Water absorption/secretion

Figure 14 Ion transport pathways responsible for water flux across intestinal epithelia. Sodium absorption in villus tip cells (left) stimulates water absorption, while chloride channel exit in crypt cells (right) stimulates water secretion.

The potent antidiuretic hormone AVP orchestrates the regulation of free water absorption, body fluid osmolality, cell contraction, blood volume, and blood pressure through stimulation of three G-protein-coupled receptor subtypes Vi-vascular types a and b, V2-renal, and V3-pituitary. Increased AVP secretion is the trademark of several pathophysiological disorders, including heart failure, impaired renal function, liver cirrhosis, and SIADH. As a consequence, these patients experience excess water retention or inadequate free-water excretion, which results in the dilution of sodium concentrations, frequently manifesting as clinical hyponatremia (serum sodium concentration <135mmol/L). This electrolyte imbalance increases mortality rates by 60-fold. Selective antagonism of the AVP V2 receptor promotes water... 

Cryptosporidium all ages/children in developing areas/immunocompromised adults/outbreaks in developed areas 7-10 days (range 5-28 days) intermittent and scant to continuous and watery prostaglandins —> cAMP-mediated apical chloride secretion and inhibition of electroneutral sodium chloride and water absorption release of IL-1, IL-8 and TNF-a... 

Although infection with C. parvum is considered predominantly secretory, histopathologic studies have revealed varying degrees of villous atrophy and infiltration of inflammatory cells beneath the epithelial mucosa [85, 86], Prostaglandins, which are known to induce cAMP-mediated apical chloride secretion and inhibit electroneutral sodium chloride and water absorption in enterocytes, have been demonstrated to be elevated in a porcine model of cryptosporidiosis [87], Inflammatory cytokines such as IL-1, IL-8 and TNF-a are induced in intestinal epithelial cell lines infected with Cryptosporidium and in animal models of cryptosporidiosis and have been postulated to play a role in pathogenesis [88, 89], Expression of TNF-a and IL-1 mRNA in the majority of jejunal biopsies of adult volunteers after experimental infection were also observed, although this did not correlate with the enteric symptoms [90]. 

An additional consideration when using in situ techniques is the volume of the luminal drug solution as water absorption and secretion during the perfusion may introduce errors in the lumenal concentrations and therefore in the calculated absorption. Various water flux correction methods have been published [42] including the co-perfusion of a non-absorbed marker such... 

Plain water crosses the walls of the intestine by osmotic action alone. However, if sodium and sugars are also present then the active transport mechanisms described earlier operate and water absorption can be enhanced. The effect is dependant on concentrations the maximum rate of water uptake occurs when the concentrations give a slightly hypotonic solution (200-250 mOsm/kg, cf. 287 mOsm/kg for isotonicity) (Wapnir and Lifshitz, 1985). Conversely, when the lumen contents are significantly hypertonic, water is secreted from plasma into the intestine by osmotic action this is a dehydrating effect. 

Kreydiyyeh et al. (2001) provided scientific evidence to confirm the laxative property of parsley, as claimed in folk medicine, and explained its mechanism of action. A perfusion technique was used to measure net fluid absorption from rat colon. The addition of an aqueous extract of parsley seeds to the perfusion buffer, and the omission of sodium, both significantly reduced net water absorption from the colon, as compared with the control. Parsley, added to a sodium-free buffer, did not lead to any further significant change in water absorption as compared with parsley alone suggesting that with parsley, sodium absorption was already inhibited. Since K+ and Cl secretion depends on the activity of the NaKCl2 transporter, the latter was inhibited with furosemide, which increased net water absorption significantly. When parsley and furosemide were... 

In the fasting state, 9 L of fluid enters the proximal small intestine each day. Of this fluid, 2 L are ingested through diet, while the remainder consists of internal secretions. Because of meal content, duodenal chyme is usually hypertonic. When chyme reaches the ileum, the osmolality adjusts to that of plasma, with most dietary fat, carbohydrate, and protein being absorbed. The volume of ileal chyme decreases to about 1 L/day upon entering the colon, which is further reduced by colonic absorption to 100 mL daily. If the small intestine water absorption capacity is exceeded, chyme overloads the colon, resulting in diarrhea. In humans, the colon absorptive capacity is about 5 L daily. Colonic fluid transport is critical to water and electrolyte balance. 

