Term
¡The cardiovascular system is the first major system to function in the embryo
¡The cardiovascular system starts to appear in week (2 or 3)
¡The system has to develop early because the growing embryo cannot satisfy its requirements by diffusion alone |
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Definition
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Establishment of the cardiogenic region
¡In week 3, Blood islands form in the visceral (splanchnic) layer of lateral plate mesoderm cranial to the developing brain. (heart develops from (endoderm or mesoderm))
¡A horseshoe-shaped endothelial tube (the primitive heart tube) develops as these blood islands coalesce. |
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¡ The master gene for heart development istranscription factor NKX2.5
¡NKX2.5 is conserved from the Tinman gene that regulates heart development in the fruit fly. |
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Definition
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Heart formation from the visceral layer of lateral plate mesoderm
--The heart forms a horseshoe-shaped tube in (front or back) of the brain.
---It forms the paired endocardial heart tubes |
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Definition
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The Heart Forms from the Visceral (Splanchnic) Layer of Lateral Plate Mesoderm. |
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Definition
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Term
Lateral folding of the body wall brings both sides of the horseshoe together
¡Fusion of the two sides creates a single heart tube from the 2 heart tubes
¡This forms the primitive heart. |
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Definition
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Term
¡Fusion of the two sides occurs except in the (caudal or cranial) most region where the poles remain separated.
¡The caudal pole forms the (venous or arterious) end of the heart.
¡The cranial end must sprout vessels to create an open path for blood flow. |
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Definition
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¡The cranial end is the arterial portion of the heart
¡ the vessels formed by sprouting are the aortic arches.
¡The heart has a mesentery at first (like the gut tube), but this tissue later degenerates. |
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Definition
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¡Formation and progression of the head (cranial) fold brings the heart tube into the thoracic region.
¡Rapid growth of the (forebrain or hindbrain) over the cardiac region is responsible for this event |
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Definition
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¡Heartbeats begin by (4 or 6) weeks.
¡Blood, which contains very few cells, passes from the venous end out of the aortic sac and into the aortic arches.
¡The first blood cells arise from the yolk sac. |
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Definition
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¡Each aortic arch passes through a pharyngeal arch on its way to the (dorsal or ventral) aorta.
¡All vessels are paired at this stage. |
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Definition
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Position of the heart during looping and the pattern of blood vessels
¡The (caudal or cranial) (venous) pole of the heart is anchored in the septum transversum
¡The septum transversum makes the central tendon of diaphragm
¡The pericardial sac is attached to the central tendon of the diaphragm |
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Definition
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Veins
¡The venous pole receives three different sets of veins:
§common cardinal veins (from the body)
§vitelline (from the yolk sac)
§ umbilical veins (from the placenta).
¡ All of these veins are paired at this time |
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Definition
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The (Venous Pole or cardinal vein) of the Heart Is Anchored in the Septum Transversum |
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Definition
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Term
¡Cardiac (looping or drooping) is the process whereby the heart tube folds on itself to create the typical heart shape and location.
¡At this stage the heart is a tube
§ it is beating |
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Definition
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Cardiac Looping
§the different regions have begun to differentiate:
▪ primitive atria
▪ primitive ventricle (left ventricle),
▪bulbus cordis ((right or left) ventricle)
▪ outflow tract (pulmonary artery and aorta) |
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Definition
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¡During looping, the atrial portion grows upward and to the (right or left), while the ventricular region grows downward and to the right.
§ This places the atria superiorly and posteriorly,
§the ventricles anteriorly and inferiorly, and
§the heart itself to the left side of the body. |
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Definition
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Shape of the heart after looping at the end of 4 weeks
¡Loooping establishes the basic shape of the heart
¡ Atrial and ventricular regions are recognizable due to creases and folds resulting from looping. |
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Definition
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Term
¡Looping relies on the same genetic cascade that regulates the establishment of sidedness.
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¡ Expression of nodal, lefty, and other genes causes expression of the transcription factor PITX2, the master gene for sidedness.
