Immune System Mechanical Barriers Quiz

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Questions and Answers

What is the primary function of mechanical barriers in the immune system?

To generate an immune response

To limit pathogen spread into the body (correct)

To directly attack pathogens

To enhance pathogen survival

Which of the following is NOT an example of a mechanical barrier?

Urine

Tears

Mucus membranes

Stomach acid (correct)

How do tears contribute to the first-line defense against pathogens?

By trapping microbes in mucus

By producing antibodies

By washing away debris and pathogens (correct)

By modifying the respiratory airways

What role does mucus play in the respiratory tract?

It traps invaders and limits their spread Signup and view all the answers

Which mechanism helps remove pathogens from the lungs?

Ciliary movement in the mucociliary escalator Signup and view all the answers

What is the function of lysozyme found in various body fluids?

To directly kill bacteria Signup and view all the answers

How does urine contribute to the body's defense against pathogens?

By washing microbes out of the body Signup and view all the answers

Which component is primarily responsible for the trapping of microbes at body entrances?

Mucus membranes Signup and view all the answers

What is the primary role of complement protein C3b?

It opsonizes pathogens for phagocytosis. Signup and view all the answers

Which of the following outcomes is directly linked to the activation of C5?

Formation of the membrane attack complex. Signup and view all the answers

What is the role of C3a and C5a in the complement pathway?

To recruit leukocytes to the site of infection. Signup and view all the answers

What process occurs when the complement protein C5b forms the membrane attack complex (MAC)?

It lyses the pathogen's plasma membrane. Signup and view all the answers

Which complement proteins are involved in the formation of the membrane attack complex?

C5, C6, C7, C8, and C9. Signup and view all the answers

Which step is initiated first in the complement activation pathway?

Binding of C3b to the pathogen. Signup and view all the answers

Which outcome is NOT a direct result of complement activation?

Natural killer cell activation. Signup and view all the answers

How does the classical pathway differ from alternative pathways in complement activation?

Classical pathway relies on antibodies for activation. Signup and view all the answers

Which outcome of the complement cascade involves tagging an invader for easier clearance by phagocytic cells?

Opsonization Signup and view all the answers

What triggers the classical complement cascade?

Binding of antibodies to an invading agent Signup and view all the answers

Which pathway of the complement cascade operates independently of antibodies?

Lectin pathway Signup and view all the answers

Which of the following best describes how the alternative pathway is activated?

By directly interacting with the invading agent Signup and view all the answers

What is one regulation method used to prevent complement proteins from damaging our own tissues?

Self-destruct feature of instability Signup and view all the answers

Which are the four cardinal signs of inflammation?

Swelling, redness, heat, and pain Signup and view all the answers

What happens to complement proteins without proper stabilization?

They become unstable and deteriorate Signup and view all the answers

Which feature of the complement cascade is responsible for causing cytolysis?

Formation of a membrane attack complex Signup and view all the answers

What is the primary function of histamine in the inflammation process?

To facilitate vasodilation and increase vessel permeability Signup and view all the answers

What role do kinins play in the inflammation response?

They induce vascular changes and stimulate pain receptors Signup and view all the answers

Which cells are primarily responsible for releasing histamine during the early stages of inflammation?

Mast cells Signup and view all the answers

What effect do vasoactive molecules have on blood vessels?

They dilate blood vessels and promote increased permeability Signup and view all the answers

What does the term 'exudate' refer to in the context of inflammation?

Fluid and plasma proteins that seep into tissue Signup and view all the answers

How do complement proteins contribute to inflammation?

By moving into tissues and promoting swelling Signup and view all the answers

Which of the following best describes the action of eicosanoids?

They amplify inflammation by triggering downstream signaling molecules Signup and view all the answers

What is one of the effects of increased vascular permeability during inflammation?

Swelling due to plasma leakage into tissues Signup and view all the answers

What initiates the resolution phase of inflammation?

The threat passing Signup and view all the answers

What role do cytokines play during the resolution phase of inflammation?

Reducing inflammation and promoting healing Signup and view all the answers

What happens to leukocytes during the late resolution phase of inflammation?

They undergo apoptosis Signup and view all the answers

What is the outcome of apoptosis of leukocytes in the resolution phase?

Reduction of inflammation Signup and view all the answers

What is formed during the resolution phase that indicates dead cells in fluid exudate?

Pus Signup and view all the answers

What process contributes to repairing damaged tissues during the resolution phase?

Angiogenesis Signup and view all the answers

How long can complete healing take during the resolution phase?

Days to years Signup and view all the answers

What happens to blood vessels during the resolution phase of inflammation?

They return to normal size Signup and view all the answers

What is chronic inflammation characterized by?

