Thorax 8: Development of the Heart and Great Vessels Flashcards
How many weeks in does the bilaminar disc become trilaminar?
2 weeks post conception
What are the 3 layers of the trilaminar disc?
- ectoderm
- mesoderm
- endoderm
When is mesoderm formed?
during week 3
Which layer of the disc does the heart tube form in and what end of the disc? What does it form from?
- mesoderm
- angiogenetic clusters as a horseshoe
- cephalic end
Which day does heart development start to occur? Why?
-day 18
-diffusion is no longer sufficient to provide nutrients
and development of both blood and vascular structures is necessary
What folding happens to the heart tube? Where does this allow the heart tube to migrate to?
- cephalo-caudal folding
- heart tube migrates from the head through the neck to the thorax of the embryo
What 3 types of cardium does the heart tube develop into? What do these become?
- Epicardium- visceral pericardium
- Myocardium- cardiac muscle
- Endocardium- endothelial lining
When does looping and folding of the heart tube occur?
week 4 around 22 days
What structures are at the caudal and cephalic end of the heart tube?
- sinus venosus
- Truncus arteriosus
Which direction does the heart tube fold to? How does this orientate the heart?
- 2 ends fold towards each other and to the right
- apex of heart is pushed to the left. rotation means right side of heart is more anterior
What happens to the heart 28 days in?
- heart pushes into the pericardial sac
- ventricles begin to trabeculate
Which vessels does the venous end receive blood from?
- cardinal
- umbilical
- vitelline veins
Which structure do the atria start to bulge out the side from?
bulbus cordis
What structures are formed from the proximal, middle and distal parts of the bulbus cordis?
- proximal forms RV
- middle forms outflow of ventricles
- distal forms PT and aorta
How are left and right caverns formed after growth from the bulbus cordis?
- bending causes narrowing, augmented by endocardial cushion growth
- endocardial cushion cells grow and then eventually begin to fuse forming left and right caverns
What forms from enlargement of truncus arteriosus?
PT and aorta
What 3 structures are formed as a result of the enlargement of the endocardial cushion cells?
- interatrial cells
- membranous part of the inter ventricular septum
- AV valves
What is the first stage in the development of the foramen ovalis? What is the name of the first channel formed between the atria?
- formation of the septum primum in-between the atria , it grows down towards endocardial atrio-ventricular cushions
- ostium primum
what is the second stage and final stage in the development of the foramen ovalis?
- formation of septum secundum in the right atrium, stiff and muscular, grows down but does not fuse with endocardial cushion
- ostium secundum
Which opening forms the foramen ovalis? What becomes the name of the fossa in the septum primum?
- the ostium secundum = foramen ovalis
- the ostium primum becomes the ostium secundum
Which weeks is the foramen ovalis formed by?
between weeks 5 and 6
What is a patent foramen ovale? How is it caused?
- the foramen ovale didn’t close the way it should have at birth
- caused by excessive cell death or reabsorption of the septum primum
Which week is the inter ventricular septum complete by?
week 7
how are left and right ridges formed in the conus?
endocardial cushion cells
What is formed from extension of the atria-ventricular cushion?
membranous portion of inter ventricular septum
How is the conotruncal septum formed?
L+R truncal ridges spiralling
How is the inter ventricular foramen closed?
- Membranous part of the inter ventricular septum
- inferior growth of truncal ridges
- inferior atrio-ventricular septum
What happens if no truncal ridges develop?
Persistent truncus arteriosus
What results if no spiral occurs in the great truncal ridges?
Transposition of the great vessels
What happens to the truncal septum in tetralogy of Fallot?
septum deviates right and does not meet the inter ventricular septum
Why does the heart show RV hypertrophy in tetralogy of Fallot?
pulmonary stenosis= narrowing of the pulmonary valve to artery hence RV has to work harder to pump blood into the pulmonary circulation
What needs to be incorporated during atrial growth?
adjacent veins
During development of the atria what change can be seen in the wall of the atrium, especially in the RA?
cristae terminalis mark the change and form the point for the formation of muscular ridges in the atrium
how do ventricles grow in size?
balloon to grow around and away from the muscular septum dividing them
How are atrioventricular valves formed?
endocardial cushion growth and cavitation to form papillary muscles and chordae tendinae
How are the semi lunar valves formed?
hollowing of endocardial tubercles
What is arterial development associated with? Which weeks do these occur?
- intimatley associated with sequential formation of pharyngeal arches with their own cranial nerve and arterial supplies
- weeks 4+5
What do arches give rise to?
structures in the head and neck
What occurs as each pharyngeal arch develops?
arteries arise from aortic sac (part of truncus arteriosus=aorta) grows through the arch and joins the dorsal aorta
How many pairs of aortic arches arise from truncus arteriosus?
6
What are the first aortic arches responsible for?
maxillary arteries
What aortic arch forms the common carotid arteries?
arch 3 with dorsal aorta
What are aortic arch 4 left and right branches responsible for?
- left= aortic arch
- right=right subclavian artery
What are aortic arch 6 left and right branches responsible for developing into?
- left= pulmonary trunk and ductus arteriosus
- right= contributes to PT
What is Patent Ductus Arteriosus? What type of murmur can be heard?
- postnatally the aortic pressure is greater than the pulmonary trunk. Blood will flow back into pulmonary circulation
- machinery murmur
What is coarctation of the aorta?
aortic narrowing after origin of L subclavian vein due to an abnormality in aortic media and intimal proliferation
What effect does coarctation have on the femoral pulses?
weakens them
What type of coarctation is most common? What happens to blood flow?
- postductal
- blood travels in subclavian to internal thoracic to intercostal vessels and back to thoracic aorta
Which nerve do the recurrent laryngeal nerves branch from? Which aortic arch do the hook around?
- vagus nerves
- 6
Why is the left recurrent laryngeal nerve carried into the thorax?
the aortic arch persists as ductus arteriosus and ligamentum areteriosum so the nerve is carried into the thorax
Why does the right recurrent laryngeal nerve not end up in the thorax?
both the 5th and 6th right aortic arches regress so the nerve hooks around the 4 aortic arch which becomes the right subclavian artery in the root of the neck
