Host Defenses Quiz

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Questions and Answers

What is the primary function of phagocytes in the immune system?

To produce antibodies

To initiate blood clotting

To survey tissue for microbes and dead cells (correct)

To increase the temperature of the body

Which type of cytokine is primarily responsible for nonspecifically inhibiting the spread of viral particles?

Interleukin-2

Interferon (correct)

Histamine

Interleukin-1

Which white blood cells are primarily involved in responding to parasitic infections?

Basophils

Macrophages

Neutrophils

Eosinophils (correct)

What is a key function of the complement system in the immune response?

Killing microbes by forming holes in their membranes Signup and view all the answers

What distinguishes fixed macrophages from wandering macrophages?

Their residence in tissues Signup and view all the answers

The term 'opsonization' refers to which of the following processes?

Coating the microbe to enhance phagocytosis Signup and view all the answers

Which cells are classified as natural killer cells?

Type of T cell with nonspecific cytotoxicity Signup and view all the answers

What triggers the activation of complement proteins?

Cleavage through a cascade reaction Signup and view all the answers

What characterizes the first line of defense in the immune system?

It consists of nonspecific barriers that block microorganism invasion. Signup and view all the answers

Which component is primarily involved in the second line of defense against infections?

Phagocytic cells responding to infection. Signup and view all the answers

What does the third line of defense specifically involve?

Chemical attacks by specific lymphocytes and antibodies. Signup and view all the answers

Which statement correctly describes the relationship between the three lines of defense in the immune system?

Most defenses overlap and have redundant effects. Signup and view all the answers

Which types of white blood cells are primarily responsible for the adaptive immune response?

Lymphocytes such as T cells and B cells. Signup and view all the answers

What is the primary function of pathogen recognition receptors (PRRs)?

To sense pathogens and trigger immune responses. Signup and view all the answers

Which leukocyte is primarily involved in humoral immunity?

B cell Signup and view all the answers

What role does the spleen play in the immune system?

Filters circulating blood to remove worn-out red blood cells. Signup and view all the answers

Which of the following best describes lymph?

It is a plasma-like liquid that transports white blood cells and debris. Signup and view all the answers

What distinguishes neutrophils from eosinophils?

Neutrophils have a lobed nucleus, whereas eosinophils have a bilobed nucleus. Signup and view all the answers

What role does diapedesis play in the immune response?

Allows leukocytes to exit blood vessels and enter tissues. Signup and view all the answers

Which component of blood constitutes the liquid portion after clotting?

Serum Signup and view all the answers

What is the main function of lymphatic vessels?

To carry lymph back to the bloodstream. Signup and view all the answers

What shared characteristic do all granulocytes have?

They contain granules in their cytoplasm. Signup and view all the answers

Which type of leukocyte is mainly responsible for destroying eukaryotic pathogens?

Eosinophils Signup and view all the answers

Which statement best describes self markers?

They are unique identifiers for immune recognition. Signup and view all the answers

What is the primary role of macrophages in the immune system?

To attack and ingest foreign microbes. Signup and view all the answers

How does chemotaxis contribute to the immune response?

It directs leukocytes towards sites of infection or inflammation. Signup and view all the answers

What cells are involved in the reticuloendothelial system (RES)?

Phagocytic cells Signup and view all the answers

What is the primary reason for the presence of lymphatic capillaries in the body?

To absorb excess water and proteins from tissues. Signup and view all the answers

Study Notes

Host Defenses

A multilevel network of innate nonspecific protections and specific immunities, categorized as the first, second, and third lines of defense.
First and second lines are innate, natural defenses present at birth, providing nonspecific resistance to infection.
Third line is adaptive immunity, specific and acquired.
Defense systems overlap and are sometimes redundant.

First Line of Defense

Innate, nonspecific barriers against microorganisms.
Includes any barrier blocking invasion at the portal of entry, preventing access to the internal environment.

Second Line of Defense

Innate, nonspecific.
More internalized system of protective cells and fluids (e.g., inflammation, phagocytosis).
Acts rapidly at local and systemic levels once the first line is breached.

Third Line of Defense ("Adaptive Immunity")

Acquired, specific immunity.
Highly specialized response tailoring the full capabilities of the immune system to individual invading microbes.
Utilizes specific lymphocytes and antibodies for targeted chemical attack on specific microorganisms.

First Line of Defense - Physical/Anatomical Barriers

Skin and mucous membranes of respiratory, urogenital, eyes, and digestive tracts.
- Outermost skin layer (epithelial cells compacted with keratin) is a strong barrier.
- Flushing effect of sweat glands, blinking, and tear production aid in prevention of pathogen entry.

