Development of lymphatic Development of lymphatic systemsystem

lymphlymph The colorless liquid lymph has about the The colorless liquid lymph has about the

same composition as the blood plasma.same composition as the blood plasma. It contains many lymphocytes and It contains many lymphocytes and

frequently red blood corpuscles. frequently red blood corpuscles. Granules and bacteria are also taken up by Granules and bacteria are also taken up by

the lymph from the connective-tissue spaces, the lymph from the connective-tissue spaces, partly by the action of lymphocytes which partly by the action of lymphocytes which pass into the lymph between the endothelial pass into the lymph between the endothelial cells and partly by the direct passage of the cells and partly by the direct passage of the granules through the endothelial cells. granules through the endothelial cells.

The lymphatic system begins to The lymphatic system begins to develop at the end of the sixth week, develop at the end of the sixth week, approximately 2 weeks after the approximately 2 weeks after the primordia of the cardiovascular primordia of the cardiovascular system are recognizablesystem are recognizable

Development of lymphatic Development of lymphatic systemsystem

The lymphatic system begins as a series The lymphatic system begins as a series of sacs  at the points of junction of of sacs  at the points of junction of certain of the embryonic veins. These certain of the embryonic veins. These lymph-sacs are developed by the lymph-sacs are developed by the confluence of numerous venous confluence of numerous venous capillaries, which at first lose their capillaries, which at first lose their connections with the venous system, but connections with the venous system, but subsequently, on the formation of the subsequently, on the formation of the sacs, regain them. sacs, regain them.

The lymphatic system is therefore The lymphatic system is therefore developmentally an offshoot of the developmentally an offshoot of the venous system, and the lining walls venous system, and the lining walls of its vessels are always endothelial. of its vessels are always endothelial.

. .

Lymphatic vessels develop in a Lymphatic vessels develop in a manner similar to that previously manner similar to that previously described for blood vessels and described for blood vessels and make connections with the venous make connections with the venous system. system.

Development of Lymph Sacs Development of Lymph Sacs and Lymphatic Ductsand Lymphatic Ducts

There are There are six primary six primary lymph sacslymph sacs present at present at the end of the the end of the embryonic periodembryonic period

Two jugular lymph sacsTwo jugular lymph sacs near the junction of near the junction of the subclavian veins the subclavian veins with the anterior with the anterior cardinal veins (the cardinal veins (the future internal jugular future internal jugular veins) .veins) .

Two iliac lymph Two iliac lymph sacssacs near the near the junction of the iliac junction of the iliac veins with the veins with the posterior cardinal posterior cardinal veins veins

One retroperitoneal One retroperitoneal lymph saclymph sac in the root in the root of the mesentery on of the mesentery on the posterior the posterior abdominal wall abdominal wall

One chyle cisternOne chyle cistern (L. (L. cisterna chylicisterna chyli) ) located dorsal to the located dorsal to the retroperitoneal retroperitoneal lymph sac lymph sac

Lymphatic vessels soon connect to the Lymphatic vessels soon connect to the lymph sacs and pass along main veins;lymph sacs and pass along main veins;

to the head, neck, and upper limbs from to the head, neck, and upper limbs from the jugular lymph sacs; the jugular lymph sacs;

to the lower trunk and lower limbs from to the lower trunk and lower limbs from the iliac lymph sacs;the iliac lymph sacs;

primordial gut from the retroperitoneal primordial gut from the retroperitoneal lymph sac and the lymph sac and the chyle cisternchyle cistern. .

Two large channels (right and left Two large channels (right and left thoracic ducts) connect the jugular thoracic ducts) connect the jugular lymph sacs with this cistern. Soon a lymph sacs with this cistern. Soon a large anastomosis forms between large anastomosis forms between these channelsthese channels

Thoracic DuctThoracic Duct The thoracic duct develops from the The thoracic duct develops from the

caudal part of the right thoracic duct, caudal part of the right thoracic duct, the anastomosis between the left the anastomosis between the left and right thoracic ducts, and the and right thoracic ducts, and the cranial part of the left thoracic duct. cranial part of the left thoracic duct.

The The right lymphatic ductright lymphatic duct is derived is derived from the cranial part of the right from the cranial part of the right thoracic duct . The thoracic duct . The thoracic ductthoracic duct and right lymphatic duct connect and right lymphatic duct connect with the venous system at the with the venous system at the venous angle between the internal venous angle between the internal jugular and subclavian veins. jugular and subclavian veins.

Development of the Lymph Development of the Lymph NodesNodes

Except for the superior part of the Except for the superior part of the chyle cistern, the lymph sacs are chyle cistern, the lymph sacs are transformed into groups of lymph transformed into groups of lymph nodes during the early fetal period. nodes during the early fetal period.

Mesenchymal cells invade each Mesenchymal cells invade each lymph sac and break up its cavity lymph sac and break up its cavity into a network of lymphatic channels-into a network of lymphatic channels-the primordia of the the primordia of the lymph sinuseslymph sinuses. . Other mesenchymal cells give rise to Other mesenchymal cells give rise to the capsule and connective tissue the capsule and connective tissue framework of the lymph nodeframework of the lymph node

lymphocyteslymphocytes The lymphocytes are derived The lymphocytes are derived

originally from stem cells in the originally from stem cells in the umbilical vesicle (yolk sac) umbilical vesicle (yolk sac) mesenchyme and later from the liver mesenchyme and later from the liver and spleen. These early lymphocytes and spleen. These early lymphocytes eventually enter the bone marrow, eventually enter the bone marrow, where they divide to form where they divide to form lymphoblastslymphoblasts. .

The lymphocytes that appear in The lymphocytes that appear in lymph nodes before birth are derived lymph nodes before birth are derived from the from the thymusthymus, a derivative of the , a derivative of the third pair of pharyngeal pouches . third pair of pharyngeal pouches . Lymph nodules do not appear in the Lymph nodules do not appear in the lymph nodes until just before and/or lymph nodes until just before and/or after birthafter birth