¡
¡ NKX2.5 (master heart gene) results in expression of Hand 1 and 2, which establish the left and right ventricles |
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Definition
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External and internal views of the heart after looping
¡At this time, no septation of the chambers has occurred
¡There will be many changes in these regions prior to the completion of their development |
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Definition
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¡Most of the (right or left) atrium (the smooth-walled part) is formed by incorporation of the sinus venosus and right sinus horn into the primitive right atrium. |
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Definition
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Formation of the atria
-All arteries and veins are paired
-blood flow in veins shifts to the (right or left)
-that in the arteries shifts to the (right or left). |
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Definition
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Formation of the right atrium
¡ Venous flow shifts to the (right or left) and the vena cavae are formed
¡ The right sinus horn is incorporated into the right atrium
¡ The opening from the left sinus horn diminishes in size. |
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Definition
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| Incorporation of the Right Sinus Horn of the Sinus Venosus into the Right Atrium |
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Definition
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¡All that remains of the (left or right) sinus horn is the coronary sinus and oblique vein of the left atrium |
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Definition
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Formation of the right and left atria
Incorporation of the sinus venosus and right sinus horn into the (right or left) atrium creates the smooth-walled portion of that structure, the sinus venarum.
¡The opening of the sinus venosus is incorporated, edges appear around the opening, which form the right and left venous valves.
The remaining primordial atrium has a trabeculated wall |
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Definition
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Right atrium formation
¡A ridge, the crista terminalis, also forms between the original trabeculated portion of this atrium and the smooth-walled part
¡The location of this ridge is marked by a depression called the sulcus (terminalis or internist). |
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Definition
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Term
Right Atrium: Incorporation of the Right Horn of the Sinus Venosus |
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Definition
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Formation of the left atria
- The single pulmonary vein grows out from the (left or right) atrium and divides into four major pulmonary veins which connect to the lungs.
-Four openings for these veins appear in the wall of the left atrium.
-Incorporation of the pulmonary veins creates the smooth-walled part of the left atrium
The remaining primodial left atrial wall is trabeculated |
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Definition
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Term
¡(Endocardial or Ectocardial) cushion tissue forms around the AV canal to create four cushions:
§anterior
§posterior
§two lateral cushions.
¡Cushions are extracellular matrix-filled expansions of tissue covered by cardiac endothelial cells.
¡The matrix-filled regions will be populated by cells from the endocardium and by neural crest cells. |
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Definition
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¡Endocardial cushion material is key to heart (septation or palpation) because it is these tissues that grow together to form all of the septa in the heart.
¡Anterior and posterior AV cushions grow together to separate the canal into two openings |
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Definition
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Term
¡Atrial septation involves growth of two overlapping septa.
¡The overlapping septa leave to an opening (ostium primum).
¡This opening will act like a valve.
¡This permits blood flow across the septum during prenatal development and provides a way to close after birth. |
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Definition
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¡A first septum (septum primum) grows (downward or upward) toward the fusing endocardial cushions in the AV canal.
¡There is an opening between the septum and AV cushions and it is called the ostium primum.
¡The ostium primum will close when a second opening (ostium secundum |
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Definition
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Atrial septation showing septum secundum
¡A (third or second) septum (septum secundum) also grows from the roof of the atrium toward the fusing AV cushions, and it overlaps septum primum.
¡It will create an opening called the foramen ovale. |
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Definition
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Interatrial septum from inside the right atrium
¡The foramen (ovale or spinosum) is the opening in the septum secundum.
¡The valve of the foramen is formed by the septum primum. |
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Definition
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Term
¡At birth pressure rises in the left atrium due to increased blood flow from the lungs, while pressure on the right decreases.
§These changes in pressure press septum primum (the valve) against septum secundum and (close or open) the foramen ovale. |
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Definition
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Ventricular septum development
¡By the beginning of the (sixth or seventh) week, growth of the ventricles in lateral and ventral directions has caused a column of muscle tissue to partially separate these two chambers.
