Dictionary

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.

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 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.

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.

resection Surgical removal of part of an organ.

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.

residual disease A disease that has not been fully eradicated.

Reiter syndrome See reactive arthritis.

rejection In transplantation biology, when the body’s immune system attacks transplanted cells, tissues, or organs. For example, a transplanted kidney may be rejected.

relapse The return of signs and symptoms of a disease after a remission.

relaxant Something that relaxes, relieves, or reduces tension. For example, a muscle relaxant is often administered during abdominal surgery to relax the diaphragm and keep it from moving during the surgery.

relaxin A hormone that is produced during pregnancy that facilitates the birth process by causing a softening and lengthening of the cervix and the pubic symphysis (the place where the pubic bones come together). Relaxin also inhibits contractions of the uterus and may play a role in determining the timing of delivery.