Development Of Heart And Pericardium Flashcards
What is the Foramen ovale?
Foramen ovale- opening between right and left atria during fetal life
What is septae?
Septae-connective tissue partition separating structures
- Interventricular- found between the ventricles
- Interatrial- found between the ventricles
- Aorticopulmonary-found between the ascending aorta and pulmonary trunk
What is partitioning?
Dividing of embryological parts to enhance function
What is the ventricular septal defect?
A breach in the interventricular septum, with resultant consequences
What is the atrial septal defect?
A breach in the interarterial septum, with resultant consequences
What does the heart develop from?
Develops from carcinogenic mesoderm
Embryo folding and flexion causes repositioning of the heart and the establishment of normal anatomical relationships
Describe formation of the heart tubes
3rd week
- Angioblastic cords/endothelial strands
- Canalize to form two heart tubes
- Lateral folding of the embryo occurs
- Heart tubes fuse to form the tubular heart (a single tube )
- Fusion occurs from the cranial to the caudal end
- Beginning of development of pericardial cavity
- Fusion occurs from the cranial to the caudal end
How is the epicardium formed?
From mesothelium all cells arising from the external surface of the sinus venosus spreading over the myocardium
What is the myocardium formed from?
From myoblasts from the first heart field (cardiac mesoderm)
What is the endocardium formed from?
From the primitive heart tube
Describe the formation of transverse sinus?
- Communication between both of the pericardial cavity
- formed be degeneration of central part of dorsal mesocardium
- In adult: pericardial reflection located posterior to aorta and pulmonary trunk, anterior to superior vena cava (SVC), superior to left atrium
Clinical significance: cardiothoracic surgeons can separate arteries from veins allowing for temporary ligation
What are the subdivisions of the tubular heart?
- Truncus arteriosus
- Bulbus cordis
- Primitive ventricle
- Primitive atrium
- Sinus Venosus
Cephalic arterial end- continuous with aortic sac
Caudal venous end- opens into the sinus venosus
-from placenta, embryo and yolk sac
What does sinus venosus receive paired veins from?
- The vitelline veins (omphalomesenteric vein)- from the umbilical vesicle
- Common cardinal veins- from the embryo
- Umbilical veins- from the chorion
Describe cardiac looing
Day 23-28
Bulbous cordis and ventricle grow faster than other regions causing it to bend itself
- Viewed from the front the bulbus cordis and primordial ventricle undergoes a de trail loop forming the U-shaped bulboventricular loop resulting in the apex of the heart to the left
- Primitive atrium and sinus venosus move dorsal (posterior) to truncus arteriosus, bulbus cordis and ventricle
What is the fate of the primitive atrium?
Left auricle
-Internal surface has a rough, trabeculated appearance
Right auricle
-Internal surface has a rough, trabeculated appearance
What is the fate of the sinus venosus?
Left horn- mostly obliterates
-remnants- the coronary sinus and the oblique vein of left atrium
Right horn- seen as sinus venarum
-smooth- walled part of right atrium
What is the fate of primitive ventricle?
Trabeculated part of the wall of the right and left ventricles
What is the fate of the bulbus cordis?
Majorly contribute to form outflow tracts of the right and left ventricles
- Right- conus arteriosus (infundibulum)
- Left- Aortic vestibule
What is the fate of truncus arteriosus?
Left- ascending aorta
Right- pulmonary trunk
Explain the partitioning of the atrioventricular (AV) canal
-Towards the end of the 4th week
- AV Endocardial cushions develop
- from cardiac jelly and neural crest cells
- forms on dorsal and ventral walls of AV canal
- Endocardial cushions grow towards each other and fuse
- divides canal into right and left AV canals
- forms AV valves
- partially separate primitive atrium from primitive ventricle
Summarize formation of the right atrium
-right horn of the sinus venosus enlarges
- Simultaneously primitive atrium enlarges
- absorbs right horn forming right atrium
- later becomes the sinus venarum (smooth part of the right atrium)
- absorbs right horn forming right atrium
-Rough walled auricle is formed by primitive atrium
Summarize the formation of the left atrium
Primordial pulmonary veins
Forms the left atrium
-primordial pulmonary veins persistently become incorporated into walls of the left atrium
-forms the oblique pericardial sinus
-Most of the wall is smooth
-Rough walled auricle is formed by primitive atrium
Where is the oblique sinus?
