Micr: From 1 Different Sources
(micro-) combining form denoting 1. small size. 2. one millionth part.
See BACTERIA; MICROBIOLOGY.... microbe
Disease of the CAPILLARIES.... microangiopathy
An optical instrument comprising adjustable magnifying lenses that greatly enlarge a small object under study – for example, an insect, blood cells, or bacteria. Some microscopes use electron beams to magnify minute objects such as chromosomes, crystals, or even large molecules. Optical microscopes are also used for MICROSURGERY when the area being operated on is otherwise inaccessible: for example, in eye and inner ear surgery; for the removal of tumours from the brain or spinal cord; and for resuturing damaged blood vessels and nerves.... microscope
The conduct of very intricate surgical operations using specially re?ned operating microscopes (see MICROSCOPE) and miniaturised precision instruments – for example, forceps, scalpels, scissors, etc. Microsurgery is used in previously inaccessible areas of the brain, eye, inner ear and spinal cord, as well as in the suturing of severed nerves and small blood vessels following traumatic injuries to the limbs or ?ngers. The technique is also used to reverse VASECTOMY.... microsurgery
The study of all aspects of micro-organisms (microbes) – that is, organisms which individually are generally too small to be visible other than by microscopy. The term is applicable to viruses (see VIRUS), BACTERIA, and microscopic forms of fungi, algae, and PROTOZOA.
Among the smallest and simplest microorganisms are the viruses. First described as ?lterable agents, and ranging in size from 20–30 nm to 300 nm, they may be directly visualised only by electron microscopy. They consist of a core of deoxyribonucleic or ribonucleic acid (DNA or RNA) within a protective protein coat, or capsid, whose subunits confer a geometric symmetry. Thus viruses are usually cubical (icosahedral) or helical; the larger viruses (pox-, herpes-, myxo-viruses) may also have an outer envelope. Their minimal structure dictates that viruses are all obligate parasites, relying on living cells to provide essential components for their replication. Apart from animal and plant cells, viruses may infect and replicate in bacteria (bacteriophages) or fungi (mycophages), which are damaged in the process.
Bacteria are larger (0·01–5,000 µm) and more complex. They have a subcellular organisation which generally includes DNA and RNA, a cell membrane, organelles such as ribosomes, and a complex and chemically variable cell envelope – but, unlike EUKARYOTES, no nucleus. Rickettsiae, chlamydia, and mycoplasmas, once thought of as viruses because of their small size and absence of a cell wall (mycoplasma) or major wall component (chlamydia), are now acknowledged as bacteria; rickettsiae and chlamydia are intracellular parasites of medical importance. Bacteria may also possess additional surface structures, such as capsules and organs of locomotion (?agella) and attachment (?mbriae and stalks). Individual bacterial cells may be spheres (cocci); straight (bacilli), curved (vibrio), or ?exuous (spirilla) rods; or oval cells (coccobacilli). On examination by light microscopy, bacteria may be visible in characteristic con?gurations (as pairs of cocci [diplococci], or chains [streptococci], or clusters); actinomycete bacteria grow as ?laments with externally produced spores. Bacteria grow essentially by increasing in cell size and dividing by ?ssion, a process which in ideal laboratory conditions some bacteria may achieve about once every 20 minutes. Under natural conditions, growth is usually much slower.
Eukaryotic micro-organisms comprise fungi, algae, and protozoa. These organisms are larger, and they have in common a well-developed internal compartmentation into subcellular organelles; they also have a nucleus. Algae additionally have chloroplasts, which contain photosynthetic pigments; fungi lack chloroplasts; and protozoa lack both a cell wall and chloroplasts but may have a contractile vacuole to regulate water uptake and, in some, structures for capturing and ingesting food. Fungi grow either as discrete cells (yeasts), multiplying by budding, ?ssion, or conjugation, or as thin ?laments (hyphae) which bear spores, although some may show both morphological forms during their life-cycle. Algae and protozoa generally grow as individual cells or colonies of individuals and multiply by ?ssion.
Micro-organisms of medical importance include representatives of the ?ve major microbial groups that obtain their essential nutrients at the expense of their hosts. Many bacteria and most fungi, however, are saprophytes (see SAPROPHYTE), being major contributors to the natural cycling of carbon in the environment and to biodeterioration; others are of ecological and economic importance because of the diseases they cause in agricultural or horticultural crops or because of their bene?cial relationships with higher organisms. Additionally, they may be of industrial or biotechnological importance. Fungal diseases of humans tend to be most important in tropical environments and in immuno-compromised subjects.
