Embryology Flashcards
What is the most important gene involved in heart anomalies?
NKX2.5: involve in the further differential growth of the heart during the heart-tail folding phase
What are the 3 big phases of cardio-vascular development?
- Gastrulation
- Head-tail and lateral folding
- Heart folding and separation
What happens during gastrulation?
The primitive ectoderm from primitive streak will separate (EMT) into cardiogenic precursors, hemangioblasts and yolk sac.
- Cardiogenic precursors will form the anterior endoderm, inducing cardiogenic mesenchyme and endothelial tubes.
- The hemangioblast will form stem cells and angioblasts
- The yolk sac hemopoesis will be the first hemopoietic organ
Describe the formation of the 3 layers of the heart during the Heart-tail lateral folding phase of the CV development
Endocardial tubes and primitive symmetrical vessel are formed at the trilaminar embryo phase. The neural crest forms 2 symmetrical tubes surrounded by the mesenchyme and the visceral pericardial cavity. Then, the 2 tubes fuse together and form a single heart tube. The pericardium cavity will envelope the fused tube and this completes the 3 layers of the heart wall (epicardialization). The 3 layers of the heart are:
- Endocardium (cardiac jelly, endothelium)
- Myocardium (3 types of myocytes: contractile, myo-conducting and myo-endocrine)
- Epicardium (mesothelium and underlying mesenchyme, coronary vessel precursors)
Describe the vascular/angiogenesis of the CV system
- Atrium, sinus venosus with INFLOW vessels positioned posteriorly to Bulbus Cordis and OUTFLOW vessels.
- Change in directions of hemodynamic flow
- INFLOW valve region (future tricuspid and bicuspid valves) and OUTFLOW valve region (future pulmonary and aortic valves) are positioned adjacently.
Symmetrical paired veins enter the sinus venosus (SV). After, the formation of the veins becomes asymmetrical.
Describe the development of the heart tube during the heart-tail lateral folding phase of CV development
The differential growth of the heart is controlled by a cascade of gene expression (NKX-2, Hand 1, Hand 2) in the muscular wall as new myocytes are added to form the definitive heart chambers. Folding of the heart tube and changes in hemodynamic goes from a single tube, paired and symmetrical to a dorsal folding and bulboventricular looping.
Describe the chamber formation: Endocardial cushion formation in the Atrio-Ventricular canal and outflow tract
- Bulboventricular looping
- Shunting of the venous blood to the right side: two shunts form an asymmetrical venous system. The Vitelline veins form yolk sac and umbilical form placenta. All the venous blood goes in the he right Sinus Venosus, which will enlarge and fuse with the right atrium.
The endothelium in the region of the Atrio-ventricular canal undergoes a process of EMT to form mesenchyme of the endocardial cushion: the primitive tricuspid and the primitive bicuspid valves. EMT is a significant embryonic mechanism involved in valve formation.
Describe the formation of the inter-atrial septum
- Diversion of the blood away from the lungs (most of the blood volume will be shunted to the LA to the aorta (systemic circulation). The sinus venosus with its two protruding valves (into the RA) contributes to the RA (smooth portion) and to the Inter-atrial septum (IAS).
- Initial single opening of the pulmonary vein in the LA which gradually becomes incorporated in the LA wall as two then four tributaries become incorporated (forming the four pulmonary veins opening into the smooth portion of the LA). There is still a shunt from the right to the left ventricle (foramen secundum).
Decribe the functional closure of the IAS
With the expansion of the lung alveoli and closure of the ductus arteriosus, (higher LA pressure than RA) there is functional closure. Functional closure is complete by the 6th week (90% infants) and complete in all infants by 3 months Eventually fibroblastic growth seals the attachment of the valve.
Describe the aortico-pulmonary septum closure
Blood entering the common ventricle through the tricuspid and bicuspid valves spirals into the bulbus cordis and truncus arteriosus facilitated by the bulbo-ventricular looping and forming inter-ventricular septum from the floor (of the common ventricle). Completion of the septation of the ventricles and aorta and pulmonary artery (from truncus arteriosus) occur simultaneously. Important mechanisms:
- Hemodynamics of the spiraling two cords of blood,
- Downward growth of bulbar ridges formed from migratory neural crest cells.
Finally, the pulmonary and aortic valves form from the junction of Bulbus Cordis and Truncus Arteriosus. Note that the coronary arteries grown into the cusp, not from the cups.
What are the 4 main congenital abnormalities related to the CV development?
- Dextocardia
- Down syndrome and abnormal heart formation
- Probe Patency of the IAS
- Outflow anomalies
What is Dextocardia?
Dextocardia, or situs inversus, is a rare congenital condition in which the apex of the heart is located on the right side of the body. There is a transposition of the great vessels and venous blood goes in the aorta, but the survival is allowed by the fact that the intraventricular septum is defective (shunt) and a small amount of oxygenated blood goes in the RV.
What is the heart abnormality involved in Down syndrome?
The absence of fusion or incomplete fusion of endocardial cushions
What is Probe Patency of the IAS?
An incomplete sealing of the IAS
What are the Outflow anomalies?
- Persistent truncus arteriosus
- Tetralogy of Fallot
- Pulmonary stenosis
- Membranous IVS defect
- Overriding aorta
- RV hypertrophy - Congenital mitral stenosis
