CP 1- Embryology MNTS notes Flashcards
in cardiac emmbryo
what happens by the 3rsd week
the heart is already beating
in cardiac emmbryo
what happens by the 6th week
The fetus has pretty much attained a premature adult cardiac configuration
where does the heart rest?
midline structure that rests on the diaphragm at the costal margin. It angles toward the left.
It is anterior to the aorta and the vertebral column
what does the heart’s position imply?
that, during development, we need to form a
ventral pumping system and dorsal vessels during development.
what term is used to describe the position of the atria and of the ventricles?
anteroinferior ventricles and posterosuperior atria
whats the valve between the R atrium and L ventricle
tricuspid valve or right atrioventricular valve
what is the valve that leads to the lungs
pulmonic
what is the valve between the left atrium and the left ventricle
mitral
what is the valve that leads to the aorta
aortic valve
where is the ovum fertilized?
in the ampulla of the fallopian tube (AKA oviducts, uterine tubes, and salpinges (singular salpinx)
how long before the zygota implants? where does it implant?
4-5 days onto the endometrium
when it implants where does the zygote get its nutrients?
does this last long?
simple diffusion (secretions and O2 dissolved in fluids).
Simple diffusion
won’t work for long, so it will have to develop a method for a more direct oxygenation.
What characteristics should the developed system of exchange between the mother and embryo have?
This means that
we need a system to pump blood from mom to baby, but we also need a system to pump blood from
baby to mom so that the fetus can support its own developing circulatory system
what happens by day 6
the
syncitiotrophoblast invades into the endometrium and will form spaces between cells that coalesce into
trophoblastic lacunae.
how does the uteroplacental circulation form?
what does this facilitate?
-When the syncitiotrophoblast gets to the endometrial blood vessels, the
endothelial lining of the capillaries will rupture and the lacunae will fill with mom’s blood.
-Because of the small pressure gradient in the endometrium (only about 40/38), we can get enough circulation to nourish the embryo more directly with its mother’s blood.
Describe the way in which the embryo circulation allows for gas, nutrient and exchange.
Eventually, as the embryo forms its own
circulation and blood cells, the embryonic blood will come into close contact (but doesn’t mix) with
maternal blood and allow for the diffusion of oxygen, nutrients and waste across the placental barrier.
On what day would the trophoblastic lacunae fill with blood?
What is clinically significant about this?
-The trophoblastic lacunae fill with blood at about day
14, which would be the normal time for a woman to start
her next period.
-This is the reason for “spotting” and a woman might not realize she’s pregnant until her 2nd missed period 7 weeks into gestation.
-This poses a problem because important things like the heart and nervous system have already developed at this point and may be subject to alcohol and other toxins. This is apparently a bigger problem with teens and is a big reason for why doctors give “the talk” to teenagers.
what are the 2 parts of the blastocyst?
the trophoblast and the inner cell mass (ICM).
What happens on the inside while the early placenta is forming?
What happens initially?
the ICM is also developing at this time. Initially, it becomes the hypoblast, which lines the blastocoelic cavity.
What part of the ICM is excluded from the embryo proper?
What does it induce?
The hypoblast is pretty much excluded from the
embryo proper (except for a small role in early
organization of the heart), but it does induce the
cells above it to become epiblast, which do give
rise to the embryo proper.
What happens as the bilaminar disk grows?
-We will begin to see some disparities in the uniformity of the embryo.
Where is the oropharyngeal membrane?
what is another name for it?
-Anterior to the primitive streak as it regresses posteriorly is the oropharyngeal membrane (or prochordal plate).
What happens in the oropharyngeal membrane?
What will happen to it?
We will build our face around this membrane and it will eventually break down, all but at the place “where you stick your finger in your mouth and it makes you gag”.
By what is the oropharyngeal membrane induced before it breaks down?
This induction leads to formation of what?
where it this location?
Before it breaks down, however, the hypoblast will induce
a small part of it to become the anterior visceral endoderm (AVE). Note that this is anterior to the
Prechordal plate.