Pathogenic (that is, disease-causing) microorganisms have special characteristics, or virulence factors, that enable them to colonise their hosts and overcome or evade physical, biochemical, and immunological host defences. For example, the presence of capsules, as in the bacteria that cause anthrax (Bacillus anthracis), one form of pneumonia (Streptococcus pneumoniae), scarlet fever (S. pyogenes), bacterial meningitis (Neisseria meningitidis, Haemophilus in?uenzae) is directly related to the ability to cause disease because of their antiphagocytic properties. Fimbriae are related to virulence, enabling tissue attachment – for example, in gonorrhoea (N. gonorrhoeae) and cholera (Vibrio cholerae). Many bacteria excrete extracellular virulence factors; these include enzymes and other agents that impair the host’s physiological and immunological functions. Some bacteria produce powerful toxins (excreted exotoxins or endogenous endotoxins), which may cause local tissue destruction and allow colonisation by the pathogen or whose speci?c action may explain the disease mechanism. In Staphylococcus aureus, exfoliative toxin produces the staphylococcal scalded-skin syndrome, TSS toxin-1 toxic-shock syndrome, and enterotoxin food poisoning. The pertussis exotoxin of Bordetella pertussis, the cause of whooping cough, blocks immunological defences and mediates attachment to tracheal cells, and the exotoxin produced by Corynebacterium diphtheriae causes local damage resulting in a pronounced exudate in the trachea.
Viruses cause disease by cellular destruction arising from their intracellular parasitic existence. Attachment to particular cells is often mediated by speci?c viral surface proteins; mechanisms for evading immunological defences include latency, change in viral antigenic structure, or incapacitation of the immune system – for example, destruction of CD 4 lymphocytes by the human immunode?ciency virus.... microbiology
Abnormal smallness of the head, usually associated with LEARNING DISABILITY. It may occur as a result of infection of the fetus by, for example, RUBELLA (German measles) or from hypoxic damage to the brain before or during birth.... microcephaly
See MICROSCOPE.... electron microscope
Microgram is the 1/1,000th part of a milligram. The abreviation for it is µg. (See APPENDIX 6: MEASUREMENTS IN MEDICINE.)... microgram
A unit of measurement. 1 um = 1 thousandth of a mm.... micrometer
The 1/1,000th part of a millimetre. The abbreviation for it is µm. (See APPENDIX 6: MEASUREMENTS IN MEDICINE.)... micrometre
Condition in which objects appear smaller than normal. It can be due to disease of the macula of the EYE.... micropsia
One of the three genera of dermatophytes (fungi) which cause tinea (see RINGWORM). Microsporum of human or animal origin is an important cause of tinea capitis, or ringworm of the scalp.... microsporum
A spherical gram-positive bacterium (see BACTERIA; GRAM’S STAIN). It occurs in colonies and is usually harmless in humans. However, micrococcus can become pathogenic and cause abscesses (see ABSCESS), ARTHRITIS, ENDOCARDITIS or MENINGITIS.... micrococcus
A small red blood cell.... microcyte
The technique of dissecting very small structures under a microscope. Miniature surgical instruments are manipulated via geared connections that convert the coarse movements of the surgeon’s ?ngers into miniscule movements, making it possible to dissect and separate even individual CHROMOSOMES.... microdissection
A laboratory instrument for cutting sections of biological tissues for study under a MICROSCOPE. It is widely used in biological and PATHOLOGY laboratories.... microtome
A binocular MICROSCOPE used for MICROSURGERY on, for example, the EYE and middle EAR; this microscope is also used for suturing nerves and blood vessels damaged or severed by trauma and for rejoining obstructed FALLOPIAN TUBES in the treatment of INFERTILITY in women.... operating microscope
Surgery to relieve pressure on the spinal cord, or a nerve root emerging from it, that is caused by protrusion of the soft core of an intervertebral disc (see disc prolapse). The procedure is performed under general anaesthesia and involves removing the protruding tissue via a small incision in the outer coat of the disc.... microdiscectomy
A rare congenital disorder of the eye. Affected children are born with an abnormally small eye on one or both sides.... microphthalmos
A very small, single-celled living organism that cannot usually be seen by the naked eye. The most important micro-organisms in medicine are those that cause disease. This ‘pathogenic’ group, however, forms only a small proportion of the enormous number of known microorganisms. The main pathogenic ones are BACTERIA. Others are fungi and RICKETTSIA. Though not true cells, viruses (see VIRUS) are usually classi?ed as micro-organisms. (See also MICROBIOLOGY.)... micro-organism
Gels or creams, currently under investigation, designed to reduce the risk of anal or vaginal transmission of viruses such as HIV (see also AIDS/ HIV). The aim is to kill or to inactivate the virus, creating a barrier to mucosal cells or preventing the infection from taking hold after it has entered the body. Large-scale trials were launched in Africa in 2004, using dextrin sulphate and PRO-2000 gel.... microbicides
The mobile embryo of certain parasitic nematode worms which are found in the blood or lymph of patients infected with ?larial worms. The micro?lariae develop into larvae in the body of a blood-sucking insect, for example, a mosquito.... microfilaria
corresponds to a large extent with what used to be known as ‘secondary anaemia’. It takes its name from the characteristic changes in the blood.... microcytic hypochromic anaemia
(Buch-Ham.) Roem.
