| second cranial nerve | <anatomy, nerve> The optic nerve. The nerve carrying impulses for the sense of sight. Projection from the vertebrate retina to the midbrain. Embryologically, a CNS tract rather than a peripheral nerve. Popular experimental preparation for studies of regeneration of retino tectal projections in lower vertebrates and also for studies of glial cell lineage in CNS. Synonym: cranial nerve II. (18 Nov 1997) |
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| second cuneiform bone | A bone of the distal row of the tarsus; it articulates with the medial and lateral cuneiform, navicular, and second metatarsal bones. Synonym: os cuneiforme intermedium, mesocuneiform, middle cuneiform bone, second cuneiform bone, wedge bone. (05 Mar 2000) |
| second degree A-V block | See: atrioventricular block. (05 Mar 2000) |
| second degree burn | A burn involving the epidermis and dermis and usually forming blisters that may be superficial, or by deep dermal necrosis, followed by epithelial regeneration extending from the skin appendages. Synonym: partial-thickness burn. (05 Mar 2000) |
| second finger | The second finger (the thumb being counted as the first). Synonym: digitus secundus, forefinger, index, second finger. (05 Mar 2000) |
| second gas effect | When a constant concentration of an anaesthetic like halothane is inspired, the increase in alveolar concentration is accelerated by concomitant administration of nitrous oxide, because alveolar uptake of the latter creates a potential subatmospheric intrapulmonary pressure that leads to increased tracheal inflow. (05 Mar 2000) |
| second growth | A second generation of timber of merchantable age. (05 Dec 1998) |
| second heart sound | The second sound heard on auscultation of the heart; signifies the beginning of diastole and is due to closure of the semilunar valves. Synonym: second sound. (05 Mar 2000) |
| second incisor | Second maxillary or mandibular permanent or deciduous tooth on either side of the midsagittal plane of the head. Synonym: lateral incisor. (05 Mar 2000) |
| second law of thermodynamics | <physics> All of the chemical and physical processes in a closed system tend to drive that system toward maximum entropy. Clausius statement: No device can operate in a cycle and allow heat to transfer from a colder body to a hotter body unless other compensating activities are taking place. Kelvin-Planck statement: no device can operate in a constant-temperature cycle and convert the heat it receives into work, unless other other compensating activities are taking place. (09 Oct 1997) |
| second line chemotherapy | <oncology> Chemotherapy given for a tumour which has already failed to respond to a first chemotherapy regimen (called first line). (16 Dec 1997) |
| second-look operation | Exploratory celiotomy within a year after apparently curative resection of intra-abdominal cancer, in patients with no sign or symptom of recurrence, to resect an occult tumour if present. (05 Mar 2000) |
| second meiotic division | The second of two consecutive divisions of the nucleus of an eukaryotic cell during the process of meiosis. It includes the following stages of meiosis: prophase II, metaphase II, anaphase II, and telophase II. (09 Oct 1997) |
| second messenger | <molecular biology> In many hormone sensitive systems the systemic hormone does not enter the target cell but binds to a receptor and indirectly affects the production of another molecule within the cell, this diffuses intracellularly to the target enzymes or intracellular receptor to produce the response. This intracellular mediator is called the second messenger. Examples include cyclic AMP, cyclic GMP, IP3 and diacylglycerol. (18 Nov 1997) |
| second messenger systems | Systems in which an intracellular signal is generated in response to an intercellular primary messenger such as a hormone or neurotransmitter. They are intermediate signals in cellular processes such as metabolism, secretion, contraction, phototransduction, and cell growth. Examples of second messenger systems are the adenyl cyclase-cyclic AMP system, the phosphatidylinositol diphosphate-inositol triphosphate system, and the cyclic GMP system. (12 Dec 1998) |