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Cardiology Exam > Cardiac Embryology > Flashcards

Cardiac Embryology Flashcards

1
Q

development of the heart - step 1 [formation of primitive heart tube]

A

*heart forms from mesoderm derived from the primitive tube
*the linear heart tube begins to beat as soon as it is formed, around day 15
*at days 18-20, the mesodermal cells expand anteriorly while forming a tube that encircles the endocardial cells

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2
Q

development of the heart - step 2 [division into 5 segments]

A

*primitive heart tube is divided into 5 regions; from superior (arterial pole) to posterior (venous pole), the regions are:
1. truncus arteriosus
2. bulbus cordis
3. primitive ventricle
4. primitive atrium
5. sinus venosus

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3
Q

structures that will ultimately form from each segment of primitive heart tube

A
  1. truncus arteriosus → ascending aorta & pulmonary trunk (pulmonary arteries)
  2. bulbus cordis → outlet of ventricles/RIGHT VENTRICLE
  3. primitive ventricle → inlet of ventricles/LEFT VENTRICLE
    NOTE - ATRIOVENTRICULAR CANAL FORMS BETWEEN PRIMITIVE VENTRICLE & PRIMITIVE ATRIUM
  4. primitive atrium → right & left atria
  5. sinus venosus → left & right horns:
    left horn → coronary sinus
    right horn → part of right atrium
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4
Q

development of the heart - step 3 [heart looping]

A

*as the primitive heart tube grows longer, it begins to fold in on itself, bulging and looping TOWARD THE RIGHT (normal looping):
-primitive ventricle moves down, anteriorly and toward the right
-primitive atrium moves up, posteriorly and toward the left, eventually moving behind the primitive ventricle

note - heart looping is usually complete between days 30-35

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5
Q

development of the heart - step 4 [septation of the heart & great vessels]

A

*3 septa need to form within the heart for it to mature and become functional:
a. septation of the atria (to form RA & LA)
b. septation of the ventricles (to form RV & LV)
c. septation of the great vessels (to form aorta & pulmonary trunk)

note - these septations occur “simultaneously”

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6
Q

endocardial cushions

A

*4 swellings of the heart tube at the junction between the primitive atrium and primitive ventricle
*crucial for both atrial and ventricular septation
*help form the atrial & ventricular septa, as well as the AV valves (mitral & tricuspid)
*composed of several cell types, including NEURAL CREST CELLS

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7
Q

development of the heart - step 4a [ATRIAL septation, detailed]

A

*atrial septation is the process of dividing the primitive atrium into a right & a left atrium
1. foramen primum: the original opening between what will become the RA & LA
2. septum primum: this fold grows downward from the atrial roof to fuse with the endocardial cushions & close the foramen primum
3. foramen secundum: forms in the septum primum by apoptosis, leaving the new foramen secundum as the only opening b/w RA & LA (foramen primum is closed off)
4. septum secondum: this fold grows downward from the roof & walls of the RA and expands to cover most of the foramen secundum; simultaneously, the superior part of septum primum degenerates, creating the FORAMEN OVALE
5. atrial septation: at birth, foramen ovale valve & septum secundum FUSE to form atrial septum; foramen ovale is now closed

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8
Q

development of the heart - step 4a [ATRIAL septation, SIMPLE]

A

foramen primum → closed by septum primum, & foramen secundum forms (via apoptosis) → septum secundum covers most of the foramen secundum & foramen ovale forms → at birth, foramen ovale valve & septum secundum fuse to close off foramen ovale

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9
Q

foramen ovale

A

*the hole that is located in the septum between the 2 atria of the fetal heart
*permits blood to bypass the lungs by flowing directly from the right atrium to the left atrium in the fetus
*covered by a flap-like portion of the septum primum, known as the valve of the foramen ovale
*closes off shortly after birth due to the fusion of the foramen ovale valve with the septum secundum → blood cannot pass between the atria anymore (normal adult cardiac circulation)

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10
Q

development of the heart - step 4b [VENTRICULAR septation, detailed]

