Medical Glossary Index:

M

Macula- the area of the retina that allows fine details to be observed at the center of vision; also refers to any small, flat spot on the skin

Macular degeneration- gradual loss of vision due to deterioration of nerve tissue in the retina

Magnesium- a mineral that is essential for many body functions, including nerve impulse transmission, formation of bones and teeth, and muscle contraction

Magnetic resonance imaging (MRI)- a technique that uses magnetic fields and radio waves to create high-quality cross-sectional images of the body without using radiation

Malabsorption- an impaired ability of the lining of the small intestine to absorb nutrients from food

Malaria- a parasitic disease spread by mosquitos that causes chills and fever; potentially fatal complications in the liver, kidneys, blood, and brain are possible

Malformation- abnormal development of an organ or tissue

Malignant- a word used to describe a condition that is characterized by uncontrolled growth and/or that can be fatal, such as a cancerous tumor

Malignant hyperthermia- a reaction to certain anesthesia gases involving intense muscle contractions and a high fever

Malignant melanoma- the most serious type of skin cancer, in which a mole changes shape, darkens, becomes painful, and/or bleeds easily

Mallory-Weiss syndrome- a condition associated with alcoholism in which the lower end of the esophagus tears, causing vomiting of blood

Mammography- an X-ray procedure done to detect breast cancer

Mammoplasty- a general term for a cosmetic operation on the breasts; includes breast reduction, enlargement, and reconstruction after a mastectomy

Mandible- another term for the lower jaw

Mania- a mental disorder characterized by extreme excitement, happiness, overactivity, and agitation; usually refers to the high of the highs and lows
experienced in manic-depressive disorder

Manic-depressive disorder- a mental disorder characterized by extreme mood swings, including either mania, depression, or a continuing shift between the two extremes

MAO inhibitor- see Monoamine oxidase inhibitor antidepressant

Marfan's syndrome- a rare genetic disorder that affects connective tissue, leading to abnormalities of joints, bones, tendons, ligaments, arteries, and/or the
heart

Mast cell- a type of cell present in most body tissues that releases substances in response to an allergen, which causes symptoms such as inflammation

Mastectomy- a surgical procedure in which all or part of the breast is removed
to prevent the spread of cancer

Mastitis- inflammation of the breast, which is usually caused by a bacterial infection

Maxilla- one of two bones that form the upper jaw, the roof of the mouth, and
the center portion of the face

Measles- an illness caused by a viral infection, causing a characteristic rash and
a fever; primarily affects children

Meconium- thick, sticky, greenish-brown stool passed by a postmature fetus,
or one experiencing fetal distress, into the amniotic fluid, or by an infant during the
first couple of days after birth

Medial- a term used to describe something situated on or near the midline of the body or a body structure

Median nerve- a nerve running down the arm to the hand; controls muscle movement in the forearm and hand and conveys sensation from part of the hand

Mediastinoscopy- investigation of the central chest compartment using an endoscope that is inserted through an incision in the neck

Medulla- the center part of an organ or body structure; sometimes used to refer to the lower part of the brain stem

Medulloblastoma- a type of cancerous tumor, occurring in the section of the brain that controls posture and balance; found mainly in children

Megacolon- a severely swollen large intestine, causing severe constipation and abdominal bloating; may be present at birth or develops later

Megaloblastic anemia- a type of anemia in which a lack of the vitamin B12 or folic acid interferes with red blood cells and causes them to be enlarged and deformed, resulting in tiredness and weight loss

Meiosis- the type of cell division that occurs only in the ovaries and testicles, producing cells with half the genes of the original cell; these cells then form eggs and sperm

Melanin- the pigment that gives skin, hair, and eyes their coloring

Melanocytes- cells that produce the pigment melanin

Melanocyte-stimulating hormone- a hormone that coordinates pigmentation
of the skin, eyes, and hair

Melanoma- a skin tumor composed of cells called melanocytes

Menarche- the beginning of menstruation

Meniere's disease- a disorder of the inner ear, causing hearing loss, ringing in
the ear, and the sensation that one's surroundings are spinning

Meninges- the three membranes that surround and protect the spinal cord and brain

Meningioma- a rare noncancerous tumor developing in the protective
membranes covering the brain called the meninges; can cause headaches and problems with vision and mental function

Meningitis- inflammation of the meninges; usually caused by infection by a microorganism (meningitis caused by bacteria is life-threatening; viral meningitis is milder)

Meningocele- a protrusion of the meninges through an opening in the skull or spinal cord due to a genetic defect

