Lymphatic System The Body’s Defense System

Nonspecific Defense First Line of Defense –Skin –Mucous Membrane –Secretions

First Line of Defense This is a mechanical barrier that protects the body from all types of pathogens Protective Chemicals –Acid pH of skin secretions toxic to bacteria –Stomach mucosa secretes HCl to kill pathogens that are ingested –Saliva contains lysozyme to kill bacteria –Mucus traps microorganisms in digestive and respiratory pathways

Nonspecific Defense Second line of defense –Phagocytic Cells –Antimicrobial proteins –Inflammatory Response

Second Line of Defense Cells and Chemicals –Phagocytes like macrophages and neutrophils engulf foreign particles and digest them with enzymes –Natural Killer Cells are lymphocytes that lyse and kill cancer cells and virus infected cells and act spontaneously without need to “recognize” intruder, they react to sugars on the cell surface and release perforins to disintegrate the target cell’s membrane –Inflammatory response which is triggered by tissue injury

4 Symptoms 1. Redness 2. Heat 3. Swelling 4. Pain Sometimes immobility is included as a fifth symptom

Inflammatory Response Chemical Alarm – Release Histamine and Kinins –They cause blood vessels to dilate (Redness and Heat) –Capillaries to leak – (Swelling or Local Edema) –Activate pain receptors –Attract phagocytes and White Blood Cells – Movement may be impaired This prevents further damage to tissue Gets rid of cellular debris and pathogens Sets the stage for repair / forcing the person to rest –Chemotaxis: cells follow chemical gradient

More on Inflammatory Response After 1 hour neutrophils arrive from bloodstream through capillaries (Diapedesis) After 12 hours monocytes become macrophages and that is when inflammation begins to subside Clotting proteins begin to wall off the area to prevent spread of pathogens Fibrin mesh forms a scaffolding for repair Heat generated increases metabolic rate and speeds up the healing process

Specific Defense Immune System Third line of defense –Lymphocytes –Antibodies –Macrophages

The Third Line of Defense Immune response –Lymphocytes mediate –Protective antibodies –T cells (T Lymphocytes) Act specifically and directly (more about this later)

Antimicrobial Chemicals Interferon –Viruses take over a cell in order to reproduce –Cells that are infected secrete proteins (interferon) –This binds to nearby cells to protect them from the virus Compliment Proteins –20 plasma proteins –Activated when fixed to fungi or foreign cells –Binds to sugars like antibodies on a cell surface –Put holes in target cell surface –Amplifies inflammatory response –Cause cell surfaces to become sticky (Opsonization)

Fever High body temperature Regulated by the hypothalamus White Blood Cells secrete Pyrogens Liver and spleen take up iron and zinc to starve bacteria Increases metabolic rate to speed up repair High fevers =dangerous Low grade = beneficial