A

*ventricular septation is the process of dividing the primitive ventricle into the RV & LV through the formation of the interventricular septum
*interventricular septum has 2 parts:
1. muscular portion: begins in floor of primitive ventricle & grows upward toward the endocardial cushions
2. membranous portion: forms from the endocardial cushions & aorticopulmonary septum; grows downward to fuse with the muscular portion

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11
Q

development of the heart - step 4b [VENTRICULAR septation, SIMPLE]

A

*interventricular septum forms in the primitive ventricle by FUSION OF THE MUSCUALR PORTION (arises from the floor of primitive ventricle) WITH THE MEMBRANOUS PORTION (arises from the endocardial cushions)
*the formation of the interventricular septum results in the division of the primitive ventricle into a right ventricle and a left ventricle

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12
Q

development of the heart - step 4c [TRUNCAL septation, detailed]

A

*truncal septation is the process of dividing the truncus arteriosus into the pulmonary trunk and the ascending aorta so that each ventricle has its own outflow tract
1. neural crest cells migrate to into the truncus wall & form 2 parallel vertical bulges (truncal ridges) opposite each other along the length of the truncus
2. as the truncal ridges ascend in the wall, their locations gradually shift 180 degrees, forming a SPIRAL
3. these parallel ridges grow across the lumen and fuse to form the 180 degree spiraled AORTICOPULMONARY SEPTUM, which separates the ascending aorta and pulmonary trunk

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13
Q

development of the heart - step 4c [TRUNCAL septation, SIMPLE]

A

neural crest cells form truncal ridges along the length of truncus arteriosus → truncal ridges ascend and shift 180 degrees → ridges fuse and form 180 degree spiraled aorticopulmonary septum → separation of the aorta & pulmonary trunk

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14
Q

development of the heart - step 4c [truncal septation]: RESULTING ANATOMIC LOCATIONS OF AORTA & PULMONARY TRUNK

A

*pulmonary trunk lies on the left side of the aorta before branching into the pulmonary arteries
*right pulmonary artery must travel underneath aortic arch to reach the right lung

*resulting blood flow due to the spiral of the aorticopulmonary septum:
1. venous blood travels from right ventricle through the pulmonary artery (which lies left)
2. arterial blood travels from left ventricle through the aorta (which lies right)

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15
Q

development of the heart - step 5 [development of the AV VALVES]

A

*recall: the atrioventricular canal region was the invagination between the primitive ventricle and primitive atria
*during heart tube folding, the AV canal moves midline and connects largely over the left ventricle with some extent into the RV. It will continue to move midline and expand in order to be centered equally over both ventricles as the ventricles are growing
*AV valves start off as a common valve that divide equally over the ventricles
*different sets of endocardial cushions will start to expand and fuse together which will pinch the valve in an anterior / posterior manner to septate the valves

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16
Q

1st aortic arches - adult derivatives

A

*right and left maxillary arteries

17
Q

2nd aortic arches - adult derivatives

A

*stapedial arteries (regresses)
*hyoid artery

18
Q

3rd aortic arch - adult derivatives

A

*right and left common carotid arteries
*right and left proximal internal carotid arteries

19
Q

4th aortic arches - adult derivatives

A

*LEFT: aortic arch
*RIGHT: proximal right subclavian artery

20
Q

5th aortic arches - adult derivatives

A

*regress; do not form any adult arteries

21
Q

6th aortic arches - adult derivatives

A

*LEFT: left proximal pulmonary artery & ductus arteriosus
*RIGHT: right proximal pulmonary artery

22
Q

cardinal veins

A

*anterior cardinal veins (precardinal veins) contribute to formation of internal jugular veins, and, together with the common cardinal vein, form the superior vena cava
*ducts of Cuvier (common cardinal veins) open into sinus venosus
*postcardinal veins (posterior cardinal veins) join with R and L cardinal veins to form left common cardinal veins, which empty into sinus venosus; most of postcardinal veins regress, and what remains forms renal segment of IVC & the common iliac veins

23
Q

fetal circulation - defined

A

*describes the blood flow through the fetus’s cardiovascular system from the placenta (maternal blood) to the fetal tissues and back to the placenta

