Salivary Glands

Organs Associated with the Digestive Tract
Introduction
The organs associated with the digestive tract include the major salivary glands, the pancreas, the liver, and the gallbladder. Products of these organs facilitate transport and digestion of food within the gastrointestinal tract, the main functions of the salivary glands are to moisten and lubricate ingested food and the oral mucosa, to initiate the digestion of carbohydrates and lipids with amylase and lipase, and to secrete innate immune components such as lysozyme and lactoferrin, the pancreas secretes digestive enzymes that act in the small intestine and hormones important for the metabolism of the absorbed nutrients. Bile, whose components are necessary for digestion and absorption of fats, is made in the liver but stored and concentrated in the gallbladder, the liver also plays a major role in carbohydrate and protein metabolism, inactivates many toxic substances and drugs, and synthesizes most plasma proteins and factors necessary for blood coagulation.
Salivary Glandes
Exocrine glands in the mouth produce saliva, which has digestive, lubricating, and protective functions, with a normal pH of 6.5 to 6.9, saliva also has an important buffering function and in some species is also important for evaporative cooling, there are three pairs of large salivary glands: the parotid , submandibular , and sublingual glands ,in addition to the numerous minor mucosal salivary glands throughout the oral cavity, which secrete about 10% of the total saliva volume.
A connective tissue capsule surrounds each major salivary gland, the parenchyma of each consists of secretory units on a branching duct system arranged in lobules, separated by septa of connective tissue, the secretion of each gland is either serous, seromucous, or mucous, depending on its content of the glycoprotein mucin. Saliva from the parotids is serous and watery, the submandibular and sublingual glands produce a seromucous secretion, while that of the
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minor glands is mostly mucous, saliva is modified by the cells of the duct system draining the secretory units, with much Na + and Cl – reabsorbed while certain growth factors and digestive enzymes are added.
Three epithelial cell types comprise the salivary secretory units:
? Serous cells are polarized protein-secreting cells, usually pyramidal in shape, with round nuclei, well-stained RER, and apical secretory granules , joined apically by tight and adherent junctions, serous cells form a somewhat spherical unit called an acinus , with a very small central lumen , serous acinar cells secrete enzymes and other proteins.