Glossary of Medical Terms

Last Reviewed: February 27, 2018

Abaxial: situated out of or directed away from the axis; lying outside the axis of any body or part; situated at the opposite extremity of the axis of a part.

Adenosis: 1) A rarely used term for a more or less generalized glandular disease; 2) Glandular tissue in one or more sites in which it is not usually found.

Alkaline phosphatase: any of the phosphatases that are optimally active in alkaline medium and occur in especially high concentrations in bone, the liver, the kidneys, and the placenta.

Alopecia: baldness or absence of hair from skin areas where it is normally present.

Anaplasia: reversion of cells to a more primitive or undifferentiated form.

Anemia: Any condition in which the number of red blood cells per mm3, the amount of hemoglobin in 100 ml of blood, and/or the volume of packed red blood cells per 100 ml of blood are less than normal; clinically, generally pertaining to the concentration of oxygen-transporting material in a designated volume of blood, in contrast to total quantities as in oligocythemia, oligochromemia, and oligemia. Anemia is frequently manifested by pallor of the skin and mucous membranes, shortness of breath, palpations of the heart, soft systolic murmurs, lethargy, and fatigability.

Anisokaryosis: variation in size of cell nuclei, greater than the normal range for a tissue.

Annular: ring-like.

Apocrine gland: a gland whose secretory product includes and apical portion of the secretory cell such as the secretion of lipid droplets in lactation.

Appendicular skeleton: the bones of the limbs including the shoulder and pelvic girdles.

Arrector pili muscles: bundles of smooth muscle fibers, attached to the deep part of the hair follicles, passing outward alongside the sebaceous glands to the papillary layer of the dermis; they act to pull the hairs erect, causing "goose bumps" or "goose flesh" (cutis anserina) in humans but increasing depth (efficiency) of fur/hair coats of most animals.

Atrophic: decrease in size or wasting away of a body part or tissue.

Atypia: state of being not typical.

Axial skeleton: articulated bones of head and vertebral column, i.e., head and trunk, as opposed to the appendicular skeleton, the articulated bones of the upper and lower limbs.

Benign: denoting the mild character of an illness or the nonmalignant character of a neoplasm.

Bulla/Bullae: a large vesicle or blister on the skin.

Cancellous bone: bone in which the spicules or trabeculae form a three-dimensional latticework (cancellus) with the interstices filled with embryonal connective tissue or bone marrow.

Circumscribed: bounded by a line; limited or confined.

Cloudy swelling: swelling of cells due to injury to the membranes affecting ionic transfer; causes an accumulation of intracellular water (Synonym: Hydropic degeneration).

Coalesce: to grow together.

Colostrum: milk secreted for a few days after parturition and characterized by high protein and antibody content.

Congestion: presence of an abnormal amount of fluid in the vessels or passages of a part or organ; especially, of blood due either to increased influx or to an obstruction to outflow.

Contralateral: relating to the opposite side, as when pain is felt or paralysis occurs on the side opposite to that of the lesion.

Costochondral junction: the junction of a rib and costal (rib) cartilage.

Cryptorchid: one affected with cryptorchidism.

Cryptorchidism: failure of one or both of the testes to descend.

Cutaneous: relating to the skin.

Dermis: a connective tissue layer of the skin located below the epidermis. It contains blood vessels, lymphatic vessels, nerve endings, sweat and sebaceous glands.

Desmoplasia: fibroblast hyperplasia It results in a disproportionate amount of fibrous connective tissue. This is seen especially in the stroma of a carcinoma.

Direct bone formation: development of osseous tissue within mesenchymal tissue without prior cartilage formation, such as occurs in the frontal and parietal bones (Synonym: Intramembranous ossification).

Direct extension: spread of a disease into a tissue area from an adjacent lesion.

Distally: situated away from the point of attachment or origin or a central point especially of the body.

Eccentric nucleus: a nucleus that is located at the periphery of the cell, rather than being centrally located.

Endochondral ossification: formation of osseous tissue by the replacement of calcified cartilage; long bones grow in length by endochondral ossification at the epiphysial cartilage plate where osteoblasts form bone trabeculae on a framework of calcified cartilage (Synonym: Indirect bone formation).

Endocrine gland: organs or glands that secrete regulatory substances directly into the circulation and not through a duct.

Endophytic: a tumor which grows inward in finger-like projections from the superficial epidermis.

Endosteum: a layer of vascular connective tissue and cells lining the inner surface of bone in the central medullary cavity.

