CP1 & CP2 - Embryology Handout notes Flashcards
apex of the heart
The lowest superficial part of the heart. It is directed downward, forward, and to the left, and is overlapped by the left lung and pleura. -wiki
relative position of the ventricles and atria
ventricles are anterior to atria
what is a summary of what the embryology of the heart builds?
the embryo will build a structure on the midline, with a posterior inflow tract for blood, a ventrally located pumping apparatus, and an outflow tract that is directed towards the head.
how do the morula and zygote get their nutrition.
from diffusion.
Where is the inner cell mass located in the embryo
Note the position of the inner cell mass is such that it is
located eccentrically within the sphere, close to the uterine wall.
how does the blastocyst implant into the endometrium?
what does the area become?
what is the name of the cells that do this?
where are their precursors?
Before the vascular system develops, the zygote implants into the endometrium and develops a syncytium from invasive, multinucleated trophoblastic cells.
what are the spaces that develop in the in the syncitium?
lacunae
Allantois
is a part of a developing amniote’s conceptus (which consists of all embryonic and extra-embryonic tissues). It helps the embryo exchange gases and handle liquid waste.
edge of the syncytiotrophoblast erodes into
some of the maternal blood vessels.
describe the lacunae.
On what day does blood begin to fill these structures? how does this happen?
These little lacunar spaces are somewhat interconnected. At 13-14 days post-fertilization, enough erosion will have occurred for maternal blood to flow from the maternal sinusoids into the lacunae, eventually filling them.
what are the blood vessels that are eroded by the syncytiotrophoblast called?
when does this occur?
what is the result of this?
- sinusoids
- At 13-14 days post-fertilization, enough erosion will have occurred for maternal blood to flow from the maternal sinusoids into the lacunae, eventually filling them.
Differential pressure levels in the lacunae will:
what is this called and what is an important characteristic?
When does this occur?
- cause blood to wash through the lacunae and back into maternal veins in the uterine wall.
- This is uteroplacental circulation – it is entirely maternal,
- beginning about 14 days after fertilization.
compare simple diffusion to uteroplacental circulation
-more efficient than simple diffusion, but it will not be good enough to support the development of the rapidly growing embryo.
HIgh resolution US suggests what about the rate of flow?
During what period?
-That rate of flow may be very low during the first 10 weeks of gestation; this remains a point of controversy.
what does the Embryonic circulatory system arise from?
In large part from the extraembryonic mesenchyme, where blood islands are forming.
How do cells form a vascular tree?
They clump together with the cells in the middle sloughing off to become blood cells, while the ones on the outside become the lining of the blood vessels. This is the beginning of a vascular tree
what is formation of blood vessels by formation of a vascular tree called?
what type of cells are formed? From what?
This type of vessel formation is vasculogenesis
-The differentiation of cells from the mesenchyme into both blood cells and endothelial cells
Where do the first blood vessels occur?
where else do they form?
blood islands form how long after that?
- The first blood vessels occur along the wall of the yolk sac.
- Some develop on the connecting stalk, as well as the allantois. These are all extraembryonic.
- Within a couple days, blood islands will also form in the embryo.
What happens in the embryo proper in the beginning of cardio embryology?
mesodermal cells ingress through the primitive streak some of them receive signals that determine them to become portions of the developing heart and circulatory system.
Cells that ingress near the cranial end of the primitive streak develop into
the outflow tract
Cells that ingress in mid-streak develop into
ventricle
Cells that ingress caudally develop into
atrium
As the cells ingress at different locations, there are areas of diff. conc. of what?
what does this do?
- retinoic acid concentrations,
- it primes them to receive inductive signals.
what is the source of the inductive signals?
what is this area a part of?
what is it close to?
- anterior visceral endoderm
- a specialized area of hypoblast near the caudal end of the presumptive prechordal plate.
where and in what shape do the ingressed cells assemble?
What is this area called?
- in a horseshoe shape around the anterior visceral endoderm and cranial end of the primitive streak.
- They are located subjacent and anterior to the neural plate, at the cephalic end of the embryo.
- This horseshoe-shaped area is known as the cardiogenic plate.
what is the anterior visceral endoderm?
- An area of the hypoblast that is associated with the epiblast.
- It releases inductive signals that affect ingressing mesodermal cells to become the cardiogenic plate
define: Vasculogenesis
how is it different from angiogenesis?
- Vasculogenesis is differentiation of cells to produce blood vessels where none existed
- as opposed to angiogenesis, which occurs by sprouting of “buds” from pre-existing vessels. Angiogenesis is what goes on in most tumors and in people as they get older.
What is the cardiogenic plate made from?
what is it anterior to?
