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Medical Dictionary


substernomastoid (sub-ster′no-mas′toyd)
Beneath the sternomastoid muscle; denoting a group of deep cervical lymph nodes.

substitute (sub′sti-toot)
1. Anything that takes the place of another. 2. In psychology, a surrogate. blood s. any material ( e.g., human plasma, serum albumin, or a solution of such substances as dextran) used for transfusion in hemorrhage and shock. plasma s. a solution of a substance ( e.g., dextran) used for transfusion in hemorrhage or shock as a s. for plasma. SYN: plasma expander. volume s. infusion of cell-free or volume-expanding fluids such as dextran for replacement of fluid lost from the circulation as part of the prevention or treatment of circulatory shock.

substitution (sub-sti-too′shun)
1. In chemistry, the replacement of an atom or group in a compound by another atom or group ( e.g., s. of H by Cl in CH4 to give CH3Cl). 2. In psychoanalysis, an unconscious defense mechanism by which an unacceptable or unattainable goal, object, or emotion is replaced by one that is more acceptable or attainable; the process is more acute and direct, and less subtle, than sublimation. [L. substitutio, to put in place of another] generic s. the dispensing of a chemically equivalent, less expensive drug in place of a brand-name product that has an expired patent. stimulus s. SYN: classical conditioning. symptom s. an unconscious psychological process by which a repressed impulse is indirectly manifested through a particular symptom, e.g., anxiety, compulsion, depression, hallucination, obsession. SYN: symptom formation.

substrate (S) (sub′strat)
1. The substance acted upon and changed by an enzyme; the reactant considered to be attacked in a chemical reaction. 2. The base on which an organism lives or grows; e.g., the s. on which microorganisms and cells grow in cell culture. [L. sub-sterno, pp. -stratus, to spread under] insulin receptor s.-1 a cytoplasmic protein that is a direct s. of the activated insulin receptor kinase. Insulin exposure results in its rapid phosphorylation at multiple tyrosine residues. Its phosphorylated sites associate with high affinity to certain cellular proteins. IRS-1 thus acts as an adaptor molecule that links the receptor kinase to various cellular activities regulated by insulin. IRS-1 is also phosphorylated after stimulation by insulinlike growth factor-1 and several interleukins. suicide s. a competitive inhibitor that is converted to an irreversible inhibitor at the active site of the enzyme. SYN: mechanism-based inhibitor, suicide inhibitor.

substratum (sub-stra′tum)
Any layer or stratum lying beneath another. [L. see substrate]

substructure (sub-struk′choor)
A tissue or structure wholly or partly beneath the surface. implant denture s. the metal framework which is placed beneath the soft tissues in contact with, or embedded into, bone for the purpose of supporting an implant denture superstructure.

subsulfate (sub-sul′fat)
A basic sulfate; a sulfate that contains some base unneutralized and still capable of combining with the acid.

subtarsal (sub-tar′sal)
Below the tarsus.

subtentorial (sub-ten-to′re-al)
Beneath the tentorium cerebelli.

subterminal (sub-ter′mi-nal)
Situated near the end or extremity of an oval or rod-shaped body.

subtetanic (sub-te-tan′ik)
Denoting tonic muscular spasms or convulsions that are not entirely sustained but have brief remissions.

subthalamic (sub-tha-lam′ik)
Related to the subthalamus region or to the s. nucleus.

subthalamus (sub-thal′a-mus) [TA]
That part of the diencephalon that lies wedged between the thalamus on the dorsal side and the cerebral peduncle ventrally, lateral to the dorsal half of the hypothalamus from which it cannot be sharply delineated. It is composed of the subthalamic nucleus (corpus luysi), the zona incerta, and the fields of Forel; laterally it expands in a winglike fashion into the reticular nucleus of the thalamus; caudally it is continuous with the midbrain tegmentum. SYN: ventral thalamus.

subthyroideus (sub-thi-royd′e-us)
A muscular bundle formed of fibers derived from the thyroarytenoid and vocalis muscles.

subtilisin (sub-ti-li′sin)
A proteinase formed by Bacillus subtilis and other species, similar to the serine proteinases of other molds and bacteria; it catalyzes the hydrolysis of a few specific peptide bonds in certain proteins, converting chymotrypsinogen to chymotrypsin and ovalbumin to plakalbumin in this manner, and cleaves pancreatic ribonuclease into S-peptide and S-protein. SYN: subtilopeptidase.

subtilopeptidase (sub′ti-lo-pep′ti-das)
SYN: subtilisin.

