Pancreas Anatomy and Function

Pancreas Anatomy

• The pancreas is an elongated, tapered organ measuring approximately 12-15 cm.
• Location is retroperitoneal
• Located in the epigastrium and left hypochondrium regions.
• Consists of three parts: head, body, and tail.

Pancreas Functional Considerations

• Has dual function due to two major types of secretory tissue
• Exocrine Gland: secretes digestive juice and is localized in the acinar cells.
• Endocrine Gland: releases hormones and is localized in the islet cells, also known as Islets of Langerhans.

Pancreatic Functions: Endocrine

• Islets of Langerhans: Responsible for the pancreas's endocrine functions.
• Alpha Cells: Secrete glucagon, accounting for 20% of islet cells.
• Beta Cells: Secrete insulin, comprising 75% of islet cells.
• Delta Cells: Secrete somatostatin.
• Pancreatic polypeptide cells: Produce pancreatic polypeptides.
• Enterochromaffin cells: Secrete serotonin.

Pancreatic Functions: Exocrine

• Acinar Cells: Responsible for the pancreas's exocrine functions.
• Produce pancreatic juice, which contains amylase, lipase, trypsin, chymotrypsin and carboxypeptidases.

Exocrine Cells

• Consist of numerous lobules made up of acini, comprised of secretory cells.
• Each lobule has a tiny duct that drains and units to form the pancreatic duct.
• The pancreatic duct joins the common bile duct and ends by the ampulla of Vater.
• Sphincter of Oddi controls the duodenal opening of the ampulla.

Pancreatic Juice

• Secreted by the exocrine pancreas.
• Consists of water, mineral salts and enzymes.
• Contains amylase, lipase, trypsinogen and chymotrypsinogen.

Pancreatic Juice Functions

• Involved in the digestion of proteins, carbohydrates and fats.
• Trypsinogen and chymotrypsinogen are inactive enzyme precursors
• They are activated by enterokinase into trypsin and chymotrypsin.
• These convert polypeptides into tripeptides and dipeptides.
• Amylase converts polysaccharides (starch) into disaccharides.
• Lipase converts fats into fatty acids and glycerol.
• Bile salts aid lipases by emulsifying fats.

Pancreas Secretion Control

• The regulation of pancreatic exocrine function occurs through three mechanisms: cephalic, gastric, and small intestinal phases.
• Cephalic phase: Mediated by the central nervous system, stimulated by sight, smell of food (Pavlov).
• Gastric phase: Triggered by ingestion and stomach distention.
• Intestinal phase: Initiated by proteins and fats in the small intestine, which increase pancreatic secretions via hormonal and neurotransmitter mechanisms.
• Cholecystokinin is secreted from the small intestine and stimulates the secretion of protease enzyme.
• Secretin stimulates the production of bicarbonate-rich pancreatic juice.
• Somatostatin, present in the pancreas, stomach and central nervous system, is released in response to the sight of food.

Endocrine Cells

• Hormone-producing cells are arranged in nests or islets called Islets of Langerhans.
• Hormones are secreted directly into circulation without access to the pancreatic ductular system.

Endocrine Cells Functions

• Five main types of islet cells exist, each corresponding to different secretory components.
• Beta cells (most common): Responsible for insulin production.
• Alpha cells: Produce glucagon.
• D cells: Produce somatostatin.
• Pancreatic polypeptide cells: Produce pancreatic polypeptide.
• Enterochromaffin cells: Produce serotonin.

Insulin function

• Reduces blood glucose levels.
• Secretion is stimulated by increased blood glucose levels after eating.

Glucagon function

• Increases blood glucose level
• Secretion is stimulated by low blood glucose and exercise.
• It is decreased by somatostatin and insulin.

Somatostatin function

• Inhibits the secretion of insulin and glucagon
• Inhibits the secretion of GH from the anterior pituitary.

Pancreatitis

• Defined as inflammation of the pancreatic tissue
• Also known as autodigestion
• Classified as either acute or chronic.
• Acute pancreatitis: acute inflammation that resolves both clinically and histologically.
• Chronic pancreatitis: Histologic changes persist even with the cause removed.

Acute Pancreatitis symptoms

• Epigastric abdominal pain that radiates to the back, is severe, boring and persistent without relief.
• Sitting up, leaning forward may reduce pain while coughing and vigorous movement may accentuate.
• Nausea and vomiting.