Nonspecific Chemical Defenses

Stomach acid: Inhibits bacterial attachment and entry.
Mucous coat: Impedes bacterial attachment.
Nasal hair: Traps larger particles.
Sebaceous secretions: Contain lysozyme to hydrolyze bacterial cell walls.
Tears, sweat, skin's acidic pH, saliva, and digestive juices: Inhibit microbial growth.
Vaginal secretions: Have an acidic pH, inhibiting growth

Immunology

The study of all biological, chemical, and physical events surrounding immune system function.
The immune system is a complex and diffuse network of cells and fluids throughout the body, including fluids and tissues/organs.

Surveillance

Continuously scouts the body for foreign material.
Distinguishes between self (self markers) and foreign markers (antigens).
Attacks and destroys foreign invaders.

Definitions

Leukocytes (white blood cells): Innate capacity to recognize foreign material (non-self) from normal cells (self).
Pathogen recognition receptors (PRRs): Receptors on white blood cells (WBCs) (e.g., toll-like receptors) that sense pathogens via pathogen-associated patterns (PAMPs) on microorganisms.

Immune System Subdivision

Extracellular fluid (ECF): Fluid outside cells.
Reticuloendothelial system (RES): Connective tissue fluids and fibers, rich in phagocytic cells (macrophages).
Blood: Contains plasma (liquid portion) and formed elements (blood cells).
- Serum: Plasma minus clotting factors.

Reticuloendothelial System (RES)

Connective tissue fibers interconnecting cells and organs.
Inhabited by phagocytic cells (mononuclear phagocyte system), ready to attack and ingest microbes

Blood Origin, Composition, and Function

Whole blood comprises plasma and formed elements.
Plasma is about 92% water, with various proteins, globulins, clotting factors, hormones, and other components for various bodily functions.
Formed elements are made in red bone marrow.
Erythrocytes (RBCs): Most numerous, carry oxygen and carbon dioxide.
Platelets: Formed elements crucial in blood clotting.
Leukocytes (WBCs): Includes granulocytes (neutrophils, eosinophils, basophils), and agranulocytes (monocytes, lymphocytes).

Leukocytes-types

Basophils: Dark blue granules, release potent chemicals influencing immediate allergy/inflammation.
Mast cells: Non-motile, bound to connective tissue, involved in releasing histamine.
Lymphocytes: Specific immune response – B cells (antibodies, humoral immunity), T cells (cell-mediated immunity, modulate immune functions).
Monocytes & Macrophages: Phagocytic; final differentiation of monocytes leads to macrophages.
Dendritic cells: Trap pathogens, participate in immune reactions.

Lymphatic Fluid and Vessels

Lymph is plasma-like fluid carried by lymphatic circulation.
Lymphatic capillaries permeate most body parts except CNS, bone, thymus, and placenta.
Return lymph to circulation, toward the heart, involving skeletal muscle contractions.

Lymph Organs/Tissues

Primary organs: Sites for lymphocyte origin/maturation (bone marrow, thymus).
Secondary organs/tissues: Encounter sites for microbes and immune responses (lymph nodes, spleen, gut-associated lymphoid tissue (GALT)).

Inflammation

Body’s response to injury; aids in destruction/spread of microbes.
Classics signs: rubor (redness), calor (heat), tumor (swelling), and dolor (pain).
Increased blood flow to injured tissues; fluids and cells (WBCs, microbes, debris) collect to form pus, preventing spread of infection.

Fever

Abnormally elevated body temperature, regulated by the hypothalamus.
Exogenous pyrogens: Products of microbes.
Endogenous pyrogens: Substances released by immune cells (e.g., IL-1, TNF) during phagocytosis.
Fever benefits by inhibiting microbial multiplication, limiting nutrient availability to pathogens, and stimulating immune responses.

Phagocytosis

General activities of phagocytes: survey tissue compartments for microbes, particulate matter, and dead/injured cells, ingest and eliminate materials
Includes neutrophils, eosinophils, and monocytes/macrophages.

Cytokines

Chemical mediators produced by immune cells and damaged tissue, regulating, stimulating, and limiting immune reactions.
Examples: histamine, IL-1, IL-2, interferon.

Interferon

Cytokine released by host cells to nonspecifically inhibit viral spread.
Types: alpha, beta, and gamma, targeting different cell types (lymphocytes, fibroblasts, epithelial cells, T-cells).

Complement System

Complex system of 26 blood proteins working concertedly to destroy bacteria and some viruses.
Pathways: Classic and alternate pathways activate in cascade reaction.
Forms membrane attack complex (MAC) to kill microbes by creating holes in their surfaces.
Functions: Chemotaxis, opsonization of microbes (coating for enhanced phagocytosis), and inflammation stimulation.

Natural Killer (NK) Cells

Type of T cell (nonspecific cytotoxic).
Destroy virus-infected cells and tumor cells.
Found in different tissues.
Activated by various stimuli/cytokines.

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Description

Test your knowledge on the multilevel network of host defenses, including the first, second, and third lines of defense. Explore the differences between innate and adaptive immunity, and how these systems work together to protect against infections.