Dictionary

Body systems

Anatomy and the conditions of each body system, from the heart and lungs to the skin.

macrophageA large white blood cell in the tissues that swallows and digests germs, dead cells and debris.

macular degenerationAn eye disease in which the macula, the center of the retina used for sharp, straight-ahead vision, slowly breaks down.

magnesium sulfate toxicityHarm from a blood magnesium level that rises too high, usually during magnesium sulfate treatment.

major depressive disorderA mental illness in which a person has a low mood or loses interest in almost everything for at least two weeks.

malformationA body part or organ that formed in an abnormal way before birth.

malignantCancerous: describing a tumor whose cells grow out of control, invade nearby tissue and can spread through the body.

malignant hyperthermiaA rare inherited reaction to certain general anesthesia drugs in which the muscles' metabolism speeds up out of control.

Mallory-Weiss tearA tear in the lining where the esophagus meets the stomach.

malnutritionPoor nutrition from too little, too much or the wrong balance of nutrients.

mandibleThe lower jawbone, the only bone of the skull that moves.

maniaA period of unusually high energy, mood and activity that is clearly different from the person's usual self.

marrowThe soft tissue inside bones; red marrow makes blood cells and yellow marrow stores fat.

mast cellAn immune cell in the tissues that releases histamine and other chemicals during allergic reactions and inflammation.

mastectomySurgery to remove all or part of a breast.

mastitisInflammation of the breast tissue, often with infection, most common in people who are breastfeeding.

maternalHaving to do with a mother, or with a woman during pregnancy, birth and the weeks after.

maturationThe process of becoming fully grown or developed.

McBurney pointA spot on the lower right abdomen about one-third of the way from the front of the hip bone to the navel.

mean arterial pressureThe average pressure in the arteries over one heartbeat, used as a measure of how well blood reaches the organs.

measlesA very contagious illness caused by the measles virus; also called rubeola.

meatusAn opening or passage in the body, such as the urinary opening or the ear canal.

mechanical ventilationBreathing support from a machine, a ventilator, that pushes air into the lungs through a tube or a mask.

meconiumA newborn's first stools: thick, sticky and dark green to black.

medialToward the middle line of the body.

medullaThe inner part of an organ; most often the medulla oblongata, the lowest part of the brainstem.

meiosisCell division that makes eggs or sperm, each with half the usual number of chromosomes.

melaninThe dark pigment that gives color to the skin, hair and eyes.

melanocyteA cell in the bottom layer of the skin's outer layer that makes melanin, the pigment that gives skin and hair their color.

melanomaA cancer that starts in melanocytes, the cells that give skin its color.

melatoninA hormone made by the pineal gland in the brain, mostly at night, that helps control the sleep-wake cycle.

melenaBlack, sticky stool that looks like tar.

membraneA thin layer of tissue that covers, lines or separates parts of the body, or the outer layer of a cell.

menarcheA person's first menstrual period.

meningesThe three thin layers of tissue that cover and protect the brain and spinal cord.

meningitisInflammation of the meninges, the membranes that cover the brain and spinal cord.

menopauseThe time in a woman's life when menstrual periods stop for good, counted once there has been no period for 12 months in a row.

menorrhagiaMenstrual periods that are very heavy or last longer than usual.

menstrualHaving to do with menstruation, the monthly shedding of the lining of the uterus as bleeding from the vagina.

menstrual cycleThe monthly series of hormone-driven changes in the ovaries and uterus that prepare the body for possible pregnancy.

menstrual periodThe days each month when the lining of the uterus is shed and passes out of the vagina as bleeding.

menstruationThe monthly shedding of the lining of the uterus, which leaves the body as blood through the vagina.

mental illnessA health condition that changes a person's thinking, mood or behavior and causes distress or problems in daily life.

mental statusA person's state of mind at a given time: how alert they are, what they know and how they think, speak and behave.

metabolicRelating to metabolism, the chemical processes that turn food into energy and build and break down substances in the body.

metabolic acidosisA state in which the blood is too acidic because the body has too much acid or has lost too much bicarbonate.

metabolic alkalosisAn acid-base imbalance in which the blood holds too much bicarbonate, so its pH rises above 7.45.

metabolic syndromeA group of risk factors, such as a large waist, high blood pressure, high blood sugar and abnormal blood fats, occurring together.

metabolismAll the chemical processes in the body's cells that make energy, build tissue and break substances down.

metastasisThe spread of cancer cells from where the cancer started to other parts of the body.

MHAn abbreviation with more than one meaning, most often mental health or malignant hyperthermia; the setting shows which.