| circle | 1. A ring-shaped structure or group of structures. 2. A line or process with every point equidistant from the centre. Synonym: circellus. Origin: L. Circulus (05 Mar 2000) |
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| circle absorption anaesthesia | Inhalation anaesthesia in which a circuit with carbon dioxide absorbent is used for complete (closed) or partial (saemiclosed) rebreathing of exhaled gases. (05 Mar 2000) |
| circle of willis | <anatomy> A group of arteries surrounding the base of the brain. (27 Sep 1997) |
| closed circle | A circuit for administration of an inhalation anaesthetic in which there is complete rebreathing with carbon dioxide absorption. (05 Mar 2000) |
| condenser circle | <microscopy> The image of the aperture iris diaphragm of the substage condenser as seen in the back focal plane of the objective. (05 Aug 1998) |
| Haller's circle | <anatomy, nerve> A network of branches of the short ciliary arteries on the sclera around the point of entrance of the optic nerve. Synonym: circulus vasculosus nervi optici, circulus arteriosus halleri, circulus zinnii, Haller's circle, Zinn's corona, Zinn's vascular circle. (05 Mar 2000) |
| semi-closed circle | A circuit for administration of an inhalation anaesthetic in which partial rebreathing with carbon dioxide absorption is combined with loss from the circuit of a portion of respired gases through valves. (05 Mar 2000) |
| Huguier's circle | <anatomy> Anastomosis around the isthmus of the uterus (junction of the cervix with the body) between the right and left uterine arteries. (05 Mar 2000) |
| nicked circle | <molecular biology> During extraction of plasmid DNA from the bacterial cell, onestrand of the DNA becomes nicked. This relaxes the torsional strain needed to maintain supercoiling, producing the familiar form of plasmid. (09 Oct 1997) |
| defensive circle | An obsolete term for the addition of a secondary affection that limits or arrests the progress of the primary affection, as thought to occur when pneumothorax supervenes on pulmonary tuberculosis, the former having a therapeutic effect on the latter. (05 Mar 2000) |
| objective circle | <microscopy> When the focused objective is examined by with- drawing the ocular and viewing its back focal plane through the microscope bodytube, the limiting boundary of the objective, the circumference of the white spot of light, is the objective circle. (05 Aug 1998) |
| Zinn's vascular circle | <anatomy, nerve> A network of branches of the short ciliary arteries on the sclera around the point of entrance of the optic nerve. Synonym: circulus vasculosus nervi optici, circulus arteriosus halleri, circulus zinnii, Haller's circle, Zinn's corona, Zinn's vascular circle. (05 Mar 2000) |
| least diffusion circle | In the configuration of rays emerging from a spherocylindrical lens system, the place where diverging rays of the lens first forming a line image are balanced by converging rays of the second lens. (05 Mar 2000) |
| acromial arterial network | A vascular network between the acromion and the skin of the shoulder, formed by anastomoses of the acromial branch of the suprascapular artery with the acromial branch of the thoracoacromial artery. Synonym: rete acromiale, acromial plexus. (05 Mar 2000) |
| alveolar-arterial oxygen difference | The difference or gradient between the partial pressure of oxygen in the alveolar spaces and the arterial blood: P(A-a)02. Normally in young adults this value is less than 20 mm Hg. See: alveolar gas equation. (05 Mar 2000) |