Human Body Defenses and Inflammation

Human Body Defenses

Human body defenses are the physiological mechanisms protecting against infection by pathogens, including bacteria, viruses, parasites, and fungi.

Types of Defenses

Innate Defenses

• These are defenses we are born with.
• They are non-specific, responding similarly to various pathogens.
• Include the first and second lines of defense.

First Line of Defense: Surface Barriers

• Skin: Protects from the external world unless breached.
• Mucous Membranes: Line passageways with external openings, such as the gastrointestinal, respiratory, and genitourinary tracts.

Second Line of Defense: Internal Defenses

• These defenses come into play if pathogens penetrate the surface barriers.
• Phagocytes: White blood cells that engulf and digest foreign cells.
• Natural Killer Cells: Release toxic granules to kill foreign cells.
• Antimicrobial Proteins: Kill bacteria or inhibit their growth.
• Inflammation and Fever: Non-specific responses to infection.
• Innate defenses work quickly but are less effective than adaptive defenses.

Adaptive Defenses

• Develop over time with exposure to different pathogens.
• Specific: Develop specific tools to attack individual pathogens.
• Include specialized white blood cells called lymphocytes.
• B Lymphocytes (B cells): Produce specific antibodies for each pathogen.
• T Lymphocytes (T cells): Facilitate cellular immunity.
• Adaptive immunity involves memory cells that remember pathogens, allowing for a quicker and more effective response upon re-exposure.
• For example, with chickenpox, the immune system remembers the virus and can mount an attack before symptoms appear.

Innate Immune Responses

First Line of Defense: Chemical and Mechanical Barriers

• Skin: Stratified squamous, keratinized cells form a barrier unless damaged.
• Sebum and Sweat: Slightly acidic secretions inhibit bacterial growth.
• Ear Wax: Traps incoming pathogens.
• Tears: Wash over eyes and contain lysozyme, an enzyme that cuts bacterial cell walls.
• Saliva: Contains lysozyme.
• Gastric Fluid: Low pH inhibits bacterial growth.
• Respiratory Tract: Mucus-lined membranes trap pathogens; cilia brush away debris.
• Genitourinary Tract: Urine washes away bacteria and inhibits growth due to low pH.

Second Line of Defense

• Antimicrobial Proteins: Kill bacteria or inhibit their growth.
• Iron-Binding Proteins: Sequester iron, inhibiting bacterial growth.
• Phagocytes: Engulf and digest foreign cells; can be fixed in tissues or wander through blood and lymph.

Inflammation

• A nonspecific response to infection or injury.
• Cardinal signs include redness, swelling, heat, pain, and loss of function.

Inflammation

Functions of Inflammation

• Limits the spread of pathogens.
• Stimulates and promotes an immune response.
• Removes debris from damaged tissue.
• Sets the stage for tissue repair.

Overview

• Inflammation is the body's response to injury or infection.
• It's a nonspecific innate defense response.
• Occurs in connective tissue around the inflamed tissue or organ.
• Inflammation is often indicated by the suffix "-itis," like appendicitis (inflamed appendix) or tonsillitis (inflamed tonsils).

Connective Tissue

• Areolar connective tissue is found wrapped around muscles and organs.
• Composed of:
  • Extracellular matrix (ground substance and protein fibers like collagen, elastin, and reticular fibers).
  • Cells (fibroblasts, macrophages, lymphocytes, fat cells, and mast cells).

Mast Cells

• Key cells in inflammation.
• Filled with granules containing inflammatory chemicals.
• Release inflammatory chemicals into the surrounding area upon injury or infection, including histamine, complement, kinins, and prostaglandins.

Signs and Symptoms of Inflammation

Five Cardinal Signs

1. Redness
2. Pain
3. Heat
4. Swelling
5. Loss of Function

Mechanisms

1. Redness: Vasodilation of arterioles increases blood flow (hyperemia).
2. Heat: Increased blood flow carries more heat to the injured area.
3. Swelling: Blood capillaries become more permeable, allowing fluid leakage into the interstitial space.
4. Pain: Pain receptors are stimulated by increased temperature, inflammatory chemicals, and swelling.
5. Loss of Function: Result of pain and swelling that limits movement.

Flowchart of Inflammatory Process

1. Tissue injury or infection occurs.
2. Chemical mediators are released, stimulating:
   • Vasodilation of arterioles, leading to increased blood flow, heat, and redness.
   • Increased capillary permeability, causing fluid leakage.
   • Stimulation of white blood cells to go to the injured area.
3. Ultimately leads to healing.

Why Signs and Symptoms are Beneficial

• Redness: Increased blood flow delivers more white blood cells to the injury site.
• Pain: Signals something is wrong and limits movement to allow repair.
• Heat: Increases the rate of chemical reactions and metabolic rate, promoting faster repair.
• Swelling: Limits movement and allows white blood cells to migrate into the interstitial space.
• Loss of Function: Limits movement, allowing faster repair.

Chemotaxis and Emigration

• White blood cells are attracted to the injury site by a chemical trail (chemotaxis) from inflammatory mediators.
• Increased permeability of blood vessels allows white blood cells to move out of the blood into the surrounding tissue (emigration).

Inflammatory Chemicals

Examples

Refer to the given table for the source, cells releasing, and physiological effects of various inflammatory chemicals.

Phagocytosis Process

1. Microbe is attracted to the phagocyte due to released inflammatory chemicals.
2. Phagocyte identifies the microbe as a foreign cell.
3. Phagocyte adheres to the microbe and engulfs it into a phagosome.
4. Phagosome merges with a lysosome (containing digestive enzymes and low pH).
5. Lysosome releases digestive enzymes to digest and kill the microbe.
6. Indigestible materials are secreted out of the cell.