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Pancreas

Medically Reviewed by Anatomy Team

Table of Contents

The pancreas is a vital glandular organ in the human body that serves both endocrine and exocrine functions. It plays a critical role in digestion and metabolism.[2] Structurally, it is soft, elongated, and tapered, with a lobular appearance due to its glandular tissue. The pancreas is composed of acinar cells, which produce digestive enzymes, and pancreatic islets, which regulate hormone secretion. It is a retroperitoneal organ, meaning it is located behind the peritoneal cavity.

Location

The pancreas is located in the upper abdomen, behind the stomach.[7] It spans horizontally across the posterior abdominal wall, with its head nestled in the curve of the duodenum, the body extending behind the stomach, and the tail tapering toward the spleen.[4]

Anatomy

The pancreas is a soft, elongated, lobulated gland located in the abdominal cavity. It has a dual role as an endocrine and exocrine organ and is anatomically divided into distinct parts, each with unique features and structural components.

Gross Anatomy

Parts of the Pancreas

Head:

  • The widest part of the pancreas, located within the C-shaped curve of the duodenum.[6]
  • The uncinate process, a projection of the head, extends posteriorly, lying behind the superior mesenteric vessels.

Neck:

  • A short, narrow segment connecting the head and body.
  • It lies anterior to the superior mesenteric vein and portal vein.

Body:

  • The elongated, central portion of the pancreas.
  • It crosses the midline, lying posterior to the stomach.

Tail:

  • The narrow, tapering end of the pancreas.
  • It extends to the hilum of the spleen and is the only intraperitoneal part of the pancreas.

Surface Features

Capsule

The pancreas is covered by a thin connective tissue capsule, which extends inward to form septa dividing the gland into lobules.[5]

Microscopic Anatomy

  • Exocrine Component:
    • Composed of acinar cells arranged in clusters (acini).
    • Acini are connected to a system of ducts that converge into the main pancreatic duct.
  • Endocrine Component:
    • Composed of islets of Langerhans, which are scattered throughout the pancreas.
    • The islets contain alpha, beta, delta, PP, and epsilon cells, each secreting specific hormones.

Duct System

  • Main Pancreatic Duct (Duct of Wirsung):
    • Runs the entire length of the pancreas, collecting enzymatic secretions from smaller ducts.
    • Joins the common bile duct at the ampulla of Vater, opening into the duodenum through the major duodenal papilla.
  • Accessory Pancreatic Duct (Duct of Santorini):
    • Drains the anterior portion of the head and may empty into the duodenum independently through the minor duodenal papilla.

Vascular Supply

Arterial Supply:

Supplied by branches of the celiac trunk and superior mesenteric artery.

  • The head is primarily supplied by the pancreaticoduodenal arteries.
  • The body and tail are supplied by the splenic artery.

Venous Drainage:

Drains into the portal vein via the splenic and superior mesenteric veins.

Lymphatic Drainage:

Drains into nearby lymph nodes, including the pancreaticosplenic, celiac, and superior mesenteric nodes.

Nervous Supply

Autonomic Innervation:

  • Sympathetic Nerves: Derived from the celiac and superior mesenteric plexuses.
  • Parasympathetic Nerves: Supplied by the vagus nerve.[3]
  • These nerves regulate both exocrine and endocrine secretions.

Developmental Anatomy

  • The pancreas originates embryologically from the foregut.
  • It develops from two buds (dorsal and ventral) that fuse during embryogenesis to form the complete organ.

Function

The pancreas has two primary roles in the body: exocrine and endocrine functions. These roles are critical for digestion, metabolism, and maintaining blood glucose levels. Each function is performed by specialized components of the pancreas.

Exocrine Functions

The pancreas produces and secretes digestive enzymes and bicarbonate-rich fluid essential for digestion. These secretions are delivered to the small intestine via the pancreatic duct.

  • Production of Digestive Enzymes:
    The exocrine pancreas, composed of acinar cells, synthesizes enzymes that break down macronutrients:

    • Amylase: Breaks down carbohydrates into simple sugars.
    • Lipase: Digests triglycerides into glycerol and free fatty acids.
    • Proteolytic Enzymes: Break proteins into smaller peptides and amino acids.
      • Trypsin and chymotrypsin are secreted as inactive precursors (trypsinogen and chymotrypsinogen) and activated in the duodenum.
    • Nucleases: Break down nucleic acids into nucleotides.
  • Secretion of Bicarbonate:
    The pancreas secretes bicarbonate ions (HCO₃⁻) via ductal cells, which neutralize stomach acid entering the duodenum. This creates an optimal pH for enzymatic activity in the small intestine.
  • Regulation of Exocrine Secretions:
    The secretion of enzymes and bicarbonate is controlled by hormones released from the small intestine:

    • Secretin: Stimulates bicarbonate secretion in response to acidic chyme.
    • Cholecystokinin (CCK): Stimulates the release of digestive enzymes in response to fats and proteins.

