When does the lymphatic system begin to develop in the embryo?

The lymphatic system starts developing at the end of the 5th week of embryonic life, approximately one week after the cardiovascular system begins to form.

What are the six primary lymph sacs formed during embryonic development?

Six primary lymph sacs form: two jugular lymph sacs, two iliac lymph sacs, one retroperitoneal lymph sac, and one cisterna chyli. They are located at key venous junctions and near the mesentery.

How does the thoracic duct develop?

The thoracic duct develops in three stages: first, a lymphatic plexus forms; second, right and left longitudinal channels appear; third, only specific parts persist to form the definitive duct.

Where do lymphocytes originate during development?

Lymphocytes originate from mesenchymal stem cells, initially in the yolk sac and later from the liver and spleen. They then seed the bone marrow for differentiation and reach lymph nodes via the thymus and circulation.

How do lymph nodes form from the primary lymph sacs?

Lymph nodes develop from mesenchymal cells surrounding the primary lymph sacs. These cells invade the sacs, breaking them into sinuses, and form the capsule and framework, transforming most sacs into lymph node groups.

What structures develop from the dorsal mesogastrium and pharyngeal pouches?

The spleen develops from mesenchyme in the dorsal mesogastrium, while the palatine tonsil forms from endoderm of the second pharyngeal pouch and associated mesenchyme.

What is the difference between the thoracic duct and right lymphatic duct?

The thoracic duct drains into the left subclavian-internal jugular vein junction, while the right lymphatic duct drains into the same junction on the right side. The thoracic duct forms from specific embryonic channels, whereas the right duct develops from the cranial right longitudinal lymph channel.

Lymphatic Development – Sacs, Ducts & Nodes

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