Dictionary

ribosome A tiny structure in the cytoplasm of a cell (outside the nucleus) that functions as the protein factory for the cell.

ribozyme An RNA molecule that has enzymatic activity. See also ribonucleic acid.

rickets A disease of infants and children that disturbs normal bone formation (ossification), leading to failure to mineralize bone. Rickets softens bone, producing osteomalacia, and permits marked bending and distortion of bones. Other features of rickets include softness of the infant’s skull (craniotabes), enlargement of the front end of the ribs (creating the “rachitic rosary”),…

rickets, celiac Rickets caused by failure of the intestines to absorb calcium and fat from foods. See also celiac sprue.

rickets, hypophosphatemic A rare genetic form of rickets that is characterized by low blood phosphate level (hypophosphatemia), defective intestinal absorption of phosphate, and unresponsiveness to vitamin D. The basic problem in hypophosphatemic rickets is decreased resorption of phosphate by the tubules in the kidney. Females typically have less severe disease than males. The condition is…

rickets, renal Rickets-like bone malformations that are caused by prolonged inflammation of the kidneys.

rickets, vitamin D–resistant See rickets, hypophosphatemic.

Rickettsia A member of genus Rickettsia, a family of microorganisms that, like viruses, require other living cells for growth, but also resemble bacteria in that they use oxygen, have metabolic enzymes and cell walls, and are susceptible to antibiotics. Rickettsiae cause a series of diseases, including Rocky Mountain spotted fever, typhus, and trench fever. Rickettsiae…

rickettsial diseases Infectious diseases caused by Rickettsiae. See also Rickettsia.

rickettsialpox A mild infectious disease first observed in New York City that is caused by Rickettsia akari and is transmitted from its mouse host by chigger or adult mite bites. Features include fever, a dark spot that becomes a small ulcer at the site of the bite, swollen glands (satellite lymphadenopathy) near the site of…

rickettsiosis Infection with Rickettsia. See also Rickettsia.

rickettsiosis, North Asian tick-borne One of the tick-borne rickettsial diseases of the eastern hemisphere, similar to but less severe than Rocky Mountain spotted fever. Symptoms include fever, a small ulcer (eschar) at the site of the tick bite, swollen glands near the site of the bite (satellite lymphadenopathy), and a red, raised (maculopapular) rash.