Cuticle cells

Wool fibers consist of cells, where battened ovedapping cuticle cells form a protective sheath around cortical cells. In some coarser fibers, a central vacuolated medullary cell type may be present. 

In fine wool such as that obtained from merino sheep, the cuticle is normally one cell thick (20 x 30 x 0.5 mm, approximate dimensions) and usually constitutes about 10% by weight of the total fiber. Sections of cuticle cells show an internal series of laminations (Figs. 1 and 2) comprising outer sulfur-rich bands known as the exocuticle and inner regions of lower sulfur content called the endocuticle (13). On the exposed surface of cuticle cells, a membrane-like proteinaceous band (epicuticle) and a unique hpid component form a hydrophobic resistant barrier (14). These hpid and protein components are the functional moieties of the fiber surface and are important in fiber protection and textile processing (15). 

In an alkaline solution, the cuticle—the outermost layer of a strand of hair—swells up, softens, and becomes rougher. The cuticle is made up of translucent, flattened cells that line the hair shaft like shingles on a roof. The cuticle gets rougher when the cells do not lay flat. When the raised cuticle cells of one piece of hair get stuck on the raised cuticle cells of another piece of hair, the hair tangles. The raised cells also reflect light differently than smooth, flat cells, making the hair appear dull. 

Therefore, most shampoos and conditioners are slightly acidic. In acidic solutions, the cuticle shrinks and hardens. This smoothes the raised cuticle cells and causes them to lie flatter. Smooth cuticle cells lead to hair that is less tangled and shinier. 

The increase in the electronegative PCD potential can be explained by the increase in the aspartic acid concentration in the enzymatic bath released during the interaction of wool with enzymes. However, the changes in the methionine and cysteine concentration may suggest changes in the structure of the cuticle cells. 

The cortex forms the bulk of fine animal hairs and is derived from highly differentiated spindle-shaped cells that are densely packed with keratinous proteins. The long axes of the cortical cells are oriented parallel to the fiber length, and elongated cavities near the center of the cells are similarly oriented. These cavities are derived from the nuclei of the developing cells and contain debris usually referred to as nuclear remnants. Between cortical cells there is a layer 250-300 A in thickness which is similar to that found between cuticle cells this also is referred to sometimes as intercellular cement. Many nonkeratinous inclusions are found within the cortical cells and these are believed to be cytoplasmic debris. 

The two major morphological parts in the structure of wool are cuticle and cortex. The epi-cuticle of wool fibres surrounds each cuticle, it consists of approximately one-quarter fatty acid and three-quarters protein by mass. The hydrophobic epiCLiticle acts as a barrier to dyes which enter the wool fibre between cuticle cells through the highly cross-linked cell membrane complex (CMC). Enzyme from the liquor can diffuse into the interior of the fibre and hydrolyse parts of the endocuticle and proteins in the cell membrane complex, completely damaging the fibre if not controlled. In contrast, the catalytic action of enzyme on cotton is confined to the surface and the amorphous region only. 

Sandhu and Robbins [204] found that hair fibers shaken with SLS and ALS solutions lost more protein than in water alone. Marshall and Ley [205] were able to extract protein from cuticle cells after a short 1 minute agitation in 1% SLS. 

Lynch MH, O Guin M, Hardy C, et al. Acidic and basic hair/ nail (hard) keratins their colocalization in upper cortical and cuticle cells of the human hair follicle and their relationship to soft keratins. / Cell Biol. 1986 103 2593-2606. 

Wools and other similar mammalian hairs are largely composed of keratin proteins. However, unlike the other natural proteinaceous fibre, silk, wool is cellular in nature the fibres consist of relatively hard, flattened, overlapping cuticle cells, which surround the central cortical cells in some fibres, these may in turn surround a hollow medulla (Figure 23). 

The schematic diagram of Figure 1-21 illustrates the internal structure of cuticle cells. Each cuticle cell contains a thin outer membrane, the epicuti-cle. Different estimates of the thickness of this membrane have been cited (25 to 250 angstroms) however, 50 to 100 angstroms is probably the most common estimate [62, 63]. Beneath the cuticle cell membranes are three major layers the A layer, a resistant layer with a high cystine content... 

Figure 1-21. Schematic diagram of the proposed structure of a cuticle cell in cross section.

Figure 1-22. Transmission electron micrograph of a cross section of a hair fiber treated with silver methenamine, illustrating high and low sulfur layers of cuticle cells (stained = high-sulfur regions). Kindly provided by R. Wickett B. Barman.

EndocuUde is the innermost layer of each cuticle cell It consists of amorphous proteins... 

Cortical cells may be isolated from human hair by procedures involving either shaking in formic acid [48, 49] or enzymatic digestion [46, 50, 51]. Another procedure involves shaking hair fibers in water to strip the cuticle cells from the hair to provide cortex with intact cell membranes free of cuticle... 

Because bleaching increases the ratio of acidic to basic amino acids [122], the isoionic point should decrease with increasing oxidation. One might also anticipate a similar decrease in the isoelectric point of hair with bleaching because the A-layer of the cuticle cells is rich in cystine. 

The two major layers of cuticle cells, the exocuticle and endocuticle, may be expected to behave differently with respect to moisture regain. The exocuticle, because of its high cross-fink density, should not swell so readily as the endocuticle, with its paucity of cross-links and high density of ionic groups. Swelling of the endocuticle on regain could convert it to a gellike structure, and this could contribute to the DFE in animal hairs [120,125, 127,131]. 

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