Development of the Heart

Introduction

• The presentation focuses on the development of the heart.
• The process is broken down into stages to facilitate understanding.
• The main goal is to develop a heart tube and a pericardial cavity.

Initial Formation of the Heart Tube

1. Embryo Orientation

   • Top view of the embryo: cranial (head) and caudal (tail) aspects.
   • Gastrulation process: cells from the epiblast move through the primitive streak.
   • Formation of mesoderm between the ectoderm and endoderm.

2. Mesoderm Development

   • Mesoderm clumps in the cranial aspect, forming the heart in the head initially.
   • Two views for understanding heart tube development: cross-sectional and sagittal.

Cross-Sectional View

1. Layers and Mesoderm Components

   • Three layers: ectoderm, mesoderm, endoderm.
   • Mesoderm: par axial mesoderm, intermediate mesoderm, lateral mesoderm.

2. Heart Tube Formation

   • Heart tube develops from the splanchnic layer of the lateral plate mesoderm.
   • Endoderm secretes VEGF to stimulate mesoderm differentiation.
   • Formation of angioblasts (blood vessels and heart tube) and hemocytoblasts (blood cells).

3. Lateral Folding and Fusion

   • Lateral folding leads to the fusion of heart tubes and pericardial cavities.
   • Formation of a singular heart tube and pericardial cavity.
   • Dorsal mesocardium connects the heart tube to the posterior wall.

4. Heart Tube Structure

   • Layers: endocardium (inner) and myocardium (outer).
   • Cardiac jelly is secreted by myocardium between the layers.

Sagittal View

1. Cranial-Caudal Folding

   • Cardiogenic mesoderm moves from the head to the thorax.
   • Folding moves the heart tube into the pericardial cavity.

2. Heart Tube Sections

   • Dorsal aorta, truncus arteriosus, bulbous cordis, primitive ventricle, primitive atria, and sinus venosus.
   • Blood flow is from sinus venosus to dorsal aortae.

Cardiac Looping

• Importance of dyneins for proper looping.
• Issues with dyneins can result in dextrocardia or situs inversus.
• Process involves movement of truncus arteriosus and bulbous cordis, leading to a proper heart shape.

Development of Heart Chambers and Valves

1. Endocardial Cushion Formation

   • Neural crest cells form endocardial cushions.
   • Fusion of cushions forms the septum intermedium, separating atria and ventricles.

2. Atrioventricular (AV) Canals and Valves

   • Formation of right and left AV canals.
   • Development of mitral and tricuspid valves from the septum intermedium.

3. Septation of Atria

   • Formation of septum primum, ostium primum, and ostium secundum.
   • Development of septum secundum and foramen ovale.

4. Ventricular Septation

   • Formation of muscular and membranous portions of the interventricular septum.
   • Potential for ventricular septal defects if not properly formed.

5. Inflow Tracts

   • Development from sinus venosus: superior and inferior vena cava, coronary sinus.
   • Right atrium receives blood from these inflow tracts.

6. Outflow Tracts and Septation

   • Formation of aorticopulmonary septum from neural crest cells.
   • Separation into pulmonary trunk and aorta.
   • Formation of semilunar valves.

Conclusion

• The presentation covered the complex process of heart development.
• Key steps involve the formation and looping of the heart tube, septation of chambers, and development of valves.
• Understanding these processes is crucial for identifying potential congenital heart defects.