Unit Three Lecture: Microbial Pathogenicity and Host Defenses

These flashcards cover the vocabulary and key concepts of microbial pathogenicity, the three lines of host defense, and the components of the innate and adaptive immune systems based on the lecture transcript.

Incubation Period

The phase of disease development that occurs between the initial infection and the first appearance of signs and symptoms.

Prodromal Period

A stage of disease characterized by early, mild symptoms where a patient may feel like they are "coming down with something."

First Line of Defense

A surface protection system composed of anatomical and physiological barriers, such as mucous membranes and skin, that prevent microbes from entering sterile body compartments.

Second Line of Defense

A cellular and chemical system including phagocytes, inflammation, and fever that activates immediately if infectious agents bypass surface defenses.

Third Line of Defense

Specific host defenses uniquely developed for each microbe through specialized white blood cells; this form of immunity is usually long-term and possesses memory.

Lysozyme

An antimicrobial enzyme found in tears, saliva, and the urinary system that helps destroy bacterial cell walls.

Keratin

A hard, compact protein found in the skin that is tough, resistant, and provides a physical barrier against pathogen entry.

Stratum Corneum

The outermost layer of the epidermis consisting of 15 to 40 layers of constantly shedding flattened dead cells with a waterproof seal made of fatty acid chains and cholesterol.

Acid Mantle

A chemical defense of the skin produced by sudoriferous and sebaceous glands, maintaining a pH of $4.7 - 5.7$.

Mucociliary Escalator

A mechanical defense in the respiratory system where cilia move mucus and trapped particles away from the lungs.

Kupffer Cells

Resident macrophages in the liver that filter pathogens from the systemic circulation and the hepatic portal system.

Histamine

An inflammatory chemical released by mast cells and basophils that causes vasodilation and makes venules leaky.

Diapedesis

The process by which leukocytes, such as neutrophils and monocytes, squeeze through blood vessel walls to reach infected tissue.

Fever

A systemic response that increases body temperature to inhibit microbial growth and enhance immune response; it is considered dangerous at $> 105^{\circ}F\, (40.7^{\circ}C)$ and lethal at $> 108^{\circ}F\, (42^{\circ}C)$.

Complement Proteins

A "rapid response team" of plasma proteins that travel as precursors and undergo cascading activation to result in the Membrane Attack Complex (MAC), opsonization, and inflammation.

Thymus

A primary lymphoid organ posterior to the sternum where T lymphocytes mature; it is largest during childhood and is eventually replaced by adipose tissue with age.

Red Pulp

The part of the spleen that recycles erythrocytes and acts as a reservoir for erythrocytes and thrombocytes.

Hematopoiesis

The process occurring in the red bone marrow that produces approximately 100 billion leukocytes per day.

Neutrophils

The most abundant granulocytes ($40 - 70\%$) that act as first responders to infection, primarily targeting bacteria through phagocytosis.

Eosinophils

Granulocytes that primarily target helminths and assist in allergic responses; they are characterized by red-orange granules and a bilobed nucleus.

Monocyte

The largest type of leukocyte which circulates in the blood before differentiating into macrophages or dendritic cells.

Natural Killer (NK) Cells

Large granular lymphocytes that provide early defense by cytotoxic destruction of virus-infected cells and tumor cells.

Major Histocompatibility Complex (MHC) Class I

Molecules found on all nucleated cells responsible for self-recognition and the activation of cytotoxic T lymphocytes.

Professional Antigen Presenting Cells (APCs)

A group of cells including macrophages, dendritic cells, and B lymphocytes that express MHC Class II to activate the adaptive immune response.

Plasma Cells

Large, effector B cells that produce and release approximately 2000 antibodies per second into the blood.

Immunoglobulin G (IgG)

The most abundant antibody ($75\%$) in extracellular fluid that provides long-term immunity and can cross the placenta from mother to fetus.

Immunoglobulin A (IgA)

A dimeric antibody found in saliva, tears, and mucus that protects mucosal surfaces.

Immunoglobulin M (IgM)

A pentameric antibody that serves as the first responder during primary exposure and is effective at agglutination and activating complement.

Herd Immunity

Community protection that occurs when a high percentage of the population is immune to an etiologic agent, thereby protecting vulnerable individuals.

CD4+ T Lymphocyte

Also known as Helper T cells, these are the master coordinators of the adaptive immune response that activate B lymphocytes and cytotoxic T lymphocytes.

CD8+ T Lymphocyte

Also known as Cytotoxic T cells, these identify and destroy infected, malignant, or damaged cells using perforin and granzymes.

Latent Infections

Persistent viral infections where the virus remains dormant or inactive in tissues, often through DNA integration, and remains asymptomatic.