Term
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Definition
| Blood islands form a primitive heart tube U shape, similar and next to the intraembryonic coelom in the lateral plate and cardiogenic mesoderm. Head fold brings it to thoracic position. |
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Term
| Describe the early steps of heart formation from cardiogenic region to the heart tube in the chest. (6) |
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Definition
Angiogenesis
The R and L heart tubes fuse – three layers of paired tube fuse during cranial and lateral folding
The resulting tube lengthens and develops alternate constrictions and swellings
Bulbus cordis and primordial ventricle grow quickly initiating folding
Heart continues to bend and loop and SV and atrium bend dorsal to bulbus cordis
Sinus venosus expands as heart loops; looping and folding aligns the outflow tract and initiates septation |
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Term
| When the R and L heart tubes fuse, what three layers are involved and what germ layer(s) are those derived from? |
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Definition
Three layers of paired tubes fuse during cranial and lateral folding; all 3 are derived from the lateral mesoderm
i. Endothelial cells from endoderm
ii. Cardiac jelly, the CT between endothelium and mesoderm- from mesoderm
iii. Primordial myocardium surrounds cardiac jelly
iv. Epicardium forms later: mesothelial cells migrate from sinus venosus over myocardium- from mesoderm |
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Term
| Describe blood flow in the early heart tube (6) |
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Definition
Blood flow: through a sequence of chambers in the single heart tube (venous→ arterial end)
i. Sinus venosus- receives umbilical, vitelline and common cardinal veins.
ii. Atrium
iii. Ventricle: and bulbus cordis grow faster than the rest of the heart, making loop
iv. Bulbus cordis: grows fast and cause heart looping
v. Truncus arteriosus, continuous with aortic sac and pharyngeal arteries→ aorta and pulmonary trunk
vi. Aortic sac→ aortic arches |
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Term
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Definition
h. Veins bring deoxy blood to heart through the sinus venosus (with the exception of the umbilical vein which is oxygenated and very nutrient rich)
i. Veins and arteries form from angioblastic cords
1. Vitelline veins: intermediately oxygenated blood from umbilical vesicle, the left regresses, the right forms the hepatic portal system and part of the IVC
2. Umbilical veins: well-oxygenated and nutrient rich blood from chorion, the right regresses and the ductus venosus (shuts blood from DV to IVC)
3. Common cardinal veins: carries poorly oxygenated blood from embryo to get reoxygenated |
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Term
| What happens to the blood vessels around weeks 6-8? What is the clinical significance of this, especially with the IVC? |
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Definition
a. The cardinal veins start out symmetrical but there is reorganization, degeneration, and anastomoses and branching, everything shifts to the right to form the IVC.
b. IVC is pieced together via contributions from 4 main pieces:
i. Proximal right vitelline vein → hepatic segment
ii. Right subcardinal vein → prerenal segment
iii. Subcardinal-supracardinal anastomosis→ renal segment
iv. Right supracardinal vein→ postrenal segment
c. It is clinically significant because if there are failures of rearrangement of the cardinal veins, ie: shift in opposite direction, anastomoses fail or arrange differently or degeneration fails, then it can result in:
i. Incomplete IVC or interruption of IVC: blood drains from lower limbs, abdomen and pelvis through heart via the Azygos system of veins instead.
ii. Double SVC or IVC, Left SVC
iii. But the body is largely tolerated because body adapts as it is developing. |
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Term
| How does the heart tube form the adult heart shape? What are 2 key accomplishments of this process? |
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Definition
a. Bulbus cordis grows quickly initiating folding
b. Primordial ventricle also grows quickly contributing to folding
c. Looping and folding aligns the outflow tract and initiates septation
d. AV and Ventricle partitioning accomplish this process |
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Term
| What structure/tissue plays a key role in the septation of the heart? What septa do they contribute to? What cells contribute? |
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Definition
a. Endocardial cushions, AV septum, IV septum, AP septum and neural crest cells.
i. AV canal: dorsal and ventral endocardial cushions fuse (where heart tube overlaps on itself and comes together), endothelial cells become mesencyhmal cells, then infiltrate and proliferate, along with neural crest cells. Also contribute to mitral and tricuspid valves.
ii. Endocardial cushions also contribute to:
1. Atrial septum/ Atrial partitioning
a. Septum primum grows downward toward the endocardial cushions: foramen primum was open then it closes, while the foramen secundum forms (perforations in the septum primum)
b. Septum secundum forms adjacent to septum primum, from the top of the atrium and grows down to the endocardial cushion
c. Septum primum forms valve, the foramen ovale is formed to let blood shunt from the right atrium to the left atrium in one direction
2. Ventricular septum/ Ventricle partitioning
a. Muscular interventricular septum begins to form near apex of heart and gets pushed up by cardiomyocyte proliferation and outward growth of the ventricles toward the endocardial cushions
b. The IV foramen persists until 7th week, then after that, membranous IV septum begins to form by the right and left bulbar ridges which is continuous with the aorticopulmonary septum and the endocardial cushion in the AV canal, separating the right and left ventricles.
