Development of pancreas

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					              Objectives
Briefly describe the gross anatomy of
 pancreas
Discuss the functional division of pancreas
Brief review of histology of pancreas
Discuss the development of pancreas
Describe the congenital anomalies of
 pancreas
 Gross
Anatomy
   of
Pancreas
         Gross Anatomy of Pancreas
The pancreas lies
  mostly posterior
  to the stomach.
  It extends across
  the posterior
  abdominal wall
  from the
  duodenum, on
  the right, to the
  spleen, on the
  left.
         Gross Anatomy of Pancreas
The pancreas is
  retroperitoneal
  except for a small
  part of its tail and
  consists of a head,
  uncinate process,
  neck, body, and tail
     Functional Division of pancreas
The pancreas is a complex organ
  composed of two different
  cell populations, exocrine and
  endocrine. The exocrine
  component includes acinar
  and ductal cells that secrete
  and transport digestive
  enzymes into the intestine.
  Exocrine cells make up the
  majority of the pancreas and
  are grouped together into
  acini and a highly branched
  ductal system.
        Functional Division of pancreas
The endocrine portion is
  composed of four cell
  types, alpha, beta, delta
  and PP cells that secrete
  glucagon, insulin,
  somatostatin and
  pancreatic polypeptide
  hormones into the
  bloodstream. The
  endocrine cells account
  for approximately 4% of
  the volume of the
  pancreas and they are
  grouped together into
  islets of Langerhans.
Functional Division of Pancreas
           Development of Pancreas
The mature pancreas is a
  single organ, it is initially
  derived from separate
  dorsal and ventral buds.
  During embryogenesis
  these two pancreatic buds
  are specified differently
  and arise from different
  regions: the dorsal
  pancreas from just below
  the notochord in the
  region of the stomach,
  while the ventral pancreas
  develops adjacent to the
  liver.
     Induction Signals for Development
Recent work has shown
  that signals released
  from both the
  notochord and
  endothelial cells are
  important for proper
  specification of the
  dorsal pancreas, while
  signals released from
  the cardiac mesoderm
  affect ventral pancreas
  development
     Development of Pancreatic Buds
In humans, the dorsal and
   ventral pancreatic buds first
   appear 30 days after
   fertilization, whereas
   genetic controls essential
   for induction begin slightly
   before this time. As with
   formation of glands in
   general, pancreas
   development requires an
   epithelial-mesenchymal
   interaction.
                  Pancreatic Buds
In this case, the
   mesenchyme induces
   the endoderm to
   proliferate and to
   branch, perhaps under
   the influence of
   fibroblast growth
   factors, and it is this
   endoderm that will
   form both the exocrine
   and endocrine cells of
   the organ.
                   Pancreatic Buds
The pancreas is formed by
  two buds, dorsal and
  ventral, originating from
  the endodermal lining
  of the duodenum.
  Whereas the dorsal
  pancreatic bud is in the
  dorsal mesentery, the
  ventral pancreatic bud
  is close to the bile duct.
             Rotation of Duodenum
When the duodenum
 rotates to the right and
 becomes C-shaped, the
 ventral pancreatic bud
 moves dorsally in a
 manner similar to the
 shifting of the entrance
 of the bile duct. Finally,
 the ventral bud comes
 to lie immediately
 below and behind the
 dorsal bud.
      Fusion of Two Pancreatic Buds
Later the parenchyma and
  the duct systems of the
  dorsal and ventral
  pancreatic buds fuse.
  The ventral bud forms
  the uncinate process
  and inferior part of the
  head of the pancreas.
  The remaining part of
  the gland is derived
  from the dorsal bud.
      Formations of Ducts of Pancreas
The main pancreatic duct
  (of Wirsung) is formed by
  the distal part of the
  dorsal pancreatic duct
  and the entire ventral
  pancreatic duct. The
  proximal part of the dorsal
  pancreatic duct either is
  obliterated or persists as a
  small channel, the
  accessory pancreatic duct
  (of Santorini).
          Accessory Pancreatic Duct
The main pancreatic
  duct, together with
  the bile duct, enters
  the duodenum at the
  site of the major
  papilla; the entrance
  of the accessory duct
  (when present) is at
  the site of the minor
  papilla. In about 10%
  of cases the duct
  system fails to fuse,
  and the original
  double system
  persists.
 Schematic drawings of the development of the
               human pancreas
Schematic drawings of
  the development of
  the human pancreas at
  6 weeks and 8 weeks
  and gestation. Growth
  and rotation of the
  duodenum (indicated
  by arrows in and cause
  movement of the
  ventral pancreatic bud
  towards the dorsal bud
  and their eventual
  fusion.
  Schematic drawings of the development of the
                human pancreas
Union of the distal part of the
  dorsal pancreatic duct and
  the entire ventral
  pancreatic duct forms the
  main pancreatic duct. The
  proximal part of the dorsal
  pancreatic duct usually
  disappears but it may
  persist as an accessory
  duct . Dotted lines indicate
  the level of the
  corresponding
  diagrammatic transverse
  sections shown on the
  right.
                Annular Pancreas
The pancreas develops from
  ventral and dorsal
  diverticula from the
  foregut. The dorsal bud
  forms most of the head,
  neck, and body of
  pancreas. The ventral bud
  rotates around the bile
  duct to form part of the
  head and the uncinate
  process. If the ventral bud
  splits (becomes bifid) the
  two segments may encircle
  the duodenum.
                Annular Pancreas
The duodenum is
  therefore constricted
  and may even undergo
  atresia, i.e. absent due
  to developmental
  problems. After birth,
  the child may fail to
  thrive and vomit due to
  poor gastric emptying.
  Sometimes annular
  pancreas is diagnosed
  in utero by ultrasound
  scanning.
                Annular Pancreas
The obstruction of the
  duodenum may
  prevent the fetus from
  swallowing enough
  amniotic fluid, which
  may increase the
  overall volume of
  amniotic fluid in the
  amniotic sac
  surrounding the fetus
  (polyhydramnios).
        Accessory Pancreatic Tissue
Accessory pancreatic tissue
  may be anywhere from the
  distal end of the esophagus
  to the tip of the primary
  intestinal loop. Most
  frequently, it lies in the
  mucosa of the stomach and
  in Meckel's diverticulum,
  where it may show all of the
  histological characteristics
  of the pancreas itself.