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▪ Digestive glands :- Salivary glands , Pancreas , Liver , Gallbladder , Accessory digestive glands
▪ Products of these galnds facilitate transport and digestion of food within the gastrointestinal tract.
Salivary gland
▪ There are three pairs of large salivary glands - Parotid , Submandibular and Sublingual glands
▪ Functions - a) To wet and lubricate the oral mucosa and the ingested food
b) To initiate the digestion of carbohydrates and lipids
c) To secret germicidal protective substances - The secretory contents contain amylase and lingual
lipase activities, IgA, lysozyme.
▪ 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 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.
1. The secretory portion :- contains Acinus
1) Serous acinus - pyramidal, typical protein-secreting cells with round nuclei, accumulation of ER in the
basal part, an apex filled with protein-rich secretory granules
2) Mucous acinus - cuboidal , columnar, flattened and condensed nuclei located at the bases of the cells
3) Mixed acinus - mucous acinar with serous demilune
▪ Each acinus contain two types of cells ;
(1) Secretory cells — serous or mucous
a) Serous cells - cluster together to form the Serous acinus . Pyramidal or cuboidal . Contain round
basally-located nucleus , Golgi , RER , mitochondria and Acidophilic zymogen granules in the apical part.
Joined apically by tight and adherent junctions, serous cells form a somewhat spherical unit called an
acinus . Function is to secret salivary amylase
b) Mucous cells - cluster together to form the Mucous acinus . Pale-stained , slight-blue ,with a flattened
nuclei against the basal membrane , Golgi , RER , mitochondria , Mucinogen granules ( apical granules
with hydrophilic mucins that provide lubricating properties in saliva) . Function is to secrete mucus .
(2) Non-secretory cells — Myoepithelial cells
▪ inside the basal lamina surrounding acini, tubules, and the proximal ends of the duct system . These
small, flattened cells extend several contractile processes around the associated secretory unit or duct
and their activity is important for moving secretory products into and through the ducts.
2. The conducting system :- contain Ducts — Intercalated ducts , Striated ducts , Interlobular ducts
a) Intercalated duct - the beginning of the duct lined with simple squamous/ cuboidal epithelium
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, b) striated duct (secretory duct) - striated simple tall columnar cells with nuclei near the apex
▪ Simple columnar cells in the striated duct contains basal striations and round apical-located nucleus
▪ Function - to reabsorb Na+ ions from the initial secretion
▪ The more columnar striated duct cells have many infoldings of their basolateral membrane , all
aligned with numerous mitochondria that , by light microscopy , appear as faint basal striations
radiating toward the nuclei . Striated ducts reabsorb Na+ ions from the initial secretion .
c) Interlobular ducts - pseudostratified or stratified cuboidal epithelium
d) Main duct - nonkeratinized-stratified squamous epithelium
▪ secretory acini and tubules empty into short intercalated ducts and several of these ducts join to form a striated
duct.
▪ Ducts from each lobule converge and drain into interlobular excretory ducts with increasing size and thicker
connective tissue layers.
▪ Before emptying into the oral cavity , the main duct of each gland is lined with nonkeratinized stratified squamous
epithelium.
Differences in the large salivary glands
1. Parotid Glands
▪ A branched acinar gland and composed of exclusively of serous cells
▪ Intercalated and striated ducts are easily observed within the lobules
2. Submandibular Gland - ( produce 2/3 of all saliva )
▪ A branched tubuloacinar gland , with both mucous and serous cells
▪ 90% the human submandibular gland contain serous acinar and 10% consist of mucous acinar with serous
demilune
▪ Striated ducts are easily observed in the human submandibular gland, but intercalated ducts are short
▪ Within the mixed units grouped serous cells occur distally on short mucous tubules and often assume a
crescent-shaped arrangement called a serous demilune .
3. Sublingual Gland - ( smallest of the major glands )
▪ A branched tubuloacinar gland formed of serous and mucous cells
▪ Predominantly mucous cells ; serous cells are present almost exclusively on demilunes of mucous
▪ Intralobular ducts are not well developed
▪ A rich vascular and nerve plexus surrounds the secretory and duct components of each lobule.
▪ The capillaries surrounding the secretory units provide fluid important for saliva production, 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.
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