Webster's New World Medical Dictionary

ribosome
A tiny structure in the cytoplasm of a
cell (outside the nucleus) that functions as the pro-
tein factory for the cell.
ribozyme
An RNA molecule that has enzymatic
activity. See also 
ribonucleic acid.
rickets
A disease of infants and children that dis-
turbs normal bone formation (ossification), leading
to failure to mineralize bone. Rickets softens bone,
producing osteomalacia, and permits marked bend-
ing and distortion of bones. Other features of rick-
ets include softness of the infant’s skull
(craniotabes), enlargement of the front end of the
ribs (creating the “rachitic rosary”), thickening of
the wrists and ankles, lateral curving of the spine
(scoliosis), abnormal forward–backward curving
of the spine (kyphosis and lumbar lordosis), and
deforming and narrowing of the pelvis. As the child
begins to walk, the weight on the soft shafts of the
legs results in knock-knees or, more often, bowlegs.
Until the first third of the 20th century, rickets was
usually due to lack of direct exposure to sunlight or
to lack of vitamin D, calcium, and phosphorus, but
nutritional rickets has become relatively rare in
industrialized nations. In developing countries, vita-
min D–deficiency rickets continues to be a prob-
lem. Rickets in developed countries is usually now
due to other causes, such as disorders that create
vitamin D deficiency by interfering with the absorp-
tion of vitamin D through the intestines; diseases of
the liver, kidney, or other organs that impair the
normal metabolic conversion and activation of vita-
min D; and conditions that disrupt the normal bal-
ance in the body between calcium and phosphorus.
rickets, celiac
Rickets caused by failure of the
intestines to absorb calcium and fat from foods. See
also 
celiac sprue.