0.5 Glossary  (Page 8/18)

H

• hair follicle a structure embedded in the dermis from which hair grows
• halophile organism that depends on high concentrations of salt in the environment to grow
• halotolerant organism that grows in the presence of high salt concentration but does not require it
• Hansen’s Disease chronic bacterial infection of peripheral nervous tissues caused by the acid-fast bacterium, Mycobacterium leprae ; also known as leprosy
• hantavirus pulmonary syndrome acute lung infection by a hantavirus following inhalation of aerosols from the urine or feces of infected rodents
• haploid having one copy of each chromosome
• hapten a molecule that is too small to be antigenic alone but becomes antigenic when conjugated to a larger protein molecule
• hard chancre a generally painless ulcer that develops at the site of infection in primary syphilis
• Hashimoto thyroiditis hypothyroidism caused by an autoimmune disease affecting thyroid function
• healthcare-associated infection (HAI) an infection acquired in a hospital or other health-care facility unrelated to the reason for which the patient was initially admitted; nosocomial infection
• heavy chains longest identical peptide chains in antibody molecules (two per antibody monomer), composed of variable and constant region segments
• helical virus cylindrical or rod shaped
• helicase enzyme that unwinds DNA by breaking the hydrogen bonds between the nitrogenous base pairs, using ATP
• helminth a multicellular parasitic worm
• helper T cells class of T cells that is the central orchestrator of the cellular and humoral defenses of adaptive immunity and the cellular defenses of innate immunity
• hemagglutination visible clumping of red blood cells that can be caused by some viruses, bacteria, and certain diseases in which antibodies are produced that bind to self-red blood cells
• hematopoiesis formation, development, and differentiation of blood cells from pluripotent hematopoietic stem cells
• hematuria condition in which there is blood in the urine
• hemolysin class of exotoxin that targets and lyses red blood cells, as well as other cells
• hemolytic disease of the newborn (HDN) type II hypersensitivity reaction that occurs when maternal anti-Rh antibodies cross the placenta and target fetal Rh+ red blood cells for lysis
• hemolytic transfusion reaction (HTR) condition resulting after an incompatible blood transfusion; caused by type II hypersensitivity reaction and destruction of red blood cells
• hemorrhagic fever with renal syndrome serious hemorrhagic fever caused by hantavirus infection
• HEPA filter high-efficiency particulate air filter with an effective pore size that captures bacterial cells, endospores, and viruses as air passes through, removing them from the air
• hepatitis inflammation of the liver
• herd immunity a reduction in disease prevalence brought about when few individuals in a population are susceptible to an infectious agent
• herpes keratitis eye infection caused by herpes simplex virus
• herpes simplex virus type 2 (HSV-2) the type of herpesvirus most commonly associated with genital herpes
• herpetic gingivostomatitis inflammation of the mouth and gums often caused by the HSV-1 virus
• heterolactic fermentation process producing a mixture of lactic acid, ethanol and/or acetic acid, and CO ₂ as fermentation products; the microbes that do this use pentose phosphate pathway glycolysis, which is why they generate multiple fermentation products
• heterotroph organism that uses fixed organic carbon compounds as its carbon source
• hexose monophosphate shunt see pentose phosphate pathway
• Hfr cell E. coli cell in which an F plasmid has integrated into the host cell’s chromosome
• high G+C gram-positive bacteria bacteria that have more than 50% guanine and cytosine nucleotides in their DNA
• high-energy phosphate bond bond between the negatively charged phosphate groups that holds a lot of potential energy
• histamine proinflammatory molecule released by basophils and mast cells in response to stimulation by other cytokines and chemical mediators
• histones DNA-binding proteins found in eukaryotes and archaea that aid in orderly packaging of chromosomal DNA
• histoplasmosis fungal disease caused by the dimorphic fungus Histoplasma capsulatum
• holoenzyme enzyme with a bound cofactor or coenzyme
• holozoic refers to protozoans that consume food particles through phagoctytosis
• homolactic fermentation process producing only lactic acid as a fermentation product; the microbes that do this use Embden-Meyerhof-Parnas glycolysis
• hookworm infection soil-transmitted intestinal infection caused by the nematodes Necator americanus and Ancylostoma doudenale
• horizontal direct transmission movement of a pathogen from one host to another (excluding mother to embryo, fetus, or infant) in a population through physical contact or through droplet transmission
• horizontal gene transfer introduction of genetic material from one organism to another organism within the same generation
• host range the types of host cells that a particular virus is able to infect
• HTST high-temperature short-time pasteurization is a method of pasteurization commonly used for milk in which the milk is exposed to a temperature of 72 °C for 15 seconds
• human African trypanosomiasis serious infection caused by Trypanosoma brucei and spread by the bite of the tsetse fly
• human granulocytic anaplasmosis zoonotic tickborne disease caused by the obligate intracellular pathogen Anaplasma phagocytophilum
• human immunodeficiency virus (HIV) retrovirus responsible for acquired immune deficiency syndrome (AIDS) in humans
• human papillomavirus (HPV) a group of common sexually transmitted viruses that may be associated with genital warts or with cervical cancer
• humanized monoclonal antibodies chimeric antibodies with mouse variable regions and human constant regions
• humoral immunity adaptive immunity mediated by antibodies produced by B cells
• hyaluronidase enzyme produced by pathogens that degrades hyaluronic acid between adjacent cells in connective tissue
• hybridization the joining of two complementary single-stranded DNA molecules
• hybridoma clones of cell produced by fusing a normal B cell with a myeloma cell that is capable of producing monoclonal antibodies indefinitely
• hydatid disease cystic echinococcosis, an infection caused by the tapeworm Echinococcus granulosus
• hydrophilic “water loving”; refers to a polar molecule or portion of a molecule capable of strong attraction to water molecules
• hydrophobic “water fearing”; refers to a nonpolar molecule or portion of a molecule not capable of strong attraction to water molecules
• hypersensitivity pneumonitis (HP) type III and IV hypersensitivities in the lungs that are caused by environmental or occupational exposure to allergens such as mold and dust
• hypersensitivity potentially damaging immune response against an antigen
• hyperthermophile a microorganism that has an optimum growth temperature close to the temperature of boiling water
• hypertonic medium an environment in which the solute concentration outside a cell exceeds that inside the cell, causing water molecules to move out of the cell, resulting in crenation (shriveling) or plasmolysis.
• hyphae tubular, filamentous structures that makes up most fungi
• hypodermis the layer of tissue under the dermis, consisting primarily of fibrous and adipose connective tissue
• hypotonic medium an environment in which the solute concentration inside a cell exceeds that outside the cell, causing water molecules to move into the cell, possibly leading to swelling and possibly lysis