Large glands associated with the digestive tract

1. Large glands associated with the digestive tract

2. Salivary glands • 2 main groups • 1. Major salivary glands: • paired parotid • Submandibular • Sublingual • 2. Minor salivary glands : • Buried in the C/T of lips, cheeks, tongue, palate (produce 5% of total salivary output)

4. The secretion of each gland is either serous, seromucous, or mucous, depending on its glycoprotein mucin content. • Saliva from the parotids is serous and watery. • The submandibular and sublingual glands produce a seromucous secretion, with mostly mucus from the minor glands.

5. The main functions of the salivary glands • to wet and lubricate ingested food and the oral mucosa, • to initiate the digestion of carbohydrates and lipids with amylase and lipase, • and to secrete protective bacteriostatic substances such as the immunoglobulin IgA, lysozyme, and lactoferrin.

6. In the large salivary glands, the connective tissue contains many lymphocytes and plasma cells. • The plasma cells release IgA, which forms a complex with a secretory component synthesized by the epithelial cells of serous acini and intralobular ducts. • The IgA-secretory complex released into the saliva resists enzymatic digestion and constitutes an immunologic defense mechanism against pathogens in the oral cavity.

8. Salivary glands • Compound tubuloacinar glands • Ducts open in the oral cavity • Surrounded by a C/T capsule • From capsule, C/T septa extend into the gland and divide it into lobe and lobules. • Blood vessels, lymphatics, nerves, excretory duct of glands

9. Secretoryacini are surrounded and supported by very fine loose C/T • Lymphocytes, plasma cells. • C/T of acini blends C/T of septa

10. Parenchyma of salivary glands • Functional glands • Composed of acini (alveoli) • Some portions of ducts are involved in secretory process so called as tubuloacinar glands. • Acini are spherical structures consisting of secretory epithelial cells arranged around a central cavity which continues into that of the duct draining the acinus. • The acini of salivary glands contain serous cells, mucous cells or both.

11. Serous acini • Serous acini are generally spherical structures, the mucous end pieces are more often tubular. • Pyramidal in shape • With a broad base facing the basal lamina • Narrow apical surface facing the lumen of the acinus. • Basally located spherical nucleus.

12. Basal region of cell contains numerous mitochondria, RER, free ribosomes • Apex contains zymogenic granules • well developed GA is present between nucleus and secretory granules • Basal region (basophilic due to ribosomes • Apical region (acidophillic due to zymogenic granules)

13. Adjacent serous cells are joined to each other by junctional complexes • apical to junctional complexes intercellular canaliculi exist between the adjacent serous cells • Serous cells produce thin watery secretion which is rich in digestive enzymes.

14. Mucous cells • Pyramidal in shape • Nuclei are oval (or flattened) and pressed against the basal plasmalemma • Apical region of each mucous cells is occupied by numerous mucinogen granules , stained poorly and appear to be empty

15. Mucous cells contain mitochondria, moderate amount of RER, very large golgi apparatus(which add carbohydrates to proteins to produce glycoproteins of mucinogen which is a precursor of mucin). • Adjacent cells are bound together by apical junctional complexes and do not exhibit intercellular canaliculi.

16. The mucous cells secrete mucin which mixes with water and coverted to mucus which is a gel like lubricant- protect the delicate mucous membrane. • Mucous cells are most often organized as tubules rather than acini and produce mostly mucins.

17. Myoepithelial cells, • are found inside the basal lamina of the secretoryunits • and (to a lesser extent) the initial part of the duct system • Surrounding the secretory portion myoepithelial cells are well developed and branched (and are sometimes called basket cells), whereas those associated with the initial ducts are spindle-shaped and lie parallel to the duct's length.

18. Myoepithelial cells prevent distention of the endpiece when the lumen fills with saliva and their contraction accelerates secretion of the product. • Has a body and many long processes • Cell body contains nucleus and small amount of organelle • Cell process contain actin and myosin. • Stained poorly and cannot be easily identified.

19. Duct system of salivary glands • Compound salivary glands have highly branched duct system • 3 types • 1. intercalated ducts intralobular ducts • 2. striated ducts • 3. excretory ducts

20. Intercalated ducts • In the intralobular duct system,secretoryendpieces empty into intercalated ducts, lined by cuboidal epithelial cells, • Have small diametre • Cuboidal epithelial cells have capability to divide and differentiate into secretory cells and ductal cells • These cells also secrete carbonic anhydrase (secrete bicarbonate and absorb chloride ions from it) • and several of these short ducts join to form striated ducts • Intercalated ducts in parotid and submandibular are long • Very short in sublingual

21. Striated ducts • The columnar cells of striated ducts often show radial striations extending from the cell bases to the level of the nuclei. • Larger caliber • Stain intensely with eosin • Nucleus is central • Due to presence of prominent eosinophillic striations, these ducts are called striated ducts

22. Ultrastructurally the striations consist of infoldings of the basal plasma membrane • Numerous mitochondria are aligned parallel to the infolded membranes which contain ion transporters. • Such folds greatly increase the cell surface area, facilitating ion absorption, and are characteristic of cells specialized for ion transport.

23. Absorbtion of Na+ • Secretion of K+ so reduce the tonicity of saliva

24. Excretory ducts. • The striated ducts of each lobule converge and drain into ducts located in the connective tissue septa separating lobules, where they become interlobular, or excretory ducts. • Interlobular= pseudostratified or stratified cuboidal epithelium, • Interlobar=pseudo stratified columnar epithelium containing a few mucous cells. • The main duct = stratified columnar epithelium and then nonkeratinized-stratified squamous epithelium.

25. Interlobular ducts join to form interlobar ducts, which ultimately drain into main duct of the gland which drain secretory products of the gland into oral cavity • interlobular, interlobar and main ducts are purely secretory, i.e. they are simple conduits and donot modify the secretory product.

26. Vessels and nerves enter the large salivary glands at a hilum and gradually branch into the lobules. A rich vascular and nerve plexus surrounds the secretory and ductal components of each lobule. • The capillaries surrounding the secretory end pieces are very important for the secretion of saliva, which is stimulated by the autonomic nervous system. • Parasympathetic stimulation, usually elicited through the smell or taste of food, provokes a copious watery secretion with relatively little organic content. • Sympathetic stimulation inhibits such secretion, and produces the potential for dry mouth often associated with anxiety.