Biology - Human Body Systems - Immune system - How Immunity Works

5 steps. Step 1: 'BARRIERS (1st line) - Skin, mucus, tears, stomach acid, friendly bacteria on skin. These prevent pathogens from entering.' Step 2: 'NON-SPECIFIC RESPONSE (2nd line) - Inflammation: blood flow increases, area swells. Phagocytes: white blood cells that engulf and digest pathogens. Fe