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Luminal fluid

Solubility and dissolution are processes that take place in the gastric and the luminal fluids, not on the surface of epithelial cells. Measurement of solubility ideally needs to take place at pH 1.7 (stomach) and pH 5-8 (small intestinal tract). Ideally, the screen media should resemble intestinal fluids and contain bile acid-lecithin mixed micelles. Fast and reliable techniques for assessing solubility in... [Pg.248]

Sodium reabsorption Much less than 10% of the filtered load of NaCl reaches the distal nephron. Regulation of Na uptake, occurring mainly in the principal cells of the cortical collecting tubule, is controlled by the steroid hormone aldosterone (see Section 4.4). The net effect of aldosterone is the reclamation of NaCl and potassium excretion in to the luminal fluid. [Pg.272]

Lu et al. (1992) performed a comparison of water and solute uptake in the in situ single-pass perfusion model and the isolated loops conscious rat model. Water flux in both experimental set-ups was found to be comparable. It was found that the solute (i.e. acetaminophen and phenytoin) membrane permeabilities (Pm) were consistently higher in the chronically isolated loops compared to the in situ perfusion. It was suggested that this was as a result of greater luminal fluid mixing in the in vivo system. A key advantage of the in vivo approach was that each animal can act as its own control for drug absorption studies. [Pg.56]

Permeability in the IPL has generally been measured by solute flux in the airway to perfusate direction. The flux of solutes in the perfusate to luminal fluid direction compared to absorptive flux [87] revealed a consistent disparity for a series of six hydrophilic compounds, which was suggested to be due to... [Pg.151]

Intestinal Metabolism Intestinal drug metabolism can occur by microflora present in the gut lumen, as well as by enzymes present in luminal fluids and in the intestinal mucosa [166], Metabolism of xenobiotics by gut microflora is low in comparison to metabolism by the gut mucosa and liver [62], However, the intestinal microflora (e.g., Bacteroides and Bifidobacteria) may play an important role in the first-pass metabolism of compounds that are poorly or incompletely absorbed by the gut mucosa, especially in the lower parts of the intestine. This bacterial metabolism is largely degradative,... [Pg.185]

An important functional characteristic of the proximal tubule is that fluid reabsorption is isosmotic that is, proximal reabsorbed tubular fluid has the same osmotic concentration as plasma. Solute and water are transported in the same proportions as in the plasma because of the high water permeability of the proximal tubule. Thus, the total solute concentration of the fluid in the proximal convoluted tubule does not change as the fluid moves toward the descending loop of Henle. The corollary of this high water permeability is that unabsorbable or poorly permeable solutes in the luminal fluid retard fluid absorption by proximal tubules. This is an important consideration for understanding the actions of osmotic diuretics. [Pg.242]

Thiazide diuretics act in the distal convoluted tubule, where they block Na -Cl cotransport (Fig. 21.4). The Na" -Cl cotransport takes place on the luminal surface of distal convoluted tubules. Thus, to exert their diuretic action, the thiazides must reach the luminal fluid. Since the thiazide diuretics are largely bound to plasma proteins and therefore are not readily filtered across the glomeruli, access to the luminal fluid is accomplished by the proximal tubule organic acid secretory system. The drugs then travel along the nephron, presumably being concentrated as fluid is abstracted, until they reach their site of inhibitory action in the distal convoluted tubule. [Pg.245]

The intracellular concentration of urate in the proximal tubule will ultimately be determined by the balance of influx and efflux. When the transport of urate from the peritubular fluid is high, there is a net elimination of urate across the luminal membrane. In contrast, when the transport of urate from luminal fluid is high, there is a net reabsorption across the basolateral membrane. [Pg.442]

Because water is reabsorbed in direct proportion to salt reabsorption in the proximal tubule, luminal fluid osmolality remains nearly constant along its length, and an impermeant solute like inulin rises in concentration as water is reabsorbed. If large amounts of an impermeant solute such as mannitol (an osmotic diuretic) are present in the tubular fluid, water reabsorption causes the concentration of the solute and osmolality of tubular fluid to rise, eventually preventing further water reabsorption. [Pg.323]

Organic acid secretory systems are located in the middle third of the straight part of the proximal tubule (S2 segment). These systems secrete a variety of organic acids (uric acid, nonsteroidal anti-inflammatory drugs [NSAIDs], diuretics, antibiotics, etc) into the luminal fluid from the blood. These systems thus help deliver diuretics to the luminal side of the tubule, where most of them act. Organic base secretory systems (creatinine, choline, etc) are also present, in the early (Si) and middle (S2) segments of the proximal tubule. [Pg.323]

