Intestinal homeostasis

Bashir ME, Louie S, Shi HN, Nagler- 34 Anderson C Toll-like receptor-4 signaling by intestinal microbes influences susceptibility to food allergy. J Immunol 2004 172 6978-6987. Rakoff-Nahoum S, Paglino J, Eslami-Varzaneh F, Edberg S, Medzhitov R Recognition of commensal microflora by toll-like receptors is required for intestinal homeostasis. Cell 2004 118 229-241. 

Boshuizen JA, Reimerink JH, Korteland-van Make AM, et al. Changes in small intestinal homeostasis, morphology, and gene expression during rotavirus infection of infant mice. J Virol 77 13005-13016, 2003. 

Magrone T, Jirillo E. The interplay between the gut immune system and microbiota in health and disease nutraceutical intervention for restoring intestinal homeostasis. Curr Pharm Des. 2013 19 1329-1342. 

A healthy host exists in a state of equilibrium with the gut microbiota and in this way this microbiota contributes to a balanced host immunity, to homeostasis at the intestinal mucosa and to metabolism, while the host provides it with a constant and convenient habitat, and at the same time keeps microbial numbers in check. A disorder in the host—microbiota equilibrium may hapjren where a pathogen enters the host intestine and interacts with both the host and the microbiota. If both these two components (host and indigenous microbiota) are resilient, the balance is restored with a consequent recovery of the intestinal mucosa. A disruption of the intestinal homeostasis is the result of a disturbance of the host—microbiota balance that in extreme cases may lead to the death of the host. If the pathogen acquires a niche for itself among the indigenous bacteria of the gut, it will eventually create a new equilibrium between the host and the microbiota with consequent chronic presence of the pathogen. ... 

Besides the detoxifying role played by gut bacteria towards mycotoxins and other xenobiotics, the maintenance of a correct balance in the gastrointestinal microflora is crucial for proper nutrient uptake and for an efficient protection against pathogens, according to the so-called "intestinal homeostasis." Thus an impaired balance of the intestinal microbiome, such as in a dysbiosis condition, could adversely affect human health (Figure 8.3). 

Koboziev I, Reinoso Webb C, Furr KL, Grisham MB. Role of the enteric microbiota in intestinal homeostasis and inflammation. Free Radio Biol Med. 2014 68C 122-133. 

Marcon R, Claudino R, Dutra R et al. (2013) Exacerbation of DSS-induced colitis in mice lacking kinin B, receptors through compensatory up-regulation of kinin B2 receptors the role of tight junctions and intestinal homeostasis. Brit J Pharmacol 168 389-402. 

The intestinal ecosystem is a complex microenvironment constituted by eukaryotic and prokaryotic cells where a complex network of signals that maintain the intestinal homeostasis is established. The gut microbiota is an important component of this ecosystem commensal bactaia are key players participating in the digestion process, vitamin synthesis, and other metabolite production (bile acids, lipids, amino acids, and short-chain fatty acids), which are important for maintaining health in mammals (Brestoff and Artis 2013). However, it is known that the commensal microbiota is not in direct contact with the epithelial cells due to the presence of the mucus layer (Johansson et al. 2011). 

Macrophages and DC are very important in innate and adaptive immunity, and CD lib and CD 11 c are used respectively as markers to identify them. In the gut, these cells are involved in the bacterial clearance to avoid invasion of translocating bacteria from the intestinal lumen to deep tissues and to maintain intestinal homeostasis. In previous work, we demonstrated that the main mechanism by which the probiotic strain Lact. casei CRL 431 influences the gut mucosal immunity is through activation of the innate immune response (Maldonado Galdeano and Perdigdn 2006). For this reason we analyzed whether the stress induced changes in the expression of both markers in the immune cells present in the lamina propria of the small intestine of mice. The number of CDllb+ cells... 

The intestinal microbiota, as was pointed out above, plays an important role in maintaining intestinal homeostasis and is affected by different stressor agents such as malnutrition (Zak-Gol%b et aL 2014) or pathologies such as inflammatory bowel disease (Holdet aL 2014). Under stress conditions, different populations, such as strict anaerobes, lactobacilli, and enterobactraia, can be affected (Wang and Kasper 2013). In this regard, studies performed in mice exposed to a chronic restraint stress showed that the composition of the intestinal microhiota differs from the non-stressed control mice principally with a decrease in Bactemides spp. and an increase in Clostridium spp. (Bailey et al. 

