Cardiac Development Flashcards
What are the steps of lateral folding
- The endoderm in close approximation to the primary heart field secretes vascular endothelial growth factor (VEGF) which causes primary heart field cells to differentiate:
• Angioblasts (endothelial cells)
• Cardiac myoblasts
• Haemocytoblasts - The differentiated heart cells form endothelial-lined tubes surrounded by myoblasts – called endocardial tubes
- Pockets behind the endocardial tubes also form – the future pericardial cavities
- The two endocardial tubes fold towards each other and join together. Meanwhile, the developing GI tract is push posteriorly
- After folding is complete, the heart tube sits within the pericardial cavity and is attached to the posterior wall by the dorsal mesocardium (later disappears)
- Myocardial cells secrete cardiac jelly (ECM) that separates myocardium from endothelium
What are the steps of craniocaudal folding
- The developing heart tube sits cranially initially and as craniocaudal folding occurs, is pulled caudally
- As the heart tube is pulled caudally, it also gets pulled into the pericardial cavity
- Surrounding mesoderm, known as the secondary heart tube, is also present
What is the endocardium derived from
Endothelial layer
What is the myocardium derived from
Cardiac myoblasts
What is the epicardium derived from
Surrounding mesothelial cells - from secondary heart field
What do these structures become
1. Truncus arteriosus
2. Bulbus cordis
3. Primitive ventricle
4. Primitive atrium
5. Sinus venosus
- Pulmonary trunk/ascending aorta
- Right ventricle and pulmonary veins
- Left ventricle
- Both right and left atria
- SVC, IVC and coronary sinus
When does cardiac looping start and when is it complete
Begins day 23 and complete by day 28
How does the atrial septum form
1.Septum called the septum primum grows down towards the septum intermedium but doesn’t quite reach it, leaving a hole called the ostium primum
2. Septum primum then closes ostium primum and reaches septum intermedium
3. A hole is formed in the upper part of the septum primum, called the ostium secundum
4. A second septum forms, the septum secundum
5. A hole forms in the septum secundum, leaving a foramen – the foramen ovale – which should close at birth leaving the fossa ovalis!
How is the outflow tracts formed
A aorticopulmonary septum is formed to separate the future aorta and pulmonary trunk as the bulbal and truncal septa’s grow towards each other in a spiral formation
How are the inflow tracts formed from the sinus venosus
Right horn:
• Umbilical vein regresses
• Common cardinal vein becomes SVC
• Vitelline vein becomes IVC
Left horn:
• Regresses to form single coronary sinus
When do the cardiac septae form
Between day 27 and 37
What are the the AV valves formed from
mesenchymal tissue, which becomes fibrous connective tissue
What are the semilunar valves formed from
Endocardial cushion swellings
When does the heart begin to beat
21 days
What is vasculogenesis and angiogenesis
Vasculogenesis
Formation of blood vessels, where angioblasts differentiate into endothelial cells to form a vessel
Major vessels, including the dorsal aortae and cardinal veins
Angiogenesis
Vessels sprouted from existing vessels, how rest of vascular system is formed
When do the pharyngeal arches begin to develop
Week 4 and 5 formed of a mesoderm core, an external ectoderm layer and an internal endoderm layer
How many aortic arches develop from the truncus arteriosus of the heart tube
5 aortic arches
• I – Obliterated
• II – Obliterated
• III – Common carotid, external carotids and proximal internal carotids
• IV – Left side: aortic arch/ Right side: subclavian
• VI – Pulmonary arteries
• Right aortic root/ horn forms the
brachiocephalic artery
• Left aortic root/horn forms the
proximal aortic arch
