Lymphatic SystemThe 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 DefenseImmune 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