Table 2 compiles measurements of mucus physicochemical properties in different organs and diseases reported in the literature, which will be discussed further in this review. Table 2 Mucus physicochemical properties in different organs. must contend with this critical barrier to drug delivery. bacteria, where the former contains specific glycan structures and acts as ligands to bind bacteria (Linden et al., 2002) whereas the latter performs a natural antibiotic function (Kawakubo et al., 2004). Unlike the airways where mucus is motile to maintain homeostasis for mucociliary clearance, gastric mucus is an adherent unstirred layer to act as a barrier against invasive pathogens. In the intestine, MUC2 mucin is the major component of the intestinal mucus (Pelaseyed et al., 2014). An outer loosely adherent mucus layer and an underlying firmly adherent mucus layer line the stomach and colon, whereas a single mucus layer protects the small intestine (Figure 2) (Johansson et al., 2013; Lundquist and Artursson, 2016). The small intestine mucus layer is not attached to the epithelium under normal conditions, however it was found to be firmly adherent in the cystic fibrosis disease due to dysfunctional CFTR-secreted bicarbonate (Pelaseyed et al., 2014). The thicker double layer of mucus in the EGFR-IN-3 stomach and colon functions as a protecting mechanism to EGFR-IN-3 the lining epithelium against the stomach acidic Rabbit polyclonal to RIPK3 pH and pathogens. As an additional defense against foreign pathogens in the colon, the inner mucus layer is constantly renewed by secreting surface goblet cells, with a 1C2 h turnover estimated from murine distal colonic tissue (Johansson, 2012). The thinner and loosely adherent mucus in the small intestine contributes to absorption of nutrients and other molecules, as more than 90% of nutrients (carbohydrates, proteins, lipids, water, vitamins, and minerals) are absorbed by the small intestine, while the rest is absorbed in the stomach and large intestine (Renukuntla et al., 2013). Open in a separate window Figure 2 Graph showing the thicknesses of the mucus gel layers in the rat gastrointestinal tract. The values for total mucus thickness in m are reported on top as means SE for each group. Adapted from (Atuma et al., 2001) 2.3 Cervical mucus Mucus in the endocervical epithelium concomitantly acts as a barrier against pathogens and helps regulate the reproductive function of the female reproductive tract by modulating sperm entry into the uterus. The primary mucins in the cervix are MUC4 and MUC5B, along with smaller amounts of MUC5AC and MUC6. During ovulation there is a peak in mucus production and MUC5B secretion, which correlate with high estrogen levels (Curlin and Bursac, 2013), higher pH, and decreased viscoelasticity of mucus (Svensson and Arnebrant, 2010), and subsequently, these factors combine to facilitate sperm mucus permeation. Also during ovulation, there are changes to the structure and glycosylation of mucus; specifically, there is a decrease in the number of sugar residues containing sulfate groups and sialic acid residues, and there is a resulting increase in pH (Curlin and Bursac, 2013). The cervical mucus plug comprises additionally antimicrobial activity from components such as secretory leukoprotease inhibitor, lysozyme, lactoferrin, and neutrophil defensins (Bernkop-Schnrch and Hornof, 2003; Hein et al., 2002) 2.4 Ocular mucus On the surface of the eye, mucus lining the conjunctival epithelium is secreted by goblet cells and functions as a lubricant and a stabilizer of the tear film. The precorneal EGFR-IN-3 tear film is composed of a superficial lipid layer, a central aqueous layer, and an inner EGFR-IN-3 mucus layer (Figure 3) (Ludwig, 2005). Open in a separate window Figure 3 Schematic of the precorneal tear film, composed of three layers lining the conjunctival epithelium and the corneal epithelium. Reprinted from.