Stimulant laxatives Bisacodyl, 5-15 mg daily. Senna, dosage varies, consult product labeling Correctol, Dulcolax, Ex-Lax, Senokot, various generic Stimulant laxative actions include direct irritation of intestinal mucosa or stimulation of the myenteric plexus, resulting in peristalsis. These agents may also cause alteration of fluid and electrolyte absorption, resulting in luminal fluid accumulation and bowel evacuation. [Pg.1347]

A second approach to obtain Eq. (16) is to consider the small intestine as a compartment from which the drug disappears following a first-order process. This process corresponds to the disappearance by absorption of the remaining amounts of a tested drug or xenobiotic from the perfusion fluid along the in situ absorption experiment As Ar is the amount of the tested compound in the luminal fluid at any time, t, and Ao is the initial amount (i.e. the total dose perfused), one can write ... [Pg.100]

Where Ar/Ao is the fraction of the initial dose remaining in the luminal fluid. 1 — Ar/Ar, represents the fraction of the compound absorbed, provided that no presystemic losses exist, i.e. F. If we make t equivalent to the mean absorbing time (that is, the total time along which the absorption of the compound takes place), Eq. (16) is obtained. [Pg.101]

It has to be emphasized that this expression is only applicable to compounds that are absorbed by diffusion and do not suffer a first-pass effect. The compounds that are actively absorbed (at least in part) along the enterocyte membrane, as well as those that are actively and substantially excreted to luminal fluid from the membrane or even the cytoplasm of the absorbing cells (i.e. P-gp substrates), should not be used for such approaches. For the compounds tested, the fraction of dose absorbed in vivo coincides with oral bioavailability (/ ), since they are passively absorbed and do not suffer first-pass metabolism. [Pg.102]

Macromolecules, such as proteins and peptides, are taken up by polarized epithelial cells by random pinocytosis, i.e., sampling of luminal fluid containing such molecules into apical early endosomes (AEE) as shown for MDCK cells in vitro (Leung et al. 2000). Further intracellular sorting is depicted in general terms in Fig. 3.3. Recycling to the apical surface or transcytosis is then mediated... [Pg.54]

Epithelial cells are interconnected at the apical (mucosal) side by a complex network of proteins, called the tight junctions (TJ). First thought to have merely a static role in restricting access of compounds present in the luminal fluid to the underlying subepithelial tissue and systemic circulation by the paracellular pathway, TJ are known today to be dynamic structures involved in cellular differentiation, cell signaling (Harder and Margolis 2008), polarized vesicle trafficking, and protein synthesis. [Pg.57]

The papilla is the smallest anatomical portion of the kidney. Papillary tissue consists primarily of terminal portions of the collecting duct system and the vasa recta. Papillary blood flow is low relative to cortex and medulla less than 1% of total renal blood flow reaches the papilla. However, tubular fluid is maximally concentrated and the volume of luminal fluid is maximally reduced within the papilla. Potential toxicants trapped in tubular lumens may attain extremely high concentrations within the papilla during the process of urinary concentration. High intraluminal concentrations of potential toxicants may result in diffusion of these chemicals into papillary tubular epithelial and/or interstitial cells, leading to cellular injury. [Pg.694]

Third, active transport processes within the proximal tubule may further raise the intracellular concentration of an actively transported toxicant. During active secretion and/or reabsorption, substrates generally accumulate in proximal tubular cells in much higher concentrations than present in either luminal fluid or peritubular blood. [Pg.702]

High, predictable delivery rates can be obtained independent of GI motility and the pH of luminal fluids. [Pg.1250]

Copper-containing intrauterine contraceptive devices (10-12) became popular because local inflammatory reactions in the endometrium are more marked and the contraceptive effect is thus more pronounced (SEDA-21, 234) (13). In addition, copper ions released from intrauterine contraceptive devices reach concentrations in the luminal fluids of the genital tract that are toxic to spermatozoa and embryos. The ability of copper to induce the generation of free radicals and the formation of malonaldehyde may be involved in its contraceptive effect. [Pg.902]


See other pages where Luminal fluid is mentioned: [Pg.222]    [Pg.56]    [Pg.104]    [Pg.15]    [Pg.202]    [Pg.276]    [Pg.60]    [Pg.118]    [Pg.41]    [Pg.41]    [Pg.253]    [Pg.33]    [Pg.323]    [Pg.137]    [Pg.269]    [Pg.273]    [Pg.350]    [Pg.162]    [Pg.441]    [Pg.113]    [Pg.308]    [Pg.817]    [Pg.819]    [Pg.116]    [Pg.255]    [Pg.1073]   
See also in sourсe #XX -- [ Pg.694 ]




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Luminal fluid volume

Luminous

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