Unit I

Mixed salivary gland (LP): A salivary gland showing both the serous and mucous secretory units iscalled mixed salivary gland. In the section of submandibular gland we get this picture but because of moreserous secretory units and many serous demilunes, submandibular is sometimes called as predominantlyserous gland. The duct system is similar to that of parotid salivary gland showing intercalated, striated andexcretory ducts, which can be seen under microscope as intralobular and interlobular ducts.Inside a lobule many secretory alveoli are seen with some adipose tissue and ducts. Presence of manymucous secretory units differentiates the slide of submandibular from parotid. Similarly presence of manyserous secretory units differentiates it from sublingual gland. Many mucous secretory units show serousdemilune. A serous secretory unit should be identified separately from mucous unit by the student. Serousalveolus stains dark violet, is small in size, with hardly any lumen, round basal nucleus, basal basophiliaand apical eosinophilia. Mucous alveolus stains faint pink and is large in size with a prominent lumen. Aflat basal nucleus is situated very close to the cell membrane and cytoplasm is vacuolated. Myoepithelialcells and demilunes are also seen.The demilune is a half moon shaped cluster of serous secreting cells around a mucous secretoryunit. The mucous alveolus is capped by a crescent shaped group of serous cells. The nuclei and thecytoplasm of the serous cells are like that of other serous cells lining the serous alveolus. Secretions ofthese cells reach the lumen of the mucous alveolus to which they cap, through tiny intercellular canals. Themucous secretory units are cradled in a loose basket made up of cytoplasmic processes of the myoepithelialcells lying between the bases of the secretory cells. The basement membrane of these cells lies betweenthe secretory unit and the surrounding connective tissue. The nucleus of the myoepithelial cell is central.61