L29: Heart II Flashcards
(32 cards)
1
Q
Describe steps of early development of the heart: timing, folding
A
- Develops during the middle of the third week, blood circulates at beginning of 4th
- Angioblastic cords develop in the cranial end of the embryo in an area called the cardiogenic area, after cranial fold
- Cords form canals, ie. endocardial heart tubes in the late 3rd week
- Lateral folding brings endocardial heart tube together and they fuse to form three layers
- Enlongation of heart occurs and swellings develop: a.) truncus arteriosus, bulbus codis, ventricle, atrium, sinus venosus
2
Q
How does the heart move changes positions in the embryo to be in line with the adult form of the heart?
A
- Bulbus cordis and ventricle grow faster than other regions causing heart to bend upon itself
- It bends at the junction between the ventricle and bulbus cordis, known as the bulboventricular loop (u-shaped) and the atrium and sinus venosus come to lie dorsal to truncus arteriosus, bulbus cordis and the ventricle (adult positioning)
- Inflow of blood to heart is now posterior aspect, outflow is now situated anteriorly (ventral surface)
3
Q
Describe the structures associated with the blood flow through the primordial heart.
A
Caudal to cranial
- ) sinus venosus
- ) primordial atrium
- ) atrioventricular canal
- ) primordial ventricle
- ) bulbus cordis
- ) truncus arteriosus
- ) aortic sac
- ) aortic arches
4
Q
Describe the bulboventricular loop
A
- As bulbus cordis and the ventricle grow faster than other parts of the heart, the heart bends upon itself
- This bend occurs between bulbus cordis and the ventricle and is u-shaped structure known as the bulboventricular loop – this is now the most inferior border of the adult heart
5
Q
Partitioning of heart primordium. When does this occur, when is it complete?
A
- Begins around middle of the 4th week, essentially complete by end of 5th week
6
Q
Describe partitioning of the primordial septum and formation of atria
A
- Septum primum (aka first septum) grows inferiorly, beginning separation of atrium. It closes a structure known as foramen primum. Before closing it, a second opening forms through septum primum known as foramen secundum
- To the right of septum primum, septum secundum grows inferiorly. It grows to overlap foramen sectundum and leaves an opening in it’s wall. This forms foramen oval, flap-like valve over the foramen
- ) Right atrium formation:
- Right horn of sinus venosus at the posterior wall develops into sinus venarum, the smooth part of the adult right atrium.
- The primitive right atrium itself, forms the rough anterior wall of the adult right atrium known as the pectinate muscles.
- Left horn of sinus venosus becomes the coronary sinus - ) Left atrium formation:
- Primordial pulmonary vein incorportates into the left atrium, forming the smooth walls seen in the adult left atrium
- Primordial left atrium becomes the left auricle where pectinate muscles are seen.
7
Q
Describe partitioning of the primordial ventricle
A
- Infolding of primitive ventricle that grows superiorly becomes the muscular portion of the IV septum
- Right side of endocardial cushions fuses with aorticopulmonary septum (and is now the membranous part of the IV septum) and the muscular part growing inferiorly
- This IV septum divides the primitive ventricle into right and left sides
8
Q
Describe formation of outflow tracts
A
- Truncal ridges, which are mesenchymal cells derived from neural crest form within truncus arteriosus
- Bulbar ridges, which are mesenchymal cells derived from neural crest form within the bulbis cordis
- These ridges approach each other (starting with bulbar) to fuse and undergo a 180 degree spiral due to streaming of blood from ventricles. When they fuse, they form the aorticopulmonary septum, which separates bulbus cordis from truncus arteriosus and positions correct outflow vessel with ventricles, while fusing with IV septum.
- Bulbus cordis becomes conus arteriosus of right ventricle and aortic vestibule of left ventricle
- Truncus arteriosus becomes ascending aorta and pulmonary trunk
9
Q
Describe formation of the semilunar and AV valves
A
- Semilunar valves develop from three swellings of subendocardial tissues at the junction between bulbus cordis and truncus arteriosus that restructure to form thin-walled cusps that rotate to correct adult orientation
- AV valves develop from endocardial cushions around the AV canals
10
Q
What does sinus venosus do and what does it become?
A
- Receives venous blood from chorion, yolk sac and embryo
- Develops right and left horns, which become right and left atrial structures.
- Right horn: sinus venarum in right atrium
- Left horn: coronary sinus
11
Q
What does bulbus cordis do and what does it become?
A
- Outflow portion of primordial heart (ventricle part) and becomes aortic vestibule (left ventricle) and conus arteriosus (right ventricle)
12
Q
What does truncus arteriosus become?
A
- Outflow portion of developing heart continuous with aortic sac
- Becomes pulmonary trunk and aorta
13
Q
What do the endocardial cushions become?
A
- These are thickenings in the primordial heart that assist with septation of the heart through its development
- Specifically, right side of endocardial cushions fuses with aorticopulmonary septum, forming the membranous part of the IV septum
- Proliferation of endocardial cushions around AV canals form AV valves
14
Q
What do truncal and bulbar ridges become?
