Development of the Lymphoid Organs

• There are six primary lymph sacs
• Primary lymph sacs

  • Two jugular lymph sacs near the junction of the subclavian veins with the anterior cardinal veins (the future internal jugular veins)
  • Two iliac lymph sacs near the junction of the iliac veins with the posterior cardinal veins
  • One retroperitoneal lymph sac in the root of the mesentery on the abdominal wall
  • One cisterna chyli located dorsal to the retroperitoneal lymph sac
• The lymph sacs later become interconnected by lymph nodes
• Development of the Lymph Nodes

  1. The lymph sacs are transformed into groups of lymph nodes during the early fetal period

  2. Mesenchymal cells invade each lymph sac and break up its cavity into a network of lymphatic channels-the primordia of the lymph sinuses

  3. Other mesenchymal cells give rise to the capsule and connective tissue framework of the lymph nodes
• Congenital anomalies of the lymphatic system are uncommon
• Congenital Malformations of Thymus: Di George Syndrome
• Development of the Tonsils

  1. Second pharyngeal pouch endoderm gives rise to the palatine tonsil

  2. The central part contains crypts

  3. The pouch endoderm forms the surface epithelium lining of the crypts

  4. Around the 20th week, the mesenchyme surrounding the crypts differentiates into lymphoid tissue forming lymphatic nodules of the palatine tonsils
• Development of the Spleen

  Mesenchymal cells in the splenic primordium differentiate to form the capsule, connective tissue framework, and parenchyma of the spleen
• There are six primary lymph sacs
• Primary lymph sacs

  • Two jugular lymph sacs near the junction of the subclavian veins with the anterior cardinal veins (the future internal jugular veins)
  • Two iliac lymph sacs near the junction of the iliac veins with the posterior cardinal veins
  • One retroperitoneal lymph sac in the root of the mesentery on the abdominal wall
  • One cisterna chyli located dorsal to the retroperitoneal lymph sac
• The lymph sacs later become interconnected by lymph nodes
• Development of the Lymph Nodes

  1. The lymph sacs are transformed into groups of lymph nodes during the early fetal period

  2. Mesenchymal cells invade each lymph sac and break up its cavity into a network of lymphatic channels, the primordia of the lymph sinuses

  3. Other mesenchymal cells give rise to the capsule and connective tissue framework of the lymph nodes
• Congenital anomalies of the lymphatic system are uncommon
• Congenital Malformations of Thymus: Di George Syndrome
• Development of the Tonsils

  1. The mesenchyme surrounding the crypts differentiates into lymphoid tissue, forming lymphatic nodules of the palatine tonsils

  2. The mesenchymal cells in the splenic primordium differentiate to form the capsule, connective tissue framework, and parenchyma of the spleen