Key Knowledge 7 Flashcards
pathogen
an agent that causes disease
antigen
any molecule that may trigger an immune response
non-self antigen
a molecule from outside the body that is recognised by the immune system and initiates an immune response. Also known as a foreign antigen
major histocompatibility complex (MHC) proteins
a group of proteins present on the surface of all self-cells that enables the immune system to distinguish it from non-self material. Also known as self-antigens
autoimmune disease
a disease in which an individual’s immune system initiates an immune response against their own cells
allergen
a non-pathogenic antigen that triggers an allergic reaction
allergic reaction
an overreaction of the immune system to a nonpathogenic antigen
cellular pathogen
a pathogen that has a cellular structure and exhibits the processes of a living organism. Examples include bacteria, fungi, protozoa, and parasites
non-cellular pathogen
a pathogen that neither has a cellular structure nor exhibits the processes of a living organism. Examples include viruses and prions
Bacteria
Unicellular prokaryotes that can infect almost any part of the body. Bacteria can cause disease through the production of toxins and enzymes which either affect the functioning of cells or
cause their death
Fungi
Eukaryotic organisms that include yeasts and moulds and contain long, branching filaments called hyphae.
Worms
Multicellular invertebrate parasites whose development include egg, larval, and adult stages. Can vary in length, with the longest worms being over 55 m in length
Protozoa
Single-celled eukaryotes that can be free-living or parasitic. Protozoa have many different mechanisms of action – for example, some can inhibit nucleic acid synthesis, protein synthesis, and various stages of cellular respiration.
Viruses
An infectious agent composed of genetic material (DNA or RNA) inside a protein coat (capsid). In some instances the protein coat is surrounded by a lipid envelope. Viruses are not able to independently reproduce, instead they insert their genetic material into a host’s cell and use the cell to replicate
Prions
Abnormally folded proteins that have the ability to induce normal proteins nearby to become misfolded. They only occur in mammals and affect only the brain and other neural structures. They are currently the only known infectious agents that don’t contain nucleic acids
innate immune system
a component of the immune system that is composed of generalised and non-specific defences and/or responses to pathogens. Also known as the non-specific immune system.
first line of defence
a component of the innate immune system characterised by the presence of physical, chemical, and microbiological barriers to keep pathogens out of the host organism
second line of defence
a component of the innate immune system characterised by the nonspecific response to injury and/or pathogens by a variety of cells and molecules
physical barrier
a component of the first line of defence that features solid or fluid obstacles that block pathogen entry such as skin or mucus
chemical barrier
a component of the first line of defence that features the use of enzymes, toxins, and acids to protect against pathogen invasion
physical example (plants)
• Thick bark
• Waxy cuticles of leaves
• Formation of galls to prevent the spread of infection
• Presence of thorns and trichomes to deter insects and grazers
• Closing of stomata to prevent pathogen invasion during carbon dioxide uptake
chemical example (plants)
• Chitinases – enzymes that occur in a number of different plants and have antifungal properties
• Phenols – secreted by wounded plants, repelling or killing invading
microorganisms
• Defensins – small peptides that are toxic to microbes and fungi
• Saponins – disrupt the cell membranes of various fungi
• Oxalic acid – a substance that can be toxic if ingested
• Glucanases – defend plants against fungi
microbiological barrier
a component of the first line of defence in which the presence of normal flora limits the growth of pathogenic bacteria
physical examples (humans)
• Intact skin and surfaces between external and internal environments (e.g. integumentary, respiratory, gastrointestinal, and genitourinary tracts)
• Mucous secretions and/or hairs in the respiratory tract that trap organisms, and cilia that sweep them away from the airways and into the throat where they are
swallowed and destroyed by the gastrointestinal tract
chemical example (humans)
• Presence of lysozyme enzymes in tears and saliva that destroy bacterial cell walls
• Acidic sweat that destroys pathogens growing on the surface of the body
• Stomach acid that destroys pathogen that have been eaten/swallowed
• Antibacterial compounds in earwax
• Antibacterial proteins in semen
• Low pH in the vagina
microbiological example (humans)
• Presence of bacteria on the skin, in the lower gastrointestinal tract, and the vagina
leukocytes
a group of blood cells responsible for protecting the body against pathogens and foreign material. Also known as white blood cells
phagocyte
a group of leukocytes responsible for the endocytosis and destruction of pathogens, foreign material, and cell debris
neutrophil
the most common type of leukocyte in the body. Engages in phagocytosis of pathogens and foreign material, as well as the release of cytokines
macrophage
a type of leukocyte found throughout the body that engages in phagocytosis and antigen presentation