The Immune System it protects your health. Who are the invaders? Viruses tiny protein shells filled with DNA or RNA

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1 The Immune System it protects your health Who are the invaders? Bacteria Viruses Pathogens Bacteria are very small and mostly harmless Single-celled organisms Only a few cause disease Extremely small, simple structure Take over living cells and use cell s organelles to make more viruses Parasites Viruses tiny protein shells filled with DNA or RNA Sphere Shaped Rod Shaped Human Cell Human Cell Less than 0.5% of bacteria harm humans. Your body hosts more bacterial cells than human cells! Bacterial cell is ~1/15 the size of a human skin cell Parasites & fungi can also cause disease Ticks, worms, and molds are multicelled parasites that cause disease Flu virus particle is ~1/15 the size of a bacterial cell Bacterial Cell Bacterial Cell Virus Particle Our body has several lines of defense Malaria parasites are single cells Organelles Cell Membrane Dead Keratinized Skin Cells 1

2 External barriers Skin Like a Wall Secretions Dead Keratinized Epidermal Cells Sweat has enzymes ( lysozymes ) that digest bacteria Sebaceous glands (around hair) secrete oil ( sebum ) that is acidic Like Spraying Poison Over the Wall Keratin is a durable, waterproof protein Poison Mucus Secretions from sebaceous glands & sweat glands kill microbes on skin Stomach acid Mucus traps pathogens entering nose and throat & cilia sweep the mucus away Gastric Juice ph ~2.0 Like a Sticky Slime Like a Moat of Acid Diarrhea & Vomiting Acidic Gastric Juices Protect One of the Main Body Entrances The 2nd line of defense jumps into action Vomiting Diarrhea & Vomiting purge digestive system of toxic materials Sneezing serves a similar purpose for respiratory system Like a Trampoline Mounted at the Gate Dead Keratinized Skin Cells Diarrhea 2

3 The 2nd line of defense Act when an invader penetrates the body s external barriers Nonspecific combats all types of pathogens Depends on white blood cells defensive proteins The 2nd line of defense White Blood Cells (cells that fight infection) Phagocytes Eat Invaders Like Alligators Prowling the Grounds The 2nd line of defense Problem: How do NK cells know which cells to kill? Key to Immunity: Recognizing self vs. non-self Self Cells Natural Killer (NK) cells: WBCs that destroy cancer cells cells infected with viruses NK cells release chemicals that break down the target cell s membranes and burst the cell Nonself Cell NK cell is unharmed, looks for other abnormal cells How do NK cells know which cells to kill? The 2nd line of defense: Protective proteins Key to Immunity: Recognizing self vs. non-self NK Cell Attacks If: Cell has no HLA proteins Cell has different HLA proteins Like wearing uniforms for identification HLA = Protein markers on cell surfaces Your HLA proteins are unique to you, just like your fingerprints & DNA! Proteins called Interferons tell other cells to prepare for attack to produce substances that interfere with viral reproducton Infected cells send warnings to neighboring cells 3

4 Protective proteins: Complement Proteins that assemble automatically, punch holes in the membrane of bacteria and cause them to burst Another defense mechanism: Inflammation Poison oak on the hand Any type of tissue injury triggers the inflammatory response Sx: Redness, warmth, swelling and pain Inflammation brings defenses & repairs to a specific area What happens when you cut your finger? Need Help Here! Phagocytes destroy bacteria Tissue heals Like Putting Up Signs & Opening Gates to Attract Help Histamine makes vessels leaky to bring nutrients & more defenses to area = swelling, redness Antihistamines (ex. Benadryl) block effects of histamine Responding cells eat microbes & release histamine Fever a whole-body reaction to speed up repairs Why non-specific? Possible Benefits: Defensive cells move faster Phagocytes eat faster Cells divide faster Interferons enhanced 4

5 Recap: External barriers Physical barriers How do these defenses work? Food poisoning Chemical barriers Secretions - inhibit growth of microbes 1st line of defense Salmonella Common, usually mild symptoms Caused by eating food contaminated with viruses or bacteria How does your body respond? The 2nd line of defense Vomiting Diarrhea & Vomiting purge digestive system of toxic materials Phagocytes Eat Invaders Diarrhea Protective proteins: Complement Plasma proteins that automatically assemble, Which defenses work against bacteria and viruses? Bacteria create holes in the membrane of bacteria Viruses Inflammation and cause them to burst phagocytes Complement NK cells 5

6 The immune response in action How does our immune system respond when we get a cold? How does the body respond to a viral infection? The common cold A contagious viral disease of the upper respiratory track Primarily caused by rhinoviruses The most common infectious disease in humans Cold viruses live only in the nose The major point of entry the nose 1st line of defense mucous membranes of the nose From the nose, the virus is transported to the back of the nasopharynx Cold viruses attach to cells lining the nasopharynx How a cold virus infection occurs The virus attaches to a receptor located on the surface of nasal cells. After attaching to the receptor, the virus is taken into the cell, where it starts an infection How a viral infection occurs Virus binds to the plasma membrane The virus is taken into the cell where it starts an infection Viral RNA is integrated into the cell genome The infected cell manufactures new virus. The infected cell eventually ruptures and dies, releasing newly made virus How does the body respond to a viral infection? The first responders NK cells Interferon Inflammation External barriers Skin, mucous membranes, secretions Rhinovirus Specific responses B cells produce antibodies to the virus Helper T cells Cytotoxic T cells attack virus-infected cells 6