The

Lymphatic

System

Function of the Lymphatic System

• #1: It returns excess interstitial fluid to the blood.

• Of the approx 90% returned by osmosis to the blood almost immediately; the 10% that does not return becomes part of the interstitial fluid which surrounds cells in our tissues.

Refer to page 323 of text for this picture showing the relationship of the lymphatic system to the

cardiovascular system

• During filtration in the capillaries a tissue fluid from blood plasma remains in the interstitial spaces and must be returned to the blood via lymphatic vessels.

• Without this return blood volume and BP would decrease.

Cisterna chyli

Thoracic duct

Rt lymphathic duct

• Function #2 of the lymphatic system is the absorption of fats and fat-soluble vitamins from the digestive system, and transport them to venous circulation.

• Duodenum mucosa have fingerlike projections called Villi;

• Here a specialized lymph capillaries called Lacteals that absorb fats, and the fat-soluble vitamins.

• Vitamin A, D, E, and K.

• Function # 3 is to provide the bodies defense against invading microorganisms and disease processes.

• Here complex lymphatic tissues (lymphocytes within connective tissue, that have been produced from stem cells in the red bone marrow, migrate to lymph nodes and nodules, lymph tissues, to the spleen, and thymus.

Definitions to know:

• Lymph: a fluid similar to blood plasma and derived from blood plasma that accumulates as the blood passes through capillary walls near the arterial end. Here it is picked up and removed by microscopic lymphatic vessels and returned to the blood. As soon as this fluid enters lymph capillaries it is know as lymph. Returning fluid prevents edema and helps maintain normal blood volume and BP.

• Lymphatic Vessels: unlike blood vessels these carry fluid away from the tissues. Lymph capillaries are found in all regions of the body except bone marrow, CNS, and tissues like the epidermis which has no blood vessels. The are composed of endothelium, in which simple squamous cells overlap to form a simple one-way valve. *This valve permits fluid to enter but prevents it from leaving.

• Lymph capillaries become lymphatic vessels

• small vessels become lymphatic trunks which

• merge until lymph fluid enters 2 lymphatic ducts.

• the right lymphatic duct drains lymph fluid from the RUQ of the body, and

• thoracic duct drains all of the rest.

• The lymphatic system has no pump, it depends on pressure gradients to move the lymph through the vessels. This pressure comes from the skeletal muscle action, respiratory movement and the smooth muscle contraction of the vessel walls.

• Lymph enters a lymph node through

• Afferent vessels, filter through the sinuses, and leaves the node through efferent vessels.

• As mentioned before the 2 ducts that collect lymph return the fluid to either the right or left subclavian veins..and it is plasma again.

• Plasma proteins (synthesized in the liver)– Prothrombin: clotting– Fibrinogen: clotting– Albumin: most abundant: COP(colloid osmotic

pressure) maintains blood volume/BP.– Globulins: alpha and beta: carriers of molecules like

fats. – Gamma Globulins: are antibodies produced by

lymphocytes and these initiate the destruction of pathogens for immunity.

– Plasma also carries heat: by produce of cell respiration and the production of ATP in cells. From MA-115

Gamma Globulins

• Refer to page 333 of text; figure 14-1 remember the antibodies here are plasma proteins.

• Immunoglobulins are also called antibodies (part of adaptive immunity)

• Antibodies do not kill pathogens they mark them for destruction and each one is specific for only one antigen.

• So the antibody-antigen attachment is called the antibody-antigen complex.

• Now the invader is marked for phagocytosis by either a neutrophil or a mature monocyte or macrophage.

• Also at this time a process known as complement fixation takes place.– Fixation can be complete or partial

• For bacteria the fixation is called complete and the antigen will be dead because of the bacteria’s cellular make up

• In viruses the fixation is said to be partial because only some of its proteins bond to the antigen, still it is marked for destruction by a chemical action called chemotaxis.

• See box 14-3 pg 334 tests that can be done to help in establishing whether the immune system has seen a particular antigen and if it has whether the level of antibodies is high enough to protect from the pathogen causing the patients problem.

Other organs of the lymphatic system

SpleenTonsils

Thymus

Tonsils

• These are groups of lymphatic nodules within a mucous membrane. 3 sets of 2 tonsils that are located in a ring around the oral cavity.– Pharyngeal (adenoid) are located at the

posterior wall of the nasopharynx by the entrance to the eustachian tube

– Palatine (what we call tonsils) are located in the tonsillar fossae slightly posterior, and lateral to the uvula, anterior to the oropharynx.

– Lingual tonsils are located at the base of the tongue, and are occasionally removed during a tonsillectomy.

– Designed to protect from pathogens entering via the nose, mouth, and ears. And there are large amounts of cervical lymph nodes to deal with them and protect the structures in that area.

Spleen

• Located in the ULQ of the abdominal cavity, inferior to the diaphragm and posterior to the stomach. Protected by the rib cage.

• Function: – In a fetus it produces rbcs– After that it functions like a large lymph node,

however blood flows through it not lymph fluid.

• In addition the spleen contains plasma cells that produce antibodies to foreign invaders

• Contains fixed macrophages that phagocytize pathogens, old rbcs (life span 120 days) and form bilirubin for portal circulation and then send it to the liver to be excreted in bile.

• It also stores platelets and destroys them when they are no longer useful.

• ** not considered a vital organ because we can live without it, other organs will take up the functions that it does but a person without a spleen is somewhat immunocompromized and more susceptible to various bacterial infections.

Thymus

• Located inferior to the thyroid gland, which is located in the neck, on both sides of the trachea, inferior to the larynx. The thyroid gland is part of the Endocrine system– Large in the fetus but by age 2 when the immune

system is more mature it begins to shrink and is quite tiny in adults.

• Function is to take stem cells and produce the T-cells to establish the immune system, with lymphocytes. Time is needed to do this, and this is why some vaccines are not give until the system is established enough that it can make antibodies when introduced to a antigen. Given too soon, the young child may not be able to fully develop enough to be protective.