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Histology of Pancreas and Biliary Tract

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Histology of Pancreas and Biliary Tract Powered By Docstoc
					    Histology
  of Pancreas
and Biliary Tract
 Dr. Muhammad Rafique
     Anatomy, DIMC
      13-05-2010
                     Objectives
Brief review of gross anatomy of pancreas
Discuss the histological components of pancreas
Discuss the differences between Parotid gland and Pancreas
Describe the capsule and stroma pancreas
Discuss the Parenchyma and Lobules (acini) of Pancreas
Discuss the Duct System of Pancreas
Describe the endocrine component of pancreas
Discuss the different components of biliary tract
Discuss the histological detailed of gall bladder
Gross Features of Pancreas
Pancreas is a mixed type of gland both Exocrine and
Endocrine. Exocrine portion consists of Tubulo-
alveolar gland, purely serous, Parotid Gland
Histological Components of Pancreas
The pancreas is a mixed
  exocrine and endocrine
  gland that produces
  digestive enzymes and
  hormones. The
  enzymes are stored and
  released by cells of the
  exocrine portion,
  arranged in lobules or
  acini. The hormones
  are synthesized in
  clusters of endocrine
  epithelial cells known
  as islets of Langerhans
 Differences between Pancreas and Parotid Gland
The exocrine portion of
  the pancreas is a
  compound tubulo-acinar
  gland, similar in
  structure to the parotid
  gland. In histological
  sections, a distinction
  between the two glands
  can be made based on
  the absence of striated
  ducts and the presence
  of the islets of
  Langerhans in the
  pancreas.
 Differences between Pancreas and Parotid Gland
Another characteristic detail is that
  in the pancreas the initial
  portions of intercalated ducts
  penetrate the lumens of the
  acini. Nuclei, surrounded by a
  pale cytoplasm, belong to
  centroacinar cells that constitute
  the intraacinar portion of the
  intercalated duct. These cells
  are found only in pancreatic
  acini. Intercalated ducts are
  tributaries of larger intralobular
  ducts that, in turn, form larger
  interlobular ducts lined by
  columnar epithelium, located
  within the connective tissue
  septa. There are no striated
  ducts in the pancreatic duct
  system.
    Capsule and Connective Tissue
A thin capsule of
  connective tissue covers
  the pancreas and sends
  septa into it, separating
  the pancreatic lobules.
  The acini are surrounded
  by a basal lamina that is
  supported by a delicate
  sheath of reticular fibers.
  The pancreas also has a
  rich capillary network,
  essential for the secretory
  process
  Exocrine Component of Pancreas
The exocrine component
  of the pancreas consists
  of closely packed
  secretory acini which
  drain into a highly
  branched duct system.
  Most of the secretion
  drains into the main
  pancreatic duct, which
  joins the common bile
  duct to drain into the
  duodenum via the
  ampulla of Vater.
                 Pancreatic Acini
Each acinus is made up of an
  irregular cluster of pyramid-
  shaped secretory cells, the
  apices of which surround a
  minute central lumen which
  represents the terminal end
  of the duct system. The
  smallest of the tributaries
  are known as intercalated
  ducts. Adjacent acini are
  separated by inconspicuous
  supporting tissue containing
  numerous capillaries.
            Duct System of Pancreas
The intercalated ducts drain into
  small intralobular ducts, which
  in turn drain into the interlobular
  ducts in the septa of the gland.
  The intercalated ducts are lined
  by simple low cuboidal
  epithelium, which becomes
  stratified cuboidal in the larger
  ducts. With increasing size, the
  ducts are invested by a
  progressively thicker layer of
  dense collagenous supporting
  tissue; the wall of the main
  pancreatic duct contains smooth
  muscle.
             Pancreatic Acini Cells
Cells of each pancreatic acinus
  have a roughly triangular
  shape in section, their apices
  projecting towards a central
  lumen of a minute duct. The
  acinar cells are typical
  protein-secreting cells. The
  nuclei are basally located and
  surrounded by basophilic
  cytoplasm with rough
  endoplasmic reticulum; the
  apices of the cells are packed
  with eosinophilic secretory
                                 Section of the exocrine pancreas
  granules containing            showing its main components.
  proenzymes.