Area of pericardium between the pulmonary veins
Limited by the reflection of the serous pericardium ion to the back of the heart
Describe atrial partitioning
End of 4th week
Septum primum gross from the roof of atrium towards Endocardial cushions
- Foramen primum- space between inferior edge of septum primum & the Endocardial cushions
- Growth of septum primum closes Foramen primum
- Foramen secundum- simultaneously perforations appear in septum primum
- Septum secundum grows downward, eventually overlapping Foramen secundum
- The opening between the free edges septum secundum and septum primum is called Foramen ovale or oval Foramen
What is the function of the septum primum in atrial partitioning?
Septum primum (thin and flexible ) acts like a flap valve for Foramen ovale- the flap is open when right atrial pressure exceeds left atrial pressure - allowing shunting of blood from the right atrium to the left atrium
This allows the blood to bypass the lungs, which is not yet functional
What is the cause of ostium secundum defect?
In the area of the fossa ovale
- leads to patent/open Foramen ovale defect
- disrupted or absent septa
- Intracardiac shunting of blood (left to right)
- most common in but least severe in ASD
What is the sex ratio of ostium secundum defect?
Female to male ratio: 2:1
What are the symptoms of ostium secundum defects?
Defects of both septa primum and secundum:
-excess resorption of septum primum- too short to close Foramen
- abnormal resorption of septum primum
- extra febestrations
-defective development of septum secundum with large fossa ovale
Describe Endochondrial cushion defect with a Foramen primum defect
- less common atrial septal defect
- septum primum-not fused with Endocardial cushions- patent Foramen primum defect
- Often associated with a cleft in the anterior cusp of the mitral valve
- Fusion of Endocardial cushions forms AV valve
- Failed fushion leads to an AV valve defect
-intracardiac shunting of blood (left to right)
Describe sinus venous defect
Located in the sinus venarum
Defect:
-incomplete resorption of the right horn of sinus venosus into the right atrium
-abnormal development of the septum secundum, or a combination of these factors
Intracardiac shunting of blood (left to right)
Describe common atrium
- prevelant in patients with ostium primum, ostium secundum and sinus venosus defects
- complete absence of interarterial septum
What are the atrial septum defects?
- common atrium
- sinus venosus defects
- Endocardial cushions defect with a Foramen primum defect
Ostium secundum defect
Explain the partitioning of the common ventricle
Muscular interventricular (IV) septum-develops first
- formed from myocytes from the primitive ventricle
- has a concave superior free edge (forms the IV Foramen)
- ventricular dilation leads to an increase in size of septum
IV foramen
-allows for communication between the right and left ventricles
- bulbar ridges and muscular IV septum fuses with the Endocardial cushion forming membranous IV septum
- later fuses with the articopulmonary septum
- once membranous IV septum formed, leads to closure of the IV foramen
- pulmonary trunk now forced to communicate with right ventricle
- ascending aorta now forced to communicate with left ventricle
Discuss the partitioning of Bulbus Cordis and Truncus Arteriosus by aorticopulmonary (spiral) septum
5th week
-Bulbar ridges from within the bulbus cordis (middle 1/3)
- Truncal ridges develop within the truncus arteriosus
- ridges grow towards each other, spiraling around each other (180 degrees)
- fuses forming the aorticopulmonary septum
- septum divides the truncus arteriosus and bulbus cordis into the pulmonary trunk and aorta
- fuses forming the aorticopulmonary septum
- ridges grow towards each other, spiraling around each other (180 degrees)
What are the types of ventricular septal defect?
Muscular
Membranous
What is common in both types of ventricular septal defect?
Both types of VSDs:
-more common in males than females
- accounts for about 25% of congenital heart defects
- intracardiac shunting of blood (left to right)
Describe muscular ventricular septal defect
No muscular septum results in a common ventricle
Occurs anywhere throughout the septum
-in isolation or simultaneously (“Swiss cheese” VSD)
Describe membranous ventricular septal disease
Most common type
No membranous septum- incomplete closure of the IV foramen
How are the semilunar valves developed?
3 swellings of subendicardial cushion tissue around the orifices of aorta (aortic vestibule) and pulmonary trunk (infundibulum)
Hollowed out and reshaped forming three thin-walled cusps
How are the atrioventricular valves?
-localized proliferations of endocardial cushion tissue around AV canals
What are the cardiac structures derived from neural crest cells?
- endocardial cushions (in the outflow tract)
- bulbar ridges
- truncal ridges
- spiral septum
- membranous interventricular septum
- semilunar valves
- atrioventricular valves
- pharyngeal arches
