ch.20 Lymphatic System and Lymphoid Organs and Tissues

Lymphatic system returns fluids leaked from blood vessels back to blood; consists of three parts

1. Network of lymphatic vessels (lymphatics)

2. Lymph: fluid in vessels

3. Lymph nodes: cleanse lymph

Lymphoid organs and tissues provide

structural basis of immune system by housing phagocytic cells and lymphocytes

• Structures include spleen, thymus, tonsils, lymph nodes, other lymphoid tissues

Lymphatic system;

returns interstitial fluid and leaked plasma proteins back to blood via:

• Lymphatic vessels 

• circulates 3L interstitial fluid per day

• Once interstitial fluid enters lymphatics, it is called lymph

Lymph vessels (lymphatics) include

lymphatic capillaries and larger lymphatic vessels

Lymphatic capillaries

Blind-ended vessels that weave between tissue cells and blood capillaries

more permeable than blood capillaries due to endothelial cells & minivalves

can take larger molecules & particles that capillaries cannot such as; proteins, cell debris, pathogens, cancer cells

Lacteals

• specialized lymph capillaries present in intestinal mucosa

  • Absorb digested fat and deliver fatty lymph (chyle) to the blood

-reason due to high cholsterol

• Larger lymphatic vessels - Lymph capillaries drain into increasingly larger vessels called

collecting lymphatic vessels

• consist of collecting vessels, trunks, and ducts

• have thinner walls w/ more internal valves

• anastomose more frequent

• Lymphatic trunks, which are formed by union of largest collecting vessels, drain large areas of body. regions of body they drain -

• Paired lumbar

• Paired bronchomediastinal

• Paired subclavian

• Paired jugular trunks

• Single intestinal trunk

Lymph is delivered from trunks into one of two large

lymphatic ducts

Right lymphatic duct-

drains right upper arm and right side of head and thorax

thoracic duct drains rest of body (In about half of individuals, starts out as an enlarged sac, cisterna chyli)

Lymphangitis:

condition in which lymphatic vessels appear as painful red lines under the skin 

• Caused by inflammation of larger lymphatic vessels that contain vaso vasora

Lymph system is a low-pressure system like

venous system

• Lymph is propelled by same mechanisms:

  • Milking action of skeletal muscle

  • Pressure changes in thorax during breathing

  • Valves to prevent backflow

  • Pulsations of nearby arteries

  • Contractions of smooth muscle in walls of lymphatics 

Physical activity increases flow of lymph; immobilization of area keeps needed inflammatory material in area for

faster healing 

Lymphedema:

severe localized edema 

• Caused by anything that prevents normal return of lymph to blood

• ex- tumors blocking lymphatics or removal of lymphatics during cancer surgery