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8/2/2019 HISTOLOGY of Organs Associated With the Digestive Tract for 2nd Year Mbbs (by Dr Sundus)
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8/2/2019 HISTOLOGY of Organs Associated With the Digestive Tract for 2nd Year Mbbs (by Dr Sundus)
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8/2/2019 HISTOLOGY of Organs Associated With the Digestive Tract for 2nd Year Mbbs (by Dr Sundus)
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Salivary Glands
Exocrine glands in the mouth Produce saliva
digestive, lubricating, and protectivefunctions.
pH = 6.56.9, buffering function
Three pairs of Major (large)salivary glands Parotid, Submandibular
Sublingual glands Minor glands in mucosa and
submucosa throughout the oralcavity which secrete 10% of thetotal volume of saliva.
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MEDICAL APPLICATION
Reduced function of the major salivary glands due todiseases or radiotherapy is associated with caries,atrophy of the oral mucosa and speech difficulties
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Salivary Glands Acini (singular, acinus)
cellular secretory units
Excretory ducts.
Connective tissue fibers subdividethe salivary glands into numerouslobules, in which are found thesecretory units and their excretoryducts.
The secretory units are small,saclike dilations located at theend of the first segment of theexcretory duct system, theintercalated ducts.
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Acini Cells of the Salivary Gland
two types: serous or mucous Serous cells
Pyramidal in shape. Basal spherical or round
Mucous cells Pyramidal shape Filled with a light-staining, secretory product called
mucus. Flatten displaced nucleus
Sero-mucous cells Both mucous and serous cells = mixed acini, Mucous cells predominate, Serous demilune.
Serous cells form a crescent or moonshaped cap over themucous cells
The secretions from serous cells in the demilunes enter thelumen of the acinus through tiny intercellular canaliculibetween mucous cells.
Myoepithelial cells Flattened cells Surround both serous and mucous acini. Highly branched and contractile. Basket cells
Located between the cell membrane of the secretory cellsin acini and the surrounding basement membrane.
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Salivary Gland Ducts
Intercalated Ducts
Striated Ducts
Excretory Intralobular Ducts
Interlobular and Interlobar Ducts
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Salivary Gland Ducts
Intercalated Ducts
First ducts that arise from acini
Both serous and mucous, mixedsecretory, acini.
Smallest ducts
Small lumen
Low cuboidal epithelium.
Contractile myoepithelial cellssurround some portions ofintercalated ducts.
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Salivary Gland Ducts
Excretory Intralobular Ducts
Striated ducts, in turn, join toform larger intralobular ducts ofgradually increasing size.
Interlobular and InterlobarDucts
Intralobular ducts join to form thelarger interlobular ducts andinterlobar ducts.
The terminal portion of theselarge ducts conveys saliva fromsalivary glands to the oral cavity.Larger interlobular ducts may belined with stratified epithelium,either low cuboidal or columnar
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Parotid Gland Large serous gland
Compound tubuloacinar gland. It is surrounded by a capsule
from which arise numerousinterlobular connective tissuesepta that subdivide the glandinto lobes and lobules. arteriole, venule, and interlobular
excretory ducts
Lobule Serous acini with myoepithelial
cells Adipose cells Intercalated ducts Striated ducts Intralobular excretory ducts,
These ducts join larger interlobularexcretory ducts in the connectivetissue septa that surround lobules.
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Submandibular Salivary Gland
Compound tubuloacinar gland. Mixed gland, both serous and mucous
acini. The mucous acini are larger than the
serous acini. Serous demilunes
Myoepithelial cells surround the serous, mucous acini and the
intercalated ducts.
Duct system Intercalated ducts
Striated ducts distinct basal striations in the cells are
longer than in the parotid gland. This figurealso illustrates a mucous acinus (13) thatopens into an intercalated
Intralobular excretory ducts Interlobular excretory ducts in the
interlobular connective tissue septa thatdivide the gland into lobules and lobes.
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Sublingual Salivary Gland Compound tubulo-acinar gland
Mixed gland, both serousand mucous acini
Serous demilunes.
