Development of the Heart - Part 1: The Heart Tube

Introduction

• The heart develops from the mesoderm, one of the three germ layers (ectoderm, endoderm, mesoderm).
• Mesoderm Parts:
  • Paraxial mesoderm
  • Intermediate mesoderm
  • Lateral plate mesoderm

Lateral Plate Mesoderm

• Develops cavities that form an intraembryonic cavity.
• Splits into two layers:
  • Somatic layer
  • Splanchnic layer
• Heart Development Location: Splanchnic layer.

Formation of the Heart Tube

• Starts as a cluster of cells influenced by the endoderm.
• Vasculogenesis: Formation of blood vessels from blood islands.
• Paired heart tubes form, located on each side of the embryo.

Embryo Folding

• Types of Folding:
  • Lateral folding: Sides come together, forming a single heart tube in the pericardial cavity.
  • Cephalocaudal folding: Head and tail ends bend, moving the heart towards the thoracic region.

Heart Tube Structure

• Initially a vessel with endothelium, surrounded by cardiac myoblasts.
• Layers of the Heart Tube:
  • Endocardium: Formed by endothelial lining.
  • Myocardium: Formed by cardiac myoblasts.
  • Cardiac Jelly: Connective tissue separating layers.
  • Epicardial layer: Visceral layer of the pericardium.

Heart Chambers

• Atria: Right and Left
  • Right atrium receives blood from superior/inferior vena cava and coronary sinus.
  • Left atrium receives blood from four pulmonary veins.
  • Smooth posterior wall; rough anterior wall with musculi pectinati.
• Atrioventricular Valves:
  • Tricuspid (right) and mitral (left) valves.
  • Connected via chordae tendineae to papillary muscles.
• Ventricles: Right and Left
  • Right ventricle: Pumps blood into the pulmonary trunk.
  • Left ventricle: Pumps blood into the ascending aorta.
  • Rough inflow with trabeculae carnii; smooth outflow tracts (infundibulum and aortic vestibule).
• Semilunar Valves:
  • Pulmonary (right) and aortic (left) valves.

Heart Tube Segmentation

• Arterial and Venous Ends:
  • Venous end: Sinus venosus.
  • Arterial end leads to the aortic sac and roots.
• Heart Tube Segments:
  • Truncus arteriosus: Forms ascending aorta and pulmonary trunk.
  • Bulbus cordis: Forms outflow tracts and parts of right ventricle.
  • Primitive ventricle: Forms the trabeculated part of the left ventricle.
  • Primitive atrium: Forms rough anterior atrial walls.
• Interventricular Formation:
  • Bulboventricular sulcus: Site of interventricular foramen and septum.

Cardiac Looping

• Looping Process:
  • Truncus arteriosus, bulbus cordis, and primitive ventricle bend ventrally.
  • Primitive atrium and sinus venosus shift dorsally and upward.
• Outcome: Rearranges heart tube segments to resemble a heart.

Conclusion

• The development of the heart from the heart tube involves complex processes including folding and looping.
• This lecture covers the initial formation of the heart tube, setting the stage for further development into distinct heart structures.

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• Stay tuned for Part 2, focusing on atrial development.
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