Endocrine Functions

The pancreas regulates blood glucose levels and other metabolic processes through hormones secreted by the islets of Langerhans.

  • Hormones Secreted by Islet Cells:
    • Insulin (Beta Cells):
      • Lowers blood glucose levels by promoting glucose uptake by muscle and adipose tissue.
      • Enhances glycogenesis (conversion of glucose into glycogen) and inhibits gluconeogenesis (glucose production).
      • Encourages fat storage and protein synthesis.
    • Glucagon (Alpha Cells):
      • Increases blood glucose levels by stimulating glycogen breakdown (glycogenolysis) in the liver.[8]
      • Promotes gluconeogenesis and lipolysis during fasting or energy deficit.
    • Somatostatin (Delta Cells):
      • Acts as a regulatory hormone to inhibit both insulin and glucagon secretion.
      • Reduces the secretion of exocrine enzymes and bicarbonate.
    • Pancreatic Polypeptide (PP Cells):
      • Regulates pancreatic enzyme secretion and gallbladder contraction.
      • Influences appetite and gastrointestinal motility.
    • Ghrelin (Epsilon Cells):
      • Stimulates appetite and interacts with glucose metabolism.
  • Coordination of Glucose Homeostasis: The endocrine pancreas maintains blood glucose levels within a narrow range:
    • Post-meal: Insulin is released to store glucose and reduce blood sugar.
    • During fasting: Glucagon is released to release stored glucose into the blood.

Integrated Role in Digestion and Metabolism

The pancreas works in close coordination with the digestive system and liver:

  • In digestion: It ensures that ingested nutrients are broken down and absorbed efficiently.
  • In metabolism: It maintains energy balance by regulating the availability and storage of glucose, fats, and proteins.

Clinical Significance

The pancreas plays a crucial role in digestion and metabolic regulation, and its dysfunction is associated with several serious conditions:

  • Diabetes Mellitus:
    • Type 1 Diabetes: Autoimmune destruction of beta cells leads to insulin deficiency.
    • Type 2 Diabetes: Insulin resistance and eventual beta-cell dysfunction impair glucose regulation.
  • Pancreatitis: Acute or chronic inflammation of the pancreas due to gallstones, alcohol abuse, or other causes can damage pancreatic tissue and impair its exocrine and endocrine functions.
  • Pancreatic Cancer: Often originating in the exocrine cells, pancreatic cancer is aggressive and challenging to detect early, making it one of the leading causes of cancer mortality.[1]
  • Cystic Fibrosis: A genetic disorder that leads to thickened pancreatic secretions, causing blockage of ducts and reduced enzyme secretion, resulting in malabsorption.
  • Exocrine Pancreatic Insufficiency (EPI): Reduced enzyme production causes malabsorption of nutrients, leading to weight loss, steatorrhea (fatty stools), and nutritional deficiencies.
  • Pancreatic Islet Tumors: Tumors like insulinomas, glucagonomas, and somatostatinomas disrupt hormone secretion and metabolic balance.

References

  1. Standring, S. (2020). Gray’s Anatomy: The Anatomical Basis of Clinical Practice (42nd ed.). Elsevier. ISBN 978-0702077050.
  2. Moore, K. L., Dalley, A. F., & Agur, A. M. R. (2017). Clinically Oriented Anatomy (8th ed.). Wolters Kluwer. ISBN 978-1496347213.
  3. Skandalakis, J. E., Skandalakis, L. J., & Skandalakis, P. N. (2004). Surgical Anatomy and Technique: A Pocket Manual (2nd ed.). Springer. ISBN 978-0387215822.
  4. Borley, N. R. (2005). Last’s Anatomy: Regional and Applied (11th ed.). Churchill Livingstone. ISBN 978-0443103739.
  5. Netter, F. H. (2014). Atlas of Human Anatomy (6th ed.). Saunders Elsevier. ISBN 978-1455704187.
  6. Yamada, T. (2009). Textbook of Gastroenterology (5th ed.). Wiley-Blackwell. ISBN 978-1405169110.
  7. Johnson, L. R. (2018). Gastrointestinal Physiology (9th ed.). Elsevier. ISBN 978-0323595636.
  8. Guyton, A. C., & Hall, J. E. (2021). Textbook of Medical Physiology (14th ed.). Elsevier. ISBN 978-0323597128.