Meniscectomy- surgical removal of all or part of a cartilage disk from a joint

Meniscus- a crescent-shaped pad of cartilage in joints that helps to reduce friction

Menopause- the period in a woman's life when menstruation stops, resulting in a reduced production of estrogen and cessation of egg production

Menorrhagia- excessive loss of blood during menstruation, which can be caused by disorders of the uterus

Menstrual cycle- the periodic discharge of blood and mucosal tissue from the uterus, occurring from puberty to menopause in a woman who is not pregnant

Menstruation- the shedding of the lining of the uterus during the menstrual cycle

Mesenteric infarction- death of tissue in the intestine due to lack of blood supply to that tissue

Mesenteric lymphadenitis- inflammation of lymph nodes in an abdominal membrane

Mesothelioma- a cancerous tumor occurring in the lining of the lungs and chest cavity, often associated with exposure to asbestos dust

Mesothelium- a tissue layer that lines the heart, abdomen, chest cavity, and lungs

Messenger RNA- an RNA molecule that transports the information stored in DNA out of a cell's nucleus in order to make proteins

Metabolic rate- the speed at which the body uses energy

Metabolism- a general term for all of the chemical processes that occur in the body

Metabolite- any substance that takes part in a chemical reaction in the body

Metastasis- the spreading of a cancerous tumor to another part of the body through lymph, blood, or across a cavity; also sometimes refers to a tumor that has been produced in this way

Metered-dose inhaler- an inhaler that gives a specific amount of medication
with each use

Microbe- another term for a microorganism, especially one that causes disease

Microbiology- the study of microorganisms

Microcephaly- an abnormally small head

Microdiskectomy- surgical removal of the protruding part of a prolapsed disk

Microorganism- any tiny, single-celled organism (such as a bacterium, virus, or fungus)

Microsurgery- a surgical technique that uses a special binocular microscope to operate on tiny, delicate, or hard-to-reach tissues

Micturition syncope- fainting or feeling weak while standing at the toilet; caused by an abnormal heartbeat or a drop in blood pressure

Middle ear- the small cavity between the eardrum and inner ear; contains three tiny, linked bones that transmit sound to the inner ear

Middle ear effusion- the buildup of fluid in the middle ear, which can affect hearing

Midwifery- a profession concerned with providing care to a mother and baby during pregnancy and childbirth

Migraine- a severe headache, usually accompanied by vision problems and/or nausea and vomiting, and that typically recurs

Mineral- a substance that is a necessary part of a healthy diet (such as
potassium, calcium, sodium, phosphorus, and magnesium)

Minipill- an oral contraceptive containing only the synthetic hormone progesterone (birth control pills contain estrogen and progesterone)

Miotic- a drug that causes the pupil to constrict

Miscarriage- expulsion of a fetus before it has developed sufficiently to survive on its own

Mites- small eight-legged animals, many of which burrow and feed on blood

Mitosis- the process by which most cells divide in order to reproduce

Mitral insufficiency- a problem with the ability of the mitral valve in the heart to close, which causes the heart to pump harder and reduces its efficiency

Mitral stenosis- a condition in which the mitral valve in the heart becomes narrowed, making the heart work harder to pump blood; can lead to symptoms such as shortness of breath

Mitral valve- the valve in the heart that allows blood to flow from the left atrium to the left ventricle, but prevents blood from flowing back in

Mitral valve prolapse- a common condition in which the mitral valve in the heart is deformed, causing blood to leak back across the valve; characterized by a heart murmur and sometimes chest pain and disturbed heart rhythm

Modified radical mastectomy- a treatment for breast cancer in which the entire breast, a section of the chest muscle, and lymph nodes in the chest and underarm are removed

Molar tooth- large, strong teeth at the back of the jaw, primarily used to grind food

Mole- a brown to dark-brown spot on the skin that can be flat or raised

Molecule- the smallest unit of a substance that possesses its characteristics

Molluscum contagiosum- a viral infection that causes white bumps on the skin; usually clears up in a few months

Mongolian spot- a brown to blue-black spot on the lower back and buttocks
at birth, caused by a concentration of pigment-producing cells; usually disappears
by the age of 3 or 4 years

Monoamine oxidase inhibitor antidepressant- a substance that works by stopping an enzyme that breaks down stimulating chemicals in the brain; used to treat depression

Monoclonal antibodies- an antibody that is produced in the laboratory so that
it will react with only one specific foreign protein; used to help diagnose certain kinds
of cancer

