Pancreas Anatomy and Physiology

Pancreas Anatomy

• The pancreas is a retroperitoneal organ, making it difficult to diagnose its diseases.
• It is made up of the head, neck, body, and tail, with the head lying within the 'C' of the duodenum.
• The pancreas is supplied by the superior and inferior pancreaticoduodenal vessels.
• The pancreatic tail lies within the lienorenal ligament and is the only intraperitoneal part of the pancreas.

Pancreas Blood Supply

• The pancreas receives blood supply from the coeliac trunk and the superior mesenteric artery.
• The splenic artery divides into segmental branches (Majestrial 30%) or division before hilum (distributed type 70%).

Inferior Pancreatic Artery

• The inferior pancreatic artery runs along the inferior border of the pancreas and anastomoses with the splenic artery through the dorsal, great, and caudal arteries.

Pancreatic Duct Anatomy

• The main pancreatic duct of Wirsung opens at the ampulla of Vater.
• The minor pancreatic duct of Santorini opens at the minor papilla, 2cm proximal to the ampulla.

Exocrine Pancreas

• The exocrine pancreas produces enzymes such as trypsin, chymotrypsin, elastase, carboxypeptidase A, carboxypeptidase B, colipase, lipase, phospholipase A, cholesterol ester hydrolase, amylase, and ribonuclease.

Endocrine Pancreas

• The endocrine pancreas produces hormones such as insulin, glucagon, somatostatin, gastrin, VIP, and PPP.

Aetiology of Acute Pancreatitis

• Idiopathic (10-15% of cases)
• Gallstones (50-70% of cases)
• Ethanol (25%)
• Tumors, toxins, trauma, and microbiological infections
• Malnutrition, autoimmune, surgery, and hyperlipidemia
• Hereditary causes such as PRSS1 and SPINK1 genes

Drug-Induced Pancreatitis

• Antihypertensive drugs such as ACE inhibitors
• Antiarrhythmic drugs such as procainamide
• Antithyroid drugs such as carbimazole
• Anticonvulsants such as carbamazepine and sodium valproate
• Diuretics such as frusemide, thiazides, and spironolactone
• Analgesics such as NSAIDs and opiates
• Hormones such as estrogens and OCPs
• Antibiotics such as erythromycin, penicillins, cephalosporins, and tetracyclins
• Cytotoxic drugs such as L-asparaginase, azathioprine, and 6-mercaptopurine
• Anesthetics such as propofol and acetylcholinesterase inhibitors

Acute Pancreatitis - Pathophysiology

• Premature activation of trypsin leads to autodigestion of pancreatic tissue
• Activation of inflammatory response
• Inflammatory mediators cause vasodilation, shock, ARDS, MODS, and extravascular movement of serum albumin

Acute Pancreatitis - Treatment

• Management of pancreatic pseudocyst
• Endoscopic transgastric catheter drainage
• Fluoroscopic guided transgastric catheter drainage
• Laparoscopic or open cystogastrostomy, cystoduodenostomy, or cystojejunostomy
• ERCP pancreatic stenting
• Distal pancreatectomy if pseudocyst is limited to tail of pancreas
• External drainage only in abscess
• Open laparotomy is indicated in severe conditions, failed percutaneous drainage, acute abdomen, and perforation.

Chronic Pancreatitis

• Irreversible damage to the pancreas with histologic evidence of inflammation, fibrosis, and destruction of exocrine and endocrine tissue
• Aetiology:
  • Idiopathic (40%)
  • Hereditary (25%)
  • Alcoholism (15%)
  • Obstructive (stone, divisum, tumor, stricture post surgery or ERCP)
  • Hyperlipidemia (type I and V)
  • Hyperparathyroidism
  • Autoimmune
  • Nutritional

Chronic Pancreatitis - Pathophysiology

• Direct toxicity to acinar cells
• Hypoperfusion
• Increased ductal permeability
• Sphincter of Oddi spasm or dysfunction
• Increased protein secretion and plug formation
• Reduced HCO3 secretion
• Reduced trypsin inhibitor concentration
• Hyperlipidemia

Chronic Pancreatitis - Clinical Features

• Abdominal pain:
  • Continuous, intermittent, or absent
  • Involving upper abdomen or right or left hypochondrium
  • Radiating to back or chest or flank
  • Persistent, deep-seated, unresponsive to antacids
  • Worsened by alcohol intake or a heavy fatty meal
• Malabsorption with resulting steatorrhea and mineral/vitamin deficiencies