What happens after gastrulation and the formation of the 3 primary germ layers?
What other molecule plays a role here?
-The AVE will give rise to FGF8. FGF8 causes the epiblast (now splanchnopleuric
mesoderm because it’s giving rise to the viscera instead of the body wall) that overlies the prechordal
plate to become cardiogenic mesoderm.
-Retinoic acid from the primitive node will also play a role here,
but note that it’s different than its part in periodicity during somite development.
What arrangement does the Cardiogenic mesoderm take?
Based on the fate map. What cells that are ingressing will become what cardiovascular structure?
- Cardiogenic mesoderm wraps around the prechordal plate in a horseshoe-like configuration.
- Based on the fate map, we know that cells closer to the midline will become the outflow tract (aorta and pulmonary arteries) and ventricles. Cells that migrate farther from the midline will become the atria and the inflow tracts (veins).
What is Vasculogenesis?
the vascular system actually develops first in the yolk
sac from extraembryonic mesoderm. Little clusters of cells in the “shell” of the yolk sac will become
blood islands and eventually form little vacuoles. Cells on the outside of the vacuoles will become
endothelial cells for blood vessels and cells that slough into the lumen will become the actual blood
cells. This is vasculogenesis.
How is angiogenesis different from vasculogenesis?
Angiogenesis is slightly different from Vaculogenesis because it involves the
branching of previously made vasculature. Angiogenesis is an important feature in sustaining tumor growth.
What happens in the beginning of cardiovascular embryology?
What will the horseshoe shape around the prechordal plate become?
-During the same time that the vasculature is
developing, the embryo proper is changing its configuration of the cardiogenic mesoderm.
-The horsehoe shape around the prechordal plate will become a cluster of blood cells and vessels called an angiogenic cluster. This is what
coalesces into the heart tube.
What types of folding occurs?
cephalocaudal folding and lateral folding.
What is cephalocaudal?
Describe it
-The tube is sort of folded in half by cephalocaudal folding. This brings the area of the tube that will become the heart proper into its normal human position.
-Imagine that the prechordal plate is a hinge. The heart tube is anterior to the hinge in the presumptive head region and needs to be relocated posteriorly.
Therefore, the embryo folds at this “hinge” to get the heart in the chest.
cephalocaudal has what effect on the nerves innervating the heart?
When did these nerves develop?
- This is why the nerves to the heart and the diaphragm (which also develops anteriorly) come from the neck and cranial nerves;
- the nerves developed with the structure while it was still anterior.
Describe lateral folding
Lateral folding will bring the 2 sides of the horseshoe together. The free ends will combine into a single tube in the middle of the horseshoe shape. The fused portion is known as the endocardial tube. This tube remains ventral and becomes the heart. The unfused anterior portions are the primitive aortae. They migrate dorsally and become the presumptive aortic arches.
The endocardial tube is divided into what
sections?
What do these become?
From anterior to posterior these are the truncus arteriosus (which becomes the outflow tract), the bulbus cordis (which becomes the right ventricle), the primitive ventricle (which becomes the left ventricle), the primitive atrium (which becomes both right and left atria) and the sinus venosus (which forms the incoming veins).
what is cardiac looping?
This entire primitive heart structure develops within
a pericardial sac and the tube grows faster than the sac. Therefore, as the tube gets longer, it has to fold up to fit inside of its designated space. This is called cardiac looping.
describe cardiac looping specifics
What is one Clinical correlate? How common is this?
- When the heart tube loops, it bulges toward the left, which gives us our leftward facing cardiac shadow. The anterior wall of the heart tube is actually quite thick and is filled with a jelly that helps to avoid kinking of the tube so that it won’t fold like a garden hose. This bulging also causes the atria to be pushed posteriorly and superiorly and the ventricles to be pushed anteriorly and inferiorly.
- Nb: there are malformations where the heart tube bulges to the right, but these are rare.
What is the last part of heart embryology after looping?
