Dictionary

DNA cloning The use of DNA-manipulation procedures to produce multiple copies of a single gene or segment of DNA. See also DNA, recombinant.

DNA, recombinant DNA made up of DNA molecules of different origins, joined together by using recombinant DNA technology. A recombinant DNA molecule is constructed (recombined) from segments from two or more different DNA molecules. Under certain conditions, a recombinant DNA molecule can enter a cell and replicate there.

DNA, mitochondrial The DNA of the mitochondrion, a structure situated in the cytoplasm of the cell rather than in the nucleus, where all the other chromosomes are located. Abbreviated mtDNA. mtDNA is inherited from the mother. There are 2 to 10 copies of the mtDNA genome in each mitochondrion. mtDNA is a double-stranded, circular molecule….

DNA 1 Deoxyribonucleic acid, one of the two molecules (along with RNA) that encode genetic information. DNA is double-stranded. The two strands are held together by weak hydrogen bonds between base pairs of nucleotides to form a double helix. The double helix looks something like an immensely long ladder twisted into a helix, or coil….

DMD Duchenne muscular dystrophy. See muscular dystrophy, Duchenne.

dizziness, presyncopal Dizziness before fainting. Some symptoms of dizziness, such as “wooziness,” feeling as though one is about to black out, and tunnel vision may be presyncopal and are due to insufficient blood flow to the brain. These symptoms are typically worse when standing, improve with lying down, and may be experienced by healthy individuals…

dizziness, anxiety as a cause of One cause of dizziness is overbreathing (hyperventilation) due to anxiety. Relief can be had by breathing in and out of a paper bag to increase the level of carbon dioxide in the blood. In persistent cases, as in repeated panic attacks, antianxiety medication can be helpful.

dizziness Painless head discomfort with many possible causes, including disturbances of vision, the brain, the balance (vestibular) system of the inner ear, or the gastrointestinal system. Dizziness is a medically indistinct term. Laypersons use it to describe a variety of conditions, ranging from lightheadedness or unsteadiness to vertigo. See also lightheadedness; unsteadiness; vertigo.

diverticulum, Meckel An outpouching of the small bowel. About 1 in every 50 people has a Meckel diverticulum. Meckel diverticula are usually located about 2 feet before the junction of the small bowel and the colon (the large intestine) in the lower-right abdomen. Meckel diverticula can become inflamed, ulcerate, and perforate (break open or rupture),…

diverticulum A small bulging sac that pushes outward from the bowels. The plural is diverticula. As a person ages, pressure within the large intestine (colon) causes diverticula. Diverticula can occur throughout the colon but are most common near the end of the S-shaped segment of the colon located in the lower-left part of the abdomen…

diverticulosis The condition of having diverticula, small outpouchings from the large intestine (colon). Diverticulosis can occur anywhere in the colon but is most typical in the sigmoid colon, the Sshaped segment of the colon located in the lowerleft part of the abdomen. The incidence of diverticulosis increases with age. As a person ages, the walls…

diverticulitis Inflammation of diverticula along the wall of the the large intestine (colon). For diverticulitis to occur, there must be outpouchings of the large intestine (diverticulosis). Diverticulitis can be diagnosed with barium X-rays of the colon or with sigmoidoscopy or colonoscopy. Antibiotics are usually needed to treat acute diverticulitis. Liquid or low-fiber foods are advised…