Pancreas

Abstract

Gross anatomy

Overview

Characteristics

  • Glandular organ
  • Length: 12–15 cm
  • Weight: approx. 70 g

Location

Function

  • Endocrine: produces somatostatin, glucagon, insulin
  • Exocrine: produces digestive enzymes to aid the absorption of macronutrients
  • Pancreatic juice contains bicarbonate which neutralizes chyme

Parts of the pancreas and vasculature

Location Arterial blood supply of the pancreas Venous blood supply of the pancreas
Head
  • Within the C-shaped duodenal curvature
  • Crossed by the common bile duct
  • Contains the uncinate process (crossed by the superior mesenteric vessels)
  • Superior pancreaticoduodenal branches (from the gastroduodenal artery)
  • Inferior pancreaticoduodenal branches (from the superior mesenteric artery)
  • Collateral circulation: superior and inferior pancreaticoduodenal branches form anastomoses between the celiac trunk and superior mesenteric artery
Pancreatic veins → splenic veins → portal vein
Neck
Body
  • Dorsal pancreatic artery (from the splenic artery of the celiac trunk)
Tail

Pancreatic duct (duct of Wirsung): extends from the tail to the head of the pancreas

Lymphatics

  • Celiac, superior mesenteric, and para-aortic lymph nodes

Microscopic anatomy

Microscopic anatomy

The pancreas is composed of two tissue types:

  • Exocrine pancreas (> 90% of the pancreas)
    • Function: produces digestive enzymes that are secreted into the gastrointestinal tract
    • Characteristics: composed of tubuloacinar glands
      • Serous gland composed of lobes → lobules → tubuloacini
      • Acini: composed of secretory cells that produce digestive enzymes (see below)
      • Acini contain centroacinar cells: cells of the ducts that extend into the lumen of the acini
      • Acini secrete proenzymes into progressively larger ducts, which merge into the pancreatic duct of Wirsung
    • Histology: basophilic rough ER at the basal end of the cells; eosinophilic proenzyme granules at the apical end of the cells

Unlike salivary glands, pancreatic exocrine glands lack myoepithelial cells in the tubuloacini and do not possess striated ducts!

The majority of pancreatic malignancies are located in the head of the pancreas and originate from epithelial cells within the tubules!

Exocrine pancreas

Synthesis: proenzymes; (inactive precursor enzymes) are excreted by the pancreatic acini; secretion into the duodenum → activation of proteolytic enzymes

Cystic fibrosis is caused by a defective chloride channel that impairs pancreatic water and electrolyte secretion. This results in obstruction of the pancreatic ducts, with subsequent maldigestion and malabsorption.

Acute pancreatitis results in activation of pancreatic enzymes within the pancreatic ducts with subsequent autodigestion of pancreatic tissue!

Elevated pancreatic lipase is a diagnostic marker for acute pancreatitis! Elevated amylase occurs in acute pancreatitis and mumps!

Endocrine pancreas

Cell types and hormones

Cell type Proportion of endocrine pancreas Location within the pancreatic islets Hormone Function Feedback mechanism
α-cells
  • 20%
  • Peripheral
  • Glucagon
β-cells
  • 70−80%
  • Central
  • Anabolic effect
  • Stimulation
  • Inhibition
    • α2 stimulation
PP cells (formerly: γ-cells)
  • 1%
  • Dispersed
  • ↑ Gastric secretion of gastric acid
  • ↓ Pancreatic exocrine secretions
  • Promotes satiety
  • Stimulation: fasting
  • Inhibition: intake of food
δ-cells
  • 5%
  • Dispersed
  • Somato-“stasis” = inhibits secretion of other hormones
  • ↓ Gastric secretion of gastric acid and pepsinogen
  • ↓ Secretion of pancreatic and small intestine fluid
  • ↓ Gallbladder contraction↓ drainage
  • ↓ Secretion of insulin and glucagon
  • ↓ Secretion of growth hormone
  • Splanchnic vasoconstriction
  • Analog: octreotide
ε-cells
  • 1%
  • Dispersed
  • Stimulation: fasting, sleep deprivation
  • Inhibition: intake of food

β-islet cells, located on the inside of Langerhans islets, produce insulin!

Insulin synthesis

Insulin synthesis and secretion by the pancreatic β-cells can be broken down into the following steps:

  1. Insulin gene transcription and translation in the rERpreproinsulin (precursor protein)
  2. Signal proteases remove the signal peptide of preproinsulinproinsulin
  3. Protein folding and formation of one disulfide bridge in the α chain and two disulfide bridges between the α and β chains
  4. Proinsulin transported to the Golgi apparatus → packaged in membrane-bound secretory granules with proprotein convertases
  5. Proinsulin is cleaved by proteases → mature insulin + C-peptide
  6. Secretion of insulin and C-peptide in equimolar proportions via exocytosis

C-peptide is released by the β-cells in an equimolar proportion to insulin but is not present in exogenous insulin. It can, therefore, be used to differentiate between endogenous and exogenous hyperinsulinism.

Embryology

  • Origin: derived from the endoderm surrounding the foregut
  • Steps
  • Impaired development:
    • Annular pancreas: a ring surrounding the duodenum is formed due to fusion and incomplete rotation of the pancreatic buds during foregut rotation → causes constriction of the duodenum
      • Associated with Down syndrome
      • Symptoms
        • Antenatal: Polyhydramnios
        • Postnatal: feeding difficulties, non-bilious vomiting, abdominal distention
      • Imaging findings: Double-bubble sign on x-ray
    • Pancreas divisum: ventral and dorsal buds fail to fuse (common, asymptomatic anomaly)
      • The dorsal pancreatic duct drains into the duodenum via the minor duodenal papilla
      • May cause chronic abdominal pain or pancreatitis in a minority of cases

Clinical significance

Disorders associated with the exocrine pancreas

Disorders associated with the endocrine pancreas

last updated 12/13/2018
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