Epidermis: the epidermis is the outer, protective, non-vascular layer of the skin. It contains 5 different cell layers, which will be listed from most superficial to deep: stratum corneum (keratin layer), stratum lucidum (clear layer), stratum granulosum (granular layer), stratum spinosum (prickle cell layer) and stratum basale (basal cell layer). The stratum lucidum may at times be absent in certain parts of the body.

Epiphyseal closure: the process during bone maturation in which the epiphysis fuses with the diaphysis (Synonym: Physeal closure). Lengthwise bone growth can occur until epiphyseal closure has occurred.

Epiphysis: A part of a long bone developed from a center of ossification distinct from that of the shaft and separated at first from the latter by a layer of cartilage (Plural: Epiphyses).

Epithelioid: resembling or having some of the characteristics of epithelium.

Epithelium: the purely cellular avascular layer covering all free surfaces, cutaneous, mucous, and serous, including the glands and other structures derived therefrom.

  • Columnar Epithelium: of, relating to, being, or composed of tall narrow somewhat cylindrical or prismatic epithelial cells.
  • Cuboidal Epithelium: composed of nearly cubical cells.
  • Stratified Squamous Epithelium: composed of layers of scale-like cells.

Erythema: redness of the skin caused by dilation and congestion of the capillaries, often a sign of inflammation or infection.

Exocytosis: the process whereby secretory granules or droplets are released from a cell; the membrane around the granule fuses with the cell membrane, which ruptures, and the secretion is discharged.

Exophytic: a neoplasm or lesion which grows outward from the epithelial surface.

Flocculent: resembling wool especially in loose fluffy organization; resembling tufts of cotton or wool; denoting a fluid, such as the urine, containing numerous shreds or fluffy particles of gray-white or white mucus or other material.

Frond: a large leaf, usually with many divisions.

Fusiform: spindle-shaped; tapering at both ends.

Gynecomastia/Gynecomasty: excessive development of the male mammary glands, due mainly to ductal proliferation with periductal edema; frequently secondary to increased estrogen levels, but mild gynecomastia may occur in normal adolescence.

Hematogenous: involving, spread by, or arising in the blood.

Hematopoietic: pertaining to or related to the formation of blood cells.

Holocrine gland: a gland whose secretion consists of disintegrated cells of the gland itself, ex., a sebaceous gland.

Homogenous: of uniform structure or composition throughout.

Hyalinized: relating to the formation of hyalin.

Hyalin: a clear, eosinophilic, homogenous substance occurring in cellular degeneration.

Hydropic degeneration: swelling of cells due to injury to the membranes affecting ionic transfer; causes an accumulation of intracellular water (Synonym: Cloudy swelling).

Hyperchromatic: 1) abnormally highly colored, excessively stained, or over pigmented; 2) showing increased chromatin.

Hyperkeratosis: hypertrophy of the stratum corneum within the epidermis.

Hyperplastic: an abnormal increase in the number of cells in an organ or tissue.

Hypertrophy: an increase in the size of cells in an organ or tissue.

Idiopathic: relating to a disease where the cause is unknown; denoting a disease of unknown cause.

Immunophenotype: the immunochemical and immunohistological characteristics of a cell or group of cells.

Inclusion bodies: distinctive structures frequently formed in the nucleus or cytoplasm (occasionally in both locations) in cells affected with certain filtrable viruses; may be demonstrated by means of various stains, especially Mann eosin methylene blue or Giemsa techniques and visible by light microscopy. Nuclear inclusion bodies are usually acidophilic and are of two morphologic types: 1) granular, hyaline, or amorphous bodies of various sizes; 2) more circumscribed bodies frequently with several in the same nucleus (and no reaction in adjacent tissues). Cytoplasmic inclusion bodies may be: 1) acidophilic, relatively large, spherical or ovoid, and somewhat granular, as in variola or vaccinia, or rabies; 2) basophilic, relatively large complex combinations of viral and cellular material. In some instances, inclusion bodies are known to be infective and probably represent aggregates of virus particles in combination with cellular material, whereas others are apparently not infective and may represent only abnormal products formed by the cell in response to injury.

Indirect bone formation: formation of osseous tissue by the replacement of calcified cartilage; long bones grow in length by endochondral ossification at the epiphysial cartilage plate where osteoblasts form bone trabeculae on a framework of calcified cartilage (Synonym: Endochondral ossification).

Infundibulum/Infundibular: a funnel or funnel-shaped structure or passage.

