Sebaceous Glands Ebook
Sebaceous glands are found in the mucosa of 60 to 75 of adults and are seen as pale yellow spots in the upper lip and buccal mucosa. The openings of minor salivary glands are evident in many areas. In general, the oral mucosa has a more concentrated network of vessels than is present in the skin. Almost all venous return from the oral mucosa enters the internal jugular vein. Lymphatic capillaries are also present in the lamina propria and arise as blind beginnings in the papillae.
Tin, stannic or tin(IV) oxide was at one time used as an oral medicament in the treatment of superficial staphylococcal infections. Tin was claimed to be excreted via sebaceous glands and thus concentrated at sites of infection. More recently, organic tin derivatives (Fig. 2.26) have been used as fungicides and bactericides and as textile and wood preservatives (Smith 8c Smith, 1975).
A dermoid cyst contains dermal structures (hairs, sebaceous glands), whereas more rarely there is only an epithelial (epidermoid cyst) or a conjunctival lining (conjunctival dermoid). Although dermolipomas are not cystic, they are conveniently classified with dermoid cysts as they arise from cutaneous epithelium sequestered within the conjunctival recesses -typically laterally and occasionally associated with a minor clefting of the outer canthus or with Goldenhar's syndrome. The abnormal epithelium, which often bears hairs and sebaceous glands that cause chronic conjunctivitis, is associated with localised prenatal formation of cutaneous-type fat, which is evident as an underlying bright yellow mass. The differential diagnosis is subconjunctival fat prolapse, which tends to present in obese adults and is not associated with an abnormal conjunctival surface.
The skin is composed of two layers, the epidermis and dermis (figure 2.1). The epidermis is a stratified squamous epithelium consisting primarily of keratinocytes in various stages of differentiation, from mitotically active basal cells (stratum basale or stratum germinatiuum) to the heavily keratinized superficial cells (stratum corneum) that are continually sloughed. Keratinocytes are held together laterally by adhesion belts, desmo-somes, and tight junctions to form a water-impermeable sheet. The ECM of the stratum basale contains hyal-uronic acid (HA), a large polyionic, nonsulfated glycos-aminoglycan (GAG) that binds water, and the basal cells express the CD44 receptor for HA (Chen and Abatangelo, 1999). Stem cells in the stratum basale are constantly dividing to self-renew and give rise to more differentiated keratinocytes that migrate (or are pushed) upward to replace the cells of the stratum corneum as they slough off. Three other nonepithelial cell types are found in lesser...
The epidermis of the mammalian skin is a continuous, multilayered epithelium interspersed with several appendages hair follicles, sebaceous glands, and sweat glands. The regions of epidermis between the hair follicles and their associated sebaceous and sweat glands are termed the interfollicular epidermis (IFE). Stem cells have been isolated directly from the basal epidermal layer of the outer root sheath of the bulge by the generation of ROSA26 mice transgenic for the reporter genes P-galactosidase or green fluorescent protein (GFP) under the control of keratin promoters specific to bulge cells (Morris et al., 2004 Tumbar et al., 2004 Khavari, 2004). The reporters were activated at anagen by transcription factors targeting these promoters, thus marking the bulge cells (figure 3.6). The cells could be followed in vivo or they could be isolated for in vitro studies by FACS. In vivo, the marked cells contributed primarily to the regenerated hair. Only a few labeled cells were found in...
Because the stratum corneum is the main barrier to drug absorption its structure has been closely studied. The most widely used description is the 'bricks and mortar' model (Figure 8.2) in which the keratinocytes form the hydrophilic bricks and the intercellular lipid is the mortar, so that there is a continuous hydrophobic path through the stratum corneum. There is no direct hydrophilic path since the lipid effectively 'insulates' the keratinocytes from each other, and techniques such as electroporation (q.v.) are required to form a continuous hydrophilic path. The lipids consist mainly of ceramides, fatty acids, and cholesterol. Alkanes are commonly present although they are almost certainly derived from environmental sources. It is particularly difficult to study the intercellular lipids since they are easily contaminated with lipids from the sebaceous glands (squalane and triglycerides) or from epidermal fat3. The dermis contains blood vessels, nerves, hair follicles, sebum and...
An interesting and important fact is that both regeneration and scarring occur simultaneously in excisional wounds. While the dermal connective tissue heals by fibrosis, the epidermis and the vasculature regenerate, though the epidermis may lack structures such as hair follicles and sebaceous glands. Regeneration of the basic epidermal structure and the vasculature are constant features associated with repair by regeneration or scarring and reflect selective pressure for re-forming a barrier to the external environment and nourishment and oxygenation of underlying tissue. Why epidermal and endothelial cells respond to the wound environment by regenerating and dermal fibroblasts do not is a question of considerable interest.
iP Despite their name, these cysts are not derived from sebaceous glands. Sebaceous cysts result from the cystic proliferation of epidermal cells within the dermis. The source of this epidermis is often the infundibulum of the hair follicle. Inflammation is usually a foreign body, granulomatous reaction to material contained within the cysts.
The skin on the palm is the thickest in the body as a result of a thickened stratum corneum in the epidermis layer (the dermis is as thick as on the dorsum of the hand). The skin has a rich supply of sweat glands but contains no hair or sebaceous glands. Examination of the palmar hand shows a multitude of flexor creases ( lines of the hand) and papillary ridges (fingerprints). The function of the latter is controversial, but they may function to improve grip, like the tread on a car tire. Skin of the hand is held firmly in place by its attachment to the underlying palmar fascia, and a tight network of fibrous bands connects the two.
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