24
Q

fetal circulation - overview

A

*RIGHT ventricle is the work-horse of fetal circulation:
-produces 2/3rds of cardiac output
-88% of its output goes through the ductus to the systemic circulation; only 12% goes to pulmonary circulation
*oxygenated blood comes from placenta into umbilical vein
*most of the oxygenated blood gets shunted across the foramen ovale (from RA to LA)

25
Q

ductus arteriosus

A

*a blood vessel in the fetus that connects the main pulmonary artery to the proximal descending aorta

26
Q

fetal circulation - pathway

A
  1. oxygenated blood from the placenta flows through the umbilical vein, through ductus venosus, into IVC to enter the right atrium
  2. from the right atrium, the majority of the blood is directed by the Eustachian valve into the foramen ovale
  3. blood flows from RA through foramen ovale into the LA
  4. blood from the LA enters the LV and exits through the aorta out to the body
  5. some deoxygenated blood from the SVC travels from the RA through the tricuspid valve into the right ventricle, where a small portion goes to pulmonary circulation, while the majority passes from the pulmonary trunk into the aorta through the ductus arteriosus
27
Q

changes to fetal circulation at birth

A

*lungs replace placenta as source of oxygen (STARTS with baby respiration)
*as lungs expand & fill with oxygenated air, pulmonary resistance drops rapidly → more blood goes through lungs and returns to left atrium → increased left atrial pressure (relative to right atrium) → CLOSES FORAMEN OVALE
*as amount of oxygen increases, circulating levels of prostaglandin E1 decrease → CLOSES DUCTUS ARTERIOSUS
*as RV pressure drops, over time, RV wall thickness resolves
*as LV pressure rises, over time, LV wall thickens

28
Q

closure of the foramen ovale

A

*as lungs expand & fill with oxygenated air, pulmonary resistance drops rapidly → more blood goes through lungs and returns to left atrium → increased left atrial pressure (relative to right atrium) → CLOSES FORAMEN OVALE

29
Q

closure of ductus arteriosus

A

*as amount of oxygen increases, circulating levels of prostaglandin E1 decrease (it was a response to global hypoxia in the fetus) → CLOSES DUCTUS ARTERIOSUS

30
Q

problems associated with abnormal heart looping

A

*normal heart = D-looped ventricles
*abnormal looping can result in:
1. L-looped ventricles [heart looping toward left instead of right]
2. D-TGA [normal looping, but transposition of great vessels]
3. L-TGA [L-looping AND transposition of great vessels]

31
Q

ventriculoatrial & ventriculoarterial concordance with D-TGA & L-TGA

A

*normal: left atrium → left ventricle → aorta [ventriculoatrial concordant & ventriculoarterial concordance]
*D-TGA: left atrium → left ventricle → PULMONARY ARTERY [ventriculoatrial concordant; ventriculoarterial DISCONCORDANT]
*L-TGA: left atrium → RIGHT ventricle → AORTA [ventriculoatrial DISCONCORDANT; ventriculoarterial DISCONCORDANT]

32
Q

problems associated with abnormal atrial septation

A
  1. failure of septum primum to fuse with endocardial cushion → ostium primum atrial septal defects → associated with cleft mitral valve leaflet
  2. failure of septum secundum to cover ostium secundum → ostium secundum atrial septal defects
33
Q

problems associated with abnormal ventricular septation

A

*failure of LV septum to form → functionally single ventricle

34
Q

other causes of single ventricle

A
  1. hypoplastic right heart:
    -tricuspid atresia
    -under-developed RV
    -pulmonic valve atresia
    -pulmonary artery atresia
  2. hypoplastic left heart syndrome:
    -mitral atresia
    -under-developed LV
    -aortic valve atresia
    -aorta atresia
35
Q

problems associated with neural crest migration/conotruncal septation

A

*Tetralogy of Fallot (four abnormalities that results in insufficiently oxygenated blood pumped to body):
1. overriding aorta
2. small pulmonary artery
3. ventricular septal defect
4. right ventricular hypertrophy

note - 1&2 results in a deviated conotruncal septum

36
Q

problems associated with AV valve formation

A

*failure of superior and inferior endocardial cushions → AV canal defect (ostium primum ASD + inlet VSD)
*often associated with Trisomy 21

Cardiology Exam (52 decks)

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