subtraction (sub-trak′shun)
A technique used to enhance detectability of opacified anatomic structures on radiographic or scintigraphic images; a negative of an image made before introduction of contrast medium or radionuclide is photographically or electronically removed from a later image; commonly used in cerebral angiography. SEE ALSO: digital s. angiography, mask. energy s. digital radiography using higher- and lower-energy exposures, either by double exposure at 2-kV levels or by interposing a copper filter that absorbs the lower-energy photons between two phosphor plates, with computer calculation of high-Z and low-Z images (bone and soft tissues, respectively); makes use of the fact that lower-energy x-rays are absorbed by more high-Z substances, such as calcium and copper, because of the photoelectric effect. SEE ALSO: Z, photoelectric effect, phosphor plate.

subtrapezial (sub-tra-pe′ze-al)
Beneath the trapezius muscle; denoting a nerve plexus.

subtribe (sub-trib)
In biologic classification, a division between tribe and genus.

subtrochanteric (sub-tro-kan-ter′ik)
Below any trochanter.

subtrochlear (sub-trok′le-ar)
Below any trochlea.

subtuberal (sub-too′ber-al)
Lying below any tuber.

subtympanic (sub-tim-pan′ik)
Below the tympanic cavity.

subumbilical (sub-um-bil′i-kal)
SYN: infraumbilical.

subungual, subunguial (sub-ung′gwal, sub-ung′gwi-al)
Beneath the finger or toe nail. SYN: hyponychial (1) . [L. unguis, nail]

subunit (sub′oo-nit)
1. A unit that forms a distinct part of a larger structure. SEE ALSO: monomer. 2. The single protein or polypeptide chain that can be separated from an oligomer protein without cleaving covalent bonds other than disulfide bridges between cysteinyl residues. 3. A single biopolymer separated from a larger multimeric structure.

suburethral (sub-u-re′thral)
Beneath the male or female urethra.

subvaginal (sub-vaj′i-nal)
1. Below the vagina. 2. On the inner side of any tubular membrane serving as a sheath.

subvalvar, subvalvular (sub-val′var, sub-val′vu-lar)
Below any valve.

subvertebral (sub-ver′te-bral)
Beneath, or on the ventral side, of a vertebra or the vertebral column.

subvirile (sub-vir′il)
Deficient in virility.

subvirion (sub-vir′e-on)
An incomplete viral particle. [sub- + virion]

subvitrinal (sub-vit′ri-nal)
Beneath the vitreous body.

subwaking (sub-wak′ing)
Denoting the mental state between sleeping and waking.

subzonal (sub-zo′nal)
Below or beneath any zona or zone, such as the zona radiata or zona pellucida.

subzygomatic (sub-zi-go-mat′ik)
Below or beneath the zygomatic bone or arch.

succagogue (suk′a-gog)
1. Stimulating the flow of juice. 2. An agent having such an effect. [L. succus, juice, + G. agogos, leading]

succedaneous (suk-se-da′ne-us)
1. Relating to a succedaneum. 2. Relating to the permanent or second teeth that replace the deciduous or primary teeth. [see succedaneum]

succedaneum (suk-se-da′ne-um)
A substitute; a drug or any therapeutic agent that has the properties of and can be used in place of another. [L. succedaneus, following after, substituting, fr. suc-cedo, to follow, to take the place of, fr. sub, under, + cedo, to go]

succenturiate (suk-sen-tu′re-at)
In anatomy, substituting for, or accessory to, some organ. [L. suc-centurio, pp. -atus, to substitute]

succinate (suk′si-nat)
A salt of succinic acid. active s. SYN: succinyl-coenzyme A. s. dehydrogenase a flavoenzyme that catalyzes the removal of hydrogen from succinic acid and converts it into fumaric acid; e.g., s. + FAD ⇆ fumarate + FADH2; this complex is a part of the tricarboxylic acid cycle. SYN: fumarate reductase (NADH), fumaric hydrogenase.

succinate semialdehyde (suk′sin-at sem-e-al-de -hid)
An intermediate in the catabolism of γ-aminobutyrate. s. dehydrogenase an enzyme that catalyzes the reaction of s. and either NAD+ or NADP+ to form succinate and NADH (or NADPH); a deficiency of this enzyme is associated with 4-hydroxybutyric aciduria.

succinic acid (suk-sin′ik)
An intermediate in the tricarboxylic acid cycle; several of its salts have been variously used in medicine.

succinic thiokinase
SYN: succinyl-CoA synthetase.

succinimide (suk′sin-a-mid)
Chemical class of drugs from which the antiepileptic agents ethosuximide, methsuximide, and phensuximide are derived. Unsubstituted s. has been used as an antiurolithic.

succinylacetone (suk′sin-il-as′e-ton)
A minor metabolite that is elevated in individuals with tyrosinemia IA.

