Contact
Dr. Patton

L  e  a  r  n  i  n  g       O  u  t  l  i  n  e

Lymphatic and Immune Systems

Lion Tracks

Press the
Panic Button

Starling's Law of the Capillaries

	In a capillary, there are inwardly directed forces and outwardly directed forces that are balanced or imbalanced Osmotic pressure Hydrostatic pressure (pressure of fluid against a membrane)
	At the arterial end of a capillary Outwardly directed forces (mostly blood pressure) causes net diffusion of water and small solutes OUT of the blood (and into the IF [interstitial fluid])
	At the venous end of a capillary Inwardly directed forces (mostly tissue fluid pressure and osmotic pressure of the blood plasma) causes net diffusion of water and small solutes INTO the blood (and out of the IF)
	About 10% (varies greatly) of the fluid that OUGHT to return to the blood capillary does not This "extra" interstitial fluid (IF) in the tissue may accumulate, causing painful swelling and potentially fatal damage to the tissue Blood would also loose too much fluid to maintain health The lymphatic system includes a system of vessels that drains this excess fluid away and returns it to the blood supply

Lymphatic drainage

	Lymphatic capillaries    pp     GA    GA Blind-end tubules that begin in a tissue and continue as tributaries to larger and larger vessels, like creeks running into large streams, into rivers, into the lake Lumen (hollow part) of capillaries is "always open" like storm drainage pipe because tiny fibers attached to surrounding tissue cells hold it open from the outside This allows water and small particles to drain into the capillaries easily (without much of a pressure gradient) The drained fluid is now called "lymph" or "lymphatic fluid" Numerous SL (semilunar) valves keep lymph from flowing back toward tissue Drain away excess fluid as described above Also drain away fats absorbed in the digestive tract (otherwise the fats would increase blood viscosity and slow blood flow during absorption of a meal)
	Lymphatic vessels and ducts     GA Lymphatic vessels eventually all drain into the: Right lymphatic duct drains lymph from the superior right quadrant of body ---into the right subclavian vein (just before the systemic blood enters the right atrium of the heart) Thoracic duct  drains lymph from the lower right quadrant and entire left side of body into the left subclavian vein Numerous SL valves and lymph nodes (and other lymphoid organs)
	Lymphokinesis (kinesis = "movement") One-way flow (linear;  unlike "circular flow" of cardiovascular system) toward the blood/heart Lymphatic pump Similar to venous pumps Lymphokinesis averages about 125 ml/hr (that's 3 L/day)

Also known as lymphatic filariasis, this condition occurs when parasitic worms (any of several types of filaria worms) infest the lymphatic system.  The filaria are transmitted by mosquitoes to the blood and can build a population in the lymph nodes, blocking fluid drainage from arms, legs, genitals, or breasts.  It is called elephantiasis (literally, "elephant condition") because in extreme cases, the arms and legs look like the limbs of an elephant. Elephantiasis affects over a 100 million people around the world.  However, most cases are not as extreme as in this photo!

Immunity is protection/defense     pp

	Often, a military warfare model is used to illustrate immune function    pp
	Immunity is carried out by many cells and tissues of the body, not just those classically identified as "immune cells" or "immune tissues"
	Defense / protection against variety of "enemies" Nonself particles have unique identifying marker molecules Similar to the insignia of enemy aircraft, vehicles, soldiers Self-tolerance--we do not attack our own cells Examples of "enemies" Pathogens (see above) Cancer cells (your own cells that have become cancerous) Physical damage (burns, cuts, etc.)
	Two strategies of immunity    pp Innate immunity Called "innate" immunity because it does not require prior exposure to a pathogen Also called nonspecific immunity Mechanisms that are "on standby" at all times and are effective against a variety of different "enemies" Innate immune mechanisms respond rapidly (always "on alert") Adaptive immunity Called "adaptive immunity" or "acquired immunity" because it changes to work against new pathogens upon exposure to them Also called specific immunity Mechanisms that are effective against specific (one kind only) "enemies" Adaptive immune mechanisms respond more slowly because they take time to prepare and develop

Innate (nonspecific) defenses

	There are many innate strategies; here we discuss just a few of them Many of these innate defenses also work in cooperation with, or are supplemented by, additional adaptive defense mechanisms
	Species resistance
	Lines of defense (as in military model)
	Surface barriers - skin and mucous membranes
	Phagocytes - neutrophils, eosinophils, macrophages Antigen-presenting cells (APCs) digest the enemy particle and display the unique protein markers to signal the adaptive immune system Examples Macrophages = large, phagocytic cells found in many areas of the body Dendritic cells (DCs) = branched phagocytes, often at/near external barriers
	Natural killer (NK) cells NK cells are lymphocytes that "patrol" the body, looking for abnormal cells (esp. cancer cells and virus-infected cells) to kill NK cells kill by direct contact with enemy cell NK cells each have two receptors Killer-activating receptor binds to common cell markers (thus, binds even to self cells) Killer-inhibiting receptor binds to certain self markers, thus preventing killing of self cells The self markers are MHC (major histocompatibility complex) proteins unique to every individual Kill by various methods May release perforins, which are proteins that form holes in the plasma membrane of the cell to be killed Sodium diffuses in, then water osmoses inward, causing the cell to swell and burst (cytolysis) In nucleated cells, this influx of ions may trigger apoptosis (programmed cell death), also resulting in cytolysis May also release granzymes that can enter the cell and trigger apoptosis
	Defensive proteins (cytokines) Interferons (IFNs) are released by dying, virus-infected lymphocyte or other cell     pp Interferons "call in" other immune cells (NK cells and macrophages) that destroy virus-infected cells, protecting the body from further spread of viral infection Interferons also "interfere" with the ability of viruses to replicate in other nearby cells --also stopping the viral infection Interferons are paracrine agents, regulating nearby cells Complement is a group of about 20 different plasma proteins Individual complement proteins are designated C1, C2, C3, and so on Complement molecules are activated in a cascade of chemical reactions triggered by innate or adaptive mechanisms Complement can act directly, as do perforins Form MACs (membrane attack complexes) that poke holes in the outer membrane Complement can act indirectly as a chemotactic agent or regulating immune cells in some other way Chemotaxis    pp Chemical attractants are released from damaged tissue cells and immune system cells to "call over" immune cells to the site of injury

Adaptive (specific) defenses

Two strategies of adaptive defense    pp Antibody-mediated immunity uses antibodies (immunoglobulins [Ig]) Also called humoral immunity because antibodies are dispersed in the blood plasma (humor = "body fluid") Antibodies are Y-shaped plasma proteins made by B-lymphocytes (B-cells) that bind to specific antigens (markers or particles that have a complementary shape to the active site on an antibody molecule) and cause them harm  Antibody-mediated immunity is like "shelling" the "enemy"  --the antibodies are like "homing missiles" directed as specific distant targets Cell-mediated immunity (or cellular immunity) uses cells (T-lymphocytes = T cells) that directly attack another cell such as an infected cell or cancer cell