E2.Defense - Body Defenses Pathogens Pathogen an agent...

Body Defenses
Heyer 1
Body Defenses
Pathogens & Immunity
Pathogens
• Pathogen: an agent causing a disease
• Microbe: microscopic organism
(most are not pathogens)
– Bacteria
– Protists (eukaryotic, single-celled)
– Multicellular (fungi, parasites)
• Infectious particles (non-living)
– Viruses: nucleic acids wrapped in protein capsid
– Prions: rogue proteins
Pathogens
First line of Defense:
Barriers
• Stratified squamous epithelia
– Skin; mucous membranes
• Flushing action
– Urine, tears, saliva, sweat, oil glands
• Mucus traps
– Respiratory, digestive, and vaginal tracts
• Lysozyme (enzyme digests bacterial walls)
– Tears, sweat, saliva
• Acidic pH
– Stomach, vaginal secretions
• High body temperature
• Competition from microflora (resident microbes)
Second line of Defense:
Non-specific Responses
• Macrophages and Fixed Phagocytes
– Phagocytosis of any “non-self” cell
• Inflammation
Inflammatory Response
• Hallmark symptoms of inflammation:
redness, heat, swelling and pain

Body Defenses
Heyer 2
Third line of Defense:
Specific Responses (Immunity)
The Lymphatic System
• B-lymphocytes & antibody-mediated defense
– Esp. vs. bacteria, chemical toxins, & free viruses
• T-lymphocytes & cell-mediated defense
– Esp. vs. eukaryotic pathogens: parasites,
viral-infected cells, cancerous cells, & transplanted
tissues
The Lymphatic System
• Lymphatic
circulation
• Lymphoid
tissues
The Lymphatic System
• Lymphatic
circulation
Lymphatic vessel with valve
The Lymphatic System
• Lymphoid
tissues
The Lymphatic System
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