Digestive

system
Part 3
Digestive system
The liver and pancreas :
Digestive system
The liver :
Digestive system
The liver :
With the exception of the skin , liver considered as the largest organ in the body ( weight
about 1.5 Kg).
Function of liver :
The liver play a major role in metabolism of lipids, carbohydrates ,and proteins.
It inactivates and detoxifies drugs and substances by oxidation, conjugation ,etc.
It participate in iron metabolism.
It produce bile.
It synthesize plasma proteins and factors of blood coagulation.
Digestive system
The liver :
Liver histology :
Digestive system
The liver :
Liver histology :
Digestive system
The liver :
Liver histology :
The liver covered by a thin connective tissue capsule known as ( glisson capsule ).
In the hilum the portal vein and hepatic artery enter , and right and left hepatic duct and
lymphatic vessels exit
The capsule send a trabeculae which divided the lobes of liver into large number of lobules
called hepatic lobules .
These lobules are not sharply delimited because the trabeculae are incomplete.
Each hepatic lobule is hexagonal in shape in its center there is a central vein.
On each angle , there is portal space which contain the portal triads.
Digestive system
The liver :
The structure found in portal area :
Branch of portal vein
Arteriole branch of hepatic artery.
Inter lobular bile duct which lined by
simple cuboidal epithelia.
Lymphatic vessels
So we called this area as portal triads .
Digestive system
The liver :
Digestive system
The liver :
Portal lobule :
It is a triangular area has a portal space in its center and on each angle there is a central vein
So the lobe is formed by 3 regions of 3 adjoining hepatic lobule.
Hepatic acinus :
Represent the part of 2 adjacent areas of 2 different hepatic lobules
It supplied by terminal branches of hepatic portal vein , terminal branches of hepatic
artery, and drained by terminal branches of bile duct.
The terminal branches of portal vein are called (distributing vein) Which rounds around
the periphery of hepatic lobule
Digestive system
The liver :
Hepatocytes :
The hepatocytes are arranged in form of plates, these are
anastomosed freely with central vein
The space between the plates of hepatocytes is occupied by sinusoids .
The surface of each hepatocytes is contact with the wall of sinusoids
through the ( space of Disse ) , and with the surface of other
hepatocytes forming ( bile canaliculai ) .
The hepatocytes has large rounded centrally located nucleus (most
cells have one nucleus & 15% of them have 2 nuclei)
Digestive system
The liver :
Bile canaliculi :
Are the first portion of bile duct system
They are tubular spaces limited by plasma
membrane of two hepatocytes .
The canaleculi form a complex
anastomosing net work along liver plates
& terminating in region of portal canal .
The bile flow in the direction opposite to
that of blood (i.e from the center of the
classic lobule to it periphery)
Digestive system
The liver :
Bile canaliculi :
At periphery bile enters the bile ductule or (Herings canal) then after short distance.
Bile ductule become inter lobular bile ducts, these ducts fused together and formed right
and left hepatic ducts which fused to form common hepatic duct which receiving cystic
duct from gall bladder and form common bile duct which drains into the duodenum.
Digestive system
The liver :
Liver sinusoids :
It has Irregular out line , its lining discontinuous layer and fenestrated endothelial cells
In addition to lining epithelial cells , there is another cell which is phagocytic cell known
as (kupffer cell) .
The space between lining hepatic sinusoid and hepatocytes is known as ( space of Disse )
Digestive system
The liver :
Liver blood supply :
The liver is receives blood from 2 sources :
Portal vein that carries oxygen-poor ,nutrient rich blood from the abdominal visceral organ.
Hepatic artery that supplies oxygen – rich blood
Digestive system
The liver :
Portal vein system :
Hepatic portal vein → hepatic portal venule → distributing venule → small inlet venule →
liver sinusoids → central vein →Sub lobular vein → hepatic vein → venacava.
Digestive system
The liver :
Portal vein system :
The portal vein branches repeatedly send small venules (portal venules ) to portal triads .
The portal venules branches into distributing veins that run around the periphery of the
lobule .
From the distributing veins , small inlet venules empty into sinusoids which run radially,
converging in the center of the lobule to form the central vein ( c.v) .
As the c.v. progress along the lobule , it receive more & more sinusoids , and increase in
diameter , at its end it leaves the lobules at its base by merging with sub lobular vein .
The sub lobular vein converge and fuse forming large 2 hepatic vein that empty into
anterior vena cava
Digestive system
The liver :
Arterial system : Hepatic artery→ inter lobular arteries → sinusoids.
Digestive system
Gall bladder :
Its pear shaped organ which attached to the lower surface of the liver
It serves as storage of bile which produced by the liver and also acts by concentrating bile
by reabsorbing of water from bile .
The wall of gall bladder consist of :
Mucosa : lined by simple columnar epithelia and lamina propria is c.t layer & this layer is
highly folded when its empty .
Fibro muscular layer : smooth muscle + loose connective tissue
Connective tissue layer containing blood vessel lymphatic and nerve supply .
Serosa : absent at area of attachment of gall bladder to the liver, and found in free surface
of bladder.
Digestive system
Pancreas :
Digestive system
Pancreas :
The pancreas is mixed exocrine and endocrine gland
The exocrine composed of compound tubulo acinar gland
The pancreas is covered by a thin capsule of connective tissue that send septa into it ,
separating the pancreatic lobules
The acini are surrounded by delicate sheath of reticular fiber .
The exocrine pancreatic acinus is composed of several serous cells surrounding a lumen.
The exocrine secretion such as {trypsinogen, chymotrypsinogen, lipase , phospholipase ,
ribonuclease , etc. }
Is controlled by 2 hormones secretin and cholecystokinin which produced by
enteroendocrine cells of duodenal mucosa.
Islets of Langerhans : Are multihormonal endocrine microorgans of pancreas
They appear as rounded clusters of cells embedded with exocrine pancreatic tissues .
Digestive system
Pancreas :
Digestive system
Pancreas :
The exocrine part consist of secretory acini which drain into branched duct system
Each secretory acinus is made up of pyramid shape secretory cells
The apices of it surrounded a minute central canal represent the terminal end of duct
system.
The smallest duct known as intercalated ducts ( which lined by simple cuboidal epithelium )
It drain into intralobular duct and then into inter lobular duct which by stratified cuboidal
cells.
Digestive system
The endocrine tissue :
Composed of groups of secretory cells surrounded by delicate capsule
The secretory cell supported by fine collagenous net work containing fenestrated capillaries
The secretory cells are alpha, beta &delta which secrets glucagon, insulin & somatostatin
respectively