mesothelioma A malignant tumor of the mesothelium, the thin lining of the surface of the body cavities and the organs that are contained within them. Most mesotheliomas begin as one or more nodules that progressively grow to form a solid coating of tumor surrounding the lung, abdominal organs, or heart. Mesothelioma occurs most commonly in…
messenger RNA The key intermediary in gene expression, which translates the DNA’s genetic code into the amino acids that make up proteins. Abbreviated mRNA.
metabolic disease A metabolism disorder, such as albinism, cystinuria, phenylketonuria (PKU), and some forms of gout, sun sensitivity, and thyroid disease. There are hundreds of known metabolic diseases. Advances in the diagnosis and treatment of metabolic diseases have improved the outlook for many of these conditions so that early diagnosis, if possible in infancy, can…
metabolism The whole range of biochemical processes that occur within a living organism. Metabolism consists of anabolism (the buildup of substances) and catabolism (the breakdown of substances). The term metabolism is commonly used to refer specifically to the breakdown of food and its transformation into energy.
metabolism, inborn error of See metabolic disease.
metacarpal One of the five cylindrical bones that extend from the wrist to the fingers.
metaphase chromosome A chromosome in the stage of its cell life in which it is most condensed and easiest to see separately. Because metaphase chromosomes are easier to study than others, they are often chosen for karyotyping and chromosome analysis.
metastases, meningeal See meningitis, neoplastic.
meningitis, meningococcal Inflammation of the meninges due to infection with the bacterium Neisseria meningitidis. Meningococcal meningitis typically starts like the flu, with the sudden onset of an intense headache, fever, sore throat, nausea, vomiting, and malaise. But, unlike with the flu, a stiff neck and intolerance of lights are frequent symptoms of meningococcal meningitis. Within…
meningitis, Mollaret A rare form of aseptic meningitis characterized by a recurrent pattern with symptom-free intervals between episodes. Symptoms of Mollaret meningitis, which last from 1 to 7 days, include headache, neck ache, fever, and neck stiffness. With this type of meningitis, there is usually rapid onset of symptoms and resolution without residual damage to…
meningitis, neoplastic Inflammation of the meninges due to cancer that has spread from the original (primary) tumor to the meninges. The name neoplastic meningitis is a misnomer because the condition is not inflammatory. It is more properly called meningeal carcinomatosis or meningeal metastases.
meningitis, viral Inflammation of the meninges that is due to a virus, such as mumps virus or coxsackievirus, that is shed in the feces, sputum (spit), and nasal discharges. Viral meningitis is contagious, and it occurs most frequently in children. It can be a complication of common childhood diseases, including chickenpox. Symptoms include fever, headache,…