Sodium absorption

This reaction is accompanied by a blackening of the vitreous siUca and a flaking of the surface. As evidence for the diffusion step, the sodium absorption by the much denser quartz is 12 mg/(1000 hcm ) at 350°C, whereas vitreous siUca absorbs 23 mg/(1000 hcm ) at 286°C (94). Molten sodium is much less reactive. 

O In CF, the cystic fibrosis transmembrane regulator (CFTR) chloride channel is dysfunctional and usually results in decreased chloride secretion and increased sodium absorption, leading to altered viscosity of fluid excreted by the exocrine glands and mucosal obstruction. 

After absorption in the small bowel, remaining undigested food passes from the ileum through the ileocecal valve to the colon. A major role of the colon is absorption of fluid. Some of the water and sodium absorption achieved by the colon is facilitated by short-chain fatty acids (SFCAs) formed from digestion of certain dietary fibers by colonic bacterial enzymes. 

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 rate equation describes the variation in response variable R (with initial value of Rq) the measure response appears at a constant rate (zero order) of and is eliminafed by the first-order constant. The indirect response models will generally fall info fwo caf-egories inhibition or stimulation function. The inhibition response is classically described in ferms of IC q, fhe drug concenfration fhaf produce 50% of maximal inhibition (e.g., action of S5mfhefic glucocorticoid on adrenal glands or effecf of furosemide on sodium absorption in fhe loop of Henley) and is a number from 0 fo 1 where 1 represents total inhibition ... 

Examine the spectrum below. It is the absorption spectrum for sodium. Absorption spectra are produced when atoms absorb light of specific wavelengths. 

A nephron, showing the major sites and percentage (in braces) of sodium absorption along with other features of solute transport. The filtered load = GFR (180 L/day) Xplasma Na+ (140 mEq/L) or 25,200 mEq/day. About 1% of this amount is excreted in voided urine. Sites where tubular fluid is isosmotic, hypertonic, or hypotonic relative to plasma are shown. POT, proximal convoluted tubule LH, loop of Henle DOT, distal convoluted tubule CCD, cortical collecting duct TAL, thick ascending loop. 

Liddle s syndrome is an autosomal dominant form of hypertension. It is a disorder of the renal epithelial sodium channel, which has three subunits, a, j, and y, and mutations within the first two are associated with increased sodium channel activity [7, 36]. This causes excessive sodium absorption in the distal nephron of the kidney. It gives rise to hypoglycemia, low -renin, and low aldosterone. 

The active Irunsport of chloride has also been demonstrated across ihe wall of the IVog stomach, rat ileum, dog ileum, and the human ileum. Experiments have produced a double exchange model in which bicarbonate secretion and chloride absorption are linked hy an isoelectric mechanism to hydrogen ion secretion and sodium absorption across the human ileum. In 1972. a group of researchers proposed a similar model of coupled transport... 

Fordtran, J.S. (1975) Stimulation of active and passive sodium absorption by sugars in the human jejunum. Journal of Clinical Investigation, 55 728-37. 

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... 

The incidence of classic CAH-P450c21 in the United States ranges from 1 10,000 to 1 18,000, with approximately 75% of patients with CAH-P450c21 exhibiting classic salt wasting (White and Speiser, 2000). Aldosterone is essential for normal sodium homeostasis and acts to enhance sodium absorption and potassium excretion (Fig. 33-3). In the relative absence of aldosterone, there is an increase in sodium loss... 

Four general pathophysiologic mechanisms disrupt water and electrolyte balance, leading to diarrhea. These four mechanisms are the basis of diagnosis and therapy. They are (1) a change in active ion transport by either decreased sodium absorption or increased chloride secretion (2) a change in intestinal motility (3) an increase in luminal osmolarity and (4) an increase in tissue hydrostatic pressure. These mechanisms have been related to four broad clinical diarrheal groups secretory, osmotic, exudative, and altered intestinal transit. 

Malmstadt and Chambers (M2), using an air-propane flame, obtained high accuracy by their standard addition method in the 1-100 ppm range with their nullpoint instrument. It is stated that a small decrease of sodium absorption was found when potassium equaled or exceeded the sodium concentration, and that depression was also seen with high con-... 

Intestinal absorption of salt and water is stimulated by angiotensin II and aldosterone. Angiotensin II stimulates the absorption of Na by the jejunum and ileum. Nerves leading from the brain to the gut may also control sodium absorption by the gut. Angiotensin II in the brain may play a part in this mechanism. Aldosterone seems to have no effect on salt absorption by the small intestines. The kidney is controlled by the nervous system. The nervous control of salt absorption by the kidney seems to play only a minor role in salt balance. Aldosterone stimulates the colon to absorb Na. Plasma angiotensin II is not thought to have a direct effect on salt absorption by the colon. The material described here is outlined in Figure 10.11. 

Studies of human jejunal biopsy specimens from cystic fibrosis patients demonstrated that loperamide can restore sodium absorption to normal levels. 

The mineralocorticoids have a main action on the distal tubules in the kidney to increase sodium absorption, with concomitant increased excretion of K and H. Aldosterone is the main endogenous mineralocorticoid. It is produced in the outermost layer of the adrenal cortex (the zona glomerulosa). An excessive secretion of mineralocorticoids (e.g. in Conn s syndrome) causes marked salt and water retention, with a resultant increase in the volume of extracellular fluid, alkalosis, hyperkalaemia and often hypertension. A decrease in secretion (e.g. Addison s disease) causes a disproportional loss of Na compared to fluid loss, so osmotic pressure of the extracellular fluid is reduced. This results in an increase in intracellular compared to extracellular fluid volume. The concomitant decrease in excretion of K results in hyperkalaemia with some decrease in bicarbonate. The control of synthesis and release of aldosterone is complex and involves both the renin-angiotensin system and the electrolyte composition of the blood. As with other... 

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