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Medical and Healthy Living Glossary - M

This page of our online glossary of medical and healthy living is for medical and healthy living terms beginning with the letter 'M'.

• Macronutrients - A general term for those nutrients that the body requires in relatively large amounts to produce energy, such as carbohydrates, proteins and fats.
• Malaria - A tropical disease caused by the parasite Plasmodium, which enters the body after a bite from a female mosquito. Malaria is a recurrent disease. It produces headaches, shivering, vomiting, sweating and sometimes hallucinations which are caused by toxins coming from the waste of the parasite Plasmodium in the blood.
• Marrow (Bone Marrow) - The soft inner part of long bones, where blood cells are created.
• Measles (Rubeola) - An extremely infectious disease of children caused by a virus and characterized by the presence of a red rash. It occurs in epidemics every two or three years. After an incubation period of 10-15 days, the initial symptoms are those of a cold, with coughing, sneezing and high fever. It is at this stage that the disease is most infectious and spreads from one child to another in airborne droplets before measles has been diagnosed. This is the main factor responsible for the epidemic nature of the disease. Small red spots with a white centre (known as Koplik spots) may appear in the mouth on the inside of the cheeks. Then a characteristic rash develops on the skin, spreading from behind the ears and across the face and also affecting other areas. The spots and fever gradually disappear and no marks are left on the skin, most children making a complete recovery. However, complications can occur, particularly pneumonia and middle ear infections. Measles can be a serious disease as it weakens the body’s resistance to other diseases, particularly bronchitis and ear infections which can result in deafness. It can be prevented by immunisation. If caught by an adult, measles can be very serious.
• Medulla - The soft, inner part of some glands, organs, hair, and bones.
• Melanoma - A tumor formed of dark pigmented cells. ABCD is what you must remember if you want to know if there is a risk that you are developing a melanoma: A = Asymmetry, ie. the two sides are not quite the same, and the mole does not have a perfect shape; B = Border, the edge becomes irregular; C = Color, there may be a change in colour, with the mole becoming darker; D = Diameter, any increase in diameter should be considered an important factor. Among other features, pain is rarely an important feature but itching could be one.
• Membrane - A thin lining or covering layer of tissue which lines or covers an organ.
• Meninges - Three membranes that surround the brain and the spinal cord. The meninges are divided into three layers: the tough outer layer (dura mater) which protects the brain and spinal cord; the middle layer (arachnoid mater) and the delicate inner layer (pia mater) which contains the blood vessels.
• Meningitis - The inflammation of the meninges, causing a person to have violent headaches, fever, and stiff neck muscles, and sometimes to become delirious. Meningitis is a serious viral or bacterial disease which can cause brain damage and even death. The bacterial form can be treated with antibiotics.
• Metabolism - A term which covers all the chemical and physical changes which are continually taking within the body to keep it alive and functioning. Metabolic processes can be divided into two broad categories - reactions that break down complex chemicals into simpler substances in order to release energy (catabolism), and those that build up complex substances in the organs and tissues, to store energy or to provide for the body's growth and repair (anabolism). Naturally thin people will often have a fast metabolism.
• Metabolite - A substance produced by metabolism, or a substance taken into the body in food and then metabolised.
• Microbe - A microorganism which may cause disease and which is only visible through a microscope. For example, bacteria, viruses, and protozoa.
• Microbial Contamination - In the case of food, food tainted with disease-carrying bacteria, parasites, or viruses.
• Microgram (mcg or µg) - A unit of weight equivalent to one-millionth of a gram or a thousandth of a milligram.
• Micronutrients - Vitamins and minerals are together called micronutrients, because although they are essential for good health, the body requires them only in very small amounts.
• Microorganisms - Life-forms only visible through a microscope. For example, bacteria, viruses, protozoa, some algae and fungi.
• Milligram (mg) - One-thousandth of gram or 1000 micrograms.
• Millilitre or Milliliter (ml) - One-thousandth of a litre. There are 5 ml in a teaspoon, 15 ml in a tablespoon and around 600 ml in a pint.
• Mitochondrion - A tiny structure found inside cells where energy-producing chemical reactions take place.
• Monocyte - The largest type of white blood cell (leucocyte) found in the blood and lymph fluids. It has a nucleus shaped like a kidney and destroys foreign bodies such as bacteria and tissue particles.
• Monounsaturated Fat (Monounsaturated Fatty Acids) - A form of fat which is thought to protect against heart disease and atherosclerosis. Olive oil, peanuts and avocados areall rich in monounsaturates.
• Morula - Ball of cells formed an early stage in the development of an embryo when a fertilized egg starts to divide.
• Motor Nerve (Efferent Nerve) - A nerve that carry signals from the central nervous system to the muscles and cause movements.
• Motor Neurone Disease - A disease which affects the nerve cells which control the movement of the muscles. Motor neurone disease has three forms: progressive muscular atrophy (PMA), which affects movements of the hands, lateral sclerosis, and bulbar palsy, which affects the mouth and throat.
• Mucous Membrane or Mucosa - The wet membrane that lines the mouth, nasal sinuses, stomach, intestines and many other parts of the body. It secretes mucus, which acts as a protective barrier and lubricant, as well as a medium for carrying enzymes.
• Mycotoxins - Toxins which are produced by fungi.
• Myofibre - Bundles of cells found in muscle fibre.
• Myofibril - Muscle-building blocks made up of two proteins, myosin and actin.