The cardiogenic plate is formed from splanchnopleuric mesoderm (i.e., mesenchyme related to the wall of the gut) of the lateral plate, and is anterior to the presumptive brain before folding.
What happens after the formation of the cardiogenenic plate?
Two axes of folding of the lateral plate take place simultaneously
what is brought from being positioned anteriorly to the brain to being being placed posterior to the head?
What is this type of folding called?
Cephalocaudal folding brings the cardiovascular tube, which began anterior to the brain, to a position inferior to the head.
Nerves that stream downwards from the brain stem to the heart are a result of this folding.
Cephalocaudal folding
There are two structures that curved during Cephalocaudal folding.
Name them.
-the paired primitive aortae.
What two structures did not bend during Cephalocaudal folding?
where do they remain?
what do they become?
The endocardial tubes.
They remain parallel to the neural tube and become the ventrally located heart.
what happens in lateral folding?
describe what happens.
Lateral folding brings the endocardial tubes together and they fuse. However, they were already joined at the very front of the lateral plate, so they only need to come together at their more caudal regions.
What will become the aortic arches?
The bends that arose from the dorsal aorta being pulled down ventrally
What is the segment that connects between the heart and the aortic arches
The truncus arteriosus
what is directly below the truncus arterious?
a swelling called the bulbus cordis (bulb of the heart).
What is below the Bulbus cordis
the primitive ventricle.
Adjacent to the ventricle is another small chamber
called the atrium
On either side of the atrium are tributaries called the:
sinus venosus
What does the sinus venosus do?
Bring blood in from a number of veins. It is the inflow tract involved with the atrium.
In what direction does the blood in the sinus venosus travel?
What is the caveat?
From the body, to the sinus venosus, through the atrium, through the ventricle, to the bulbus cordis, through truncus arteriosus, to the aortic arches, into the dorsal aorta and around the body.
Caveat: if it were going in one direction, however, in the early embryo it probably goes in both directions
What are the subsections of the Embryology handout?
The Beginning - Diffusion
First Placental Bloodflow is Maternal:
Now the Embryo Prepares:
Folding them together: at the heart of it all:
Twisting a hose into a pump:
Ventricle bifurcation:
Atrial bifurcation:
Changes at birth:
Response to injury:
Where is the cardiovascular tube located now (after the folding)
What is the open area it’s in called?
in the midline and located ventrally, is anchored at two points but most of it is free-floating in an open area called the COELOM.
Why is the tube forced to bend?
It is growing a little faster than the coelom expands. Consequently, as the tube gets longer, it is forced to bend.
What happens to the sinus venosum as the cardivascular tube grows?
What direction does it move to?
- The sinus venosus (the inflow tract involved with the atrium) shifts cephalically behind the ventricle.
- it moves up and to the right, coming up behind the heart. It always does that in normal people.
Nota bene
What direction does the sinus venosus go?
What direction does the atrium go?
Why is this significant?
How are the 2 oriented in relation to each other?
what is pushed to cardiac tube to what side?
what is this bent region of the heart called? where does it end up?
The way it bends, the sinus venosus always goes up and to the right, the atrium always goes behind, and that is how the inflow tract and outflow tract get in the same position, although the inflow tract is posteriorly located.
This pushes the bend in the cardiac tube to the left, which puts the apex of the heart on the left side.
The bulbus cordis is connected and inferior to what structure?
the truncus arteriosus
What begins to form when the structure composed of the bulbus cordis and the truncus arteriosus fold back on the atria?
The beginnings of the R and L atria begin to form
Does the bulbus cordis give us a R and L ventricle?
NO.
The bulbus cordis looks like it is going to give us a ventricle on each side, but it does not do this
After the R and L Atria begin to form, and as the heart continues to grow, what happens to the ventricles?
The ventricle gets broad laterally and the bulbus cordis leans back on the ventricle.
what is located where the bulbus cordis attached to the ventricle?
Where is this feature located relative to where the blood travels to get out of the heart?
What does this area become?
- Where the bulbus cordis is attached to the ventricle, there is a little ripple in the floor of the ventricle.
- That ripple is slightly medial to where the blood is traveling to get out of the heart. So it is a little to the left of the base of the bulbus cordis.
This is the site of the early interventricular septum.
after the early interventricular septum forms, what happens to it?
The septum then “grows” as the walls of the presumptive ventricles expand leaving the tissue of the septum behind and adding to the bottom of the septum.
After the ventricles grow, the bulbus cordis is:
The beginning of an outflow tract for the aorta and the pulmonary trunk
Which way does the blood flow after ventricle bifurcation?
what is formed in this step by pinching?