succinylcholine (suk′si-nil-ko′len)
A neuromuscular relaxant with short duration of action which characteristically first depolarizes the motor endplate (phase I block) but which is often later associated with a curare-like, nondepolarizing neuromuscular block (phase II block); used to produce relaxation for tracheal intubation and during surgical anesthesia. SYN: diacetylcholine, suxamethonium.

succinyl-CoA (suk′sin-il)
SYN: succinyl-coenzyme A. succinyl-CoA synthetase 1. a ligase reversibly reacting succinate and CoA with ATP to produce ADP, inorganic phosphate, and succinyl-CoA; 2. a similar synthetase, but one able to use itaconate as well as succinate and GTP (or ITP) in place of ATP; a part of the tricarboxylic acid cycle. SYN: succinic thiokinase, succinyl-CoA ligase.

succinyl-CoA ligase
SYN: succinyl-CoA synthetase.

succinyl-coenzyme A (suk′si-nil-ko-en′zim)
The condensation product of succinic acid and CoA; one of the intermediates of the tricarboxylic acid cycle and a precursor in the synthesis of heme. SYN: active succinate, succinyl-CoA.

succinyldicholine (suk′si-nil-di-ko′len)
Succinylcholine chloride.

succinylsulfathiazole (suk′si-nil-sul′fa-thi′a-zol)
The most effective of the poorly absorbed bacteriostatic sulfonamides used for sterilization of the intestinal tract.

succisulfone iminodiethanol (suk-si-sul′fon)
An antimicrobial agent.

succorrhea (suk-o-re′a)
An abnormal increase in the secretion of a digestive fluid. [L. succus, juice, + G. rhoia, a flow]

succubus (suk′u-bus)
A demon, in female form, believed to have sexual intercourse with a man during sleep. Cf.:incubus. [L. succubo, to lie under]

succuss (su-kus′)
To make succussion.

succussion (su-kush′un)
A diagnostic procedure that consists in shaking the body so as to elicit a splashing sound in a cavity containing both gas and fluid. [L. sucussio, fr. suc-cutio (subc-), pp. -cussus, to shake up, fr. quatio, to shake] hippocratic s. a splashing noise produced by shaking the body when there is gas or air and fluid in the stomach or intestine, or free in the peritoneum, thorax, and, rarely, the pericardium.

suck (suk)
1. To draw a fluid through a tube by exhausting the air in front. 2. To draw a fluid into the mouth; specifically, to draw milk from the breast. [A.S. sucan]

suckle (suk′l)
1. To nurse; to feed by milk from the breast. 2. To suck; to draw sustenance from the breast.

J.P., French anatomist, 1840–1870. See S. anastomoses, under anastomosis, S. canals, under canal, S.-Hoyer anastomoses, under anastomosis, S.-Hoyer canals, under canal.

sucralfate (soo-kral′fat)
Sucrose octakis (hydrogen sulfate) aluminum complex; a polysaccharide with antipeptic activity, used to treat duodenal ulcers by providing a protective coating to allow healing.

sucrase (soo′kras)
SYN: sucrose α-d-glucohydrolase.

sucrate (soo′krat)
A compound of sucrose.

sucrose (soo′kros)
A nonreducing disaccharide made up of d-glucose and d-fructose obtained from sugar cane, Saccharum officinarum (family Gramineae), from several species of sorghum, and from the sugar beet, Beta vulgaris (family Chenopodiaceae); the common sweetener, used in pharmacy in the manufacture of syrup, confections, etc. SYN: saccharose, saccharum. s. octaacetate an alcohol denaturant.

sucrose α-d-glucohydrolase
An enzyme hydrolyzing sucrose and maltose in a complex with isomaltase; hence, it hydrolyzes both sucrose and isomaltose; found in the intestinal mucosa; a deficiency of this enzyme results in defective digestion of sucrose and linear α1,4-glucans. SYN: sucrase.

sucrosemia (soo-kro-se′me-a)
The presence of sucrose in the blood. [sucrose + G. haima, blood]

sucrosuria (soo-kro-soo′re-a)
The excretion of sucrose in the urine. [sucrose + G. ouron, urine]

suction (suk′shun)
The act or process of sucking. SEE ALSO: aspiration (1) , aspiration (2) . [L. sugo, pp. suctus, to suck] posttussive s. a s. sound heard on auscultation over a pulmonary cavity at the end of a cough. Wangensteen s. a modified siphon that maintains constant negative pressure, used with a duodenal tube for the relief of gastric and intestinal distention. SYN: Wangensteen tube.

suctorial (suk-to′re-al)
Relating to suction, or the act of sucking; adapted for sucking.


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