Epithelium structure

Development of a colorectal neoplasm is a multistep process of genetic and phenotypic alterations of normal bowel epithelium structure and function leading to unregulated cell growth, proliferation, and tumor development. 

Killion, J.J. et al., Maintenance of intestinal epithelium structural integrity and mucosal leukocytes during chemotherapy by oral administration of muramyl tripeptide phosphati-dylethanolamine, Cancer Biother. Radiopharm., 11, 363, 1996. 

The development of a colorectal neoplasm is a multi-step process of several genetic and phenotypic alterations of normal bowel epithelium structure and function, leading to unregulated cell growth, proliferation, and tumor development. Since the majority of colorectal cancers develop sporadically, with no inherited or familial disposition, efforts have been directed toward identifying these alterations and learning whether detection of such changes may lead to improved cancer detection and/or treatment outcomes. 

The importance of respiratory heat and water losses is not confined to the respiratory structures. Inspiration of cold, hot, or dry air poses the potential threats of thermal injury or desiccation to the airway epithelium" - T8,69 g challenge to whole-body thermoregulation. 

The basement membrane is a structure that supports overlying epithelial or endothelial cells. The primary fimction of the basement membrane is to anchor down the epithelium to its loose connective tissue underneath. This is achieved by cell-matrix adhesions through cell adhesion molecules. 

Sensory receptors that structurally and functionally belong to the G protein coupled receptor superfamily. Olfactory receptors are a large GPCR family with >300 members in human that are expressed in neurons of the nasal olfactory epithelium where they sense mostly volatile olfactory molecule. The overall number of olfactory receptors differs widely between species and an expansion of different recqrtors is in particular obvious in species that depend on their olfactory sense for survival. 

It may be safely assumed that each of these sets of receptor locations is structurally somewhat heterogeneous, and that it occupies a specific area of the sensory epithelium, with a characteristic, possibly very complex, topology. Because knowledge of this taste modality is still minimal, the topological structure of the taste modality is pure speculation. One such speculation was offered by Beets. To simplify his reasoning, Beets assumed the topology to refer to a two-dimensional area of the sensory... 

The mechanisms by which the taste (and also the olfactory) system senses chemical compounds is assumed to occur by way of a chemoreceptory system that interacts effectively with a broad, structural variety of stimulant molecules, by means of a receptor epithelium consisting of the mosaic of adjacent, peripheral membranes of many receptor cells, exposed to a medium carrying stimulus molecules. A receptor cell is conveniently and, for our present purpose, sufficiently defined as a cell equipped to interact, according to some mechanism, with stimulus molecules, to convert the effect of this interaction into a signal, and to project this signal into the system. The taste receptor is thus a differentiated, epithelial cell synaptically contact-... 

The cornea is the first structure of the eye to be in contact with incident light. It is composed of five distinct layers lying parallel to its surface the outer epithelium, which is continuous with the epithelial layers of the conjunctiva the epithelial basal lamina the keratocyte-containing stroma, which is a collagen structure arranged so that it is transparent Descemet s membrane and, finally, the endothelium adjacent to the aqueous humour. 

The retina comprises two principal components, the non-neural retinal pigment epithelium and the neural retina. The retinal pigment epithelium is an essential component of the visual system both structurally and functionally. It is important for the turnover and phagocytosis of photoreceptor outer segments, the metabolism of retinoids, the exchange of nutrients between the photoreceptors, and the choroidal blood vessels and the maintenance of an efficient outer blood-retinal barrier. 

Structurally, the large intestine is similar to the small intestine, although the luminal surface epithelium of the former lacks villi. The muscularis mucosa, as in the small intestine, consists of inner circular and outer longitudinal layers. Figure 6 illustrates a photomicrograph and diagrammatic sketches of this region. 

One of the key parameters for correlating molecular structure and chemical properties with bioavailability has been transcorneal flux or, alternatively, the corneal permeability coefficient. The epithelium has been modeled as a lipid barrier (possibly with a limited number of aqueous pores that, for this physical model, serve as the equivalent of the extracellular space in a more physiological description) and the stroma as an aqueous barrier (Fig. 11). The endothelium is very thin and porous compared with the epithelium [189] and often has been ignored in the analysis, although mathematically it can be included as part of the lipid barrier. Diffusion through bilayer membranes of various structures has been modeled for some time [202] and adapted to ophthalmic applications more recently [203,204]. For a series of molecules of similar size, it was shown that the permeability increases with octa-nol/water distribution (or partition) coefficient until a plateau is reached. Modeling of this type of data has led to the earlier statement that drugs need to be both... 

JL Madara, JR Pappenheimer. (1987). Structural basis for physiological regulation of paracellular pathways in intestinal epithelium. J Membr Biol 100 149-164. 

G proteins regulate intracellular concentrations of second messengers. G proteins control intracellular cAMP concentrations by mediating the ability of neurotransmitters to activate or inhibit adenylyl cyclase. The mechanism by which neurotransmitters stimulate adenylyl cyclase is well known. Activation of those neurotransmitter receptors that couple to Gs results in the generation of free G(IS subunits, which bind to and thus directly activate adenylyl cyclase. In addition, free Py-subunit complexes activate certain subtypes of adenylyl cyclase (see Ch. 21). A similar mechanism appears to be the case for G(IO f, a type of G protein structurally related to G that is enriched in olfactory epithelium and striatum (Ch. 50). 

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