Family: Rutaceae.
Habitat: Bihar, Orissa, Bengal, Sikkim, Nepal, Assam, Khasi, Aka and Lushai hills.
Action: Bark of the root, stem and branches—used in the treatment of tubercular cases.
The root contains coumarins, mi- cromelin, phebalosin and yuehchak- ene.Micromelum pubescens Blume, synonym M. minutum (Forst. f.) Seem. is found in the Andamans. The plant is used in Malaya and Indonesia for phthisis and chest diseases. The root is chewed with betel for coughs.The leaves contain coumarins, mi- cropubescin and phebalosin.The bark contains phebalosin. The roots contain micromelumin, phe- balosin, imperatorin, angelical, lime- ttin, scopoletin, minumicrolin and murrangatin.
Family: Lamiaceae; Labiatae.
Habitat: Kumaon, Upper Gangetic plain, Bihar, Orissa, Western Ghats, Nilgiris.
Folk: Pudinaa (var.).
Action: Plant—carminative. Used as a substitute for Mentha piperata Linn.
The plant yields an essential oil (1.6%) which contains mainly pulegone (80%).Micromeria biflora Benth., equated with Indian Wild Thyme, is found in tropical and temperate Himalayas, and in Western Ghats and hills of South India.The principal constituent of volatile oil of Camphorata sp. is camphor; of Citrata sp. is citral; of menthata and Pulegata sp. is d-menthone; and pulegone.... micromelum integerrimum
Non-ionising electro-magnetic radiations in the frequency range of 30–300,000 megahertz. They are emitted from electronic devices, such as heaters, some domestic ovens, television receivers, radar units and DIATHERMY units. There is no scienti?c evidence to justify the claims that they are harmful to humans, or that they produce any harmful e?ect in the GENES. The only known necessary precaution is the protection of the eyes in those using them in industry, as there is some evidence that prolonged exposure to them in this may induce cataract (see EYE, DISORDERS OF).... microwaves
A prefix meaning small, as in microorganisms (tiny organisms).... micro-
the electrical potential generated by the cochlea in response to an acoustic stimulus. It can be detected by *auditory brainstem response audiometry or *electrocochleography and is useful in the diagnosis of *auditory neuropathy spectrum disorder.... cochlear microphonic
Plant medicines that destroy or inhibit growth of disease-causing bacteria or other micro-organisms. Aniseed, Barberry, Bayberry, Bearberry, Benzoin, Blood root, Buchu, Camphor, Caraway oil, Catechu, Cayenne, Cinnamon, Clove, Cornsilk, Coriander, Echinacea, Elecampane, Eucalyptus, Fennel seed, Garlic, Gentian, Goldenseal, Guaiacum, Heather flowers (Calluna), Hemlock Spruce bark, Juniper, Kava Kava, Kino, Labrador tea, Lavender, Liquorice, Lovage root, Mandrake, Marigold, Marjoram, Meadowsweet, Mountain Grape, Myrrh, Nasturtium, Olive, Orthosiphon, Parsley root, Peppermint, Peruvian balsam, Plantain, Propolis, Rosemary, Rue, Sage, St John’s Wort, Southernwood, Thuja, Thyme, Turmeric, White Pond Lily, Wild Indigo, Wood Sage, Wormwood, Yarrow. ... anti-microbials
a light microscopic technique used to increase optical resolution and contrast.... confocal microscopy
n. the microbe population living in the intestine (sometimes formerly called gut flora).... gut microbiota
adj. describing microorganisms that grow best at very low oxygen concentrations (i.e. below the atmospheric level).... microaerophilic
a laboratory measurement used as a screening test for the first signs of kidney damage in *diabetes mellitus. It detects an increase in the very small levels of the protein albumin present in urine, relative to the concentration of creatinine. It is best measured in an early morning urine sample. See microalbuminuria.... microalbumin:creatinine ratio
n. the presence of albumin in the urine at levels that are higher than normal (>30 mg/24 hours) but lower than those detected by standard urine protein dipsticks (>300 mg/24 hours). The usual screening method for microalbuminuria is to measure the *microalbumin:creatinine ratio. In people with diabetes microalbuminuria is an important risk factor for the development of progressive kidney damage and (particularly in those with type 2 diabetes) coronary heart disease. At an early stage of microalbuminuria its presence may be reversed by careful control of blood pressure and blood glucose.... microalbuminuria