An inflammatory response that lasts too long Signup and view all the answers

What role do pyrogens play in fever?

They trigger the hypothalamus to raise body temperature Signup and view all the answers

How does fever enhance the immune response?

By increasing leukocyte production Signup and view all the answers

What effect does low-grade fever have on the body?

It is considered protective and may be allowed to run its course Signup and view all the answers

Which of the following is a consequence of chronic inflammation?

Promotion of certain cancers Signup and view all the answers

What physiological change occurs during a fever?

Body temperature rises above 37°C Signup and view all the answers

Which of the following statements about fever is true?

Fever can limit the growth of certain pathogens Signup and view all the answers

Which component is NOT typically associated with pyrogens?

Interferons Signup and view all the answers

Study Notes

Chapter 11: Innate Immunity

Innate immunity is a physiological process coordinated by the immune system to eliminate antigens.
The immune system has two key branches: innate and adaptive immunity.
Both branches share common features: recognizing diverse pathogens, eliminating identified invaders, and discriminating between self and foreign antigens.
Innate immunity is inborn and ancient, present in all eukaryotic organisms.
It's characterized by generalized or nonspecific responses.
Adaptive immunity, unique to vertebrates, develops over time and is specific to pathogens.
Adaptive immunity requires more time (4-7 days) to fully activate compared to innate immunity.

Clinical Case: The Case of the Missing Bleach

The clinical case is in the Mastering Microbiology Study Area.
Innate immunity is used to find out the cause of the mystery.

Overview of the Immune System and Responses

Students should be able to describe the features of innate and adaptive immunity.
Students should be able to describe how normal microbiota impacts immune responses and limits pathogens.

Immune Responses Are Classified as Either Innate or Adaptive

An immune response is a physiological process coordinated by the immune system to eliminate antigens.
Our immune system has two key branches: innate and adaptive immunity.
Common to both: recognize diverse pathogens, eliminate identified invaders, and discriminate between self and foreign antigens.

Immune Responses Are Classified as Either Innate or Adaptive (Innate Immunity)

Innate is inborn, ancient protection existing in various forms in all eukaryotic organisms.
Generalized or nonspecific immune responses.
Innate immunity protects against a wide variety of invaders.

Immune Responses Are Classified as Either Innate or Adaptive (Adaptive Immunity)

Found only in vertebrate animals.
Adaptive immunity matures over time.
The responses are tailored to specific pathogens.
Adaptive immunity takes longer to fully activate (4-7 days) than innate immunity.
It exhibits immunological memory.

Immune Responses Are Classified as Either Innate or Adaptive (Innate vs. Adaptive Immunity)

Feature	Innate Immunity	Adaptive Immunity
Response time	Immediate	4-7 days (after innate)
Organisms that have it	All eukaryotes (multicellular and unicellular eukaryotic organisms)	Only vertebrates
Distinguishes self from foreign	Yes	Yes
Kills invaders	Yes	Yes
Effective against diverse threats	Yes	Yes
Tailors response to a specific antigen	No	Yes
Remembers antigen and amplifies response upon later exposure	No	Yes

Collaboration Between Innate and Adaptive Immunity

The immune system has three collaborating lines of defense.
These lines include barrier defenses, cellular and molecular defenses, and adaptive defenses.

Normal Microbiota Has a Role in Shaping Immune Responses and Conferring Protection

Microbes live symbiotically on and in our bodies.
They fine-tune our immune system to fight pathogens and tolerate nonpathogens, food, and self-tissues.
Changes in microbiota can confuse the immune system, potentially leading to allergies and autoimmunity.
The hygiene hypothesis suggests a link between reduced diversity and levels of microbes and negatively affecting immune responses.

Introduction to First-Line Defenses

First-line defenses aim to prevent pathogen entry.
These defenses are categorized as mechanical, chemical, and physical barriers.
Examples of mechanical barriers include tears, urine, saliva, and mucus membranes.
Chemical barriers include lysozyme (found in secretions like tears and breast milk), hydrochloric acid in the stomach, and fatty acids in sweat and earwax.
Physical barriers include epithelial tissue (lining body cavities and entrances) and skin (epidermis comprised of tightly packed dead epithelial cells).
Antimicrobial peptides (AMPs) are proteins that destroy a wide spectrum of viruses, parasites, bacteria, and fungi.
AMPs can stimulate leukocytes, modulate inflammation, and clear pathogens by phagocytosis.

First-Line Defenses Aim to Prevent Pathogen Entry

First-line defenses attempt to prevent pathogen entry.
Mechanical, chemical, and physical barriers sub-categorize first-line defenses.

