Basal membrane

Figure 41-14. The transcellular movement of glucose in an intestinal cell. Glucose follows Na+ across the luminal epithelial membrane. The Na+ gradient that drives this symport is established by Na+ -K+ exchange, which occurs at the basal membrane facing the extra-ceiiuiarfiuid compartment. Glucose at high concentration within the ceii moves "downhill" into the extracel-iuiarfiuid by fadiitated diffusion (a uniport mechanism).

D). Due to lack of proteolytic enzymes in this pathway, HRP will not be released rather, it will adhere to the basal membrane for possible basal-to-apical transcytosis... 

Figure 8.1 (A) Cross-sectional view of the organization of the small intestine, illustrating the serosa, the longitudinal and circular muscle layers (=muscularis externa), the submucosa, and the intestinal mucosa. The intestinal mucosa consists of four layers, the inner surface cell monolayer of enterocytes, the basal membrane, the lamina propria (connective tissue, blood capillaries), and the muscularis mucosae, (B) Schematic representation of an enterocyte (small intestinal epithehal cell) (according to Tso and Crissinger [151], with permission).

Microvillous Border Membrane and Basal Membrane Vesicles... 

M. Inuyama, F. Ushigome, A. Emoto, N. Koyabu, S. Satoh, K. Tsukimori, H. Nakano, H. Ohtani, and Y. Sawada. Characteristics of L-lactic acid transport in basal membrane vesicles of human placental syncytiotrophoblast. Am J Physiol. 283 C822-C830 (2002). 

The blood-brain barrier is markedly different from peripheral capillaries Peripheral capillaries are fenestrated with openings up to 50 nm wide. In contrast, cerebral endothelial cells are closely connected by tight junctions and zonulae occludentes, resulting in extremely high transendothelial resistances of up to 1500-2000 12 cm2 [16] (Figure 17.1). The capillaries are surrounded by a basal membrane enclosing intermittently pericytes, which have been postulated to be involved in host defense. The outer surface of the basement membrane is covered by astrocytic foot processes. Most likely, secretion of soluble growth factors by astrocytes plays an important role in endothelial cell differentiation. 

In the central nervous system (brain and spinal cord), capillary endo-theUa lack pores and there is little transcytotic activity. In order to cross the blood-brain barrier, drugs must diffuse transcellularly, i.e., penetrate the luminal and basal membrane of endothelial cells. Drug movement along this path requires specific physicochemical properties (p. 26) or the presence of a transport mechanism (e.g., L-dopa, p. 188). Thus, the blood-brain barrier is permeable only to certain types of drugs. 

Tropocollagen molecules are firmly linked together, particularly at their ends, by covalent networks of altered lysine side chains. The number of these links increases with age. Type IV collagens form networks with a defined mesh size. The size-selective filtering effect of the basal membranes in the renal glomeruli is based on this type of structure (see p. 322). 

The ECM has a very wide variety of functions it establishes mechanical connections between cells it creates structures with special mechanical properties (as in bone, cartilage, tendons, and joints) it creates filters (e. g., in the basal membrane in the renal corpuscles see p.322) it separates cells and tissues from each other (e.g., to allow the Joints to move freely) and it provides pathways to guide migratory cells (important for embryonic development). The chemical composition of the ECM is just as diverse as its functions. 

The secretion of T4 and T3 requires the uptake of follicular contents across the follicular cell apical membrane, the enzymatic release of T4 and T3 from peptide linkage within Tg, and the transport of T4 and T3 across the follicular cell basal membrane to the blood. Several of the steps in synthesis and secretion of T4 and T3 may be compromised by iodine deficiency or disease and can be blocked selectively by a variety of chemicals and drugs. 

There are differences in the ease of extravasation of macromolecules from the bloodstream into different tissues [14, 104, 105]. Capillaries in the liver, spleen, and bone marrow have incomplete basal membranes and are lined with endothelial cells which are not continuously arranged. Capillaries in the muscle have a somewhat tighter arrangement, and there is an almost impermeable barrier which isolates the central nervous system from circulating blood. The rate of glomerular filtration of macromolecules depends on their hydrodynamic radius, the threshold being approx. 45 A [106]. Structure of the macromolecule is of utmost importance, since shape, flexibility, and charge influence the penetration and possible readsorption in the tubular epithelia [100]. 

ELBI for 15 min causes alteration of endotheUocytes of the luminal surface of the aorta. The fine folds of their surface become smooth. The endotheUocytes swell and intercellular space is increased denuding the basal membrane. These changes have been noticeable within 1 h after irradiation and completely disappeared after 6 h. 

Irradiation for 60 min caused more damage. Partial detachment and desquamation of endotheUocytes from the basal membrane took place (Fig. 30.1c). Thrombocytes, fibrin threads and erythrocytes were found on the surfaces of denudated zones. 

Irradiation for 60 min resulted in the desquamation of some cells from the basal membrane and the formation of denudated areas of the intima. The affected areas were covered with thrombocytes, erythrocytes and fibrin threads. But 1-2 days after irradiation the intima microrelief of the vein returned to normal. There were no thrombi formations either in the aorta or the vein. 

Thus the effect of ELBI on the aorta and vein endothehocytes depends on the duration of irradiation. Irradiation for 15 and 30 min caused reversible changes which were expressed in changes of the normal cell forms, appearance of craterlike depressions and surface defects, swelling of nuclei and oedema. Irradiation for 60 min had a more pronounced effect on the inner surface of blood vessels resulting in detachment of endothehocytes from the basal membrane and their desquamation. Restoration of the endothelial structure after 15 and 30 min of laser irradiation... 

The sweet taste and olfactory responses to a variety of stimuli are examples of chemical senses that utilize protein receptors for initial detection of the stimulus. Most bitter compounds have a hydrophobic component which enables their direct interaction with the cell membrane however, some evidence suggests a protein receptor mechanism. The cooling sensation is treated as a chemesthetic sense, where stimulation takes place at the basal membrane. However, compounds that evoke this response have very specific structural limitations, and most are related to menthol. For purposes of discussion, bitter and cooling sensations will be discussed under generalized receptor mechanisms. 

Chemesthesis. The term chemesthesis has been introduced to classify thermal and painful sensations experienced in the mouth (26). Chemesthesis refers to a chemical sensibility (mouthfeel) in which certain chemicals direcdy activate nerve fibers at the level of the basal membrane in the mouth. The sensations are analogous to similar effects at the skin surface where there is a close anatomical and functional relationship. Sensations include the "hot" of capsaicin and piperine, which are active components of chili and pepper, the coolness of menthol and the irritation of chemicals such as salt at high concentrations [FIGURE 4]. Some of the descriptive terms used to make qualitative distinctions in food sensations include pungency, freshness, tingling, burning and sharpness. 

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