Mononucleosis- an infection caused by a virus that invades a type of white
blood cell called a monocyte, causing fever, sore throat, and swollen lymph nodes

Monounsaturated fat- a type of fat that is thought to be beneficial in the prevention of coronary heart disease; found in foods such as olive oil and peanut oil

Morbidity- the state of being ill or having a disease

Morning sickness- nausea and vomiting experienced early in a pregnancy, affecting about half of all pregnant women

Mortality- the death rate, measured as the number of deaths per a certain population; may describe the population as a whole, or a specific group within a population (such as infant mortality)

Motor nerve- a nerve that carries messages to a muscle that cause the muscle to contract

Motor neuron disease- degeneration of the nerves in the spinal cord and brain that are responsible for muscle movement, causing weakness and muscle
deterioration

Mouth-to-mouth resuscitation- a method of artificial breathing in which someone rhythmically forces air into the lungs of a person who has stopped
breathing

MRI- see Magnetic resonance imaging

MS- see Multiple sclerosis

Mucocele- a sac or body cavity that is swollen because of the production of mucus by the cells in its lining

Mucolytic- a drug that lessens the sticky quality of phlegm and makes it easier to cough up

Mucous membrane- the soft, pink layer of cells that produce mucus in order to keep body structures lubricated; found in structures such as the eyelids, respiratory tract, and urinary tract

Mucus- a slippery fluid produced by mucous membranes that lubricates and protects the internal surfaces of the body

Multi-infarct dementia- dementia caused by multiple strokes

Multiple-gated acquisition scan- a technique for evaluating heart efficiency by measuring blood flow into and out of the heart

Multiple myeloma- a cancer that causes uncontrolled production of white blood cells in the bone marrow

Multiple pregnancy- the presence of more than one fetus in the uterus, such as occurs with twins

Multiple sclerosis- a disease in which the protective coverings (myelin) of nerve fibers in the brain are gradually destroyed; symptoms vary from numbness to paralysis and loss of control of bodily function

Mumps- a viral infection that causes inflammation of salivary glands; primarily affects children

Murmur- a characteristic sound (heard through a stethoscope) of blood flowing irregularly through the heart; can be harmless or may be an indication of disease

Muscle fibers- specialized, contracting cells that are bundled together to form muscles

Muscle relaxants- a group of drugs used to relieve muscle spasm and to treat conditions such as arthritis, back pain, and nervous system disorders such as stroke and cerebral palsy

Muscle tone- the natural tension in resting muscles

Muscle wasting- the degeneration of a muscle (loss of bulk), caused by disease or starvation

Muscular dystrophy- a rare genetic disorder in which muscles degenerate gradually and strength is lost

Mutagen- anything that can increase the rate of abnormal change in cells, which can lead to cancer

Mutation- a change in the genetic information within a cell

Myalgia- the medical term for muscle pain

Myasthenia gravis- a disease in which the muscles, mainly those in the face, eyes, throat, and limbs, become weak and tire quickly; caused by the body's
immune system attacking the receptors in the muscles that pick up nerve impulses

Mycobacterium- a type of slow-growing bacterium; resistant to the body's defense mechanisms and are responsible for diseases such as tuberculosis and
leprosy

Mycoplasma- the smallest free-living microorganisms

Mycosis- any disease caused by a fungus

Mydriatic- a drug that causes the pupil to dilate (widen)

Myelin sheath- the fat- and protein-containing material that surrounds and protects some nerves

Myelitis- inflammation of the spinal cord, which can cause headaches, fever, muscle stiffness, pain, weakness, and eventually paralysis

Myelocele- protrusion of the spinal cord and its coverings out from the spine;
one of the more severe forms of spina bifida

Myeloma- a cancer affecting cells in the bone marrow; sometimes used as an abbreviation for multiple myeloma

Myelosclerosis- buildup of fibrous connective tissue in the bone marrow, affecting the production of blood components

Myocardial infarction- the death of an area of heart muscle as a result of being deprived of its blood supply; characterized by severe pain in the chest; commonly called a heart attack

Myocarditis- inflammation of the heart muscle, which can be caused by a virus, certain drugs, or radiation therapy

Myocardium- the medical term for heart muscle

Myomectomy- the surgical removal of a noncancerous tumor from muscle

Myopathy- a muscle disease, usually one that results in the deterioration of
muscle

Myopia- the medical term for nearsightedness

Myositis- muscle inflammation, causing pain and weakness

Myringotomy- a surgical opening in the eardrum that allows for drainage

Myxoma- a noncancerous tumor made of mucous material and fibrous
connective tissue