Pathology & Disease Exam 4

Bacteria

Prokaryotes that have a cell membrane but lack membrane-bound nuclei and organelles

Viruses

Obligate intracellular parasites that depend on the host's metabolic machinery to replicate

Prions

Misshapen forms of host proteins that lack genetic material

Fungi

Eukaryotes with thick cell walls composed of complex carbohydrates (beta-glucans, chitin, & glycoproteins)

Protozoa

Single-celled eukaryotes that are major causes of disease & death in developing countries

Helminths

Parasitic worms that are highly differentiated multicellular organisms

Transmission of pathogens

Skin, oral secretions, respiratory secretions, feces, blood, urine, genital tract, vertical transmission (mother to fetus)

Routes of entry

Breaks in the skin or other cutaneous structures (ex. eye), alimentary from food/water contaminated with fecal material, inhalation into the respiratory tract, retrograde ascension into the urogenital tract

Entry & dissemination of microbes

Some proliferate locally at the site of initial infection while others penetrate the epithelial barrier & spread to distant sites by lymphatics, blood, or nerves

Sequence of infectious disease

Portal of initial encounter, cross a barrier system, encounter mucosa-associated lymphoid tissues (MALTs) within the extracellular matrix, spread to local lymphoid aggregates, afferent lymphatic vessels, regional lymph nodes, efferent lymphatic vessels, thoracic duct & anterior vena cava to the vascular system, target cells in a systemic organ system causing dysfunction/lysis & disease

Ability of microbes to cause disease

Relies heavily on the presence of target substances/cells within a susceptible individual & virulence factors of the pathogen, which can be integral to the microbe's biological structure or synthesized using metabolic processes of the target cell as needed to replicate

Virulence factors

Molecules & properties of microbes that enable them to replicate & cause disease; allow the microbe to colonize target/invade substances/cells &/or tissues at portals of entry, evade barrier systems & defense mechanisms, suppress innate & adaptive immune responses, & acquire nutrition from target substances/cells &/or tissues

Target substances/cells

Specific types of cells/substances required by a microbe to successfully replicate & complete its life cycle; often based on ligand-receptor interactions in which proteins expressed on the surface of microbes bind to receptors on membranes of target cells or mucus associated with these cells

Groups of target cells

Cells initially encountered at the portal of entry, cells used to spread microbes locally, regionally, or systemically, & cells located systemically within other organ systems; microbes can use more than one to complete their lifecycle

Epithelial cells & their extracellular matrix

Most common cell type used by microbes

Simple epithelium

Single-layered cells that are divided into squamous, cuboidal, & columnar subtypes based on their morphologic structure

Stratified epithelium

Multi-layered cells that are divided into squamous, cuboidal, & columnar subtypes based on their morphologic structure

Mucosa-associated lymphoid tissues (MALTs)

General term used to categorize lymphoid nodules composed of lymphocytes, macrophages, & dendritic cells; each, some, or all of these cell types can serve as target cells for specific diseases

Cell polarity

Mechanism used by microbes in apical & basolateral domains that sets up a polarity to the cell; microbes can enter & exit the cell due to expression of different receptors at these domains

Transcytosis

Normal function of many cell types used to move macromolecules across cells in microvesicles known as endosomes; also used by microbes to cross barriers with the help of M cells (areas that lack mucus layer)

Receptor-mediated endocytosis

Use of specific virulence factors that allows microbes to enter cells (generally at the apical surface) & leave via exocytosis at the basolateral surface & enter lamina propria

Systemic spread

Passive via dispersal of cell-free microbes in lymph or plasma within the circulatory system to randomly encounter appropriate target cells; active via leukocyte trafficking

Leukocyte trafficking

Active spread of microbe infected leukocytes (macrophages, lymphocytes, dendritic cells); these cells carry microbes in circulation as they normally would travel, but when they reach a target cell, a series of events occurs that allows the microbe to escape leukocytes & enter the target cell

Virulence

Ability of bacteria to damage host tissues; depends on the bacterium's ability to adhere to host cells, invade host cells, and deliver toxins; controlled by genes in plasmids & can vary by strain

Pyogenic bacteria

Group of pathogenic bacteria that cause a predominant tissue reaction of acute inflammation; produce pus by releasing factors that increase the permeability of blood vessels & attracting leukocytes

Toxigenic bacteria

Group of pathogenic bacteria that produce disease-causing toxins which can cause enzymatic lysis, pore formation, inhibition of protein synthesis, dysfunction of ion pumps, & selective protein inactivation

Toxigenesis

Toxins produced by bacteria can be structural components of the bacteria themselves released after the bacteria are destroyed; can also be soluble peptides released by the bacteria while it is alive

Endotoxins

General term used to characterize any outer membrane-associated toxin of the cell wall, but mostly refers to lipopolysaccharide; released from dead gram-negative bacteria; toxic to most animal cells/tissues/organs & can be lethal if large quantities are absorbed by or released into the circulatory system; release can cause activation of proinflammatory cytokines & nitric oxide, leading to the activation of complement & coagulation cascades

Lipoteichoic acid

Located in the cell wall of gram-positive bacteria; behaves as a gram-positive endotoxin because its actions mimic lipopolysaccharide