
When do the pharyngeal arches appear?
During week 4 (~28 days)
True or false: The development of the aortic arches is related to the development of the head and neck
True
What are the aortic arches?
They are 6 pairs of arteries that form on the right and left dorsal aortas–one pair (right and left) for each pharyngeal arch.
What happens to the 1st aortic arch?
It is the earliest to disappear. It contributes to the maxillary and external carotid arteries
What happens to the 2nd aortic arch?
Disappears.
Dorsal portion => stapedial artery
What happens to the 3rd aortic arch?
Carotid arteries
What happens to the 4th aortic arch?
Right side => Right brachiocephalic artery, right subclavian artery
Left side => transverse aortic arch
What happens to the 5th aortic arch?
Disappears
What happens to the 6th aortic arch?
Proximal portion of right => proximal right pulmonary artery
Proximal portion of left => proximal left pulmonary artery
Distal portion of left => ductus arteriosus
Which aortic arch is typically asked about on rounds?
6th aortic arch. As long as you have the 6th aortic arch vessels formed, the surgeons can fix a baby born without a pulmonary valve or pulmonary artery. However, if you’re born without 6th aortic arch vessels, you are left only with collateral vessels which are almost impossible to make use of or to repair.
True or false: Lungs of fetus is full of fluid
True
In embryos, where does oxygenated blood come from?
From placenta
_______ goes from the placenta to mix with deoxygenated blood
Ductus Venosus
What is the patent foramen ovale?
It’s a one way valve that opens from the right atrium to the left atrium. 1/3 of the blood returning to the embryonic heart travels from the right atrium to the left atrium across the septum.
The other 2/3 goes to the right ventricle and into the pulmonary artery
What is the ductus arteriosus?
About 6-8% of blood flows to the fetal lung (to start establishing lung vessels.. but small amount). The ductus arteriosus carries 55-60% of combined ventricular output from the pulmonary artery to the aorta and to the rest of the fetus.
What supplies blood flow to the head and neck of a fetus?
1/3 of the blood went from the RA to the LA across the foramen ovale. In the LA, it combines with the 6-8% of blood that did go through the lungs (still deoxygenated because the lungs are full of fluid) and this blood all goes to the LV and then out the aorta.
How many people have patent foramen ovale?
1-3%
Out of the ductus arteriosus, ductus venosus, and foramen ovale, which one doesn’t always disappear?
Foramen ovale. (probe foramen ovale). It’s big enough for a probe to go through so theoretically blood could go through but blood doesn’t because the pressure on the right side of the heart drops with inspiration.
How does the ductus arteriosus close?
Functional closure of the ductus arteriosus usually occurs 10-15 hours after birth (delayed at higher elevation)
Contraction and cellular migration of the medial smooth muscle in the wall of the ductus results in intimal thickening with protrusion into the lumen.
Anatomic closure occurs in the 2nd-3rd week of life-vascular remodeling. The internal elastic membrane of the ductus fragments, the intimal and media proliferate, mucoid lakes form in the intimal and media, and byline mass forms that totally occludes the lumen.
By age of 1 year, the ductus arteriosus has closed in ____ % of children
> 98%
Patent ductus arteriosus is found more often in which 3 circumstances?
Premature birth, high elevation (>9,000 feet), maternal rubella infection
How does the ductus arteriosus close?
The ductus arteriosus is thought to have fewer elastic fibers and more muscular tissue than the aorta and pulmonary artery. The increased PaO2 after birth results in contraction of the spiral muscular fibers in the wall of the PDA. This response is weaker in premature infants.
What does the ductus arteriosus turn into?
Ligamentum arteriosum
The ductus arteriosis is persistence of the ____ portion of the ____ aortic arch.
Distal, 6th
Incidence of PDA is ___% of all congenital heart defects
5-12%
What is the incidence of PSA in infants that weigh
70%
about 1/3 of those have spontaneous closure and the others can be fixed with operation
