| schatzki's ring | A congenital anatomic narrowing in the lower 1/3 of the oesophagus that is the result of inappropriate embryological development of the oesophagus. Symptoms include difficulty swallowing and chest pain (under the sternum). Treatment involves the use of a fibreoptic endoscope using a dilator to open up the narrowed segment of the oesophagus. (27 Sep 1997) |
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| heterocyclic compounds, 1-ring | A class of organic compounds containing a ring structure made up of more than one kind of atom, usually carbon plus another atom. The ring structure can be aromatic or nonaromatic. (12 Dec 1998) |
| heterocyclic compounds, 2-ring | A class of organic compounds containing two ring structures, one of which is made up of more than one kind of atom, usually carbon plus another atom. The heterocycle may be either aromatic or nonaromatic. (12 Dec 1998) |
| heterocyclic compounds, 3-ring | A class of organic compounds containing three ring structures, one of which is made up of more than one kind of atom, usually carbon plus another atom. The heterocycle may be either aromatic or nonaromatic (12 Dec 1998) |
| heterocyclic compounds, bridged-ring | A class of organic compounds which contain two rings that share a pair of bridgehead carbon atoms. (12 Dec 1998) |
| Schwalbe's ring | The periphery of the cornea marking the termination of Descemet's membrane and the anterior border of the trabecular meshwork; an important landmark in gonioscopy. Synonym: Schwalbe's ring. (05 Mar 2000) |
| scleral ring | The appearance of the sclera adjacent to the optic disk when the retinal pigment epithelium does not extend to the optic nerve. (05 Mar 2000) |
| purine imidazole-ring cyclase | <enzyme> Recyclises ring-opened purine formamidopyrimidines in irradiated DNA, restoring the c-8 to n-9 band, does not require ATP Registry number: EC 6.3.3.- Synonym: purir cyclase (26 Jun 1999) |
| pyranose ring | <chemistry> A six-membered cyclic haemiacetal or ketal. (09 Jan 1998) |
| pyrrole ring | <biochemistry, chemistry> A heterocyclic ring structure, found in many important biological pigments and structures that involve an activated metal ion, for example chlorphyll, hem. (18 Nov 1997) |
| signet ring | The early stage of trophozoite development of the malaria parasite in the red blood cell; the parasite cytoplasm stains blue around its circular margin, and the nucleus stains red in Romanowsky stains, while the central vacuole is clear, giving the ringlike appearance. (05 Mar 2000) |
| signet-ring cell carcinoma | <tumour> A poorly differentiated adenocarcinoma composed of cells with a cytoplasmic droplet of mucus that compresses the nucleus to one side along the cell membrane; arises most frequently in the stomach, occasionally in the large bowel or elsewhere. (05 Mar 2000) |
| signet ring cells | Altered basophilic cells of the anterior lobe of the pituitary that develop following castration; the body of the cell is occupied by a large vacuole that displaces the nucleus to the periphery, giving the cell a resemblance to a signet ring. Synonym: signet ring cells. (05 Mar 2000) |
| S ring | <molecular biology> The static part of the bacterial motor: a ring of 15 or 17 sub units (one or less more than the M ring), anchored to the inner surface of the cell wall. (10 Mar 1998) |
| neonatal ring | In deciduous teeth, a line of demarcation between prenatal and postnatal enamel. Synonym: neonatal ring. (05 Mar 2000) |