Basal laminas epithelium

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 cyclophyllidean oncosphere is well supplied with musculature and the general pattern of muscles appears to be similar in most species. So in both Hymenolepis citelli (which penetrates an invertebrate gut) and E. granulosus (which penetrates a vertebrate gut) there are 16 somatic muscle cells (146, 839). However, E. granulosus has 16 hook muscle cells but H. citelli has only 13. In E. granulosus, the hook muscles have been shown to insert at the collar and base of the hooks and at the basal lamina of the embryonic epithelium. Each pair of hooks has three muscle systems associated with it (a) a protractor system, for hook extensions (b) an abductor system, which draws the hooks together and (c) a retractor system which pulls the hooks into the body (839). 

What happens at the instant when an odor-active molecule comes in touch with our nasal cavity 205 The first interaction of odorant molecules takes place in the olfactory receptor neurons, which are embedded in the pseudostratified columnar epithelium (or simply, olfactory epithelium), which is located in the posterior nasal cavity in the case of mammals. Olfactory sensory neurons express receptor proteins on the surface membrane of the cilia, which gain access to the extracellular region covered with mucus. The airborne odorants are dissolved into the mucus, bind with the receptors, and then the receptor protein triggers a signal transduction cascade. This results in the opening of the cation channel that would depolarize the sensory neuron and eventually elicit a train of action potentials in the axon. The olfactory axon leads to the olfactory bulb through basal lamina and lamina propria. 

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. 

Electron microscopic examination of livers taken from numerous premature infants (before 90 days of age) suggests that paucity in non-syndromic patients may result from primary ductal plate insult there are undulations and breaks in the basal lamina and lymphocytic infiltration of the duct epithelium as well as canalicular dilatations with blunting of microvilli. (511) The cause is unknown. Apparently, one and the same event is involved, yet with different manifestation forms in childhood and in adulthood as well as with varying degrees of severity. (498)... 

Where a stromal surface meets the epithelium, the fibroblasts interact with epithelial cells to form a basal lamina. This thin, flexible layer of specialized extracellular matrix (40 to 120 nm thick) underlies all epithelial cell sheets or tubes and is detected by... 

Fig. 3.2 Relationship of the connective tissue stroma to an epithelium. Fibroblasts secrete unique types of laminin proteins that interact with each other and type IV collagen, to form a basal lamina (yellow) that is tightly attached to the connective tissue (stromal) cells and also to the associated muscle or epithelial cell. The kidney glomerulus is a specialized tissue in which the stroma is absent and endothelial cells and epithelial cells are separated by the basal lamina which filters the blood as the first step in urine collection. The attachment of an epithelium to stromal collagen is discussed in detail in Chap. 5 (Fig. 19-55 in The Molecular Biology of the Cell. B. Alberts et al., 4th Ed. 2002. Garland Science, Taylor Francis Group, NY)...

The basal cells of a layered epithelium such as skin or gingiva (Sect. 5.2.1), or the periosteal cells covering bone, have such high nutrient demands that they need to be close to a rich capillary bed. Thus, although capillaries permeate the stroma, they are especially dense beneath the basal lamina of a layered epithelium (Sect. 13.3.1) or within a periosteum (Sect. 9.2.1). The gingival-tooth interface is especially susceptible to bacterial agents that... 

This chapter describes the organization of the major proteins that form a basal lamina which connects an epithelium to its underlying stroma (Sect. 1). The organization and major protein composition of oral and gingival epithelium and the junctional epithelial dental attachment at the base of a gingival sulcus are described (Sect. 2). 

At the base of a gingival sulcus, the junctional epithelium mediates the epithelial attachment. This epithelium possesses two basal laminas, an outer one that is continuous with the sulcular epithelium around the free gingiva and an inner one which mediates the actual... 

Basal cells that stop dividing also stop secreting a basal lamina and lose their attachment. They are squeezed by adjacent, dividing basal cells into the body of the junctional epithelium and are expelled into the base of a sulcus. The few tight junctions in the body of the junctional epithelium are consistent with its permeability to interstitial fluid. The rapidly dividing cells of both internal and external basal layers express K5 and K14 like all stratified epithelial basal cells, but the interior cells express K4 and K13, not K1 and K10 (Fig. 5.11). The composition of the internal basal lamina is described in Fig. 5.7b. 

Finally, the ameloblasts secrete an unusual basal lamina, which partially mineralizes into the surface enamel crystals, the enamel cuticle. By this time, the enamel organ has shrunk so that its outer layers have merged with the ameloblast layer at the completed enamel surface postmaturation stage). This reduced enamel epithelium is rubbed off as the teeth erupt, but the enamel cuticle is abraded more slowly and gradually replaced by proteins from saliva, the acquired pellicle (Sect. 12.1.3). 

MDCK cells form a polarized epithelium when grown on a porous membrane filter coated on one side with collagen and other components of the basal lamina. With the use of the special culture dish shown here, the medium on each side of the filter (apical and basal sides of the monolayer) can be experimentally manipulated and the movement of molecules across the layer monitored. Anchoring junctions and tight junctions form only if the growth medium contains sufficient Ca ". ... 

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