Recording-2025-03-06 Chapter12 Bio225

The body has multi-level defenses against microorganisms, categorized into three lines:
- First Line of Defense: Physical and chemical barriers.
- Second Line of Defense: Innate immune responses (non-specific).
- Third Line of Defense: Acquired immune responses (specific).

Constant exposure to microorganisms from various sources:
- Environment: water, food, soil, air, people, pets, surfaces.
Defensive mechanisms are crucial for blocking invasions through different portals of entry, which vary by microorganism.
Some pathogens can bypass these defenses, necessitating an understanding of how they work.

Physical and Chemical Barriers:
- Skin:
  - Stratum corneum (outer layer) as tough, waterproof barrier.
  - Keratin helps in cell compactness. Thicker skin areas (hands, soles) provide more protection.
  - Regular sloughing of skin removes microbes (ex. sloughed skin contributes to household dust).
- Hair:
  - Periodic shedding carries away microbes.
- Sweat Glands:
  - Flush out microbes, contain antimicrobial substances (e.g., salt).
- Mucous Membranes:
  - Coats entry points (eyes, GI tract, respiratory tract, genitourinary areas).
  - Mucus prevents attachment of microbes.
  - Tears:
    - Contain lysozyme, which destroys bacteria with peptidoglycan.
- GI Tract:
  - Saliva contains lysozyme; vomiting/diarrhea aids in expelling harmful substances.
- Respiratory Tract:
  - Nasal hairs trap particles; ciliated epithelium moves mucus upwards to clear pathways.
- Genitourinary Tract:
  - Continuous urine flow and pH balance prevent UTI.

Innate Immune Response:
- Involves rapid responses to pathogens: inflammation, fever, phagocytosis, antimicrobial proteins.
- Non-specific, responds to a broad range of pathogens and irritants.
- Inflammation:
  - Involves redness (rubor), heat (calor), swelling (tumor), and pain (dolor).
  - Mechanisms include vascular changes (vasodilation).
- Phagocytosis:
  - Processes by which immune cells (phagocytes) engulf microbes and debris. Key cells include neutrophils, monocytes (which become macrophages), and dendritic cells.
  - Phagocytes present antigens to alert adaptive immune response (T cells, B cells).

Structure and Role:
- One-way system working alongside the circulatory system. Key components include lymph nodes, spleen, thymus, and mucosal associated lymphoid tissue (MALT).
- High density found in areas of frequent microbial contact (hands, feet, etc.) for better surveillance and response.

Specific Immune Response:
- Developed through exposure to specific pathogens: Includes T cells and B cells.
- Generates long-lasting immunity through specialized responses to encountered antigens (immunogenic information).

Sebaceous Glands: Secrete sebum to moisturize skin and add an additional layer of antimicrobial protection.
Acidic pH in skin, GI tract (from hydrochloric acid), and vaginal vault protect against microbes.
Antimicrobial Proteins:
- Interferon: Warnings to neighboring cells about viral infection; stimulates overall immunity.
- Complement System: Series of proteins that enhance immune response, destroy pathogens via membrane attack complexes.
- Antimicrobial Peptides: Short proteins that disrupt microbial membranes.

Defined as elevated body temperature (101.4°F in humans) and aids in fighting infections by inhibiting microbial growth and enhancing immune function.
Triggered by pyrogens which reset hypothalamic thermostat.
May have health implications if prolonged; high fever can cause brain damage or other complications.