A
- Truncal ridges are structures within truncus arteriosus
- Bulbar ridges are structures within bulbis cordis
- These fuse to form the aorticopulmonary septum, which separates truncus and bulbis, fusing with IV septum and allow for correct positioning of outflow vessels
15
Q
What does aorticopulmonary septum become?
A
- separates truncus arteriosus and bulbis cordis, fuses with IV septum and allows for correct positioning of outflow vessels
16
Q
What is total anomalous pulmonary vein?
A
- When the primary pulmonary vein becomes incorporated into the right side of the interatrial septum, drains into right instead of left atrium
- As a result, blood returning from lungs is placed into right atrium, right ventricle and goes back to the pulmonary circuit
17
Q
What is foramen ovale, what is ductus arteriosus, what is ductus venosus?
A
- Foramen ovale = connection between right and left ventricle to bypass pulmonary circuit and move blood systemically during fetal period. After birth, becomes fossa ovalis
- Ductus arteriosus = connection between pulmonary trunk/artery and aorta to bypass pulmonary circuit and move blood systemically during fetal period. After birth, becomes ligamentum arteriosum.
- Ductus venosus = connection between left umbilical vein and IVC to bypass liver circulation (via portal and hepatic vein) and allows oxygenated blood to get systemically more quickly. After birth, becomes ligamentum
18
Q
How does blood move from fetus to placenta?
A
- Branches of internal iliac arteries are the left and right umbilical arteries that travel through umbilicus to placenta
19
Q
Why is interatrial septum thick superiorly, thin inferiorly?
A
- Superior aspect has both septum primum and secundum, while inferior aspect has only septum primum
20
Q
Describe ASDs in terms of secundum type or primum type. How do these arise?
A
- ASDs refers to failure of interatrial septum to develop correctly
- These failures as dependent on issues with foramen primum or secundum to correctly develop, leading to presence of common atrium
- Primum type results from defect with endocardial cushion
- Usually a patent fossa ovalis is not clinically significant if some overlap is present as pressure on left side keeps flap valve closed. Worse is no overlap
21
Q
Describe VSDs. How do these arise?
A
- More clinically significant than ASDs
- Can arise with failure of membranous part to fuse with muscular part or vice versa.
- Leads to blue baby
22
Q
What disorders result from abnormal division of truncus arteriosus? What defect are you always guaranteed?
A
- ) persistent truncus arteriosus
- ) transposition of great vessels
- ) pulmonary stenosis
- ) tetralogy of Fallot
- ) pulmonary atresia
- ) aortic stenosis and atresia
* Guaranteed a VSD with all of these
23
Q
What is persistant truncus arteriosus?
A
- Failure of truncus arteriosus to divide into pulmonary trunk and aorta
- Has VSD
- Aorticopulmonary septum never came down
24
Q
What is transposition of great vessels?
A
- Right ventricle has aorta outflow
- Left ventricle has pulmonary trunk outflow
- Swirling of blood flow never happened
- With VSD
25
What is pulmonary, aortic stenosis?
- Narrowing of pulmonary trunk/aorta as a result of unequal division of truncus arteriosus
- VSD occurs with these
26
What is tetralogy of Fallot?
- Congenital heart defect involving four anatomical abnormalities of heart. Most common cause of blue baby syndrome
1. ) Aorticopulmonary septum goes primarily towards aorta causing a small pulmonary trunk
2. ) Aorta that overrides the VSD
3. ) Right ventricle needs to pump harder and becomes hypertrophied
4. ) VSD as aorticopulmonary septum was defective
27
What does aortic sac become?
- Portion of the ascending aorta, braciocephalic artery (with branches) and most of the aortic arch
- Aortic sac gives rise to the aortic arches
28
What are the adult derivatives of the aortic arches?
1st: maxillary artery bilaterally, most regresses
2nd: hyoid and stapedial arteries bilaterally, most regresses
3rd: proximally gives common carotid bilaterally, distally gives internal carotid arteries
4th: right gives right subclavian artery, left gives portion of aortic arch
5th: no derivatives
6th: proximally gives portions of pulmonary artery bilaterally, distally on left gives ductus arteriosus and regresses distally on right
29
What is unique about the derivatives of the 4th aortic arch?
- Gives off right subclavian and portion of aortic arch
30
Why is the left recurrent laryngeal nerve located under the aortic arch while the right recurrent laryngeal nerve is under the right subclavian artery?
- Recurrent laryngeal nerve originally loops under the 6th aortic arch during development.
- Distally, the 6th aortic arch on the right regresses, but not on the left, causing the right recurrent laryngeal to hook around the right subclavian
31
What aortic arch persists in total to form ductus arteriosus in the embryo? What does it become in the adult?
- 6th aortic arch, it becomes the ligamentum arteriosum in adult
32
What is the relationship of the ductus arteriosus to a congenital defect called coarctation of the aorta?
- Coarctation of aorta refers to congenital condition whereby aorta narrows in the area where the ductus arteriosus inserts or proximally or distal to this area.