Although it is being found that vitamin D metaboUtes play a role ia many different biological functions, metaboHsm primarily occurs to maintain the calcium homeostasis of the body. When calcium semm levels fall below the normal range, 1 a,25-dihydroxy-vitainin is made when calcium levels are at or above this level, 24,25-dihydroxycholecalciferol is made, and 1 a-hydroxylase activity is discontiaued. The calcium homeostasis mechanism iavolves a hypocalcemic stimulus, which iaduces the secretion of parathyroid hormone. This causes phosphate diuresis ia the kidney, which stimulates the 1 a-hydroxylase activity and causes the hydroxylation of 25-hydroxy-vitamin D to 1 a,25-dihydroxycholecalciferol. Parathyroid hormone and 1,25-dihydroxycholecalciferol act at the bone site cooperatively to stimulate calcium mobilization from the bone (see Hormones). Calcium blood levels are also iafluenced by the effects of the metaboUte on intestinal absorption and renal resorption. 

The steroid hormone 1,25-dihydroxy vitamin D3 (calcitriol) slowly increases both intestinal calcium absorption and bone resorption, and is also stimulated through low calcium levels. In contrast, calcitonin rapidly inhibits osteoclast activity and thus decreases serum calcium levels. Calcitonin is secreted by the clear cells of the thyroid and inhibits osteoclast activity by increasing the intracellular cyclic AMP content via binding to a specific cell surface receptor, thus causing a contraction of the resorbing cell membrane. The biological relevance of calcitonin in human calcium homeostasis is not well established. 

A major regulator of bone metabolism and calcium homeostasis, parathyroid hormone (PTH) is stimulated through a decrease in plasma ionised calcium and increases plasma calcium by activating osteoclasts. PTH also increases renal tubular calcium re-absorption as well as intestinal calcium absorption. Synthetic PTH (1-34) has been successfully used for the treatment of osteoporosis, where it leads to substantial increases in bone density and a 60-70% reduction in vertebral fractures. 

In addition to its role in regulating calcium homeostasis, vitamin D is required for the intestinal absorption of calcium. Synthesis of the intracellular calciumbinding protein, calbindin, required for calcium absorption, is induced by vitamin D, which also affects the permeability of the mucosal cells to calcium, an effect that is rapid and independent of protein synthesis. 

Although skeletal muscle comprises the bulk of muscle tissue in the body, smooth muscle is far more important in terms of homeostasis. Most smooth muscle is found in the walls of tubes and hollow organs. Contraction and relaxation of the smooth muscle in these tissues regulates the movement of substances within them. For example, contraction of the smooth muscle in the wall of a blood vessel narrows the diameter of the vessel and leads to a decrease in the flow of blood through it. Contraction of the smooth muscle in the wall of the stomach exerts pressure on its contents and pushes these substances forward into the small intestine. Smooth muscle functions at a subconscious level and is involuntary. It is innervated by the autonomic nervous system, which regulates its activity. 

Puddington, L., Olson, S. and Lefrancois, L. (1994) Interactions between stem cell factor and c-kit are required for intestinal immune homeostasis. Immunity 1,... 

Two inherited human diseases that represent abnormal copper metabolism are Menkes syndrome and Wilson s disease. Menkes syndrome, with symptoms similar to those of copper deficiency, is characterized by a progressive brain disease, abnormally low copper concentrations in liver and other tissues, and diminished ability to transfer copper across the absorptive cells of the intestinal mucosa (USEPA 1980 Aaseth and Norseth 1986). Wilson s disease (hepatolenticular degeneration) is the only significant example of copper toxicity in humans. Wilson s disease is an autosomal recessive disorder that affects normal copper homeostasis and is characterized by excessive... 

In a normal human adult, about 2 g of zinc is filtered by the kidneys daily and about 0.3 to 0.6 mg is actually excreted each day (Goyer 1986). Zinc homeostasis in rats, unlike most mammals, is maintained by zinc secretion from the intestines rather than by regulation of zinc absorption (Elinder 1986). Initial uptake of zinc from the rat gastrointestinal tract involves binding to albumin and transport of the zinc-albumin complex from intestine to liver (Hoadley and Cousins 1988). 

---