Intramembranous ossification: development of osseous tissue within mesenchymal tissue without prior cartilage formation, such as occurs in the frontal and parietal bones (Synonym: Direct bone formation).

Involution: return of an enlarged organ to normal size.

Leukopenia: any situation in which the total number of leukocytes (white blood cells) in the circulating blood is less than normal for that species.

Lipoblast: an embryonic fat cell.

Lamellar: arranged in thin plates or scales.

Lumen/Lumina: the interior space of a tubular structure, such as an artery or the intestine.

Lymphangiectasia: dilation of lymphatic vessels found within tissues. This process may result in lymphangioma.

Lymphatics: small, thin channels similar to blood vessels. They do not carry blood, but collect and carry tissue fluid from the body to ultimately drain back into the blood stream.

Lytic: pertaining to lysis; used colloq. as an abbreviation for osteolytic.

Malignant: this term may mean a more severe or frequently fatal form of an illness. Also, when referring to a neoplasm, it is locally invasive, is destructive and metastatic.

Metacarpal bones: five long bones (numbered I to V, beginning with the bone on the radial or thumb side) forming the skeleton of the metacarpus; they articulate with the bones of the distal row of the carpus and with the five proximal phalanges.

Metaphyseal: relating to a metaphysis.

Metaphysis: a conical section of bone between the epiphysis and diaphysis of long bones (Plural: Metaphyses).

Metaplasia: abnormal transformation of an adult, fully differentiated tissue of one kind into a differentiated tissue of another kind; an acquired condition, in contrast to heteroplasia; transformation of one tissue into another.

Metaplastic: pertaining to metaplasia.

Metatarsal bone: the five long bones numbered I to V beginning with the bone on the medial side forming the skeleton of the anterior portion of the foot, articulating posteriorly with the three cuneiform and the cuboid bones, anteriorly with the five proximal phalanges.

Micelle: any water-soluble aggregate, spontaneously and reversibly, formed from amphophile (molecule having a polar water-soluble group attached to a water-insoluble hydrocarbon chain) molecules.

Microenvironment: a small or relatively small usually distinctly specialized and effectively isolated habitat (as a forest canopy) or environment (as of a nerve cell).

Mitotic activity/Mitotic figures: the microscopic appearance of cells undergoing mitosis (cellular division).

Monomorphic: having but a single form, shape, or structural pattern; unchangeable in shape.

Moth-eaten pattern: a pattern of bone destruction characterized by multiple small holes in the bone.

Multicentric: a tumor consisting of a primary tumor with other cancerous growths nearby in surrounding tissues.

Myoepithelium: spindle-shaped, contractile, smooth muscle-like cells of epithelial origin that are arranged longitudinally or obliquely around sweat glands and the secretory alveoli of the mammary gland; stellate myoepithelial cells occur around lacrimal and some salivary gland secretory units.

Necrosis: pathologic death of one or more cells, or of a portion of tissue or organ, resulting from irreversible damage.

Neurohypophysis: portion of the pituitary gland composed of the infundibulum and the nervous lobe of the hypophysis.

Neutral lipid: a triester of fatty acid and glycerol; triglyceride.

Non-pruritic: not itchy.

Orthokeratotic: the formation of an anuclear keratin layer within the normal epidermis.

Osteoid: newly formed organic bone matrix prior to calcification.

Osseous: bony, of bone-like consistency or structure.

Osteoblast: a bone-forming cell that is derived from mesenchymal osteoprogenitor cells and forms an osseous matrix in which it becomes enclosed as an osteocyte.

Osteoclast: a large multinucleated cell, possibly of monocytic origin, with abundant acidophilic cytoplasm, functioning in the absorption and removal of osseous tissue.

Osteocyte: a cell of osseous tissue that occupies a lacuna and has cytoplasmic processes that extend into canaliculi and make contact by means of gap junctions with the processes of other osteocytes.

Oxytocin: a neurohypophysial hormone that causes myometrial contractions at term and promotes milk release during lactation.

Palisading cells: in pathology, a row of elongated cells parallel to each other.

Palliative: reducing the severity of; denoting the alleviation of symptoms without curing the underlying disease.

Palpation: a simple technique in which the doctor presses lightly on the surface of the body to feel the organs and tissues underneath.

Parturition: the action or process to giving birth to offspring.

Peduncle: a narrow stalk by which a tumor or polyp is attached.

Pedunculated: having, growing on, or being attached by a peduncle.

