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Mucus (/ ˈ m j uː k ə s /, MEW-kəs) is a slippery aqueous secretion produced by, and covering, mucous membranes. It is typically produced from cells found in mucous glands , although it may also originate from mixed glands, which contain both serous and mucous cells.
Mucins (/ ˈ m juː s ɪ n /) are a family of high molecular weight, heavily glycosylated proteins (glycoconjugates) produced by epithelial tissues in most animals. [1] Mucins' key characteristic is their ability to form gels; therefore they are a key component in most gel-like secretions, serving functions from lubrication to cell signalling to forming chemical barriers. [1]
Every day, seven liters of fluid are secreted by the digestive system. This fluid is composed of four primary components: ions, digestive enzymes, mucus, and bile. About half of these fluids are secreted by the salivary glands, pancreas, and liver, which compose the accessory organs and glands of the digestive system.
Psychological and physical stress can induce a variety of alterations in intestinal function. These include changes in gut motility, intestinal permeability, ion flux, fluid balance and mucus secretion. Furthermore, acute and chronic stress in animal models has shown that stress can cause degradation of intestinal barrier function. [4]
One example of glycoproteins found in the body is mucins, which are secreted in the mucus of the respiratory and digestive tracts. The sugars when attached to mucins give them considerable water-holding capacity and also make them resistant to proteolysis by digestive enzymes. Glycoproteins are important for white blood cell recognition.
The mucus produced by these cells is extremely important, as it prevents the stomach from digesting itself. [5] Parietal cells produce potent hydrochloric acid, which damages cells. Gastric chief cells produce pepsinogen, which is activated by the acid to form pepsin. Pepsin is a protease that can digest and damage stomach cells.
Salivary immunoglobulin A serves to aggregate oral bacteria such as S. mutans and prevent the formation of dental plaque. [28] Tissue repair: Saliva can encourage soft-tissue repair by decreasing clotting time and increasing wound contraction. [29] Digestion: Saliva contains amylase, which hydrolyses starch into glucose, maltose, and dextrin.
A peptide hormone, gastrin, produced by G cells in the gastric glands, stimulates the production of gastric juice which activates the digestive enzymes. Pepsinogen is a precursor enzyme ( zymogen ) produced by the gastric chief cells , and gastric acid activates this to the enzyme pepsin which begins the digestion of proteins .