Acute Pancreatitis Signs

• Patients acutely ill and feverish with abdominal tenderness and guarding.
• In severe disease, tachycardia and hypotension may develop, with hypoactive bowel sounds.
• Severe necrotizing pancreatitis may show periumbilical (Cullen's sign) and flank ecchymosis (Gray Turner's sign).

Acute Pancreatitis Investigations: Lab

• Serum amylase and Lipase levels are elevated.
• They may be increased in renal failure, perforated ulcer, mesenteric vascular occlusion, intestinal obstruction associated with ischemia.
• WBC is elevated
• Hyperglycemia.
• Serum Ca levels are reduced with the formation of Ca "soaps".
• Serum bilirubin levels are elevated due to pancreatic edema compressing the common bile duct (CBD).

Acute Pancreatitis Investigations: Imaging with X-Ray

• Abdomen images may show pancreatic calculi and Calcified GB stone
• Used to exclude perforated duodenal Ulcer
• Chest images may show atelectasis and Left pleural effusion

Acute Pancreatitis Investigations: Imaging US

• May detect gallstones, dilation of the common bile duct, swollen pancreas.

Acute Pancreatitis Investigations: Imaging CT and MRI

• Contrast Enhanced CT: Best visualization of the pancreas.
• MRI & MRCP: Assess the degree of pancreatic damage and identify gallstones in the biliary tree.

Complications of Pancreatitis

• Pancreatic: acute fluid collection, necrosis, ascites, pancreatic abscess and pseudocyst.
• Intestinal: Paralytic ileus and GIT hemorrhage.
• Hepatobiliary: CBD obstruction and Portal vein thrombosis
• Systemic: Acute renal failure, Circulatory shock, Adult respiratory distress syndrome and Disseminated intravascular coagulation (DIC).

Principles of Pancreatitis management

• IV fluids to replace water and electrolytes.
• Enteral feeding is better than parenteral
• For Severe pain, give pethidine but no morphine
• ERCP to remove obstructing stone – drain cholangitis
• Role of surgery is reserved for severe necrotizing pancreatitis

Chronic Pancreatitis Symptoms

• Can be similar to acute or no pain reported
• Steatorrhea: Reduced lipase and protease secretions, less than 10% remaining.
• Islet cell destroyed leads to decreased insulin secretion causing glucose intolerance.
• Marked loss of weight due to anorexia and malabsorption.

Chronic Pancreatitis Investigations: Lab

• Serum amylase and lipase levels are frequently normal, usually from loss of pancreatic pancreatic function.
• Tests of Exocrine pancreatic functions may show a fecal elastase test
• Tests of Endocrine pancreatic functions include Fasting, 2 hour post-prandial blood sugar and HBA1C.

Chronic Pancreatitis Investigations: Imaging

• X-ray: can show Pancreatic calculi and calcifications
• US or CT: can detect abnormalities in the size and constistency of pancreas, presence of pseudocyst and dilated pancreatic ducts
• MRCP: Show abnormalities of the main pancreatic duct and side branches.
• EUS: Used to assess of chronic pancreatitis and complications.

Chronic Pancreatitis treatment

• Similar to acute for relapse
• Stop Alcohol and smoking
• Dietary measures: Small feedings restricted in fat and protein, to reduce enzyme secretion
• Acid suppression used
• Pain relief with narcotics and Percutaneous or EUS guided celiac plexus block or neurolysis.
• Pancreatic pseudocyst: EUS vs surgical drainage if no spontaneous resolution.
• Exocrine insufficiency: PERT and vitamins(A,D,E,K)

Cancer Pancreas Risk Factors

• Male gender
• Over the age of 60
• African American, Ashkenazi Jewish descent
• Family history
• Chronic alcoholics, smokers, diabetics and obese individuals
• Regular consumers of red meat
• Those with chronic or hereditary pancreatitis.

Clinical Picture of Pancreas Cancer

• Common presentations include nausea, vomiting, and weight loss.
• Epigastric pain radiates to the back.
• Obstructive jaundice depending on site
• Can cause diabetes, exocrine, steatorrhea, paraneoplastic syndrome, thrombosis, arthritis, nodules

Pancreas Cancer Investigations

• Tumor markers (CA 19-9) are sensitive, but not specific.
• Imaging involves US/CT/MRI/MRCP, used to detect tumour
• Assess resectability and operability
• It can take biopsy FNA + FNB
• ERCP will Relieve obstruction + stent insertion + Biopsy

Pancreas Cancer Treatment

• Radical: Pancreaticodudenal resection (Whipple operation).
• Palliative: Surgical bypass (choldechojujenostomy), endoscopic stent placement for obstruction and pain management.