Medical Terminology Glossary
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macrophage - a phagocytic cell derived from a monocyte; may be fixed or wandering

macula - discolored spot or colored area; a small, thickened region on the wall of the utricle and saccule, that serves as a receptor for static equilibrium

macula lutea - a yellow spot in the center of the retina

malaise - discomfort, uneasiness, & indisposition, often indicative of infection

malignant - referring to diseases that tend to become worse and cause death, especially the invasion and spreading of cancer

malignant melanoma - a usually dark, malignant tumor of the skin; contains melanin

malnutrition - state of poor nutrition that may be due to inadequate food intake, imbalance of nutrients, malabsoption of nutrients, inappropriate distribution of nutrients, increased nutrient requirements, increased nutrient losses, or overnutrition

mammary gland - a modified sudoriferous (sweat) gland of the female; it secretes milk for nourishment of the young

mammillary bodies - two small rounded bodies posterior to the tuber cinereum, involved in reflexes related to the sense of smell

mammography - procedure for imaging the breasts (xeromammography or film-screen mammography) to evaluate for breast disease or to screen for breast cancer

Marfan syndrome - inherited disorder that results in connective tissue abnormalities, especially in the skeleton, eyes, and cardiovascular system

marrow - soft, spongelike material in the cavities within bone; red marrow produces blood cells; yellow marrow is formed mainly of fatty tissue and has no blood-producing function

mastectomy - surgical removal of breast tissue

mastication - chewing

meatus - a passage or opening, especially in the external portion of a canal

mechanoreceptor - receptor that detects mechanical deformation of the receptor itself or adjacent cells; stimuli so detected include those related to touch, pressure, vibration, proprioception, hearing, equilibrium, and blood pressure

medial - nearer the midline of the body or a structure

medial lemniscus - a flat band of myelinated nerve fibers that extends through the medulla, pons, and midbrain; it terminates on the same side in the thalamus; sensory neurons in this tract transmit impulses for proprioception, fine touch, pressure, and vibration sensations

median aperture - one of the three openings in the roof of the fourth ventricle through which cerebrospinal fluid enters the subarachnoid space of the brain and spinal cord; also called the foramen of Magendie

mediastinum - a broad, median partition, actually a mass of tissue found between the pleurae of the lungs; it extends from the sternum to the vertebral column

medulla - an inner layer of an organ, such as the medulla of the kidneys

medulla oblongata - the most inferior part of the brain stem

medullary cavity - space within the diaphysis of a mature bone; it contains yellow marrow; also called the marrow cavity

medullary rhythmicity area - portion of the respiratory center in the medulla that controls the basic rhythm of respiration

meiosis - the type of cell division restricted to sex-cell production; involving two successive nuclear divisions, it results in daughter cells with the haploid (n) number of chromosomes

melanin - a dark (black, brown, or yellow) pigment found in some parts of the body, such as the skin

melanoblast - a precursor cell in the epidermis that gives rise to melanocytes, cells that produce melanin

melanocyte - a pigmented cell located between or beneath cells of the deepest layer of the epidermis; synthesizes melanin

melatonin - a hormone secreted by the pineal gland; may inhibit reproductive activities

membranous labyrinth - portion of the labyrinth of the inner ear that is located inside the bony labyrinth and separated from it by the perilymph; made up of the membranous semi-circular canals, the saccule and utricle, and the cochlear duct

menarche - beginning of the menstrual cycles

Meniere's syndrome - a type of labyrinthine disease characterized by fluctuating loss of hearing, vertigo, and tinnitus; due to an increased amount of endolymph that enlarges the labyrinth

meninges - three membranes covering the brain and spinal cord; include the dura mater, the arachnoid, and the pia mater; singular, meninx

meningitis - an inflammation of the meninges, most commonly the pia mater & the arachnoid

menopause - termination of menstrual cycles

menstrual cycle - a series of changes in the endometrium of a nonpregnant female; with each cycle, the lining is thickened and matured and is capable of supporting development of a fertilized ovum

menstruation - the periodic discharge of blood, tissue fluid, mucus, and epithelial cells form the uterus; it usually lasts for 5 days; it is caused by a sudden reduction in the levels of estrogens and progesterone; also called the menstrual phase or menses

merocrine gland - secretory cell that remains intact throughout the process of formation and discharge of the secretory products; e.g., the salivary and pancreatic glands

mesenchyme - an embryonic connective tissue from which all other connective tissues arise

mesentery - fold of peritoneum attaching the small intestine to the posterior abdominal wall

mesocolon - fold of peritoneum attaching the colon to the posterior abdominal wall

mesothelium - a layer of simple squamous epithelium that lines serous cavities

mesovarium - a short fold of peritoneum that attaches an ovary to the broad ligament of the uterus

metabolism - the sum total of all bio-chemical reactions that occur within an organism, including synthetic (anabolic) reactions as well as decomposition (catabolic) reactions

metacarpus - a collective term for the five bones making up the palm of the hand

metaphase - second stage of mitosis in which chromatid pairs line up on the equatorial plane of the cell

metaphysis - growing portion of a bone

metaplasia - the transformation of one cell into another

metarteriole - blood vessel that emerges from an arteriole, traverses a capillary network, and empties into a venule