n. a minute localized swelling of a capillary wall, which is found in the retina of patients with diabetic *retinopathy. It is recognized as a small red dot when the interior of the eye is examined with an *ophthalmoscope.... microaneurysm
(microblepharism) n. the condition of having abnormally small eyelids.... microblepharon
pl. n. (in radiology) an ultrasound *contrast medium consisting of suspensions of biocompatible gas-filled microspheres that are introduced into the vascular system or the Fallopian tubes in order to enhance ultrasound images.... microbubbles
n. abnormally small size of the lips. Compare macrocheilia.... microcheilia
n. the presence of abnormally small red cells (microcytes) in the blood. Microcytosis is a feature of certain anaemias (microcytic anaemias), including iron-deficiency anaemias, certain *haemoglobinopathies, anaemias associated with chronic infections, etc.... microcytosis
n. abnormal smallness or shortness of the fingers.... microdactyly
n. a surgical instrument that comprises a small powered partially guarded rotating blade to remove tissue during operative procedures. An inbuilt suction–irrigation system removes the resulting tissue fragments and blood. It is most commonly used in *endoscopic sinus surgery but can also be used to perform tonsillectomy and adenoidectomy and in some types of laryngeal and bronchial surgery.... microdebrider
n. excision of a single mammary duct that is causing nipple discharge. The duct is sent for histology to determine the presence of a papilloma or carcinoma.... microdochectomy
n. a condition in which the teeth are unusually small. It may be generalized, where all teeth are involved, or localized, where only a few teeth are involved.... microdontia
n. an extremely fine wire used as an electrode to measure the electrical activity in small areas of tissue. Microelectrodes can be used for recording the electrical changes that occur in the membranes of cells, such as those of nerve and muscle.... microelectrode
n. (pl. microfilariae) the motile embryo of certain nematodes (see filaria). The slender microfilariae, 150–300 ?m in length, are commonly found in the circulating blood or lymph of patients suffering an infection with any of the filarial worms, e.g. Wuchereria. They mature into larvae, which are infective, within the body of a bloodsucking insect, such as a mosquito.... microfilaria
n. the motile flagellate male sex cell of the malarial parasite (Plasmodium) and other protozoans. The microgamete is similar to the sperm cell of animals and smaller than the female sex cell (see macrogamete).... microgamete
n. a cell that undergoes meiosis to form 6–8 mature male sex cells (microgametes) of the malarial parasite (see Plasmodium). Microgametocytes are found in human blood but must be ingested by a mosquito before developing into microgametes.... microgametocyte
n. one of the two basic classes of *glia (the non-nervous cells of the central nervous system), having a mainly scavenging function (see macrophage). Compare macroglia.... microglia
n. abnormally small size of the tongue.... microglossia
n. a condition in which one or both jaws are unusually small. It is a symptom of various craniofacial conditions and may require surgery to correct.... micrognathia
(photomicrograph) n. a photograph of an object as viewed through a microscope. An electron micrograph is photographed through an electron microscope; a light micrograph through a light microscope.... micrograph
n. a developmental disorder of the brain in which the folds (convolutions) in its surface are small and its surface layer (cortex) is structurally abnormal. It is associated with mental and physical retardation.... microgyria
n. a measurement of the proportion of red blood cells in a volume of circulating blood. It is determined by taking a sample of the patient’s blood in a fine tube and spinning it in a centrifuge until settling is complete. See packed cell volume.... microhaematocrit
n. a surgical instrument with an oscillating blade designed for creating the corneal flap in laser *refractive surgery.... microkeratome
n. multiple tiny calcifications seen within the testes. Testicular germ-cell tumour is associated with testicular microlithiasis, but a direct relationship is not established.... microlithiasis
n. the manipulation of extremely small structures under the microscope, as in *microdissection, or *microsurgery.... micromanipulation
n. abnormally small size of the arms or legs. Compare macromelia.... micromelia
