HISTOLOGY of Organs Associated With the Digestive Tract for 2nd Year Mbbs (by Dr Sundus)

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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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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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.

Documents

HISTOLOGY of Organs Associated With the Digestive Tract for 2nd Year Mbbs (by Dr Sundus)