Centroacinar Cells
The centers of the
 acini frequently
 contain one or more
 nuclei of
 centroacinar cells
 with pale nuclei
 and sparse pale-
 stained cytoplasm;
 these represent the
 terminal lining cells
 of intercalated
 ducts.
Duct System of an Exocrine Gland
Ducts of Pancreas
 A low magnification image of equine pancreas (H&E stain) showing a large
interlobular duct in association with a pancreatic artery (A) and vein (V). An

            intralobular duct (D) is seen on the right side     .
Acini & Intralobular Duct
           Acute Pancreatitis
Damage to the pancreatic acinar cells releases
 pancreatic enzymes into the local tissues.
 These powerful enzymes cause death of
 pancreatic tissue and severe inflammation
 termed acute pancreatitis. The release of
 pancreatic lipase causes death of local fat
 cells (fat necrosis). Pancreatic amylase is
 released and can be detected at high levels
 in the blood. This is a severe life-
 threatening condition.
      Endocrine Portion of Pancreas
The embryonic epithelium of the
  pancreatic ducts consists of
  both potential exocrine and
  endocrine cells. During
  development, the endocrine
  cells migrate from the duct
  system and aggregate around
  capillaries to form isolated
  clusters of cells, known as
  islets of Langerhans,
  scattered throughout the
  exocrine glandular tissue.
  The islets vary in size and are
  most numerous in the tail of
  the pancreas. The islets
  contain a variety of cell types
  each responsible for secretion
  of one type of polypeptide
  hormone.
                 Islets of Langerhans
The islets of Langerhans are
  multihormonal endocrine
  microorgans; they appear as
  rounded clusters of cells
  embedded within the exocrine
  pancreatic tissue. most islets are
  100–200 mm in diameter and
  contain several hundred cells,
  small groups of endocrine cells
  are also found interspersed
  among the pancreatic exocrine
  cells. There may be more than 1
  million islets in the human
  pancreas. A fine capsule of
  reticular fibers surrounds each
  islet, separating it from the
  adjacent pancreatic tissue.
               Islets of Langerhans
Each islet consists of lightly
  stained polygonal or rounded
  cells, arranged in cords
  separated by a network of
  blood capillaries.
Trichrome stains allow the
  recognition of acidophils (a)
  and basophils ( b). Using
  immunocytochemical
  methods, four types of
  cells—A, B,D, and F—have
  been recognized in the islets.
      Endocrine Portion of Pancreas
The embryonic epithelium of the
  pancreatic ducts consists of
  both potential exocrine and
  endocrine cells. During
  development, the endocrine
  cells migrate from the duct
  system and aggregate around
  capillaries to form isolated
  clusters of cells, known as
  islets of Langerhans,
  scattered throughout the
  exocrine glandular tissue.
  The islets vary in size and are
  most numerous in the tail of
  the pancreas. The islets
  contain a variety of cell types
  each responsible for secretion
  of one type of polypeptide
  hormone.
                 Islets of Langerhans
The ultrastructure of these cells
  resembles that of cells
  synthesizing polypeptides. The
  secretory granules of cells of the
  islets vary according to the
  species studied. In humans, the
  A cells have regular granules
  with a dense core surrounded by
  a clear region bounded by a
  membrane. The B (insulin-
  producing) cells have irregular
  granules with a core formed of
  irregular crystals of insulin in
  complex with zinc.
The relative quantities of the four cell types
found in islets are not uniform; they vary
considerably with the islet's location in the
pancreas as shown in table.
Cell Type Quantity Position             Hormone
                                        Produced
A        20%       Usually in periphery Glucagon

B        70%       Central region     Insulin

D        <5%       Variable           Somatostatin
F        Rare      Variable           Pancreatic
                                      polypeptide
             Nerve Supply of Islets
Both the endocrine cells and the blood vessels of the islets are
  innervated by autonomic nerve fibers. Sympathetic and
  parasympathetic nerve endings have been found in close
  association with about 10% of the A, B, and D cells. These
  nerves function as part of the insulin and glucagon control
  system. Gap junctions presumably transfer the ionic
  changes associated with autonomic discharge to the other
  cells.
