Digestive epithelium

Curcumin possesses strong antioxidant capacities, which may explain its effects against degenerative diseases in which oxidative stress plays a major role. As previously described for flavonoids, it is unlikely that curcumin acts as a direct antioxidant outside the digestive tract since its concentration in peripheral blood and organs is very low (near or below 1 pM, even after acute or long-term supplementation). Indeed, it has been shown that the intestinal epithelium limits its entry into the body, as reflected by absorption studies in various models (portal blood perfusion, everted bags). ... 

Bailey, KR, Ishida, BY, Duncan, KG, Kane, JP, and Schwartz, DM, 2004. Basal reverse cholesterol transport of retinal pigment epithelium cell digested photoreceptor outer segment lipids. Invest Ophthalmol Vis Sci 45, U721. 

The mouth is the region from the lips to the pharynx. The first step in the digestive process is chewing, or mastication, which is an initial mechanical breakdown of the food that facilitates its movement to the stomach. The mouth is lined with stratified squamous epithelium that provides extra protection from injury by coarse food materials. Three pairs of salivary glands secrete saliva into the oral cavity ... 

Small-intestinal secretions. The glands of the small intestine (the Lieberkuhn and Brunner glands) secrete additional digestive enzymes into the bowel. Together with enzymes on the microvilli of the intestinal epithelium (peptidases, glycosidases, etc.), these enzymes ensure almost complete hydrolysis of the food components previously broken down by the endoenzymes. 

Entoderm The inner germ layer in developing animals which gives rise to the epithelium of the digestive tract, pharynx, and respiratory tract. 

Flatworms with an alimentary tract ingest food into this canal, where it is first digested and then absorbed by the intestinal epithelium. Ectoparasitic flatworms like monogenea are restricted to this type of food uptake. 

Iczkowski, K. A., Cheng, L., Crawford, B. G., and Bostwick, D. G. 1999. Steam heat with an EDTA buffer and protease digestion optimizes immunohistochemical expression of basal cell-specific antikeratin 34pE12 to discriminate cancer in prostatic epithelium. Mod. Pathol. 72 1-4. 

Small intestine Uptake Digestive tract Epithelial cells Everted sac, Ussing-chamber experiments using intestinal epithelium, brush border membrane vesicles, Caco-2 cells monolayer, transporter expression system... 

The second reason to consider the intracellular enzymes is because of the absorption mechanisms by which macromolecules may cross the intestinal mucosa. There are two possible mechanisms for relatively small macromolecules such as therapeutic peptides and oligonucleotides, they may be able to pass via the paracellular route between the cells, particularly if some absorption enhancers are present. For example, Tsutsumi et al. (2008) have shown in vitro that in the presence of chenodeoxycholate as an absorption enhancer modified oligonucleotides with molecular weights of nearly 3,700 and 7,400 Da could cross rat intestine via the paracellular route. In the case of the paracellular route the macromolecules will not be exposed to the intracellular enzymes and thus they will not be subject to intracellular hydrolysis. However, macromolecules, especially larger ones, will cross the epithelium via the transcellular mechanism of endocytosis. In this case they will be taken into the lysosomes that contain a formidable array of digestive enzymes (see later in Section 1.5.2). 

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