Purely serous acini are less numerous in thesublingual gland
Myoepithelial cells serous and mucous acini
Duct system Intercalated ducts
short or absent.
Non striated Intralobular ducts more prevalent
equivalent to the striated ducts
Interlobular connective tissue septa more abundant arteriole venule nerve fibers Interlobular excretory ducts.
The epithelial lining of the interlobular excretoryducts varies from low columnar in the smaller ductsto pseudostratified or stratified columnar in the largerducts.
adipose cells
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PANCREAS
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MEDICAL APPLICATION
Acute necrotizing pancreatitis
In conditions of extreme malnutrition such askwashiorkor, pancreatic acinar cells and other activeprotein-secreting cells atrophy and lose much of theirrough ER, hindering production of digestive enzymes.
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PANCREAS
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PANCREAS Exocrine Pancreas
Most of the pancreas is an exocrine gland.
Pyramid-shaped acinar cells whose apicesare filled with secretory granules.
These granules contain the precursors ofseveral pancreatic digestive enzymes thatare secreted into the excretory ducts in aninactive form.
The secretory acini are subdivided intolobules and bound together by looseconnective tissue.
Excretory ducts Start from within the center of
individual acini as pale-stainingcentroacinar cellsshortintercalated ducts Intralobularductslarger interlobular ductsmain pancreatic duct.
do not have striated ducts.
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PANCREAS
Endocrine Pancreas Scattered among the exocrine acini Pancreatic islets (of Langerhans)
Isolated, pale-staining vascularized units
Each islet is surrounded by fine fibers ofreticular connective tissue.
With special immunocytochemicalprocesses, four cell types can beidentified in each pancreatic islet:
alpha, beta, delta, and pancreaticpolypeptide (PP) cells.
Alpha cells 20% of the islets
Located primarily around the isletperiphery.
Beta cells Most numerous
70% of the islet cells
Located in the center of the islet.
The remaining cell types are few innumber and are located in variousplaces throughout the islets.
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FUNCTIONAL CORRELATIONS: ExocrinePancreas
secretin and cholecystokinin (CCK), secreted by the enteroendocrine cells in the
duodenal mucosa into the bloodstream, regulate pancreatic secretions. Secretin
Acidic chyme in the small intestine (duodenum), centroacinar cells smaller intercalated ducts. Watery fluid rich in sodium bicarbonate ions.
Neutralize the acidic chyme
Stop the action of pepsin from the stomach, Create a neutral pH in the duodenum for the action of the digestive pancreatic enzymes.
Cholecystokinin (CCK), fats and proteins in the small intestine Stimulates the acinar cells Digestive enzymes:
Pancreatic amylase for carbohydrate digestion
Pancreatic lipase for lipid digestion Deoxyribonuclease and ribonuclease for digestion of nucleic acids Proteolytic enzymes
trypsinogen,
chymotrypsinogen,
procarboxypeptidase.
Enterokinase secreted by the intestinal mucosa.
This hormone converts trypsinogen to trypsin, which then converts all other pancreatic
enzymes into active digestive enzymes.
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Pancreatic Islet
Pale-staining
Cells are arranged in cords andclumps,
between which are found
connective tissue fibers and a
capillary network.
A thin connective tissuecapsule separates the
endocrine pancreas from theexocrine serous acini.
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Pancreatic Islet (Special Preparation)
Alpha (A) cells = Glucagon The cytoplasm of alpha cells stains
pink Location = peripheral
Beta (B) cells = Insulin
Cytoplasm of beta cells stains blue.Location = center. Predominate,
Delta (D) cells. Least abundant Variable cell shape May occur anywhere in the pancreatic
islet.
Capillaries around the endocrinecells demonstrate the richvascularity of the pancreatic islets.
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FUNCTIONAL CORRELATIONS:Endocrine Pancreas
Alpha cells
glucagon,
Beta cells
insulin.
Delta cells
somatostatin.
decreases and inhibits secretory activities of both alpha (glucagon-secreting) and beta (insulin-secreting) cells through local action
within the pancreatic islets. Pancreatic polypeptide cells (PP)
pancreatic polypeptide
inhibits production of pancreatic enzymes and alkaline secretions.