Blood flows from the sinus venosus to the atrium, through the opening (which is shaped like a dumbbell or an “H”) into the ventricle.
This is pinched off to form two orifices, one to go into each ventricle.
The leaning posture of the bulbus cordis/truncus arteriosus will also provide what?
the impetus for the separation of the two atria.
Why is Atrial bifurcation more complex ?
because there are two septa required to separate the atria.
What Clinical Correlate could atrial bifurcation problems lead to?
Blue baby: Too much unoxygenated blood from the right atrium passes to the left atrium, then to the left ventricle and the rest of the body, making the baby look blue.
What causes the bending of the roof of the Atria?
The leaning of the bulbus cordis/truncus arteriosus between the atria (and between the ventricles) causes a bending in the roof of the atria.
Describe how the septum primum travels during Atrial bifurcation.
What remains?
The beginning of the septum primum (endocardium, in a sickle-shaped structure) begins to grow down from the posterior wall, with an orifice remaining open between the two presumptive atria to allow blood to move from the right to the left.
What happens as the embryo develops?
But as the embryo develops, the hole gets smaller and blood flows less freely.
Why is there not much blood destined for the left atrium at this point?
Of course, there is not much blood destined for the left atrium in the embryo because the lungs are not functioning, and, therefore, little blood is coming from them.
what is the ostium primum?
The ever-shrinking hole being closed by the septum primum. As it constricts, blood has more difficulty getting through.
Where does most of the blood returning from the body come back through?
what is this vessel pointing to?
Most of the blood returning from the body travels via the inferior vena cava, which is pointing towards the already-closed top of the septum primum.
directed flow from the inferior vena cava to the septum primum encourages what?
what results from this?
This directed flow encourages cell death in that area of the septum primum, and a new opening breaks through here.
Where is this new opening?
Where is the 1st opening (the ostium primum)?
This second opening, the ostium secundum, is in the septum primum.
Remember that both openings are in the septum primum.
What happens to these 2 openings?
The ostium secundum becomes quite large, while the ostium primum closes completely.
Blood can flow both ways, until _________ starts to form?
In which chamber does it form?
Blood can flow both ways, until the septum secundum starts to form, also in the right atrium.
What is the septum secundum?
It is a descending sickle shape from the anterior wall. It covers the ostium secundum, but does not become a complete septum; an aperture remains and allows blood through.
Compare the septum secundum to the septum primum.
The septum secundum is a secure rigid structure, unlike the septum primum, which was more like a sheet of paper.
what is formed upon completion of the septum secundum?
stiff septum secundum with a flimsy septum primum behind it.
How does blood flow from the R atrium to the left atrium? Describe how it gets through.
what is the shunt called?
The blood goes through the hole in the septum secundum, pushes against the flimsy septum primum, and exits through the ostium secundum, to the left atrium.
In the embryo/fetus, this right-to-left shunt is called the foramen ovale.
Why is passage from the right atrium and not to the lung beneficial before birth?
In an embryo, blood from the right atrium would be destined for the lungs, but because the lungs are not operating, passage to the left atrium is good.
What acts like a flutter valve between the atria?
The foramen ovale acts like a flutter valve that opens when blood is going in that direction.
What happens to the L atrium to R atrium circulation at birth?
When the baby is born and the lungs open up, the blood pressure in the atria changes. Because blood in the right atrium is no longer at a higher pressure than blood in the left atrium, the blood in the left atrium pushes the flimsy septum primum against the firm septum secundum, effectively closing the foramen ovale.
What does the foramen ovale become in adults?
what is the term for a foramen ovale that doesn’t seal off? How prevalent is that?
In the adult, this becomes the fossa ovalis.
About 25% of people have a probe-patent foramen ovale, which means you can take your thumb and push gently on it and it will open; that is to say, it doesn’t seal off.
In what kind of cases has the reopening of the valve saved the patient’s life?
There have been cases, allegedly, where people with probe-patent foramen ovale with certain kinds of congestive heart failure have had the valve reopen and it has saved their lives.
What is the first organ system to develop?
The cardiovascular system is the first to what?
The nervous system
- The cardiovascular system is the first to function, with the heart beating irregularly at 23 days after fertilization.
Name the layers of the heart from the outer area in
Which germ layer do these arise from?
epicardium, myocardium and endocardium
All three arise from the mesodermal germ layer
Which cardiac layer is continuous with the endothelium
the endocardium
What are the layers of the heart tube in the early embryo?
In early embryos, the heart tube is composed of an inner area, the endocardium, and an outer area, the epimyocardium.
What is the gelatinous material that occupies the space between the endocardium and the epimyocardium?
What is it’s function?
- A gelatinous material, called cardiac jelly, occupies the space between these two layers. Cardiac jelly has the consistency of jello.
