Embryology- Cardiovascular Flashcards
What part of mesoderm is responsible for cardiac development?
cardiogenic mesoderm
cranial to the neural tube and the future mouth.
What happens to the cardiogenic mesoderm at the end of week 3?
the splanchnic mesoderm begins to condense into a more solid arrangement of cells that form a horse‐shoe shaped cord. The cord will hollow out, forming a horse‐shoe shaped tube that will eventually form left and right heart tubes.
The right and left cardiogenic tubes arise how?
Lateral body folding occur when the lateral margins of the disc fold ventrally, eventually meeting and fusing in the ventral midline axis
these tubes eventually fuse into a single heart tube with a common chamber
Fusion of the right and left primordial heart tubes is complete by when?
end of 4th week of development
Fusion of the right and left primordial heart tubes occurs in what manner? Caudal to cranial?
cranial to caudal (gives rise to a single embryonic heart tube in the midline with a common inner chamber)
When does head to tail folding begin?
end of 3rd week
What induces head folding?
occurs as a consequence of the rapid development of the nervous system
As the anterior end of the neural tube develops and grows in mass, it induces the head to begin tucking in. This initiates a migration of the cardiogenic tissue, first through the cervical region and then ultimately into the thorax.
When is autonomic innervation to the developing heart tube established?
During migration of cariogenic tissue through the cervical region
What are the autonomic innervation to the heart?
parasympathetic- vagus
sympathetic- T1-T5
When does the heart reach its definitive position in the thorax?
end of week 4
What are the five divisions of the embryonic heart tube?
truncus arteriosus, bulbus cordis, primitive ventricle, primitive atrium, and sinus venosus (from cranial to caudal)
When does the heart gain contractability?
day 23. moving blood in a caudal to cranial direction in the still vertical heart
The cranial part of the tube represents the arterial outflow, while the caudal end of the tube represents the venous inflow.
How does the caudal (atrial) end of the vertical heart tube move during folding and looping?
superior, posterior, and to the right.
The arterial (truncal) end of the tube will move anteriorly, inferiorly, and to the left. This will be complete by the end of the 4th week.
What structures does the truncus arteriosus form?
aorta & pulmonary trunk and their semilunar valves.
What structures does the bulbus cordis form?
it gives rise to the smooth walled areas (outflow tract) of the right and left ventricles (conus arteriosus & aortic vestible).
What structures does the primitive ventricle form?
the trabeculated parts of the right and left ventricles.
What structures does the primitive atrium form?
trabeculated parts of the right and left atria (i.e. the auricles)- pectinate muscles
What is the only part of the embryonic tube that consists of right and left parts?
sinus venosus
The right horn of sinus venous forms what?
the majority of the right atrium (sinus venarum).
The left horn of sinus venous forms what?
cardiac veins on the surface of the heart (coronary sinus and the oblique vein of the left atrium).
In pre‐natal development, blood from mom is being provided through the placental circulation to the fetus via what?
umbilical vein. Deoxygenated blood is returned to the placenta via a pair of umbilical arteries.
The umbilical vein contains the blood with the highest oxygen content (~80%) as it is coming directly from mom via the placenta and through the umbilical cord.
During development, what visceral structures are not doing much work?
the liver (because mom has already processed the blood) and the fetal lungs (because blood has already been oxygenated)
What is the ductus venosus?
It allows most of the blood in the umbilical vein to bypass the liver by re‐directing it into the IVC
The blood in the ductus venosus is still ~ 80% oxygenated. Notice that a small volume of blood flows through the liver, supplying those tissues with adequate oxygenation.
Is blood in the IVC more or less oxygenated than in the umbilical vein? Why?
Less.
In the IVC, the high oxygen saturated blood from the ductus venosus is mixed with low oxygen saturated blood (~ 20%) returning from the fetal periphery. Nevertheless, blood flow from the IVC into the right atrium still has reasonable oxygen saturation of ~60‐70%.
What side of the heart has higher pressure during development? Why?
right.
Because there is a massive volume of blood entering the right atrial chamber via the IVC and the SVC. Second, there is high pulmonary resistance because the pulmonary circulation is closed.
What does the foramen ovale do?
It sends this oxygen‐rich blood from the right atrium directly into the left atrium, bypassing the pulmonary circulation of the fetus.
Notes on mixing of blood from IVC and SVC
Within the right atrium, there are two sources of incoming blood. One is from the IVC (oxygen‐rich from mom) and the other is via the SVC (oxygen‐poor from the fetal periphery). However, the right atrium does not act like a mixing bowl for these two circulations. Rather, the respective flows remain laminar, such that the oxygen‐rich IVC flow is directed towards the foramen ovale and the left atrium, and the oxygen‐poor SVC flow is directed towards the right AV valve and the right ventricle with little mixing of the two circulations.
Oxygen rich blood from the IVC goes through what structure in the developing heart?
foramen ovale to left atrium. From there it goes to systemic circulation by passing through the left ventricle (but not before supplying the heart with oxygenated blood)- the blood that is pumped out systemic is still fairly oxygenated (~65%)
How does oxygen poor blood from the SVC move through the heart?
does not go through foramen ovale. Goes from right atrium to right ventricle, and out of the pulmonary trunk, then through the the ductus arteriosus, to enter the descending aorta distal to the arch thereby bypassing the fetal pulmonary circulation without impacting the oxygen flow to the head
When does highly and poorly oxygenated blood mix?
in the descending aorta after oxygenated blood has gotten the chance to go to the head
When do the three fetal shunts close?
foreamen ovale- almost instantly following birth and first breath due to pressure change
ductus venosus and ductus arteriosus- within 24-36 hrs after birth, caused by smooth muscle contraction
The ductus venosus closes via contraction of its smooth muscle wall and forms a remnant called the?
ligamentum venosum
Foramen ovale closes in response to pressure changes in the heart, and forms a remnant called the?
fossa ovalis
The ductus arteriosus closes via contraction of its smooth muscle wall and forms a remnant called the?
ligamentum arteriosum
Where does the ligament arteriosum span?
spans between the arch of the aorta and the pulmonary trunk.
The closed umbilical vein and artery form?
the round ligament of the liver (ligamentum teres) and the medial umbilical ligaments, respectively.
neural crest cells originated from the neural folds of the neural tube and migrated into what two regions of the primitive cardiovascular system?
truncus arteriosus and the endocardial cushions
Why can’t the atria cannot be fully septated until birth?
The foramen ovale must remain open at all times during fetal life, to allow for the right‐to‐left shunting of blood.
When does atrial septation occur?
5th-8th weeks
What is the first step in atrial septation?
the downward growth of septum primum from mesoderm of the common interatrial roof
The septum primum grows toward, but initially stops just short of the endocardial cushion, leaving an opening in the developing interatrial wall called foramen primum. The right‐to‐left shunt is maintained.
NOTE: Septum primum will continue its downward growth and eventually fuses with the endocardial cushion, obliterating the foramen primum
fusion of septum primum with the endocardial cushion is dependent upon what?
NC cell migration into the cushion.