CP 1- Embryology MNTS notes

Question 1

in cardiac emmbryo

what happens by the 3rsd week

Answer 1

the heart is already beating

Question 2

in cardiac emmbryo

what happens by the 6th week

Answer 2

The fetus has pretty much attained a premature adult cardiac configuration

Question 3

where does the heart rest?

Answer 3

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

Question 4

what does the heart’s position imply?

Answer 4

that, during development, we need to form a

ventral pumping system and dorsal vessels during development.

Question 5

what term is used to describe the position of the atria and of the ventricles?

Answer 5

anteroinferior ventricles and posterosuperior atria

Question 6

whats the valve between the R atrium and L ventricle

Answer 6

tricuspid valve or right atrioventricular valve

Question 7

what is the valve that leads to the lungs

Answer 7

pulmonic

Question 8

what is the valve between the left atrium and the left ventricle

Answer 8

mitral

Question 9

what is the valve that leads to the aorta

Answer 9

aortic valve

Question 10

where is the ovum fertilized?

Answer 10

in the ampulla of the fallopian tube (AKA oviducts, uterine tubes, and salpinges (singular salpinx)

Question 11

how long before the zygota implants? where does it implant?

Answer 11

4-5 days onto the endometrium

Question 12

when it implants where does the zygote get its nutrients?

does this last long?

Answer 12

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.

Question 13

What characteristics should the developed system of exchange between the mother and embryo have?

Answer 13

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

Question 14

what happens by day 6

Answer 14

the
syncitiotrophoblast invades into the endometrium and will form spaces between cells that coalesce into
trophoblastic lacunae.

Question 15

how does the uteroplacental circulation form?

what does this facilitate?

Answer 15

-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.

Question 16

Describe the way in which the embryo circulation allows for gas, nutrient and exchange.

Answer 16

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.

Question 17

On what day would the trophoblastic lacunae fill with blood?

What is clinically significant about this?

Answer 17

-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.

Question 18

what are the 2 parts of the blastocyst?

Answer 18

the trophoblast and the inner cell mass (ICM).

Question 19

What happens on the inside while the early placenta is forming?

What happens initially?

Answer 19

the ICM is also developing at this time. Initially, it becomes the hypoblast, which lines the blastocoelic cavity.

Question 20

What part of the ICM is excluded from the embryo proper?

What does it induce?

Answer 20

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.

Question 21

What happens as the bilaminar disk grows?

Answer 21

-We will begin to see some disparities in the uniformity of the embryo.

Question 22

Where is the oropharyngeal membrane?

what is another name for it?

Answer 22

-Anterior to the primitive streak as it regresses posteriorly is the oropharyngeal membrane (or prochordal plate).

Question 23

What happens in the oropharyngeal membrane?

What will happen to it?

Answer 23

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”.

Question 24

By what is the oropharyngeal membrane induced before it breaks down?

This induction leads to formation of what?

where it this location?

Answer 24

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.

Question 25

What happens after gastrulation and the formation of the 3 primary germ layers? What other molecule plays a role here?

Answer 25

-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.

Question 26

What arrangement does the Cardiogenic mesoderm take? Based on the fate map. What cells that are ingressing will become what cardiovascular structure?

Answer 26

- 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).

Question 27

What is Vasculogenesis?

Answer 27

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.

Question 28

How is angiogenesis different from vasculogenesis?

Answer 28

Angiogenesis is slightly different from Vaculogenesis because it involves the branching of previously made vasculature. Angiogenesis is an important feature in sustaining tumor growth.

Question 29

What happens in the beginning of cardiovascular embryology? What will the horseshoe shape around the prechordal plate become?

Answer 29

-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.

Question 30

What types of folding occurs?

Answer 30

cephalocaudal folding and lateral folding.

Question 31

What is cephalocaudal? Describe it

Answer 31

-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.

Question 32

cephalocaudal has what effect on the nerves innervating the heart? When did these nerves develop?

Answer 32

- 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.

Question 33

Describe lateral folding

Answer 33

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.

Question 34

The endocardial tube is divided into what sections? What do these become?

Answer 34

``` 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). ```

Question 35

what is cardiac looping?

Answer 35

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.

Question 36

describe cardiac looping specifics What is one Clinical correlate? How common is this?

Answer 36

- 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.

Question 37

What is the last part of heart embryology after looping?

Answer 37

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.

Question 38

What forms the basis for the interatrial septum?

Answer 38

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.

Question 39

What is the 1st division of the atrium?

Answer 39

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.

Question 40

Describe the 1st division of the atrium

Answer 40

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.

Question 41

How is the Osteum secundum made?

Answer 41

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.

Question 42

What is the septum secundum

Answer 42

- 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.

Question 43

What is the foramen ovale?

Answer 43

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.

Question 44

What happens to the foramen ovale at birth? What does it become?

Answer 44

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.

Question 45

Does the foramen ovale fuse right after birth? When can this be beneficial?

Answer 45

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”.

Question 46

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?

Answer 46

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.

Question 47

Give an example of intussusception. what resulting resource consumption happens in the atrium?

Answer 47

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.

Question 48

What is the tiny piece of the atrium that remains as the original atrial tissue; What is the different about this tissue?

Answer 48

The auricle it’s rough and ridged like the ventricular walls.

Question 49

in fetal circulation What are 3 sources of blood that empty into the fetal heart.

Answer 49

- 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.

Question 50

Which veins are the only ones oxigenated in fetal circulation? What is the most oxygenated chamber of the heart?

Answer 50

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.

Question 51

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?

Answer 51

- 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.

Question 52

What is the coronary sinus

Answer 52

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