Tissue layers epithelium

Four major tissue layers, from the lumen outward, form the large intestine the mucosa, submucosa, muscularis externa, and serosa (Fig. 88-2). Complete replacement of surface epithelial cells occurs approximately weekly, with the total number of epithelial cells remaining constant in normal colonic tissue. As patients age, abnormal cells accumulate on the surface epithelium and protrude into the stream of fecal matter their contact with fecal mutagens can lead to further cell mutations and eventual adenoma formation.4... 

The oral mucosa is anatomically divided into three tissue layers (Fig. 1) [10] the epithelium, the basement membrane, and the connective tissues. 

The major limitation to developing therapeutic proteins in nonparenteral dosage forms is the poor permeability of these water-soluble and hygroscopic macromolecules across the tissue layers at the site of drug administration. These tissue layers include the epithelium of the gastrointestinal tract, the stratum corneum of the skin, and the epithelium lining of the alveoli and nasal cavity. 

In common with all epithelial interfaces (see Section 1.3.2), the epithelium of the oral cavity is supported by a basement membrane, which separates the epithelium from the underlying connective tissue layer (the lamina propria) (Figure 7.1). Oral epithelium is broadly similar to stratified squamous epithelia found elsewhere in the body, for example the skin (see Section 8.2.1), in that cells are produced by mitosis in the basal layer of the epithelium and these proliferating cells push existing cells towards the surface. The phases of this dynamic process are represented in four morphological layers ... 

The vitreous humor is a viscoelastic connective tissue composed of small amounts of glycosaminoglycans, including hyaluronic acid, and of such proteins as collagen.The collagen fibrils are anchored directly to the basal lamina, which forms the boimdaries of the lens, the ciliary body epithelium, and the neuroglial cells of the retina. Although the anterior vitreous is cell free, the posterior vitreous contains a few phagocytic cells, called hyalo-cytes, and is sometimes termed the cortical tissue layer. 

Verruca vulgaris, verruca plana, and cutaneous horn are forms of viral warts produced by the human papilloma virus (HPV).They are caused by an overgrowth of normal epithelium that may become keratinized and pigmented. Because they occur only in the superficial tissue layer, the body does not recognize them as foreign and therefore does not mount an immune reaction. They are most commonly found in children and young adults and may... 

The inner surface of the stomach consists of well-defined tissue layers the muscle and the submucosal and mucosal layers. The absorption function of stomach is minimal owing to the limited surface area, lack of villi, thick mucosal layer, and short residence time. The epithelium of the gastric mucosa secretes hydrochloric... 

A distinctive status of the eye cornea morjrfiology of animals given CMS was epithelization of the whole wound surface. Epithelium growth with immersion into sub-epithelial layer was not observed. Peripheral zones of the wound were covered with a two- to three-layer epithelium wherein a considerable quantity of cells in mitosis was observed. In this zone, collagenic fibers of the cornea itself revealed chemosis, but regulation was observed. Epithelium of adjacent zones comprised four to five layers. In the central sites of the traumatized zone, fibrillogenesis proceeded with higher activity. In contrast to the control and coimective tissue, elements at the wound base contained a few necrotized structures, and much newly formed poorly differentiated connective tissue appeared. 

Erosions or a superficial ulceration of the mucosa can occur focally or diffusely. Erosions are due to focal necrosis of the epithelium and associated stroma and are restricted to the superficial layers. Diffuse irritation accompanied by an inflammatory reaction is called enteritis. Ulcers, in contrast, are deeper lesions extending beyond the mucosa and penetrating into the adjacent tissue layers. Chronic irritation can produce proliferative lesions including dysplasia, which potentially could become malignant. 

The corneal epithelium (epithelium cornea anterior layer) is made up of epithelial tissue and covers the front of the cornea (Figure 51.4). It acts as a barrier to protect the cornea, resisting the free flow of fluids from the tears, and prevents bacteria and also therapeutic drugs from entering the epithelium and corneal stroma. The epithelium of the cornea consists of five to six layers of cells packed closely and connected by tight junctions. The cornea is composed of five layers epithelium, Bowman s membrane, stroma, Descemet s membrane, and endothelium, each of alternating polarity. This sandwich-like structure makes the cornea a crucial barrier to most lipophilic and hydrophilic drugs. To penetrate these layers, optimal lipophilicity for the permeant corresponds to log D values of 2-3. °... 

