| Hill coefficient | A measure of cooperativity in a binding process. A Hill coefficient of 1 indicates independent binding, a value of greater than 1 shows positive cooperativity binding of one ligand facilitates binding of subsequent ligands at other sites on the multimeric receptor complex. Worked out originally for the binding of oxygen to haemoglobin (Hill coefficient of 2.8). (18 Nov 1997) |
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| Hill constant | A measure of cooperativity in a binding process. A Hill coefficient of 1 indicates independent binding, a value of greater than 1 shows positive cooperativity binding of one ligand facilitates binding of subsequent ligands at other sites on the multimeric receptor complex. Worked out originally for the binding of oxygen to haemoglobin (Hill coefficient of 2.8). (18 Nov 1997) |
| Hill, Harold | <person> 20th century U.S. Radiologist. See: Hill-Sachs lesion. (05 Mar 2000) |
| Hill, Lucius | <person> U.S. Thoracic surgeon, *1921. See: Hill operation. (05 Mar 2000) |
| Hill operation | Repair of hiatus hernia; narrowing the oesophagogastric junction and attaching it to the right medial arcuate ligament. (05 Mar 2000) |
| Hill reaction | <plant biology> Reaction, first demonstrated by Robert Hill in 1939, in which illuminated chloroplasts evolve oxygen when incubated in the presence of an artificial electron acceptor (e.g. Ferricyanide). The reaction is a property of photosystem II. (11 Jan 1998) |
| Hill, Robert | <person> British plant physiologist, *1899. See: Hill reaction. (05 Mar 2000) |
| hill-sachs deformity | <radiology> Indentation or groove on posterolateral aspect of humeral head, probably due to compression of humeral head on posterior lip of glenoid, suggests repeated or chronic anterior shoulder dislocation, may occur after one episode of dislocation associated with: Bankhart lesion of glenoid (12 Dec 1998) |
| Hill-Sachs lesion | An irregularity seen in the head of the humerus following dislocation of the shoulder; caused by impaction of the head of the humerus against the edge of the glenoid. (05 Mar 2000) |
| Hill's equation | The equation,y(1-y) = [S]n/Kd, where y is the fractional degree of saturation, [S] is the binding ligand concentration, n is the Hill coefficient, and Kd is the dissociation constant for the ligand. The Hill coefficient is a measure of the cooperativity of the protein; the larger the value, the higher the cooperativity. This coefficient cannot be higher than the number of binding sites. For the oxygen binding curve of haemoglobin, an association constant, Ka, is used and the equation becomes y/(1-y) = Ka[S]n. For human blood, n equals 2.5. Compare: Hill plot. (05 Mar 2000) |
| Hill, Sir Leonard Erskine | <person> English physiologist, 1866-1952. See: Hill's sign, Hill's phenomenon. (05 Mar 2000) |
| Hill's phenomenon | <clinical sign> In aortic insufficiency, greater systolic blood pressure in the legs than in the arms; normal arterial systolic pressure in the leg is 10 to 20 mm of Hg above that in the arm, whereas in aortic insufficiency the difference may be 60 to 100 mm of Hg. Synonym: Hill's phenomenon. (05 Mar 2000) |
| Hill's sign | <clinical sign> In aortic insufficiency, greater systolic blood pressure in the legs than in the arms; normal arterial systolic pressure in the leg is 10 to 20 mm of Hg above that in the arm, whereas in aortic insufficiency the difference may be 60 to 100 mm of Hg. Synonym: Hill's phenomenon. (05 Mar 2000) |