resident In medicine, a physician who has finished medical school and is receiving training in a specialized area, such as surgery, internal medicine, pathology, or radiology. Board certification in all medical and surgical specialties requires the satisfactory completion of a residency program and successful completion of a specialty board examination.
resection Surgical removal of part of an organ.
research, controlled A study that compares results from a treated group and a control group. The control group may receive no treatment, a placebo, or a different treatment. See also blinded study; double-blinded study.
reproductive system In women, the organs that are directly involved in producing eggs and in conceiving and carrying babies; in men, the organs directly involved in creating, storing, and delivering sperm to fertilize an egg.
reproductive cloning Cloning designed to create new individuals, in contrast to the goal of therapeutic cloning. This idea has stirred great controversy and has met with almost uniform disapproval. See also therapeutic cloning.
reproductive cell An egg or a sperm cell. Each mature reproductive cell is haploid, meaning that it has a single set of 23 chromosomes and so contains half the usual amount of DNA.
reproduction The production of offspring. Reproduction need not be sexual; for example, yeast can reproduce by budding.
reportable disease A disease that must be reported to federal, state, or local health officials when diagnosed.
replication A turning back, repetition, duplication, or reproduction. See also DNA replication.
replacement therapy, hormone See hormone therapy.
repetitive stress injury An injury that occurs due to recurrent overuse or improper use. One of the best-known repetitive stress injuries is carpal tunnel syndrome, which often results from the trauma of highly repetitive work such as that of supermarket checkers, assembly-line workers, typists, word processors, accountants, and writers.
reperfusion The restoration of blood flow to an organ or to tissue. After a heart attack, an immediate goal is to quickly open blocked arteries and reperfuse the heart muscles. Early reperfusion minimizes the extent of heart muscle damage and preserves the pumping function of the heart.