At this point, we have the basic shape of the heart. All we need to do is partition it and divide the
outflow tract into the pulmonary artery and the aorta.
What forms the basis for the interatrial septum?
As the shape of the cardiac loop is formed, we
can see that the truncus arteriosus is leaning
against the primary atrium, allowing it to balloon
out on either side. This forms the basis for the
interatrial septum.
What is the 1st division of the atrium?
At this spot, an outgrowth from the superior and posterior wall of the atrium will come down, called the septum primum. This is the 1st division of the atrium.
Describe the 1st division of the atrium
It doesn’t completely separate the 2 chambers and leaves a gap at the anterior and inferior margin of the atrium, or the osteum primum.
How is the Osteum secundum made?
The IVC is the primary source of venous blood to the heart and is at relatively high pressure (remember that pressures are switched between the fetus and the adult). Blood that spurts out of the IVC will hit the septum primum and cause local cell death, creating an osteum secundum.
What is the septum secundum
- A second septum, which is thicker than the first, grows within the right atrium and occupies much of the medial wall.
- It also has a gap in the posterior and inferior region of the septum that allows passage of blood from the right atrium to the left atrium, by passing the lungs.
What is the foramen ovale?
The septum primium is much thinner than the septum secundum and acts as a flutter valve for this opening. It’s forced open, allowing blood to pass through the osteum secundum with high pressures in the right atrium, as exist in the fetus. This system is called the foramen ovale.
What happens to the foramen ovale at birth?
What does it become?
At birth, when pressures switch to
having a high left atrial pressure and a lower
right atrial pressure, the valve will slam shut
and blood won’t be able to pass through the
opening. The closure of the foramen ovale
creates a dent in the interatrial septum called
the fossa ovale.
Does the foramen ovale fuse right after birth?
When can this be beneficial?
The foramen ovale generally fuses shut
sometime after birth, but can remain mildly
open with probe-patent foramen ovale. This
isn’t usually helpful, but can be with extreme
cases of hypertension and with altitude
sickness. Dr. DeSesso calls this “kind of
cool”.
How are the wall of the atria and ventricle different?
Why this this the case?
Describe the process by which this happens. What is it called?
The walls of the atria are different from those of the ventricles because they’re smooth. This is because
the atria grow fast and instead of using their own resources and energy for this growth, they steal tissue from the veins by “telescoping”. This is called intussusception.
Give an example of intussusception.
what resulting resource consumption happens in the atrium?
For example, the left atrium originally
had only one pulmonary vein unloading its contents, but after intusussception, enough tissue from the
veins was utilized to go back 2 branch points, creating a system where 4 pulmonary veins dump into the
left atrium.
If the atria use a lot of matrial from the vasculature, they won’t have to waste their own
resources.
What is the tiny piece of the atrium that remains as the original atrial tissue;
What is the different about this tissue?
The auricle
it’s rough and ridged like the ventricular walls.
in fetal circulation
What are 3 sources of blood that empty into the fetal heart.
- Blood from the yolk sac (and therefore the
GI system as well) returns via the vitelline veins. - Blood from the body wall (muscles) and head returns via the cardinal veins.
- Blood from the placenta returns to the heart via the umbilical veins.
Which veins are the only ones oxigenated in fetal circulation?
What is the most oxygenated chamber of the heart?
Umbilical veins are the only ones that are oxygenated; the rest behave as normal, deoxygenated veins.
Because of this, the right atrium will be the most oxygenated chamber of the heart in utero.
What happens to veins as body parts migrate or disappear?
What veins drop out of the left side of the atrium?
what does this area become?
- When the body develops and veins come back to the heart, certain veins drop out as body parts migrate or disappear.
- All of the veins drop out on the left side of the atrium and the region where they originally were becomes the coronary sinus.
What is the coronary sinus
The coronary sinus is a collection of veins joined together to form a large vessel that collects blood from the heart muscle (myocardium). It delivers deoxygenated blood to the right atrium, as do the superior and inferior vena cava. -wiki
