AL 4 - Embryology 1 - Foregut, Liver & Pancreas

8/7/2019 AL 4 - Embryology 1 - Foregut, Liver & Pancreas

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Associate Professor Dr San San Thwin


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Pancreasy Has 2 parts-

y 1.Exocrine pancreas-(A ) is a compound

tubuloacinar gland,it is divided intolobes and lobules byconnective tissuesepta

y 2.Endocrine part (I) Islets ofLangerhans (I)


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Exocrine

Pancreas

y Secretory portion of pancreas is made up of only serous acini- each acinarcell (A) is pyramidal in shaped.

y Nucleus is round and basally located,y Has basophilic cytoplasm in infra nuclear regiony Apical region is filled with zymogen granules (in the supra nuclear region)

Features of

Exocrine

part is similar

to the

features of

parotidsalivary

gland where

only serous

acini were

found

Centroacinar

cell


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Exocrine Pancreas

y Zymogen granules, reddish in colour, are very prominent in the acinar celly Centroacinar cells (C) are pale staining, lining cells of intercalated duct

seen in the lumen of the serous secretory unit

y Duct system- the smallest duct is intercalated duct (ID) and is lined by lowcuboidal lining and these cells appear in the lumen of the acinus ascentroacinar cell (C)

Zymogen

granules


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Exocrine Pancreas

y Connective capsule send insepta dividing the gland intolobes and lobules

y Ductal system-Intercalatedducts join to form intralobularand then interlobular whichlater join the main pancreaticduct

y The interlobularduct (D) havestratified cuboidal lining andare surrounded by connectivetissue (CT)


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Endocrine

Pancreas

y is formed by Islets ofLangerhans which areabundant in the tail ofpancreas

y Each islet is supportedby reticular fibers withnumerous cappillaries

y There are 5 types ofcells beta, alpha , delta, PP cell and G cell


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Endocrine

Pancreasy Islets of Langerhans

consists of many types ofcells

- Beta cells secrete insulin- Alpha cells secreteglucagon

- Delta cells secretesomastatin

- G cells secrete gastrin- PP cells producepancreatic polypeptide

Islets of

Langerhans


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Liver

y

Liver is made up ofparenchymal cellsknown ashepatocytes

y There is aconnective tissuecapsule

( Glissons capsule)

y These connectivetissue continuesinside as septa todivide the liver intolobules

Connective

tissue


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Liver

y

In a classical lobule,anastomosing plates ofhepatocytes of 2 cellsthickness, radiate fromthe central vein towards

the periphery .

Central

vein

Portal triad


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Classical lobule & Portal triad

y The classical lobule ishexagonal in shape

y In the center is the central

veiny At the angles of the lobule,

are the portal triads

y Portal triad consists ofportal vein, hepatic artery

and bile duct


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Portal triad

y Consists of a tributaryor a branch ofportalvein -V( largest and

has thin wall)y Bile ductule D

(simple cuboidal orcolumnar lining)

y A branch ofHepatic

artery-A(thick wall withendothelial lining &smooth muscle)


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Liver( s

inuso

ids) a

nd po

rtal

triad)

Central

vein

Portaltriad

Sinusoids are present in between the plates of liver cells


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Liver ( sinusoids and portal triad)

sinusoid Portal triad


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Classification of lobulesy

3 types of lobulesy Hepatocytes are arranged

in hexagonal shapedlobules known asClassical lobules

y Portal lobule- is atriangular area withcentrally located portaltriad and the3 anglesformed by central veins

y Portal acinus or hepaticacinus -diamond shapedlobule


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Hepatic sinusoids

y Sinusoids (S) lie betweenthe plates of liver cells

y Sinusoids flow into thecentral vein

y

The sinusoid are lined by1.sinusoidal lining cells(discontinuous endothelialcells)and 2. Kupffer cells(KC)

y Kupffer cells are

macrophages whichphagocytose the old rbc andcellular debris

y In between the adjacentliver cells are the biliarycanaliculi (BC)

B

iliarycanaliculi


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Kupffer

cells

y Kupffer cells(indicated byarrows) areshown lining

the sinusoids (S)y Between the

hepatocytes

(H) are thebiliary

canaliculi

Biliary

canaliculi


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Hepatic sinusoids and Ito cellsy 3.Third type of cell

lining the sinusoid cell

is Ito cell or hepaticlipocyte or stellate cell.It cannot bedistiguished by lightmicroscope. Thesecells have dualfunctions- vitamin Astorage and

y production of extracellular matrix and

collagen. During liverinjury due to alcoholor infection, thesecells are thought toproduce large amountof collagen fiberscausing hepaticcirrhosis.


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Space of Disse

y Perisinusoidal space orSpace of Disse is thespace between thehepatocyte andsinusoidal lining

y Microvilli of hepatocytesoccupy this area , and

facilitates exchange ofmaterials


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Gall Bladder

y Four layers-

y Mucosa is highly folded whenit is empty

y Epithelium- simple columnar

consists of 2 types of cells, --clear cells ( more common),oval nuclei basally positionedand supranuclear region withoccasional mucigen granules

- brush cells -few in number


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Gall Bladdery In the neck region there are

simple tubuloalveolar glands(Gl) which produce mucuspresent in the bile.

y Lamina propria a- loose conn:tiss: with elastic and collagenfibers

y

Muscular layer has thin smoothmuscle mostly of obliquelyoriented fibers and somelongitudinal

y Adventitia consists of looseconn: tiss: where it is attachedto the liver

y Serosa-simple squamous

mesothelial lining in the partwhere it is not attached to theliver

y Function-to store bile and toconcentrate the bile


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AL 4 - Embryology 1 - Foregut, Liver & Pancreas

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