Comprehensive Guide to Pathogens, Immune System, and Defense Mechanisms in Biology

What is a disease?

Any harmful deviation from the normal structural or functional state of an organism, generally associated with certain signs and symptoms.

Define pathogen.

An agent that causes disease, which can be cellular or non-cellular.

What is an antigen?

Any foreign molecule that can trigger an immune response, potentially leading to the production of antibodies.

What is an allergen?

An antigen that triggers a type I hypersensitivity reaction.

What is an antibody?

A protein that binds to a specific antigen molecule, produced by B cells during the humoral immune response.

What is a vector in the context of pathogens?

A vehicle that transports something from one location or organism to another.

What is an agent in the context of disease?

Any substance, microorganism, or living entity that produces a specific effect, causes a disease, or is used to treat a condition.

What distinguishes primary pathogens from opportunistic pathogens?

Primary pathogens cause disease any time they are present, while opportunistic pathogens only cause disease when the host's defenses are weakened.

What are cellular pathogens?

Pathogens made of cells and are living, including bacteria, fungi, protozoans, worms, and arthropods.

What are non-cellular pathogens?

Pathogens that are not made of cells and are not living, such as viruses, viroids, and prions.

How do bacteria reproduce?

Asexually by binary fission, where one cell replicates its DNA and divides into two identical daughter cells.

What causes the symptoms of bacterial diseases?

Destruction of cells and tissues by bacterial enzymes, irritation by bacterial waste products, reactions to bacterial toxins, and overactive immune response.

What are some pathogenic fungi and their effects?

Examples include ringworm fungus, which causes athlete's foot and ringworm, and Candida albicans, which causes thrush and endocarditis.

What are protozoans?

Unicellular eukaryotes that can have complex life cycles requiring different host animals.

What is antigenic variation in protozoans?

The ability of protozoans to express different surface antigens at different times in their life cycle to evade the host's immune system.

What are parasitic worms?

Multicellular organisms that can infect humans and animals, often with complex life cycles involving more than one host.

What role do arthropods play in disease?

Some act as vectors for pathogens, while others can cause disease themselves, such as ticks and fleas.

What is the structure of a virus?

A virus particle is composed of genetic material (DNA or RNA) and a protein coat (capsid), and may have an envelope derived from the host cell.

How do viruses infect host cells?

By hijacking existing surface receptors to insert their genetic material, which is then expressed by the host cell's ribosomes.

What is the difference between lytic and lysogenic cycles in viruses?

In the lytic cycle, the virus causes the host cell to burst, while in the lysogenic cycle, the viral genetic material integrates into the host's genome and remains dormant.

What is the significance of the term 'antibody generator'?

It refers to antigens, which stimulate the production of antibodies during the adaptive immune response.

What is the immune system's ability to distinguish between self and non-self antigens?

It is critical to avoid launching an immune response against the body's own cells.

What cycle can a virus be triggered to enter?

The lytic cycle

What do medications do regarding viruses?

They aid with symptoms but do not kill the virus.

What are viroids?

Non-cellular pathogens that are single-stranded loops of RNA, known to infect plant cells.

How do viroids damage plant cells?

By competing for nucleotides and forming bundles that interfere with cell structure and metabolism.

What are prions?

Misfolded versions of normal cellular prion proteins that can induce other normal proteins to misfold.

What is a consequence of prion accumulation in the brain?

It kills neurons and creates open vacuoles, leading to structural damage.

What are the three lines of defense in the immune system?

1. Physical and chemical barriers, 2. Innate immune response, 3. Adaptive immune response.

What constitutes the first line of defense?

Physical barriers like skin, tears, earwax, and mucous membranes.

What is the role of mucous membranes?

They trap pathogens and contain enzymes that digest them.

What are some physical barriers in plants?

Cell wall structure, thick bark, spikes, and closed stomata.

What chemical barriers do plants produce?

Caffeine, tannins, and citronella, which are toxic or repellent to insects.

What is the function of normal flora in animals?

They prevent the growth and colonization of pathogenic microbes by competing for resources.

What is innate immunity?

The second line of defense that responds quickly to pathogens without adapting to them.

How does the innate immune response differ from adaptive immunity?

Innate immunity is non-specific and does not create immunological memory.

What are some entry points for pathogens in animals?

Eyes, mouth, nose, lungs, digestive system, urinary tract, and reproductive tract.

What role do lysozyme enzymes play in the body?

They protect the eyes against infection.

What does the skin secrete to inhibit pathogen growth?

Sebum, which contains lactic acid and fatty acids.

What happens to pathogens trapped in mucous?

They are expelled from the area or destroyed by stomach acid.

What is the response time of the innate immune system?

It is rapid, occurring within the hour of pathogen exposure.

What is a characteristic of the innate immune response?

It involves fixed responses that do not adapt over time.

What can trigger a virus to enter the lytic cycle?

Certain medications or environmental factors.

How do prions affect normal prion proteins?

They cause them to misfold, leading to more infectious prions.

What is the primary defense mechanism of the skin?

It acts as a barrier to prevent pathogen entry.

What is the role of sweat glands in skin defense?

They release salty sweat that creates an inhospitable environment for bacteria.

What happens to the brain structure due to prion accumulation?

It leads to larger ventricles and deeper valleys due to neuron death.