Mechanical Barriers

Rinse, flush, or trap pathogens to limit their spread into the body.
Examples include tears to wash debris and pathogens from eyes, urine to flush microbes from the body, saliva to limit microbes, mucus membranes (lining body entrances).
The Mucociliary escalator (cilia) sweeps away pathogens from the lungs.

Chemical Barriers

Directly attack invaders or create environments that limit pathogen survival.
Examples:
- Lysozyme: found in secretions (tears, breast milk), breaks down bacterial cell walls.
- Hydrochloric acid in stomach.
- Skin (dry, salty, slightly acidic).
- Fatty acids in sweat and earwax.

Antimicrobial Peptides (AMPs)

Proteins that destroy viruses, parasites, bacteria, and fungi.
Stimulate leukocytes; modulate inflammation, clear pathogens by phagocytosis.
Directly target pathogens, disrupting plasma membrane and/or cell walls, and targeting intracellular components.

Defensins

Key class of mammalian antimicrobial peptides that rapidly kill invaders by inserting themselves into target cell membranes.

Physical Barriers

Include structures that physically block pathogen entry.
Examples include epithelial tissue (lining every body cavity and entrance) and skin (epidermis). Dead epithelial cells, enriched with proteins and lipids, serve as a water-resistant layer.

Introduction to Second-Line Defenses and the Lymphatic System

After first-line defenses are breached, second-line defenses are triggered.
These defenses consist of assorted molecular factors and leukocytes (white blood cells).
The lymphatic system is crucial in facilitating second-line defenses.

The Lymphatic System Collects, Circulates, and Filters Body Fluids

Lymph system is interconnected and dependent upon the lymphatic system.
It collects, circulates, and filters fluid, returning it to the blood.

Lymph and Lymphatic Vessels

Plasma exits capillaries, enters interstitial spaces, and gets collected in lymphatic capillaries as lymph.
Lymph travels to lymph nodes where it is screened and filtered.
Lymph is eventually channeled into veins, returning to the circulatory system.

Primary and Secondary Lymphoid Tissues

Primary: site of leukocyte production and maturation (thymus and bone marrow).
Secondary: filter lymph, sample body sites for antigens, include lymph nodes, spleen, and mucosa-associated lymphoid tissue (MALT).

Thymus

Butterfly-shaped organ in the chest.
Site of T cell maturation.

Bone Marrow

Spongy tissue inside bones.
Site of red and white blood cell production, including B cell maturation.

Lymph Nodes

Clustered in the neck, armpits, and groin.
Filter and screen lymph before returning it to the bloodstream.

Spleen

Located in the upper left abdomen.
Filters blood, not lymph.
Removes damaged erythrocytes.

Mucosa-Associated Lymphoid Tissue (MALT)

Diffuse lymphoid tissue in mucosal linings.
Important in finding and fighting harmful microbes.
Examples include tonsils, appendix, Peyer's patches, and GALT (gut-associated lymphoid tissue).

Leukocytes Are Essential in All Immune Responses

Leukocytes are diverse cells classified as granulocytes (with granules) or agranulocytes (without granules).

White Blood Counts as a Clinical Measure

Differential white blood cell (WBC) count: rapid, inexpensive test for diagnosing if leukocytes are over- or underrepresented in a patient's blood.
Leukocytosis: increase in leukocytes.

Cooperation Between Leukocytes and Molecular Factors

After leukocyte activation, active molecules are released into the local environment.
These molecules have diverse functions like recruiting other leukocytes, restricting pathogen growth, triggering fever, and stimulating inflammation.

Cellular Second-Line Defenses

Neutrophils: most numerous WBCs, contain a multilobed nucleus, recruited first to injured tissues, release AMPs, and phagocytize foreign cells and viruses.
Eosinophils: <5% WBCs, contain reddish-orange granules, bilobed nucleus, possess granules with antimicrobial toxins, moderate phagocytes, respond to allergens and parasites.
Basophils: <1% WBCs, double-lobed nucleus, granules packed with defense molecules (e.g., histamine), combat parasites, roles in allergic responses.
Mast Cells: reside in tissues, release histamine and other mediators important in allergies and fighting parasites.
Monocytes: largest agranulocytes, horseshoe-shaped nuclei, ~10% circulating leukocytes, increase in chronic infections and inflammation, migrate to tissues and mature into macrophages, highly phagocytic.
Macrophages: reside in specific tissues, wander through other tissues, highly phagocytic.
Dendritic Cells: highly phagocytic, patrol tissues, present antigens to the adaptive immune system.
Lymphocytes: NK cells, B cells, and T cells, ~25% circulating WBCs, small compared with other leukocytes, large, rounded nucleus, limited cytoplasm.
- NK cells: innate immunity against viruses, bacteria, parasites, and tumors.
- B cells and T cells: coordinate adaptive immune response, more detail in Chapter 12.