                 Diabetes Mellitus
Insulin-dependent or type I
  diabetes (juvenile diabetes)
  results from partial or total
  destruction of B cells due
  to an autoimmune disease,
  the individual susceptibility
  to which is controlled by
  several genes. Insulin-
  independent diabetes or
  type II diabetes occurs at a
  later stage in life and is
  frequently associated with
  obesity.
      Tumors of islet cells
Tumors of islet cells may produce
 insulin, glucagon, somatostatin, and
 pancreatic polypeptide. Some
 pancreatic tumors produce two or
 more of these hormones
 simultaneously, generating complex
 clinical symptoms.
Biliary Tract
                        Biliary Tract
The daily basal secretion of bile is
  approximately 500 mL. The bile
  produced by the hepatocyte
  flows through the bile
  canaliculi, bile ductules, and
  bile ducts. These structures
  gradually merge, forming a
  network that converges to form
  the right and left hepatic ducts,
  which unite to form the
  common hepatic duct. The
  common hepatic duct, after
  receiving the cystic duct from
  the gallbladder, continues to the
  duodenum as the common bile
  duct (ductus choledochus).
         Histology of Biliary Tract
The hepatic, cystic, and
  common bile ducts are
  lined with a mucous
  membrane of simple
  columnar epithelium.
  The lamina propria is
  thin and is surrounded by
  an inconspicuous layer of
  smooth muscle. This
  muscle layer becomes
  thicker near the
  duodenum and finally, in
  the intramural portion,
  forms a sphincter that
  regulates bile flow
  (sphincter of Oddi).
Control of Secretion of Biliary Tract
The flow of bile and
  pancreatic juice into the
  duodenum is controlled by
  the complex arrangement
  of smooth muscle known
  as the sphincter of Oddi.
  The components of this
  structure include the
  choledochal sphincter at
  the distal end of the
  common bile duct, the
  pancreatic sphincter at
  the end of the pancreatic
  duct and a meshwork of
  muscle fibres around the
  ampulla.
Control of Secretion of Biliary Tract
This arrangement controls the
  flow of bile and pancreatic
  juice into the duodenum
  and at the same time
  prevents reflux of bile and
  pancreatic juice into the
  wrong parts of the duct
  system. When the
  choledochal sphincter is
  closed, bile is directed into
  the gall bladder where it is
  concentrated.
                     Gall Bladder
The gallbladder is a
  hollow, pear-shaped
  organ attached to the
  lower surface of the
  liver. It can store 30 to
  50 ml of bile. The wall
  of the gallbladder
  consists of four layers:
Mucosa
Muscularis Externa
Perimuscular connective
  tissue
Serosa / Adventitia
                            Mucosa
The wall of a gall bladder in the
  non-distended state in which the
  mucosa is thrown up into many
  folds
Mucosal Lining consists of Simple
  columnar epitheliumAt high
  magnification, the simple
  epithelial lining of the gall
  bladder is seen to consist of
  very tall columnar cells with
  basally located nuclei;
  numerous short irregular
  microvilli account for the
  unevenness of the luminal
  surface.
Lamina propria, consists of
  connective tissue, blood vessels
  and lymphatic vessels
          Muscularis Externa
The fibres of
 the muscular
 layer are
 arranged in
 longitudinal,
 transverse
 and oblique
 orientations.
            Serosa / Adventitia
Externally, there is
 a thick
 collagenous
 adventitial
 (serosal) coat
 conveying the
 larger blood and
 lymphatic
 vessels.
               Cholelithiasis
Abnormal concentration and precipitation of the
 constituents of bile may form stones (calculi) within
 the gall bladder or the extrahepatic biliary system. A
 stone may become impacted in a duct, leading to
 blockage. Complete blockage of the common bile
 duct by a stone would lead to failure of bile
 secretion and clinical jaundice. If the gall bladder is
 affected by stones then it may become inflamed
 leading to pain (chronic cholecystitis). The term
 cholelithiasis is used to refer to formation of stones
 within the biliary system.