Overview
This lecture covers how the body defends itself from invading pathogens, explains the immune system's structure, and outlines the first and second lines of defense.
Introduction to Body Defenses
- The body is constantly targeted by bacteria, viruses, fungi, and parasites seeking entry.
- Immunology is the study of host-specific defenses against pathogens (disease-causing organisms).
- Antigens are foreign substances (usually proteins) that trigger immune responses.
Types of Body Defenses
- Nonspecific defenses protect against all antigens in general, like a fence keeping everything out.
- Specific defenses (immunity) target particular antigens, like vaccines designed for one disease.
First Line of Defense
- Healthy skin acts as a barrier with many layers of dead, keratinized cells.
- Skin pH (4-5) and sweat (pH as low as 3) create an acidic, hostile environment for bacteria.
- Skin is salty, creating a hypertonic environment that dehydrates invading bacteria.
- Lysozymes in tears attack bacterial cell walls without harming human tissues.
- Mucous membranes in the mouth, nose, eyes, and stomach trap pathogens.
- Cilia (tiny hairs) and mucus help remove microbes from airways and direct them to the stomach.
- Stomach acid (pH 1-3) destroys many pathogens ingested with food.
- Normal flora (beneficial microbes) outcompete harmful invaders for space and nutrients.
Second Line of Defense
- If pathogens breach the first line, macrophages (a type of phagocyte) engulf and destroy them.
- Fever is regulated by the hypothalamus and raises body temperature to hinder pathogen survival.
- Inflammation involves swelling, heat, redness, and pain, helping trap microbes and send immune cells to injury sites.
Immune System Challenges
- Autoimmune diseases occur when the immune system attacks the body's own tissues.
- Organ transplants may be rejected, requiring immunosuppressant drugs.
- Antibiotics kill both harmful and beneficial bacteria, disrupting normal flora and causing side effects like diarrhea.
- Allergies are overreactions to harmless antigens in the environment.
Key Terms & Definitions
- Pathogen — a disease-causing organism (bacteria, virus, fungus, parasite)
- Antigen — a foreign substance that triggers an immune response
- Antibody — a protein produced by the immune system to neutralize antigens
- Nonspecific Defense — general protection against any pathogen
- Specific Defense (Immunity) — targeted protection against a particular antigen
- Macrophage — a white blood cell that engulfs and digests pathogens
- Lysozyme — an enzyme in tears and saliva that destroys bacterial cell walls
- Normal Flora — beneficial microorganisms living in the body that protect against harmful invaders
- Inflammation — a localized response with heat, redness, swelling, and pain to contain and destroy pathogens
Action Items / Next Steps
- Review differences between nonspecific and specific defenses.
- Prepare to study more on inflammation in the next lecture.