Granulocytes Include Neutrophils, Eosinophils, Basophils, and Mast Cells

Most granulocytes and agranulocytes exhibit some degree of phagocytosis.
Phagocytes (macrophages, dendritic cells, and neutrophils) target invaders like bacteria, viruses, and general debris.
Lysosomes contain enzymes that destroy targeted material.
Some microbes have virulence factors to evade phagocytosis.

Key Phagocytes: Monocytes (Macrophages) and Dendritic Cells

Monocytes are the largest agranular WBCs, with horseshoe-shaped nuclei and are about 10% of circulating leukocytes.
Levels increase with chronic infections/inflammation, autoimmune disorders, and some cancers.
They migrate into tissues and mature into macrophages.

Key Phagocytes: Monocytes (Macrophages), and Dendritic Cells

Macrophages: highly phagocytic, destroy a broad range of pathogens, fixed macrophages reside in specific tissues and wandering macrophages roam through tissues.
Dendritic cells: highly phagocytic, found in most body tissues, patrol tissues and phagocytize a wide range of antigens, and play a role in modulating the immune system and are vital for presenting antigens to the adaptive immune system.

Lymphocytes: NK Cells, B Cells, and T Cells

Account for about 25% of circulating white blood cells (WBCs).
Relatively small compared to other leukocytes.
Contain a large, rounded nucleus and limited cytoplasm.
Include NK cells, B cells, and T cells.

Natural Killer (NK) Cells

Abundant in the liver.
Provide innate protection against viruses, bacteria, parasites, and cancer cells.

T Cells and B Cells

Coordinate adaptive immune responses.
These are covered in more detail in chapter 12.

Molecular Second-Line Defenses

List at least three general roles of second-line molecular defenses.
Explain why leukocytes are central to second-line molecular defenses.
Define cytokine, and provide examples of cytokine classes and their functions.

Molecular Defense: Cytokines

Signaling proteins for cell communication, coordinating immune actions.
Most cells can create and release cytokines.
Diagnostic/therapeutic markers.
- Chemokines: Attract WBCs to needed areas, induce chemotaxis.
- Interleukins: Activate adaptive/innate immune responses, stimulate hematopoiesis, regulate inflammation, stimulate adaptive and innate immune responses.
- Interferons: Signal when pathogens (especially viruses) or tumor cells are detected; stimulate uninfected cells to mount antiviral defenses.
- Tumor necrosis factors (TNFs): Signaling proteins, stimulate inflammation, kill tumor cells, and stimulate fever.

Molecular Defense: Iron-Binding Proteins

Limit free iron availability to reduce bacterial growth.
Include hemoglobin, ferritin, lactoferrin, and transferrin.

Molecular Defense: Complement Proteins

Consist of >30 proteins that work together in a cascade fashion to boost innate defenses by triggering inflammation, phagocytosis, and lysis.
Primarily made in the liver, circulate in an inactive form.
Pathways for activation: classical, alternative, and lectin.
Outcomes: opsonization, formation of the membrane attack complex (MAC), and inflammation.

Inflammation and Fever

Inflammation: important for healing and defense.
- Three primary functions: recruit immune defenses to injured tissues, limit spread of infectious agents, and deliver oxygen, nutrients and chemical factors for recovery.
- Four cardinal signs: redness, pain, localized heat (not fever), swelling; loss of function.
- Three phases: vascular changes, leukocyte recruitment, and resolution.
Fever: regulated by the hypothalamus.
- Pyrogens induce the release of cytokines to raise the body’s baseline temperature.
- Some believe low-grade fever is beneficial to the immune system.
- High fever (40.5 °C/ 105°F or above) can be harmful or potentially fatal.

Chronic Inflammation

Inflammatory response that continues too long.
Not beneficial or protective.
Can exacerbate injury and contribute to diseases like atherosclerosis, some cancers, and neurodegenerative disorders.

Think Clinically: Case Studies

Case about a child with an ear infection and suspected bacterial meningitis.
Diagnosis focused on Streptococcus pneumoniae infection, confirmed by culture.
Discussion of the child's low levels of mannose-binding lectin (MBL).
The need for early diagnosis and treatment.
Possible implications for the child's future health.

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Description

Test your knowledge on the mechanical barriers of the immune system. This quiz covers the primary functions and mechanisms involved in the first line of defense against pathogens, including examples such as tears, mucus, and lysozyme. Challenge yourself to understand how these components work together to protect the body.