What is the Major Histocompatibility Complex (MHC)?

A cell surface glycoprotein that helps immune cells identify 'self' cells.

How do immune cells recognize non-self cells?

Through different MHC markers or the presence of other antigens.

What is the role of cytokines in the immune system?

They enhance the activity of other immune cells and function in immune cell signaling.

What are phagocytes?

Cells that circulate throughout the body to engulf and destroy pathogens.

What is phagocytosis?

The process by which phagocytic cells engulf pathogens and present antigens to T cells.

What are macrophages?

Phagocytic cells found in the circulatory system that can enter tissues and present antigens.

What is the function of dendritic cells?

They act as antigen-presenting cells and link the innate and adaptive immune systems.

Where are mast cells located and what is their role?

Found in mucous membranes and connective tissues, they defend against pathogens via inflammatory response.

What do neutrophils do?

They are the first responders to infection, releasing antimicrobial peptides and cytokines.

What is the role of eosinophils?

They target multicellular parasites and release toxic proteins to kill them.

What do basophils release and what is their function?

They release histamine to promote inflammation and are involved in allergic responses.

What are natural killer cells?

Cells that recognize and destroy virus-infected and cancerous cells through cytotoxic chemicals.

What are antigen-presenting cells (APCs)?

Cells like macrophages and dendritic cells that present antigen fragments to activate T helper cells.

What is the complement system?

A collection of proteins that assist the immune system by marking pathogens for phagocytosis and promoting inflammation.

What is opsonization?

The process of marking foreign particles for phagocytosis by immune cells.

What outcomes result from the complement cascade?

Opsonization, increased cytokine release, and cell lysis of foreign cells.

What are cytokines?

Small signaling molecules that coordinate aspects of the immune response.

What are interferons?

Cytokines produced by virus-infected cells that activate other cells to combat viruses.

What is the role of chemokines?

They are a type of cytokine that attract immune cells to sites of infection.

What role do interferons play in the immune response?

Interferons attract natural killer cells that can induce cell death.

What is the function of chemokines?

Chemokines attract leukocytes (white blood cells) to the site of infection.

What is inflammation?

Inflammation is the accumulation of fluid, plasma proteins, and leukocytes at the site of infection, causing pain, swelling, redness, heat, and loss of function.

What triggers the inflammatory response?

The interaction between leukocytes and pathogens triggers the inflammatory response.

What is a fever?

A fever is an increase in body temperature, usually in response to disease.

How do inflammatory cytokines affect body temperature?

Inflammatory cytokines stimulate the hypothalamus to increase the set temperature point to about 37.8 degrees Celsius.

What are pyrogens?

Bacterial toxins that act directly on the brain to trigger fever.

What is the aim of a fever?

To limit bacterial growth and improve enzyme activity in the inflammatory response.

What are B and T cells?

B and T cells are lymphocytes, a specific type of white blood cell involved in the adaptive immune response.

What is the role of the lymphatic system in the immune response?

The lymphatic system plays a key role in adaptive immune responses by filtering pathogens and facilitating lymphocyte activation.

What are the primary lymphoid organs?

Bone marrow and thymus.

Where do B and T cells originate?

B and T cells originate from stem cells in the bone marrow.

What is lymph?

Lymph is the fluid that drains into lymphatic vessels from body tissues.

What is the function of lymph nodes?

Lymph nodes filter lymph, trapping pathogens, foreign particles, and cellular waste.

What happens in lymph nodes during an immune response?

Antigen-presenting cells activate B and T cells, leading to clonal expansion and differentiation.

What is the main function of the spleen?

To control the number of red blood cells by destroying old or defective ones.

What is the adaptive immune response?

The adaptive immune response is the third line of defense that clears pathogens and develops memory to their antigens.

What are the two key features of the adaptive immune response?

Specificity and immunological memory.

How long does it take to activate the adaptive immune response for the first time?

Seven to ten days.

What happens to the immune response with memory?

It can take only hours to respond to a previously encountered antigen.

What allows for a larger and more rapid response to future exposures to the same antigen?

Memory in the adaptive immune response.

What type of white blood cells are specialized for adaptive immune responses?

Lymphocytes.

What do lymphocytes have that allows them to recognize specific antigens?

Receptors for specific antigens.

What is the role of B-cell receptors?

Antigen binds to one of the arms of the receptor; the two binding sites are identical.

Where do T lymphocytes develop and mature?

Develop in bone marrow and mature in the thymus.

What is the function of Helper T cells (TH)?

Stimulate other immune cells and coordinate the activity of adaptive immune cells.

What do Cytotoxic T cells (TC) do?

Identify and kill cells displaying the antigen they recognize.

What is the role of Suppressor T-cells (TS)?

Suppress other immune cells and control the end of an immune response.

What do activated B lymphocytes differentiate into?

Plasma cells that manufacture and release antibodies.

What is humoral immunity?

Involves activation of B cells and the secretion of antibodies into extracellular fluid.

What is cell-mediated immunity regulated by?

T lymphocytes.

What is required for T cell receptors (TCRs) to bind to antigens?

Antigens must be displayed by antigen-presenting cells (APCs).

What happens if a T lymphocyte reacts to a self-antigen?

It is normally destroyed to prevent an immune response against the body's own cells.