3. Aorticopulmonary septum (outflow tract)
a. Truncus arteriosus and bulbus cordis split by neural crest cells forming aorticopulmonary septum
i. Neural crest cells migrating in from pharyngeal arches
ii. Form ridges initially that then fuse
iii. Undergo spiral rotation |
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Term
| Describe atrial, ventricular and aorticopulmonary septation, and common defects associated each of these. |
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Definition
a. Atrial septal defects:
i. Ostium secundum defects, aka patent foramen ovale: common and variable
1. Small hole is okay and fairly common, usually tolerated during childhood but when there is an increase in pulmonic pressure in adulthood then surgery will be needed. (with pulmonary stenosis or other pathologies, can be more significant and contribute to cyanosis)
ii. Endocardial cushion defect with ostium primum
1. Can involve any or all aspects of the endocardial cushion as well as septum and foramen primum
2. AV septal defect occurs in 2-% of Down syndrome individuals
b. Ventricular septal defects:
i. Membranous VSD- most common congenital heart defect
1. 1 or more of 3 contributing structures fails to form
2. if it is small, then it usually closes on its own
3. a big one can cause pulmonary hypertension and must be repaired with surgery
ii. muscular VSD: usually multiple small defects
iii. Common ventricle VSD is rare |
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Term
| What is the most common congenital heart defect? |
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Definition
| a. VSDs are the most common congenital heart defects. Holes can develop anywhere in the muscular interventricular septum. The embryonic basis is the failure of the spiral septum to properly fuse with the IV septum and endocardial cushions. Blood is diverted from the right ventricle to the left through the VSD as the systemic blood pressure increases relative to the pulmonary with growth of the infant and maturation of the airway. The lungs and left side of the heart get too much blood, and congestive heart failure and pulmonary edema can result. |
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Term
| What is tetralogy of Fallot? How does it differ from transposition of the great arteries and persistent truncus arteriosus? |
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Definition
a. Tetralogy of Fallot: four cardiac deformities
i. Pulmonary valve stenosis
ii. Ventricular septal defect (VSD)
iii. Overriding aorta
iv. Hypertrophy of the right ventricle
b. Transposition of the great arteries
i. Often associated with ASDs or VSDs
ii. Not enough spinning during septation
iii. Surgery usually required within first few months
c. Persistent truncus arteriosus: spiral septum may not develop |
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Term
| What two septal defects are commonly seen together and why? |
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Definition
a. Dextrocardia: twists and folds right instead-When accompanied by situs inversus, it is usually ok, but without situs inverus, there will be multiple cardiac anomalies.
b. Persistent truncus arteriosus: a aorticopulmonary septal defect
i. Fails to divide
ii. Straddles ventricular septal defect always accompanies this because the spiral septum failed to properly fuse with the IV septum and the endocardial cushions- nothing is closed. |
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Term
| Trace the flow of blood through the fetus. Discuss the physiologic and anatomical transitions that occur in the cardiovascular system at and/or soon after birth. Be sure to include the three shunts that close, what they become, why they were open and why they close. |
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Definition
a. Ductus arteriosus: A lung shunt connecting the pulmonary trunk to the arch of the aorta. After birth it remains patent for a few weeks before forming the fibrous ligamentum arteriosum. It closes after birth to prevent blood from flowing into the pulmonary trunk from the aorta- increasing pulmonary flow and causing pulmonary overload.
b. Ductus venosus: liver bypass shunting blood from the umbilical vein into the IVC. It becomes the ligamentum venosum. It closes after birth because the baby no long needs O2 from the umbilical vein.
c. Foramen ovale: a lung shunt where blood passes from the right atrium to the left atrium. In ommon usage it refers to the entire atrial bypass that includes the foramen secundum. It closes to prevent blood from flowing into the left atrium from the right atrium. The left atrium is now functioning- able to receive pulmonary veins or oxygenated blood from the body. Before, the baby relied on the placenta for O2.
d. Venous blood goes from S/I VC→ RA→RV. Ejected to Pulmonary artery through ductus arteriosus into des aorta. Resist to flow thru collapse lung is so great only a small blood goes to pulmonary arteries. Small amount of is returned thru pulmonary veins into the LA. O2 blood from placenta enters IVC, stream across RA through Foramen ovale into left A, to supplement small venous return. Mixture enters LV→ Aortic→ carotids to supply blood, des aorta to lower body. |
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