lymph sac

Examples of lymph sac in the following topics:

• Lymphatic Tissue Development

  • The first lymph sacs to appear are the paired jugular lymph sacs at the junction of the internal jugular and subclavian veins.
  • The next lymph sac to appear is the unpaired retroperitoneal lymph sac at the root of the mesentery of the intestine.
  • The last of the lymph sacs, the paired posterior lymph sacs, develop from the iliac veins.
  • The posterior lymph sacs join the cisterna chyli and lose their connections with adjacent veins.
  • With the exception of the anterior part of the sac from which the cisterna chyli develops, all lymph sacs become invaded by mesenchymal cells and are converted into groups of lymph nodes .

• Lymphoid Tissue

  • Lymphatic vessels develop from lymph sacs that arise from developing veins, which are derived from mesoderm, the inner tissue layer of the embryo.
  • The lymphatic endothelial cells proliferate into sacs that eventually become lymph nodes, with afferent and efferent vessels that flow out from the lymph nodes.
  • This process begins with he lymph nodes closest to the thoracic and right lymph ducts, which arises from immature subclavian-jugular vein junction.
  • The lymph nodes organized around other lymph trunks, such as those in the abdomen and intestine, develop afterwards from nearby veins.
  • The thymus and bone marrow are primary lymphoid tissue, while the lymph nodes, tonsils, and spleen are secondary lymphoid tissue.

• Lymph Trunks and Ducts

  • The lymph trunks drain into the lymph ducts, which in turn return lymph to the blood by emptying into the respective subclavian veins.
  • Jugular lymph trunks, located in the neck, drain lymph fluid from the cervical lymph nodes of the neck.
  • Subclavian lymph trunks, located beneath the clavicle, drain lymph fluid from the apical lymph nodes around the armpit, which carry lymph from the arms.
  • Intestinal lymph trunk is the unpaired lymph trunk that receives chyle (lymph mixed with fats) from the intestines.
  • Two lymph ducts receive lymph from the lymph trunks.

• Distribution of Lymphatic Vessels

  • Afferent lymphatic vessels flow into a lymph node and carry unfiltered lymph fluid.
  • Efferent lymphatic vessels flow out of a lymph node and carry filtered lymph fluid.
  • Conversely, lymph nodes are not found in the areas of the upper central nervous system, where tissue drains into cerebrospinal fluid instead of lymph, though there are some lymph vessels in the meninges.
  • Lymph vessels become larger, with better developed smooth muscle and valves to keep lymph moving forward despite the low pressure and adventia to support the lymph vessels.
  • Lymph nodes found closer to the heart filter lymph fluid before it is returned to venous circulation through one of the two lymph ducts.

• Lymph Transport

  • Lymph circulates to the lymph node via afferent lymphatic vessels and drains into the lymph node in the subcapsular sinus.
  • The lymph capillaries feed into larger lymph vessels.
  • The collecting vessels typically transport lymph fluid either into lymph nodes or lymph trunks.
  • Lymph circulates to the lymph node via afferent lymphatic vessels.
  • The lymph trunks then converge into the two lymph ducts, the right lymph duct and the thoracic duct.

• The Peritoneum

  • The peritoneum provides support and protection for the abdominal organs, and is the main conduit for the associated lymph vessels, nerves, and abdominal arteries and veins.
  • The first is the greater sac or general cavity of the abdomen.
  • The second is the lesser sac or omental bursa.
  • The lesser sac is divided into two omenta: the gastrohepatic and the gastrocolic.
  • This is a midsagittal, cross-section drawing of the epiploic foramen, the greater sac or general cavity (red), and the lesser sac or omental bursa (blue).

• Yolk Sac Development

  • The yolk sac is vascularized and contributes nutrients to the embryo.
  • The yolk sac is the first element seen in the gestational sac during pregnancy.
  • Blood is conveyed to the wall of the sac by the primitive aorta.
  • The yolk sac starts forming during the second week of embryonic development, at the same time of the shaping of the amniotic sac.
  • The yolk sac is a membranous sac attached to the embryo that provides nourishment in the form of yolk.

• Structure of the Lymphatic System

  • These structures then form increasingly larger lymphatic vessels which form colaterals and have lymph-angions (lymph hearts). 
  • The larger lymph vessels contain valves that prevent the backflow of lymph.
  • Skeletal muscle contractions also move lymph through the vessels.
  • In general, the lymph vessels bring lymph fluid toward the heart and above it to the subclavian veins, which enable lymph fluid to re-enter the circulatory system through the vena cava.
  • Lymph nodes are found primarily in the armpits, groin, chest, neck, and abdomen.

• WBC Formation

  • In developing embryos, blood formation occurs in aggregates of blood cells in the yolk sac called blood islands.
  • As development progresses, blood formation occurs primarily in the spleen, liver, and lymph nodes .
  • However, maturation, activation, and some proliferation of lymphoid cells occurs in lymphoid organs (spleen, thymus, and lymph nodes).

• Lymph Nodes

  • Each lymph node has an afferent lymph vessel that directs lymph into the node, and an efferent lymph vessel called the hilum that directs lymph out of the node at the concave side of the node.
  • The hilum also contains the blood supply of the lymph node.
  • These antigens may be taken by cells into the lymph nodes.
  • The lymph nodes also filter the lymph fluid.
  • This is usually caused by increased lymph flow into the nodes.