Anisotropy

ANISOTROPY (from Greek anisos-unequal and tropos-form, direction), a property of bodies consisting in the fact that their properties in different directions are not the same. Coarse anisotropy is possessed, for example, by wood: with the naked eye it can be seen that it consists of fibers stretched in one direction; therefore, it splits easily in this direction, while in the perpendicular direction it can only be sawn or chopped. Most crystals possess anisotropy, in which it is caused by the special, ordered arrangement of atoms. Anisotropy can manifest itself in any physical properties of a body; thus, in different directions there may be different elasticity, different compressibility, different thermal conductivity and electrical conductivity. Anisotropy is especially sharply manifested in the optical properties of a body. Such optical anisotropy is characteristic of all crystal systems except the so-called regular one. A ray of light, entering an anisotropic crystal, splits into two completely different rays: the "ordinary" (polarized in the plane of the principal section) and the "extraordinary" (polarized perpendicular to it). It turns out that the speed of propagation of light in the "extraordinary" ray strongly depends on the direction. If in space the speeds of light are depicted as arrows directed from one point in different directions, and if the magnitude of each arrow is taken proportional to the speed of light in a given direction, then the ends of all arrows will lie on a certain ellipsoid (Huygens). In animal tissues, optical anisotropy is often encountered. Examples include: striated muscle fibers, in which dark anisotropic areas alternate regularly with light isotropic ones; bone tissue, which gives a clear cross pattern when examined in polarized light, etc. Under tension, anisotropy can also be detected in such structures where it does not clearly manifest in a resting state, for example, in the collagen fibers of connective tissue. For details on anisotropy in animal tissues, see in relation to each individual tissue. Anisotropic substance of muscles. Skeletal muscles consist of fibers, which under a microscope reveal an alternation of light and dark transverse stripes. The latter are anisotropic, i.e., their substance has different properties in different directions. Depending on this, the dark stripes show double refraction when examined in polarized light. Muscles in relation to polarized light are such as they would have to be if they were built from uniaxial positive crystals with the long axis parallel to the axis of the muscle fiber. Smooth muscles also show double refraction. The contractility of a muscle is associated with anisotropic substance; it has been proven that contractility and double refraction in a muscle appear simultaneously during the development of the muscle fiber. ANIS0CHROMIA (from Greek anisos-unequal and chroma-color), different intensity of erythrocyte staining, depending on the unequal content of Hb in them; anisochromia can be observed on unstained and stained blood smears, in which, along with intensely stained erythrocytes (hyperchromia), one can encounter red spheres with normal pigment content or with very lightly stained peripheral zone (hypochromia). Uneven distribution of Hb can occur in the same erythrocyte - in this case, the periphery is lightly stained, and the center represents an intensely stained disk connected to the periphery by a thin bridge of stained plasma. Anisochromia occurs with insufficient blood formation or with excessive blood formation after preliminary blood loss.