metastasis - the spread of cancer to the surrounding tissues (local) or to other body sites (distant)

metatarsus - a collective term for the five bones located in the foot between the tarsals and the phalanges

micelle - spherical aggregate of bile salts that dissolves fatty acids and monoglycerides so that they can be transported into small intestinal epithelial cells

microcephalus - an abnormally small head; premature closing of the anterior fontanel so that the brain has insufficient room for growth, resulting in mental retardation

microfilament - rodlike cytoplasmic structure about 6nm in diameter; composes contractile LETTERs in muscle fibers (cells) and provides support, shape, and movement in nonmuscle cells

microglia - neuroglial cells that carry on phagocytosis; also called brain macrophages

microphage - any granular leucocyte that carries on phagocytosis, especially neutrophils and eosinophils

microtomography - a procedure that combines the principles of electron microscopy and computed tomography to produce highly magnified, three-dimensional images of living cells

microtrabeculae - three-dimensional mesh-work of fine filaments, ca. 10-15 nm in diameter, that hold together microfilaments, microtubules, and intermediate filaments constituting the microtrabecular lattice

microtubule - a cylindrical cytoplasmic structure, ranging in diameter from 18-30 nm and consisting of the protein tubulin; provides support, structure, and transportation

microvilli - the microscopic, fingerlike projections of cell membranes of small intestinal cells; they increase surface area for absorption

micturition - the act of expelling urine from the urinary bladder; also called urination

mineralocorticoids - a group of hormones of the adrenal cortex; they affect mineral and water balance

mitochondrion - a double-membrane bounded organelle that plays a central role in production of ATP; known as the powerhouse of the cell

mitosis - division of the cell nucleus involving distribution of two sets of replicated chromosomes into separate nuclei; ensures that each daughter nucleus has the same number and kind of chromosomes as the original parent nucleus

mitral stenosis - a narrowing of the mitral valve by scar formation or a congenital defect

Mittelschmerz - abdominopelvic pain that correlates with the time of release of a secondary oocyte from the ovary

modality - any of the specific sensory entities, such as vision, smell, or taste

modiolus - central pillar or column of the cochlea

molecule - the chemical combination of two or more atoms

monocyte - a type of white blood cell characterized by agranular cytoplasm; the largest of the leucocytes

mons pubis - the rounded, fatty prominence over the symphysis pubis, covered by coarse pubic hair

morbid - diseased; pertaining to disease

morula - a solid mass of cells produced by successive cleavages of a fertilized ovum a few days after fertilization

mucin - a protein found in mucus

mucosa - a membrane that lines a body cavity opening to the exterior; also called mucous membrane

mucous cell - a unicellular gland that secretes mucus; also called a goblet cell

multiple sclerosis - progressive destruction of myelin sheaths of neurons in the central nervous system, short-circuiting conduction pathways

muscarinic receptor - a receptor found on all effectors innervated by parasympathetic (& on some innervated by sympathetic) postganglionic axons; so named because the actions of acetylcholine (Ach) on such receptors are similar to those produced by application of muscarine

muscular dystrophies - several inherited muscle-destroying diseases, characterized by degeneration of the individual muscle fibers (cells), which leads to progressive atrophy of the skeletal muscle

muscularis - a muscular layer (coat or tunic) of an organ

muscularis mucosae - a thin layer of smooth muscle fibers (cells) located in the outermost layer of the mucosa of the gastrointestinal tract underlying the lamina propria of the mucosa

mutation - any chage in the sequence of bases in the DNA molecule resulting in a permanent alteration in some heritable characteristic

myasthenia gravis - weakness of skeletal muscles caused by antibodies directed against acetylcholine receptors; results in inhibition of muscle contraction

myelin sheath - a white, phospholipid, segmented covering, formed by neurolemmocytes (Schwann cells), around the axons and the dendrites of many peripheral neurons

myelography - introduction of a contrast medium into the subarachnoid space of the spinal cord to demonstrate tumors or herniated (slipped) discs within or near the spinal cord

myocardial infarction - gross necrosis of myocardial tissue due to interrupted blood supply; also called a heart attack

myocardium - the middle layer of the heart wall, made up of cardiac muscle, composing the bulk of the heart, and lying between the epicardium and the endocardium

myofibril - threadlike structure, running longitudinally through a muscle fiber (cell) and consisting mainly of thick myofilaments (myosin) and thin myofilaments (actin, troponin, tropomyosin)

myoglobin - the oxygen-binding conjugated protein present in the sarcoplasm of muscle fibers (cells); contributes the red color to muscle

myogram - the record or tracing produced by a myograph, the apparatus that measures and records the effects of muscular contractions

myology - the study of muscles

myometrium - the smooth muscle layer of the uterus

myopia - defect in vision so that objects can be seen clearly only when very close to the eyes; nearsightedness

myosin - the contractile protein making up the thick myofilaments of muscle fibers (cells)

myotonia - continuous muscle spasm; increased muscular irritability and tendency to contract, and lessened ability to relax

myxedema - condition caused by hypothyroidism during the adult years, characterized by swelling of facial tissues