The Lymphatic System

Roles of the Lymphatics system • Functions of the lymphatic system

– Fat absorption• Intestinal lipid absorption places chylomicrons

(intestinal lipid carriers) into the lymphatic system rather than the hepatic portal system

– Systemic circulation has “first-pass” access to intestinal lipids and fat-soluble vitamins (unlike amino acids & glucose)

– Returns interstitial fluid to circulation– Retains lymphocytes (lymph-based cells) for

immunity

Lymphatic System• Consists of:

- lymph- network of vessels- lymph nodes and nodules - primary organs

- bone marrow- thymus

– Secondary organs• Spleen• Tonsils• Other tissues

– Peyers patches– Kuffers cells

Lymph (lympha = clear fluid)

• derived from tissue fluid• contains more white blood cells than plasma• must be returned to blood stream to maintain blood

volume and pressure• Lymph = plasma - proteins

Lymphatic circulation • Lymphatic circulation returns

excess tissue fluid back to the cardio-vascular system

– Blood plasma that seeps from the capillary beds is normally drawn back into the venous blood flow by diffusion/osmosis

15% does not return to venous flow and must be returned to circulation via lymphatic system

Lymphatic capillaries

Lymphatic capillaries

Lymphatic capillaries are markedly similar to veins:

• One-way valves & requirement for skeletal muscle propulsion (skeletal muscle “pump”)

Where lymphatics differ from venous system arises with lymph nodes

• Nodes or collections of reticular tissue along the lymphatic vessel tract

Lymph vessels• Capillaries merge to form larger vessels trunks

• no pump for lymph Lymph is kept moving by:

- constriction of vessels

- skeletal muscle pump

- respiratory pump

Lymphatic nodes

Note how lymph enters the lymph nodes and permeates through the reticular tissue where immature lymphocytes are located. These immature lymphocytes then sample the contents of the lymph and develop “tolerance” or “attack” postures.

Major Lymph Nodes

• cervical• axillary• inguinal• mesenteric

Lymphatic vessels and nodes

Lymph nodes usually located in characteristic locations along

the lymph network

A disease of the lymphatic system: bubonic plague

Lymphatic circulation

Remember that lymph drainage is not proportional: right lymphatic duct only drains from upper right torso into right subclavian vein.

Lymphatic System• Consists of:

- lymph- network of vessels- lymph nodes and nodules - primary organs

- bone marrow- thymus

– Secondary organs• Spleen• Tonsils• Other tissues

– Peyers patches– Kuffers cells

Primary organs: Bone marrow

The bone marrow synthesizes all 3 blood cells and elements. The B lymphocytes mature in the bone marrow before their release

Primary organs: thymus• Located in the chest, behind the sternum• Large in children – decrease in size during adulthood• Promotes maturation of T-lymphocytes• No function in adulthood?

Secondary organs: the spleen• Left, upper abdomen,

under the ribs• Catastrophic injury when

ruptured• Receives blood from the

splenic artery and export blood through the splenic vein

• Has white and red pulps– white: collection of T-

lymphocytes

– Red: red blood cells storage

Tonsils• Role: Most likely samples

pathogens passing by the mouth and upperairway – can be removed without consequences

• 3 sets:– pharyngeal tonsils =

adenoids

– Palatine tonsils

– Lingual tonsils

Other lymphatic tissues• Peyer’s patches: grouph of lymphatic

cells present along the wall of the intestine. Catch pathogens which manages to cross.

• Appendix: catches pathogen from the intestinal lumen. Frequently infected removed

• Kupffer cells: phagocytic cells present in the liver.