n. a secondary tumour that is undetectable by clinical examination or diagnostic tests but is visible under the microscope.... micrometastasis
n. mapping the pattern of a patient’s retinal sensitivity onto an image of that individual’s fundus (back of the eye) to measure the patient’s response to light stimuli at various retinal points. The data are superimposed on an image captured by a scanning laser *ophthalmoscope or by fundus photography to precisely identify areas of impaired or preserved function.... microperimetry
n. 1. a photograph reduced to microscopic proportions. 2. (loosely) a *photomicrograph.... microphotograph
n. an extremely fine tube from which minute volumes of liquid can be delivered. It can also be used to draw up minute quantities of liquid for examination. Using a micropipette it is possible to add or take away material from individual cells under the microscope.... micropipette
adj. 1. too small to be seen clearly without the use of a microscope. 2. of, relating to, or using a microscope.... microscopic
(MPA) an autoimmune disease characterized by inflammation of small blood vessels, leading to reduced kidney function and breathlessness. It is associated with the presence of antinuclear cytoplasmic antibodies (*ANCA) and can be treated with corticosteroids, cyclophosphamide, or rituximab.... microscopic polyangiitis
n. a small particle consisting of a piece of *endoplasmic reticulum to which ribosomes are attached. Microsomes are formed when homogenized cells are centrifuged. —microsomal adj.... microsome
see MESA.... microsurgical epididymal sperm aspiration
n. a congenital deformity of the external ear in which the *pinna is small or absent. The ear canal may also be absent, giving a conductive *deafness. Microtia may be associated with other congenital deformities.... microtia
adj. involving small vessels. The term is often applied to techniques of *microsurgery for reuniting small blood vessels (the same techniques are applied frequently to nerve suture).... microvascular
n. (pl. microvilli) one of a number of microscopic hairlike structures (about 5 ?m long) projecting from the surface of epithelial cells (see epithelium). They serve to increase the surface area of the cell and are seen on absorptive and secretory cells. In some regions (particularly the intestinal tract) microvilli form a dense covering on the free surface of the cells: this is called a brush border.... microvillus
(MWA) an *ablation technique in which microwaves are used to burn tumour tissues. This has some advantages over *radiofrequency ablation because the heat generated is field heating, as in conventional microwave machines. This makes it possible to get a bigger ablation zone and means that the ablation is not affected by the heat-sink effect of adjacent blood vessels.... microwave ablation
see endometrial ablation.... microwave endometrial ablation
a form of *diathermy using electromagnetic waves of extremely short wavelength. In modern apparatus the electric currents induced in the tissues have frequencies of up to 25,000 million cycles per second.... microwave therapy
a surgical technique used for removing primarily high-risk nonmelanoma skin cancers, particularly basal cell carcinoma. The technique allows the surgeon to see beyond the visible tumour as the specimen is removed and the histology checked in stages. At each stage, if the tumour involves the margins, further tissue is resected until they are clear. There is an extremely high cure rate. [F. E. Mohs (1910–2002), US surgeon]... mohs’ micrographic surgery
the formation of thrombi in arterioles and capillaries, leading to haemolytic anaemia and *thrombocytopenia. The term encompasses primary *haemolytic uraemic syndrome and *thrombotic thrombocytopenic purpura, as well as the microangiopathies that can complicate pregnancy (pregnancy-related haemolytic uraemic syndrome, *HELLP syndrome), *malignant hypertension, *scleroderma, *antiphospholipid antibody syndrome, organ transplantation, and cancer.... thrombotic microangiopathy
(TEMS) a minimally invasive surgical procedure for rectal polyps not suitable for colonoscopic resection. For early rectal cancer it can be an alternative to lower anterior resection of the rectum. The procedure is performed through the anus and rectum using an *operating microscope and microsurgical instruments.... transanal endoscopic microsurgery
Health Encyclopedia