Laboratory 4.1 Functions of the Lymphatic System

Lymphatic system

Set of organs and tissues that assist in maintaining the body's fluid balance and absorbing fats from the GI tract; houses many types of immune cells, providing places for immune surveillance and protection from infectious agents

Components of the lymphatic system

Lymph, lymph nodes, lymph vessels, the spleen, the thymus, the adenoids, the tonsils, and MALT (mucosa-associated lymphoid tissue)

Fluid exchange at cardiovascular capillaries

Fluid leaves the capillaries via hydrostatic pressure and returns at the venous end via osmotic pressure

Interstitial fluid left behind per day

About 3 liters a day is left in the tissue as interstitial fluid rather than returning to the blood vessels

Consequence of unabsorbed interstitial fluid

Would cause edema (swelling) of the tissue and eventually collapse of the cardiovascular system from loss of appropriate blood volume

Lymphatic vessels (lymphatics)

Absorb the excess interstitial fluid and return it to the cardiovascular system; include 3 types: lymphatic capillaries, lymphatic collecting vessels, and lymphatic trunks (plus ducts)

Interstitial fluid composition

Plasma and proteins; enters lymphatic capillaries associated with the cardiovascular capillary bed

Lymph

Interstitial fluid once it enters a lymphatic vessel

Why lymph flows one way

Lymphatic capillaries are closed at one end, making lymphatics a one-way route (unlike the cardiovascular circuit); lymph flows from lymphatic capillaries to the subclavian veins, joining venous circulation to return to the heart

Lymphatic capillaries

Smallest lymphatic vessels; overlapping endothelial cells (like shingles on a roof) form one-way valves (fluid enters but does not leave); exceptionally permeable compared with vascular capillaries

What lymphatic capillaries can take in

Cellular debris, pathogens, and even whole cells; metastatic cancer cells can spread to new body parts by entering lymphatic capillaries

Anchoring of lymphatic capillaries

Collagen filaments anchor them to prevent collapse

Lacteals

Modified lymph capillaries in the intestine that absorb fats

Lymphatic collecting vessels

Larger vessels that collect lymph from multiple lymphatic capillaries; extend throughout most of the body; thin walls; form many anastomoses; typically travel along superficial veins and deep arteries

Valves in lymph vessels

One-way flow valves similar in structure to the large veins; prevent backward flow of lymph, which travels under very low pressure

Lymph return to circulation (force)

Solely dependent on the squeezing action of skeletal muscles, which squeezes fluid one way through the lymphatic vessels

Lymphatic trunks

Large collecting vessels that merge as they drain major areas of the body, similar to veins converging; named for the areas they drain

Names of lymphatic trunks

Paired lumbar, bronchomediastinal, subclavian, and jugular trunks, and a single intestinal trunk

Cisterna chyli

Enlarged sac in the abdomen that receives lymph from the lumbar and intestinal trunks and then becomes the thoracic duct; receives lymph drainage from digestive organs

Lymphatic ducts

All lymphatic vessels merge before entering venous circulation at either the thoracic duct (left lymphatic duct) or the right lymphatic duct, both located in the shoulder region

Thoracic duct (left lymphatic duct)

Larger duct; drains both lower extremities, the abdomen, the left arm, and the left side of the head and neck; empties into the left subclavian vein

Right lymphatic duct

Smaller duct; drains the right arm, the right side of the head and neck, and the right thoracic area; empties into the right subclavian vein

Regional lymph node groups

Cervical nodes, axillary nodes, and inguinal nodes