immune system

not an organ system, but a population of cells that inhabit all of our organs and defend the body from agents of disease

– especially concentrated in the true organ system –

lymphatic system

lymphatic system

• network of organs and vein-like vessels that recover fluid • inspect it for disease agents • activate immune responses • return the fluid to the bloodstream

Lymphatic and Immune Systems

maintain fluid balance • protect body from infection and disease

fluid recovery

fluid continually filters from the blood capillaries into the tissue spaces

• blood capillaries reabsorb 85%

immunity

excess filtered fluid picks up foreign cells and chemicals from the tissues

• passes through lymph nodes where immune cells stand guard against foreign matter

• activate a protective immune response

lipid absorption

 lacteals in small intestine absorb dietary lipids that are 21-4 not absorbed by the blood capillaries

Lymph

composed of aggregates of lymphocytes and

macrophages that populate many organs in the body

defense cells are especially concentrated in these

organs

– separated from surrounding organs by connective tissue capsules

clear, colorless fluid, similar to plasma, but much less protein

– extracellular fluid drawn into lymphatic capillaries

lymphatic capillaries

terminal lymphatics) – penetrate nearly every tissue of the body

• absent from central nervous system, cartilage, cornea, bone and bone marrow

cells tethered to surrounding tissue by protein filaments

• gaps between cells are large enough to allow bacteria and cells entrance to lymphatic capillary

– endothelium creates valve-like flaps that open when 21-6 interstitial fluid pressure is high, and close when it is low

– tunica interna

endothelium and valves

tunica media

elastic fibers, smooth muscle

 tunica externa

 thin outer layer

 course through many lymph nodes

six lymphatic trunks

drain major portions of body

two collecting ducts:

 right lymphatic duct

thoracic duct

right lymphatic duct

receives lymph from right arm, right side of head and thorax; empties into right subclavian vein

thoracic duct

larger and longer, begins as a prominent sac in abdomen called the cisterna chyli; receives lymph from below diaphragm, left arm, left side of head, neck, and thorax; empties into left subclavian vein

subclavian veins

Mechanisms of Lymph Flow

lymph flows under forces similar to those that govern venous return, except no pump (heart)

• lymph flows at low pressure and slower speed than venous blood

• moved along by rhythmic contractions of lymphatic vessels – stretching of vessels stimulates contraction

• flow aided by skeletal muscle pump • arterial pulsation rhythmically squeeze lymphatic vessels • thoracic pump aids flow from abdominal to thoracic cavity • valves prevent backward flow

• rapidly flowing blood in subclavian veins, draws lymph into it

• exercise significantly increases lymphatic return

natural killer (NK) cells

large lymphocytes that attack and destroy bacteria, transplanted tissue, host cells infected with viruses or have turned cancerous

– responsible for immune surveillance

 T lymphocytes (T cells

B lymphocytes (B cells)

activation causes proliferation and differentiation into plasma cells that produce antibodies