Lecture on Heart Development

Introduction

• Focus on development of the heart.
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Goals

• Develop the heart tube and the pericardial cavity.
• Understand the folding processes involved.

Basic Embryology

Embryo Orientation

• Cranial (head) and caudal (tail) aspects
• Gastrulation: Formation of three layers from epiblast:
  • Ectoderm
  • Mesoderm
  • Endoderm
• Cardiogenic mesoderm forms in cranial aspect.

Heart Tube Formation

Mesoderm Differentiation

• Splanchnic layer of lateral plate mesoderm forms heart tube.
• Endoderm secretes growth factors like VEGF.
  • VEGF influences mesoderm to differentiate into angioblasts and hemocytoblasts.

Process

• Lateral plate mesoderm forms heart tubes and pericardial cavities.
• Embryo undergoes lateral folding:
  • Heart tubes fuse into a singular heart tube.
  • Pericardial cavities merge into one.

Layering of the Heart Tube

• Endocardium: Innermost layer from angioblasts.
• Myocardium: Outermost layer from cardiac myocytes.
• Cardiac jelly: Connective tissue between endocardium and myocardium.

Cranial-Caudal Folding

• Movement of the heart from cranial (head) to thoracic (chest) region.
• Heart tube gets positioned in the pericardial cavity.

Structural Segmentation

Sections of the Heart Tube

• Truncus Arteriosus: Future pulmonary artery and aorta.
• Bulbus Cordis: Future right ventricle and outflow tracts.
• Primitive Ventricle: Future left ventricle.
• Primitive Atrium: Future left and right atrium.
• Sinus Venosus: Inflow tract, evolves into the superior vena cava, inferior vena cava, and coronary sinus.

Cardiac Looping

• Importance of dyneins in proper heart bending.
• Issues can cause dextrocardia or situs inversus.

Septation

AV Canal Formation

• Neural crest cells migrate to form endocardial cushions.
• Septum intermedium forms, creating right and left AV canals.

Atrial Septation

• Septum Primum and Septum Secundum development.
• Formation of Foramen Ovale for fetal circulation.

Ventricular Septation

• Formation of the interventricular septum.
  • Muscular and membranous portions.
  • Ventricular septal defects if fusion fails.

Inflow and Outflow Tracts

Inflow Tract Formation

• Absorption of sinus venosus into the primitive atrium forming coronary sinus, SVC, and IVC.

Outflow Tract Formation

• Truncus arteriosus and bulbus cordis form outflow tracts with septation.
• Formation of aortic and pulmonary valves from endocardial cushions.

Final Heart Structure

• Formation of semilunar valves and establishment of correct chamber connections.

Conclusion

• Comprehensive discussion on heart development.
  • Encouragement for further study and support of educational content.