Hair Cycles (the inconstant portion)

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1. Histopathology of Inflammation

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F1Ch9 (R4564): This is the hair bulb of a “kinked” follicle; The section is neither purely vertical nor central. At the periphery of the bulb, near the top of the field on the left, a single row of cells with prominent trichohyaline granules is represented. Follow this layer in a superior direction and this component become multi-layered (Huxley’s layer; see F2Ch9). The most outer layer of cells is a single layer of flattened spindle cells. The sides of the bulb are outlined by a somewhat laminated fibrous membrane. At the extremity of the bulb, beneath the papilla, there is a thin zone of more cellular fibrous tissue. The papilla has myxoid qualities and is loosely cellular. In the zone of pigmented cells, the germinative cells of the hair shaft are revealed. Some of the pigmented, vacuolated cells distort the contour of the papilla. In these areas, the rounded, vacuolated cells appear to interrupt the basement membrane at the interface between the papilla and the matrical cells of the hair shaft. In the downward directed wings of the papilla, there are regional variations in cellular features and nuclear orientations.


F2Ch9: At a slightly higher (a more superficial) level, the cells of concentric domains have distinctive characteristics - so much so that even thin rows of cells have been assigned individual names. The archaic names have little utility in attempts to define the boundaries of the individual domains. In the top half of the field, the hair shaft is loosely, but regularly, cellular; the cells have thin, small, elongated nuclei with delicate chromatin; the nuclei of this zone are parallel to the long axis of the hair shaft. This cellular zone qualifies as the cellular zone of the keratinizing hair shaft. Deep to this area, clustered, pigmented hair matrical cells have round nuclei; the melanin is more coarsely clumped in the matrical cells. The oblique nature of the section provides a demonstration of the hair matrical cells. Two green arrows near the bottom of the field marks the boundary between two multi-layered zones of cells. The innermost zone that abuts upon the cluster of pigmented hair matrical cells is the germinative layer for what at a slightly higher level becomes a single layer of cuboidal, dark cells. The next, outer layer of stratified cells (at the extremity of the follicle in this field) abuts upon the dark layer without a membranous interface; the cells of this zone have pale cytoplasm and nuclei that are similar to those of the stratified cells of the dark zone. At about the level where the dark cells align to form a single layer, some of the cells of the pale zone do the same. An interface between two rows of distinctive cells, each in single file, is formed. Peripheral to the row of pale cells, there is a layer of somewhat elongated cells with prominent trichohyaline granules in the cytoplasm. A layer of plate-like cells that overlap separates the cells of the outer root sheath (the stratified clear cells) from the cells containing trichohyaline granules. These cells have pale acidophilic cytoplasm and contain small pyknotic nuclei; in areas, they are anuclear. Thus, the sleeve of cells containing trichohyaline granules is outlined on its inner and outer surfaces by a row of pale acidophilic cells. Some of the pale acidophilic cells have pyknotic nuclei and some are apparently anuclear (keratinized). Near the superficial extremity of the sleeve of granular cells, the granular cells also contribute to the population of keratinized cells. In this area, the contributions from the three sources cannot be distinguished. The keratinizing cells of the developing hair shaft form   single-cell files, each of these closely packed files are separated from their neighbors by only a straight acidophilic fiber.


F3Ch9: Beginning with the extremity of the follicle (in this field), a blue arrow defines the boundary between a row of cells, with trichohyaline granules in the cytoplasm, and the thin peripheral fibrous sheath. The “glassy membrane” is not represented at this level. The boundary between the stratified pale cells and the thin layer of granular cells is marked with a yellow arrow. A red arrow marks the interface between the stratum of pale cells, and the stratum of dark cells. Above the zone of dark cells, a cluster of matrical cells of the hair shaft is represented. At about the mid-level of this portion of the follicle, a yellow arrow identifies the interface between the file of plate-like pale acidophilic cells and the granular layer. A blue arrow identifies the interface between a file of cuboidal pale cells and the granular layer. The file of pale cuboidal cells progressively keratinize as they approach the more superficial locations along the follicular root. The interface between the file (actually a sleeve) that is in continuity with pale cuboidal germinative cells, and the file (another sleeve) that is in continuity with the dark cuboidal germinative cells is marked by a red arrow. The outer root sheath does not keratinize at this level. The column of granular cells and its ensheathing sleeves of cells in vertically oriented files contribute the layer of keratin along the surface of the inner root sheath beyond the level at which the shaft separates from the inner root sheath. It is at this point, that the actual hard cuticle of the cortex of the hair first appears.


F4Ch9: This is the same hair bulb (slightly higher magnification) as seen in F5Ch9 above). The zonal patterns now take on added significance. The file of somewhat flattened granular cells, near the top of the field to the left side of the bulb, clearly appear to have a relationship to the underlying zone of stratified pale cells. The zone of dark cells is composed of one or two cell layers. A crescentic collection of pigmented cells over the papilla represents a tangential section of the matrical cells of the hair shaft. Where the “arms” of the bulb compress the base of the papilla, the interface is defined by a thin basement membrane. At the interface between the trichogenic cells of the bulb and the papilla, there is no identifiable basement membrane.


F5Ch9 (R4919): This is the distal extremity of a follicle in a lesion of fibrous papule. It is difficult to identify a population of progenitor cells for the outer root sheath in the mixed population of cells forming the non-trichogenic portion of the bulb. I interpret the cluster of cells outlined by yellow arrows as the progenitor cells of the hair (the trichogenic portion of the bulb). Dark blue arrows identify cells that will become Henle’s layer. The cells of Huxley’s layer are easily identified by their trichohyaline granules. Red and light blue arrows identify cells of the non-trichogenic portion of the bulb. The small dark cells (green arrows) are interpreted as melanocytic precursors. If this is a correct interpretation, the cells appear to be streaming out of the papilla; perhaps, they are of neural origin. A thin basement membrane is recognizable between the trichogenic, hair matrical cells and the papilla in this field.


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