Tachykinins Neurons localized in the submucous and myenteric plexuses enterochromaffin cells in gut epithelium 1. Regulates vasomotor and gastrointestinal smooth muscle contraction 2. Mucus secretion and water absorption Direct and indirect activation of neurons in submucosa and myenteric plexuses in gut epithelium... 

During the passage through the tubules, the glomerular filtrate is not only concentrated, but its composition is considerably modified by reabsorption and secretion in the tubular cells. Several forms of tubular reabsorption are discussed in the paragraphs on sodium, potassium, chloride, and water metabolism. It appears that the mechanisms of electrolyte and water absorption vary greatly. Absorption can be passive, as is the case for chloride, or active and influenced by hormones, as is the case for sodium and water (in at least some portions of the nephron) [6]. 

The colon contains the most species-rich and densely populated human-associated microbial communities, and the most widely studied. The colonic microbiota comprises many hundreds of bacterial species, 1000s of strains and populations of about 10 cells/g contents. The physiology of the colon renders it a particularly suitable bacterial habitat, as the flow of intestinal digesta slows, allowing bacteria ready access to dietary growth substrates. The pH is moderately acidic in the proximal colon, mainly due to bacterial fermentation itself, and increases to a more neutral pH in the transverse and distal colon with secretions by the host and water absorption. Indeed, using in vitro models of the human gut microbiota, pH has been shown to be a critical modulator of both microbiota composition and metabolic activity under the physicochemical conditions of the human colon. ... 

EP3 Kidney, adrenal gland, stomach, uterus, testis, ovary, hrain, spleen, colon, heart, liver, skeletal muscle, lung Inhibition of gastric acid secretion, inhibition of water absorption, uterine contraction... 

The water absorption of a facial prosthesis is important since they may absorb saliva, sweat and/or nasal secretions from the surrounding tissue and also during washing the prosthesis in water. Any absorbed water may affect the physical properties and subsequently influence the color matching to the surrounding facial tissue [57]. 

Bde salts, cholesterol, phosphoHpids, and other minor components are secreted by the Hver. Bile salts serve three significant physiological functions. The hydrophilic carboxylate group, which is attached via an alkyl chain to the hydrophobic steroid skeleton, allows the bile salts to form water-soluble micelles with cholesterol and phosphoHpids in the bile. These micelles assist in the solvation of cholesterol. By solvating cholesterol, bile salts contribute to the homeostatic regulation of the amount of cholesterol in the whole body. Bile salts are also necessary for the intestinal absorption of dietary fats and fat-soluble vitamins (24—26). 

Bile is produced continuously by the liver bile salts are secreted by the hepatocytes and the water, sodium bicarbonate, and other inorganic salts are added by the cells of the bile ducts within the liver. The bile is then transported by way of the common bile duct to the duodenum. Bile facilitates fat digestion and absorption throughout the length of the small intestine. In the terminal region of the ileum, the final segment of the small intestine, the bile salts are actively reabsorbed into the blood, returned to the liver by way of the hepatic portal system, and resecreted into the bile. This recycling of the bile salts from the small intestine back to the liver is referred to as enterohepatic circulation. 

Water and electrolytes. Each day in an average adult, about 5.51 of food and fluids move from the stomach to the small intestine as chyme. An additional 3.5 1 of pancreatic and intestinal secretions produce a total of 9 1 of material in the lumen. Most of this (>7.5 1) is absorbed from the small intestine. The absorption of nutrient molecules, which takes place primarily in the duodenum and jejunum, creates an osmotic gradient for the passive absorption of water. Sodium may be absorbed passively or actively. Passive absorption occurs when the electrochemical gradient favors the movement of Na+ between the absorptive cells through "leaky" tight junctions. Sodium is actively absorbed by way of transporters in the absorptive cell membrane. One type of transporter carries a Na+ ion and a Cl ion into the cell. Another carries a Na+ ion, a K+ ion, and two Cl ions into the cell. 

Diarrhea is an imbalance in absorption and secretion of water and electrolytes. Diarrhea may be associated with a specific disease of the GI tract or with a disease outside the GI tract. 

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