Second Line of Defense: Cellular Responses
Part of Human Defense Systems - Non-specific — GCSE Biology
This deep dive covers Second Line of Defense: Cellular Responses within Human Defense Systems - Non-specific for GCSE Biology. Physical and chemical barriers, white blood cell responses, inflammatory response It is section 5 of 18 in this topic. Use this deep dive to connect the idea to the wider topic before moving on to questions and flashcards.
Topic position
Section 5 of 18
Practice
19 questions
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22 flashcards
Second Line of Defense: Cellular Responses
When pathogens breach the first line of defense, your body's second line of defense springs into action. This involves various types of white blood cells and inflammatory responses that work to eliminate the invaders.
White Blood Cell Types
Neutrophils - The First Responders
- Rapid response: First white blood cells to arrive at infection site (within 30 minutes)
- Short-lived: Live for only 6-7 hours but extremely effective
- Phagocytic: Engulf and digest bacteria and small particles
- Numerous: Make up 50-70% of all white blood cells
- Suicide mission: Often die after engulfing pathogens, forming pus
Macrophages - The Big Eaters
- Large and long-lived: Much bigger than neutrophils, can live for months
- Versatile: Can engulf large pathogens, dead cells, and debris
- Antigen presentation: Display pathogen fragments to activate specific immunity
- Tissue resident: Some live permanently in tissues (liver, lungs, brain)
- Cleanup crew: Remove dead neutrophils and cellular debris
Phagocytosis Process
Phagocytosis is the process by which white blood cells engulf and destroy pathogens:
- Recognition: Phagocyte recognizes pathogen as foreign using pattern recognition receptors
- Attachment: Phagocyte attaches to pathogen surface
- Engulfment: Cell membrane extends around pathogen, forming a phagosome
- Fusion: Phagosome fuses with lysosomes containing digestive enzymes
- Digestion: Enzymes break down pathogen into harmless fragments
- Elimination: Waste products are expelled from the cell
Inflammatory Response
Inflammation is a coordinated response that helps deliver immune cells to infection sites:
Vasodilation
- Blood vessel expansion: Vessels dilate to increase blood flow
- Increased delivery: More white blood cells and nutrients reach infection site
- Heat generation: Increased blood flow creates local heat
Increased Permeability
- Leaky vessels: Blood vessel walls become more permeable
- Cell migration: White blood cells can exit bloodstream into tissues
- Fluid accumulation: Results in swelling at infection site
Chemical Mediators
- Histamine: Causes vasodilation and increased permeability
- Chemokines: Attract white blood cells to infection site
- Complement proteins: Enhance inflammation and pathogen destruction
Signs of Inflammation
- Redness: Increased blood flow
- Heat: Enhanced circulation and metabolic activity
- Swelling: Fluid accumulation in tissues
- Pain: Nerve stimulation by inflammatory chemicals
- Loss of function: Protective mechanism to promote healing