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Medical Dictionary Definitions A-Z List

Medical Dictionary Definitions A - Z - «R»:

  1. Rhythm method Rhythm method
    Rhythm method: Also known as fertility awareness, natural family planning, and periodic abstinence, this approach to contraception entails not having sexual intercourse on the days of a woman's menstrual cycle when she could become pregnant or using a barrier method (such as a condom, the diaphragm ...
  2. Rhythm, sinus Rhythm, sinus
    Rhythm, sinus: The normal regular rhythm of the heart set by the natural pacemaker of the heart called the sinoatrial (or sinus) node. It is located in the wall of the right atrium (the right upper chamber of the heart). Normal cardiac impulses start there and are transmitted to the atria and down t...
  3. Rib Rib
    Rib: One of the 12 paired arches of bone which form the skeletal structure of the chest wall (the rib cage). The ribs attach to the building blocks of the spine (vertebrae) in the back. The 12 pairs of ribs consist of: True ribs: The first seven ribs attach to the sternum (the breast bone) in th...
  4. Rib cage Rib cage
    Rib cage: The structure formed by the thoracic vertebrae and ribs, the sternum (breastbone), and the costal cartilages (that attach the ribs to the sternum). A cage is an enclosure made of "open work" that usually houses animals. The rib cage was thought to resemble an animal cage (although the larg...
  5. Rib, cervical Rib, cervical
    Rib, cervical: A extra rib which arises from the seventh cervical vertebra. It is located above the normal first rib. A cervical rib is present in only about 1 in 200 (0.5%) of people. It may cause nerve and artery problems. There are normally 12 pairs of ribs in all. Each pair of ribs is attached t...
  6. Rib, false Rib, false
    Rib, false: One of the last 5 pairs of ribs. A rib is said to be "false" if it does not attach to the sternum (the breast bone). All 12 pairs of ribs attach to the building blocks of the spine (vertebrae) in the back. The 12 pairs of ribs consist of: True ribs: The first seven ribs attach to the ste...
  7. Rib, floating Rib, floating
    Rib, floating: One of the last two ribs. A rib is said to be "floating" if it does not attach to the sternum (the breast bone) or to another rib. There are usually 12 pairs of ribs in all. Each pair of ribs is attached to the building blocks of the spine (the vertebrae) in the back. The 12 pairs of ...
  8. Rib, fluctuating Rib, fluctuating
    Rib, fluctuating: One of the last two ribs. A rib is said to be "fluctuating" if it does not attach to the sternum (the breast bone) or to another rib. There are usually 12 pairs of ribs in all. Each pair of ribs is attached to the building blocks of the spine (the vertebrae) in the back. The 12 pai...
  9. Rib, sternal Rib, sternal
    Rib, sternal: One of the first 7 pairs of ribs. A rib is said to be a "sternal" rib or a "true" rib if it attaches to the sternum (the breast bone). All 12 pairs of ribs attach to the building blocks of the spine (vertebrae) in the back. The 12 pairs of ribs consist of: Sternal or true ribs: The fir...
  10. Rib, true Rib, true
    Rib, true: One of the first 7 pairs of ribs. A rib is said to be "true" if it attaches to the sternum (the breast bone). All 12 pairs of ribs attach to the building blocks of the spine (vertebrae) in the back. The 12 pairs of ribs consist of: True ribs: The first seven ribs attach to the sternum (th...
  11. Rib, vertebral Rib, vertebral
    Rib, vertebral: One of the last two ribs. A rib is said to be "vertebral" if it does not attach to the sternum (the breast bone) or to another rib. There are usually 12 pairs of ribs in all. Each pair of ribs is attached to the building blocks of the spine (the vertebrae) in the back. The 12 pairs o...
  12. Ribonucleic acid (RNA) Ribonucleic acid (RNA)
    Ribonucleic acid (RNA): A nucleic acid molecule similar to DNA but containing ribose rather than deoxyribose. RNA is formed upon a DNA template. There are several classes of RNA molecules. They play crucial roles in protein synthesis and other cell activities: Messenger RNA (mRNA) is a type of RNA ...
  13. Ribonucleoprotein (RNP) Ribonucleoprotein (RNP)
    Ribonucleoprotein (RNP): A combination of ribonucleic acid (RNA) and protein. In autoimmune diseases, antibodies can form against ribonucleoprotein. They are called anti-RNP antibodies. ...
  14. Ribosomal RNA Ribosomal RNA
    Ribosomal RNA: A molecular component of a ribosome, the cell's essential protein factory. Ribosomal RNA (rRNA) fabricates polypeptides (assemblies of amino acids that make up proteins). A tiny particulate structure located in the cytoplasm of the cell (outside the nucleus), the ribosome is composed...
  15. Ribosome Ribosome
    Ribosome: The cell's essential protein factory. A tiny particulate structure located in the cytoplasm of the cell (outside the nucleus), the ribosome is composed of two subunits, one larger than the other. Both subunits were believed to contain both RNA and protein but this is not the full story. Mo...