| 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) |
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| 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) |
| second molar | Seventh permanent or fifth deciduous tooth in the maxilla and mandible on either side of the midsagittal plane of the head following the arch form. (05 Mar 2000) |
| second-order conditioning | The use of a previously successfully conditioned stimulus as the unconditioned stimulus for further conditioning. (05 Mar 2000) |
| second-order kinetics | A term describing the reaction rate of a chemical reaction in which the rate is proportional to the product of the concentrations (in moles) of two of the reactants (also called bimolecular kinetics), or to the square of the molar concentration of the reactant if there is only one. Such a reaction might have an equation like rate = k[A][B] or rate = k[A]2, where k is the reaction rate constant, [A] is the concentration of reactant A, and [B] is the concentration of reactant B. (09 Oct 1997) |
| second parallel pelvic plane | The plane extending from the middle of the posterior surface of the pubic symphysis to the junction of the second and third sacral vertebrae, and laterally passing through the ischial bones over the middle of the acetabulum. Synonym: second parallel pelvic plane, wide plane. (05 Mar 2000) |
| second set rejection | An accelerated rejection of a transplant that occurs when an individual has been previously sensitised to the graft. (05 Mar 2000) |
| second sight | 1. <ophthalmology> Improved near vision in the aged as a result of increased refractivity of the nucleus of the lens causing myopia. Synonym: senile lenticular myopia. 2. The power of discerning what is not visible to the physical eye, or of foreseeing future events. Such as are of a disastrous kind, the capacity of a seer or prophetic vision. Source: Websters Dictionary (01 Mar 1998) |
| second signaling system | <psychology> Pavlovian term for speech in which words are considered to be the second signals capable of producing conditioned responses. (05 Mar 2000) |
| second 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-stability region | <radiobiology> A high pressure region where the plasma becomes stable to the pressure-gradient-driven ballooning instability. The plasma is stable in the limit of small pressure gradients, becomes unstable at some intermediate pressure, and then becomes stable again at still higher pressures. Tokamaks operating in the second-stability region would be more attractive because the higher pressures (beta) would provide more fusion reactivity per unit volume of plasma, allowing smaller reactors to be built. (09 Oct 1997) |
| second stage of labour | <obstetrics> The part of labour from the full dilatation of the cervix until the baby is completely out of the birth canal. The second stage of labour is also called the stage of expulsion. (12 Dec 1998) |
| second temporal convolution | A longitudinal gyrus on the lateral surface of the temporal lobe, between the superior and inferior temporal sulci. Synonym: gyrus temporalis medius, middle temporal convolution, second temporal convolution. (05 Mar 2000) |
| second tibial muscle | An inconstant muscle, of small size, arising from the back of the tibia and inserted into the articular capsule of the ankle joint. Synonym: second tibial muscle. (05 Mar 2000) |
| second tooth | One of the 32 teeth belonging to the second or permanent dentition; eruption of the permanent teeth begins from the fifth to the seventh year, and is not completed until the seventeenth to the twenty-third year, when the last of the wisdom teeth appears. Synonym: dens permanens, dens succedaneus, second tooth, secondary dentition, succedaneous dentition, succedaneous tooth. (05 Mar 2000) |