Periosteum: the thick fibrous membrane covering the entire surface of a bone except its articular cartilage. In young bones, it consists of two layers: an inner cellular layer that is osteogenic, forming new bone tissue, and an outer fibrous connective tissue layer conveying the blood vessels and nerves supplying the bone; in older bones, the osteogenic layer is reduced.

Perivascular: an area surrounding a blood or lymph vessel.

Permeative pattern: a pattern of bone destruction characterized by tiny holes that run together.

Phalanx: one of the long bones of the digits, 14 in number for each hand or foot, two for the thumb or great toe, and three each for the other four digits; designated as proximal, middle, and distal, beginning from the metacarpus (Plural: Phalanges).

Physeal closure: the process during which the epiphyses unite with the metaphysis (Synonym: Epiphyseal closure). Lengthwise bone growth can occur until physeal closure has occurred.

Pituitary gland: an unpaired compound gland suspended from the base of the hypothalamus by a short extension of the infundibulum, the infundibular or pituitary stalk.

Pleomorphic/pleomorphism: cells of various size and shape.

Polyp: a general descriptive term used with reference to any mass of tissue that bulges or projects outward or upward from the normal surface level, thereby being macroscopically visible as a hemispheroidal, spheroidal, or irregular round-like structure growing from a relatively broad base or a slender stalk; polyps may be neoplasms, foci of inflammation, degenerative lesions, or malformations.

Polypoid: resembling a polyp in gross features.

Proximally: next to or nearest the point of attachment or origin, a central point, or the point of view; especially: located toward the center of the body.

Reticulum fibers: a netlike formation or structure; a network of fibers.

Sclerosis: pathological hardening of tissue especially from overgrowth of fibrous tissue or increase in interstitial tissue.

Septum: a dividing wall or membrane especially between bodily spaces or masses of soft tissue; a thin wall dividing two cavities or masses of softer tissue (Plural: Septa).

Sessile: attached directly by the base: not raised upon a stalk or peduncle; having a broad base of attachment; not pedunculated.

Shadow cells: immature leukocytes of any type that have undergone partial breakdown during preparation of a stained smear or tissue section, because of their greater fragility; smudge cells are seen in largest numbers in chronic lymphocytic leukemia (Synonym: Smudge cells).

Spindle-shaped: fusiform; tapering at both ends.

Spongiosa: the part of a bone (as much of the epiphyseal area of long bones) made up of spongy cancellous bone.

Storiform pattern: having a cartwheel pattern, as of spindle cells with elongated nuclei radiating from a center.

Subcutaneous tissue: a layer of loose, irregular connective tissue found beneath the skin. Fat cells are usually found in this tissue, except in the auricles, eyelids, penis, and scrotum.

Synovioblast: a fibroblast of a synovial membrane.

Synovial membrane: the connective tissue membrane that lines the cavity of a synovial joint and produces the synovial fluid; it lines all internal surfaces of the cavity except for the articular cartilage of the bones.

Thrombocytopenia: a condition in which there is an abnormally small number of platelets in the circulating blood.

Trabeculae: any supportive strands of connective tissues which project into an organ and provide a structural framework for that organ.

Trabecular bone: bone in which the spicules or trabeculae form a three-dimensional latticework (cancellus) with the interstices filled with embryonal connective tissue or bone marrow.

Tumor margin: the outside limit or edge of a tumor.

Ulcer/Ulcerated: a lesion through the skin or a mucous membrane resulting from loss of tissue, usually with inflammation.

Vesicle/Vesicular: a small circumscribed elevation in the skin containing serum.

Glossary References

  1. Part I: Evaluation of the plain radiograph. Retrieved July 27, 2005.
  2. Dorlands Medical Dictionary. Retrieved July 27, 2005.
  3. Ganong, W.F. Hormonal control of calcium metabolism and the physiology of bone. Chapter 21 in Review of medical physiology 22nd ed. (pp. 382-395). Lange Medical Books/McGraw-Hill, Medical Publishing Division, New York, New York, USA.
  4. Medline Plus Merriam-Webster Online Medical Dictionary Retrieved July 26, 2005.
  5. Merriam-Webster Online Dictionary. Retrieved May through July, 2005.
  6. Pugh, M.B., Werner, B., Filardo, T.W., Binns, P.W., Francis,L.G., Lukens, R., Montgomery, B., Ferretti, B.L., Cadle, K.J, and Workman, D. (Eds.) (2000). Stedmans medical dictionary 27th ed. Lippincott, Williams, and Wilkins, Baltimore, Maryland, USA.
  7. Stedman's Online Medical Dictionary. Retrieved May through July, 2005.


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