Mucosal function

Proctor, D. F., Andersen, 1 and Lundqvist, G, R. (1977a). human nasal mucosal function at controlled temperatures. Respiration Physiology 30, 109-124. 

Andersen, I., G. R. Lundquist, and D. F. Proctor. Human nasal mucosal function in a controlled climate. Arch. Environ. Health 23 408-420, 1971. 

Approximately 1 to 1.5 L of fluid is ingested per day, and coupled with secretions from the stomach, pancreas, and proximal duodenum, approximately 8 L of chyme enters the jejunum per day. Reabsorption of 6 to 7 L occurs within the small bowel, leaving a residual of 1.5 L fluid, 90% of which is reabsorbed in the colon. This pattern of liquid reabsorption permits the elimination of fecal waste containing an average of 0.1 to 0.2 L fluid per day. Diarrhea occurs if there is an altered rate of intestinal motility, if mucosal function or permeability is altered, or if the fluid load entering the colon overwhelms colonic reabsorption. Constipation may occur if intestinal movement is inhibited or if there is a fixed obstruction. 

Bismuth subsalicylate (BSS) is used widely in humans for treatment of diarrhea and is specifically recommended for the prevention of traveler s diarrhea. The precise mechanism of action remains undetermined and although the end result of treatment with BSS is reduction in diarrhea (Figueroa-Quintanilla et al 1993), its effect is probably not related to a direct antisecretory mechanism. Salicylates have been shown to stimulate intestinal fluid and electrolyte absorption per se but it is likely that, in many cases of colitis, resolution of inflammation and restoration of a normal surface epithelium is required to restore mucosal function. When used as pretreatment or coadministered, BSS significantly reduced the fluid secretory response to E. coli LT enterotoxin and cholera toxin in intestinal loops of rabbits and pigs (Ericsson et al 1990). However, when administered even 5 min after the enterotoxins, BSS had no significant effect on enterotoxin-stimulated intestinal secretion. These results suggest that BSS adsorbs or neutralizes bacterial enterotoxins but does not alter the effect of enterotoxins once they have bound to intestinal mucosa. BSS also modulates normal... 

Hojgaard L, Mertz Nielsen A, Rune S J 1996 Peptic ulcer pathophysiology acid, bicarbonate and mucosal function. Scandinavian Journal of Gastroenterology Supplement 216 10-15... 

A wide diversity of herbal remedies have purported abilities to stimulate defense functions. Complexes of carbohydrate and lignin, which are present in some herbs, modulate enteric immune functions (Kiyohara et al, 2000), and the changes in cytokine secretion (Matsumoto and Yamada, 2000) can trigger systemic responses. The polysaccharides present in other herbal medicines augment production of immunoglobulin (Ig) A by the Peyer s patches in the small intestine (Sakushima et al, 1997 Yu et al, 1998). The responses of the enteric immune system to lectins are variable (Pusztai 1993), and can elicit systemic responses (Lavelle et al, 2000). Other phytochemicals provide protection by inducing detoxification pathways in mucosal cells (Williamson et al, 1998). 

The quantity and organization of the mucosa are critical determinants of GIT functions. Feeding chicks and rats diets with tannins causes mucosal atrophy and villus shortening, with liver damage, and decreases growth and survival... 

Iron is another vital nutrient in the development of functioning erythrocytes it is essential for the formation of hemoglobin. Lack of iron leads to a decrease in hemoglobin synthesis and ultimately red blood cells. Normal homeostasis of iron transport and metabolism is depicted in Fig. 63-2.7 Approximately 1 to 2 mg of iron is absorbed through the duodenum each day, and the same amount is lost via blood loss, desquamation of mucosal cells, or menstruation. 

Multiple factors play a role in the development of AOM. Viral infection of the nasopharynx impairs eustachian tube function and causes mucosal inflammation, impairing mucociliary clearance and promoting bacterial proliferation and infection. Children are predisposed to AOM because their eustachian tubes are shorter, more flaccid, and more horizontal than adults, which make them less functional for drainage and protection of the middle ear from bacterial entry. Clinical signs and symptoms of AOM are the result of host immune response and damage to cells caused by inflammatory mediators such as tumor necrosis factor and interleukins that are released from bacteria.4... 

The third mucosal layer is that lining the entire length of the small intestine and which represents a continuous sheet of epithelial cells. These epithelial cells (or enterocytes) are columnar in shape, and the luminal cell membrane, upon which the microvilli reside, is called the apical cell membrane. Opposite this membrane is the basal (or basolateral) plasma membrane, which is separated from the lamina propria by a basement membrane. A sketch of this cell is shown in Fig. 5. The primary function of the villi is absorption. 

In practice, estimation of Laq requires information on the rate of solute removal at the membrane since aqueous resistance is calculated from experimental data defining the solute concentration profile across this barrier [7], Mean /.aq values calculated from the product of aqueous diffusivity (at body temperature) and aqueous resistance obtained from human and animal intestinal perfusion experiments in situ are in the range of 100-900 pm, compared to lumenal radii of 0.2 cm (rat) and 1 cm (human). These estimates will necessarily be a function of perfusion flow rate and choice of solute. The lower Laq estimated in vivo is rationalized by better mixing within the lumen in the vicinity of the mucosal membrane [6],... 

Figure 7 (Left panel) Relative absorption rate for a weak acid (pKa = 3) as a function of mucosal pH for increasing barrier (membrane) permeability (Pb) with fixed unstirred aqueous layer permeability (Pul). X = pHinflectionpoint in Eq. (4). (Right panel) Partition coefficient-dependent absorption rates for salicylic acid and the weak base ephedrine. (From Ref. 19.)...

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