Byte Size Med: Development of the Heart (Part 1: Heart Tube)

Introduction

• Topic: Development of the heart, focusing on the heart tube
• Germ Layers: Ectoderm, Endoderm, Mesoderm
• Mesoderm Parts: Paraxial, Intermediate, and Lateral Plate Mesoderm
• Heart Development: Occurs in the splanchnic layer of the lateral plate mesoderm

Formation of the Heart Tube

• Initial Development: Cluster of cells stimulated by endoderm to differentiate into blood islands
• Process: Vasculogenesis forms vessels, specifically paired heart tubes
• Location: Heart sits in the pericardial cavity, formed from the intra-embryonic cavity

Embryo Folding

• Embryo Sections: Transverse and longitudinal (sagittal)
• Folding Directions: Lateral and Cephalocaudal
  • Lateral Folding: Sides come together, closing the ventral body wall
  • Cephalocaudal Folding: Bending of head and tail ends
• Heart Tube Formation: Two heart tubes fuse into one heart tube in pericardial cavity due to lateral folding

Development of Heart Structure

• Heart Tube Orientation: Venous end and an arterial end
• Layers of Heart Tube:
  • Endocardium: Formed from endothelial lining
  • Myocardium: Formed by cardiac myoblasts
  • Cardiac Jelly: Specialized connective tissue
  • Epicardium: Formed by migration of mesothelial cells

Heart Chambers and Valves

• Heart Chambers: Right Atrium, Left Atrium, Right Ventricle, Left Ventricle
  • Atria Features:
    • Right Atrium: Blood from superior & inferior vena cava, coronary sinus
    • Left Atrium: Blood from four pulmonary veins
    • Posterior wall smooth, anterior wall with muscular ridges (muscle pectinati)
  • Ventricular Features:
    • Atrioventricular Valves: Tricuspid (right), Mitral (left)
    • Muscular Features: Chordae tendinae, papillary muscles, trabeculae carneae
    • Outflow Tracts: Smooth, infundibulum (right), aortic vestibule (left)
    • Semilunar Valves: Pulmonary (right), Aortic (left)

Development of Heart Tube Structures

• Alternating Structures:
  • Truncus Arteriosus: Forms ascending aorta and pulmonary trunk
  • Bulbus Cordis: Smooth outflow tracts and right ventricle
  • Primitive Ventricle
  • Primitive Atrium
  • Sinus Venosus

Blood Path and Cardiac Looping

• Blood Pathway: Sinus venosus → Primitive Atrium → Primitive ventricle → Bulbus cordis → Truncus arteriosus
• Cardiac Looping:
  • Ventricles Enlarge: Shift ventrally and lower
  • Atria and Sinus Venosis: Shift dorsally and laterally
  • Final Arrangement: More heart-like structure with truncus arteriosus and conus cordis forming external features

Conclusion

• Next Steps: Part two will explore atrial development
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