¡This makes the muscular part of the ventricular septum. |
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Definition
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Ventricular septum development
¡By week (6 or 7), continued proliferation of endocardial cushion tissue completes formation of the ventricular septum
¡The upper portion of the interventricular is membranous and lower portion is muscular |
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Definition
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Term
AV cushion differentiation into the AV valves (mitral: left; tricuspid: right)
¡As the AV cushions separate the AV (canal or formamen) into mitral and tricuspid opening, all four cushions become fibrous
¡The attachments to the ventricular walls become cord-like, forming the chordae tendineae
¡Muscular attachment sites elongate and form the papillary muscles. |
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Definition
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Term
The outflow tract: making the pulmonary artery trunck and aorta
¡During the (sixth or seventh) week, the outflow tract, comprised of the conal and truncal arteriosus regions, begins to divide.
¡Endocardial cushions form in the two regions and grow toward each other |
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Definition
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Term
Spiraling of the conotruncal (outflow tract) septum
¡As the septum in the (outflow or inflow) tract grows, they spiral 180 degrees.
¡Spiraling causes the pulmonary channel to exit the right ventricle and the aorta to exit the left.
¡The cushions also grow downward to fuse with the anterior endocardial cushion in the AV canal |
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Definition
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More outflow tract
¡Growth of the septum completes separation of the pulmonary artery trunk (anteriorly or posteriorly) from the aortic trunk (anteriorly or posteriorly).
¡The spiral nature of the septation process can be seen in how the vessels twist around each other. |
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Definition
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Term
¡Neural (crest or tube) cells participate in septation of the outflow tract
¡The fact that crest cells participate in heart septation and that they make all of the bones of the face and some of the skull explains why many children with craniofacial defects also have cardiac defects. |
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Definition
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Term
¡Organization of the prenatal system is that the lungs are not functional and the placenta is the organ of life support for the fetus.
¡ “shunts” are established that get oxygen and nutrient-rich blood out to the developing tissues as fast as possible
These shunts are designed to close at birth so that the postnatal pattern can be established |
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Definition
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Term
¡Three shunts are established:
§Ductus venosus through the liver: This channel bypasses the liver carrying oxygenated blood from the umbilical vein to the inferior vena cava.
§The ductus venosus regulates blood flow from the placenta to the fetal heart by contracting or expanding as necessary. |
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Definition
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Term
Shunt
¡Ductus arteriosus: The ductus connects the pulmonary artery to the aorta such that most of the blood coming from the (right or left) ventricle through the pulmonary artery trunk can bypass the lung and pass directly back into the aorta then out to the body |
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Definition
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Term
Shunt
¡Foramen ovale: The foramen ovale allows passage of most of the blood from the placenta through the (inferior or superior) vena cava to pass directly across the right atrium into the left.
¡The foramen has a flapper valve created by the atrial septum (septum primum part) that opens and closes the opening. |
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Definition
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Comparison of postnatal and prenatal circulation patterns
¡To get as much oxygen and nutrient-rich blood to the (left or right) side of the heart and out into the fetal circulation by bypassing organs that are not yet functional
¡ these organs [lungs and liver] receive a small amount of blood for their own development |
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Definition
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Term
¡By about (8 or 10) weeks, heart septation is complete, and the prenatal pattern of blood flow is established.
¡
¡At birth, the umbilical cord is clamped, stopping blood flow from the placenta. |
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Definition
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Postnatal and prenatal blood flow
§the ductus venosus closes and later becomes fibrotic, forming the ligamentum (venosum or falciform) in the liver.
§The umbilical vein becomes the ligamentum teres in the free margin of the falciform ligament |
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Definition
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Postnatal and prenatal blood flow
§Pressure rises in the (left or right) atrium compared to the (left or right) due to increased blood flow from the lungs and decreased blood flow to the right side from the placenta.
§The pressure change closes the flap over the foramen ovale.
§ This flap will become fibrotic and permanently seal the opening. |
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Definition
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Term
¡Bradykinin is secreted by the (lungs or heart) and causes the ductus arteriosus to close.
¡The ductus becomes fibrotic to form the ligamentum arteriosum. |
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Definition
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