Chapter 22 The Lymphatic System and Immunity

The Lymphatic System A system consisting of lymphatic vessels through which a clear fluid (lymph) passes The major functions of the lymphatic system include: Draining interstitial fluid Transporting dietary lipids absorbed by the gastrointestinal tract to the blood Facilitating the immune responses

The Lymphatic System Components of the lymphatic system include: Lymphatic capillaries Lymphatic vessels Lymph nodes Lymphatic trunks Lymphatic ducts Primary lymphatic organs Secondary lymphatic organs and tissues

Lymphatic Vessels and Fluid Lymph is a clear to milky fluid in the extracellular fluid compartment. Extracellular fluids include: Plasma – the liquid component of blood Interstitial fluid – the clear fluid filtered through capillary walls when it enters the “interstitium” (space between cells, also called the intracellular space) Lymphatic fluid – the unaltered interstitial fluid that enters the lymphatic vessels. In the GI tract, lymphatic fluids also include absorbed dietary lipids.

Lymphatic Vessels and Fluid The flow of lymph fluid is always from the periphery towards the central vasculature. It starts as interstitial fluid. Then enters lymphatic capillaries. It travels in lymphatic vessels to the regional lymph nodes…

Lymphatic Vessels and Fluid The flow of lymph fluid continued… Lymph ascends or descends to the thorax, either to the Left or Right Lymphatic Duct. Lymph fluid’s final destination is the bloodstream, as it enters through the Subclavian veins.

Lymphatic Vessels and Fluid Lymphatic capillaries are slightly larger than blood capillaries and have a unique one-way structure. The ends of endothelial cells overlap and permit interstitial fluid to flow in, but not out. Anchoring filaments pull openings wider when interstitial fluid accumulates. There are specialized lymphatic capillaries called lacteals that take up dietary lipids in the small intestine. Chyle is the name of this “lymph with lipids”.

Lymphatic Vessels and Fluid Lymphatic capillaries showing blind ends and one way flow

Lymphatic capillaries unite to form larger lymphatic vessels which resemble veins in structure but have thinner walls and more valves. Lymphatic vessels pass through lymph nodes – encapsulated organs with masses of B and T cells. Function as lymph filters Lymphatic Vessels and Fluid

Lymphatic fluid is moved by pressure in the interstitial space and the milking action of skeletal muscle contractions and respiratory movements. An obstruction or malfunction of lymph flow leads to edema from fluid accumulation in interstitial spaces. Lymphatic Vessels and Fluid

Lymphatic Organs The lymphatic system is composed of a number of primary and secondary organs and tissues widely distributed throughout the body - all with the purpose of facilitating the immune response.