- It is a space holder that bends but does not break and likely plays a role in the looping of the heart.
What do cells in the epicardium secrete during development?
what do these molecules look like in under the microscope?
As development progresses, the cells in the epimyocardium secrete particles called adherons.
You can see adherons in a microscope; they are like little beads.
What do adherons contain?
They contain TGF-beta, some fibronectins, some proteoglycans, as well as a variety of inductive signals,
What does one of the inductive signals in adherons do?
it stimulates the endocardium to have cells migrate from it into the cardiac jelly and become the mesenchymal cells of the endocardial cushions.
Epicardium secretes the adherons, which:
diffuse through the cardiac jelly and affect the endocardium.
What happens to endocardium cells after the secretion of adherons?
What do they participate in?
Subsequently, some of the endocardium cells divide and migrate out into the cardiac jelly in the endocardial cushion area to participate in making the tissue that separates the atria from the ventricles and supports the atrioventricular valves. The cardiac jelly later disappears.
What happens in response to injury?
Can cardiac tissue regenerate?
Interestingly, current evidence indicates that cardiac muscle cells divide until approximately 20 years of age. This means regeneration can occur in children and to some extent throughout adolescence.
Anatomy of Ductus Arteriosus Before Birth
During intrauterine life
- 10% of the cardiac output passes through the lungs
- 90% is shunted via the ductus arteriosus (DA) to the aorta and systemic circulation
Anatomy of Ductus Arteriosus after Birth
After birth
• Most of the right ventricular output should pass through the lungs to facilitate proper gas exchange
• To make this possible, the ductus undergoes constriction and functional closure soon after birth
o Eighty percent (80%) of the DA in term infants close by 48 hours
o Nearly 100% by 96 hours
o Failure of this normal closure results in problems especially in preterm neonates.
Physiology of Ductus Arteriosus after Birth
Physiology
Oxygen and endothelin are very strong vasoconstrictors of the DA
Prostaglandins E2 and I2 are strong vasodilators of the DA
In utero
• Lower oxygen concentrations
• High circulating PgE2 and PgI2
o Helps keep ductus patent.
After partutition
• Sudden elevation in circulating oxygen tension
• Rapid fall in prostaglandin levels
o Result is strong vasoconstriction and functional closure of the DA soon after delivery.
o Anatomical closure occurs in the next 1-3 months.
What is VEGF
Vascular endothelial growth factor (VEGF) is a signal protein produced by cells that stimulates vasculogenesis and angiogenesis. It is part of the system that restores the oxygen supply to tissues when blood circulation is inadequate. Serum concentration of VEGF is high in bronchial asthma and diabetes mellitus.[1] VEGF’s normal function is to create new blood vessels during embryonic development, new blood vessels after injury, muscle following exercise, and new vessels (collateral circulation) to bypass blocked vessels.
Osteum primum and Osteum secundum for on what
Septum primum
The heart develops from what mesoderm?
Splanchnopleuric
Bulbous cordis becomes
Right atrium
Hand 1 and hand 2
Hand 1 - transcription factor in cardiac looping to the left side of the caudal regional of heart tube
Hand 2 follow hand 1 in the region of primitive ventricle
Majority of smooth muscle walls int right atrium
Derived from right sinus venosus
Left sinus venosus becomes
Coronary sinus
Oblique canal formed by the free edge of septum secundum does not form completely. It along with the Osteum secundum
form foramen ovale
Adherons
Don’t memorize
Tgf beta
Fibronectin
Proteoglycans
Inductive signals.
Pacemaker cells
sequester excess amount of glycogen
- believed that hemodynamics flow through developing heart causes certain areas of endocardium
To undergo shear stress and to secrete cytokine endothelin – 1, which induces differentiation of conducting system
Each pair of aortic arches is associated with a pair of.
Mesenchymal bars (pharyngeal arches) that are associated with the development of the jaws and neck
The umbilical vein travels
on the inner surface of the abdominal wall in the midline facial structure (falciform ligament) to deliver where it enters it preferential channel (duct is enosis) that bypasses most of the liver and conveys the blood to the inferior vena cava
Umbilical arteries become
Cord like medial umbilical ligaments
Causes of malformations
Isotetrinoin
Down’s syndrome
Hypoplastic left heart syndrome
Look up
Peri membranous septal defect
Look up
Excessive cell death can lead to
Aberrant septal perforation
Insufficient cell death contributes to
Epstein’s anomaly, a condition where in the tricuspid valve does not detach from the ventricular wall
Have no more targeted growth can lead to
Abnormal venous return that results from faulty incorporation of the common pulmonary vein into the left atrium
