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Anatomy and Physiology - The Immune System and Other Body Defenses

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    Study Guide Anatomy and Physiology – The Immune System and Other Body Defenses 1. Nonspecific Barriers Your body has a “first line of defense” that works all the time , even before your immune system starts making a specific response. This first line of defense is called nonspecific defense because it fights many kinds of invaders in the same way , not one specific germ. The main nonspecific barriers are: skin mucous membranes These protect the body from harmful invaders entering through: • breaks in the skin • body openings (like the mouth, nose, and other passages) How the First Line of Defense Protects You 1. Skin: Strong Physical + Chemical Barrier Skin works like a tough protective wall. It is a physical barrier , and it is also a hostile environment for microbes because it is coated with secretions: • oily secretions from sebaceous glands • acidic secretions from sweat glands The skin surface has an acidic pH of about 3 to 5 , which prevents many microbes from growing.

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    Study Guide 2. Antimicrobial Proteins on Mucous Membranes Mucous membranes produce secretions that contain antimicrobial substances. For example: • lysozyme Lysozyme helps protect you by: • breaking down bacterial cell walls Lysozyme is found in: • saliva • tears • other mucous membrane secretions 3. Cilia: Sweeping Invaders Away In the respiratory system, tiny hair - like structures called: cilia line the respiratory tubes. Their job is to: • sweep dust, microbes, and other invaders away from the lungs This helps prevent infection in deeper lung tissues. 4. Gastric Juices Kill Microbes The stomach provides another strong defense. gastric juices destroy many microbes using: • hydrochloric acid • digestive enzymes So most microbes that enter through food do not survive the stomach.

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    Study Guide 5. Symbiotic Bacteria Protect Us Your body also has “helpful” bacteria called: symbiotic bacteria These live in areas like: • the digestive tract • the vagina They help protect you because they: • outcompete harmful organisms meaning they take up space and nutrients so dangerous microbes cannot grow easily. 2. Quiz: Nonspecific Barriers 1. Question Which of the following would be considered a nonspecific barrier? Answer Choices • skin • fever • NK cells Correct Answer skin Why This Is Correct The skin is a physical barrier that blocks pathogens from entering the body. This is part of the body’s first line of defense (nonspecific defense) .

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    Study Guide 2. Question Which of the following is involved with specific defenses? Answer Choices • lysozymes • complement protein • major histocompatibility complex Correct Answer major histocompatibility complex Why This Is Correct The major histocompatibility complex (MHC) helps the immune system recognize antigens and is essential for specific (adaptive) immunity , especially T - cell responses. 3. Nonspecific Defenses The second line of defense includes immune responses that fight invaders after they enter the body . These defenses are called nonspecific because they: attack many kinds of pathogens the same way do not target one specific germ only 3.1 Key Parts of the Second Line of Defense 1. Phagocytes (Engulf and Destroy Invaders) Phagocytes are white blood cells ( leukocytes ) that destroy pathogens by: phagocytosis (engulfing and digesting them) Main phagocytes include:

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    Study Guide • neutrophils • monocytes • eosinophils Monocytes can grow larger and become powerful phagocytes called: macrophages Macrophages are important because they clean up both: • pathogens • damaged cells and debris 2. Natural Killer (NK) Cells Natural killer cells (NK cells) are a type of: lymphocyte (white blood cell that matures in lymphoid tissues) Their job is to kill: • pathogen - infected body cells • abnormal body cells (such as tumors) So NK cells are like “security guards” that eliminate dangerous cells. 3. Complement Proteins Complement proteins are a group of about: 20 proteins They are called “complement” because they support and strengthen the body’s defense reactions. They help in two main ways: • attract phagocytes to foreign cells • destroy foreign cells by causing cell lysis (breaking open the cell)

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    Study Guide 4. Interferons (IFNs) Interferons (IFNs) are chemicals released by cells that have been: invaded by viruses Interferons help protect nearby cells by causing them to produce proteins that: defend against viruses Some interferons (like gamma - IFN ) also: • increase the activity of macrophages • increase the activity of NK cells So interferons not only fight viruses directly but also boost other defenders. 3.2 The Inflammatory Response The inflammatory response is a series of nonspecific body reactions that happen when pathogens enter tissues or when tissue damage occurs. Common signs of inflammation include: • redness • swelling • heat • pain sometimes loss of function (the area may be disabled) Example: If the skin is damaged and bacteria or toxins enter, inflammation begins. Steps of the Inflammatory Response (Easy Order) 1. Chemical Alarm When an injury happens, the body releases “alarm chemicals.” These signals come from: injured cells

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    Study Guide nearby circulating cells Important alarm chemicals include: • histamine (mostly secreted by basophils — WBCs found in connective tissue) • kinins • prostaglandins (PGs) • complement proteins These chemicals alert the immune system and start defense actions. 2. Vasodilation (More Blood Flow to the Area) Histamine and other chemicals cause: vasodilation (blood vessels widen) This increases blood flow to the injured area, causing: • redness • increased local temperature (heat) The higher temperature helps because it: • stimulates white blood cells • creates an environment that is less friendly to pathogens 3. Increased Vascular Permeability Alarm chemicals also increase: vascular permeability That means blood vessels become “leakier,” allowing important things to move into the injured tissue faster, such as: • white blood cells • clotting factors • body fluids This results in: edema (swelling)

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    Study Guide Swelling can cause pain because: • it presses on nearby nerve endings • nerves may also react to toxins and chemicals like kinins and prostaglandins Important note: Aspirin reduces pain because it inhibits the production of prostaglandins . 4. Phagocytes Arrive and Destroy the Threat Next, phagocytes move to the injury site and engulf: • pathogens • damaged cells They find the injured area using: chemotaxis (movement toward chemical gradients created by alarm chemicals) 5. Complement Proteins Assist Complement proteins help in two ways: help phagocytes engulf foreign cells stimulate basophils to release more histamine So they strengthen the whole inflammatory response. 3.3 Fever (Whole - Body Response) A fever is a body - wide response to infection where body temperature rises. Higher temperature helps because it: • increases cellular metabolism (faster repair) • increases the effects of alarm chemicals • creates a hostile environment for bacteria

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    Study Guide However, if fever becomes too high, it can be dangerous because: • it may reduce the activity of enzymes needed for metabolism • pushing the body further out of homeostasis 4. Quiz: Nonspecific Defenses 1. Question Interferons are substances released by some cells to fight __________. Answer Choices • bacteria • viruses • symbiotic pathogens Correct Answer viruses Why This Is Correct Interferons are released when cells are infected by viruses . They warn nearby cells and help slow down viral spread. 2. Question Vasodilation helps bring more WBCs to an infected site. What chemical causes vessels to dilate? Answer Choices • histamine • prostaglandin • complement proteins

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    Study Guide Correct Answer histamine Why This Is Correct Histamine causes blood vessels to dilate and become more permeable , allowing more immune cells to reach the damaged area. 3. Question The inflammatory response is part of the __________. Answer Choices • specific defense • nonspecific defense • nonspecific barrier Correct Answer nonspecific defense Why This Is Correct Inflammation is part of the second line of defense , meaning it is nonspecific and responds to many types of injury or infection. 4. Question Molecules that attract phagocytes to foreign cells are called __________. Answer Choices • interferons • complement proteins • major histocompatibility complex

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