In the amphibian ovary, oocytes exist within individual follicles, surrounded by an inner layer of follicle cells, a connective tissue layer containing blood vessels, and an outer surface epithelium (Fig. 1). Maturation of these oocytes, as well as ovulation, routinely has been brought about, outside the usual breeding season, by injecting a gravid female... 

Two structures can be recognized at the immediate periphery of the glomerulus a thin hyaline membrane, called the basal membrane, and an epithelial layer of flattened cells. Where the epithelial layer reaches the vascular pole, the lining projects outward and forms a peripheral epithelial membrane (Bowman s capsule) resting on a basal membrane, which is in continuity with the interstitial tissue. The epithelium of Bowman s capsule touches the epithelium of the proximal convoluted tubule. 

Chemical characterization of reticulin is difficult because it usually occurs rather sparsely and mixed with a variety of other tissue components. However, purified reticulin from the cortex of human kidneys has been shown to consist of a combination of collagen, carbohydrate (probably glycoprotein) and possibly lipid. It is thus a complex made up of high molecular weight substances. The lamina densa may influence the transfer of molecules between connective tissue and epithelium and hence would be expected to exert control over the epithelium. It has been suggested that both connective tissue and epithelium collaborate in building up the basement membrane and that the epithelial cells behave atypically by secreting a proline-rich protein into its outer layers. 

Fig. 16. Acrylamide gel patterns of collagen subjected to colli enase derived from human gingival tissues, gingival epithelium only, and ngival connective tissues only. The characteristic control pattern on the left depicts the two o-chains and the two /I-chains (dimers of a..chains) obtained after urea denaturation. In. addition to these two layers, collagen solutions digested by eollagenase from gingival tissues and sub. scquciitly denatured display two layers representing the approximate 3/4 pieces...

The HCE-T Tissue Construct (Gillette model) uses a transfected human corneal epithelial cell line (Kahn et al., 1993) cultured on collagen-membrane cell culture inserts, which, at the air-liquid interface, stratify to form a four- to six-layer epithelium, known as the HCE-T model. Transepithelial permeabiUty (TEP) to sodium fluorescein and transepitheUal electrical resistance (TER) have been identified as physiologically relevant parameters to evaluate the barrier function of the corneal epithelium. Cell viability can be determined by the MTT assay, and histomorphology can also be used as an endpoint (Kruszewski et al., 1997). 

Figure 1 Micrograph of a rat tracheal explant The explant was initially exposed to amosite asbestos for 1 hr, then maintained in air organ eulture for 7 days, and fixed and processed for histological assessment. Note the adherent mass of fibers on the apieal epithelial surface some fibers have been taken up by the epithelium and some (arrows) have been translocated to the connective tissue layer beneath the epithelium. Cartilage is visible at the bottom of the field. Space between mass of fibers and apical surface is an artifact of cutting direction. (From Ref 161.)...

Airway cross-sections have the nominal anatomy shown in Fig. 5.16. Airway surface liquid (AST), primarily composed of mucus gel and water, surrounds the airway lumen with a thickness thought to vary from 5 to 10 mm. AST lies on the apical surface of airway epithelial cells (mostly columnar ciliated epithelium). This layer of cells, roughly two to three cells thick in proximal airways and eventually thinning to a single cell thickness in distal airways, rests along a basement membrane on its basal surface. Connective tissue (collagen fibers, basement membranes, elastin, and water) lies between the basement membrane and airway smooth muscle. Edema occurs when the volume of water within the connective tissue increases considerably. Interspersed within the smooth muscle are respiratory supply vessels (capillaries, arteriovenous anastomoses), nerves, and lymphatic vessels. 

Submucosa Layer of tissue beneath the airway epithelium. 

The presence of human papilloma virus (HPV) is associated with female genital tract diseases such as condyloma, Bowenoid papulosis, and cervical, vaginal, and vulvar intraepithelial neoplasia and carcinoma. A general concern is the association of HPV with cervical cancer (Gl). The HPV consists of an icosahedral viral particle (virion) containing 8000 base pairs, a circular, double-stranded piece of DNA surrounded by a protein capsid. Viral replication takes place within the nuclei of infected squamous epithelial cells (H5). Following infection of epithelial cells, the viral DNA penetrates throughout the entire thickness of the epithelium, but intact viruses are found only in the upper layers of tissue. 

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