Digestive Accessory Organs Overview

Overview

This lecture focuses on the accessory digestive organs—liver, gallbladder, and pancreas—covering their anatomy, functions, and how they contribute to digestion.

Liver Anatomy and Functions

• The liver is the largest visceral organ, mainly in the upper right abdomen.
• It has four lobes: right (largest), left, caudate, and quadrate.
• The falciform ligament separates the right and left lobes; the round ligament is a remnant of the fetal umbilical vein.
• The liver is attached to the diaphragm by right and left coronary ligaments.
• Porta hepatis is a fissure where the hepatic portal vein, hepatic artery proper, and common bile duct enter/leave the liver.
• The liver produces about 700 mL of bile daily, which emulsifies fats for digestion.

Gallbladder Anatomy and Functions

• The gallbladder stores up to 70 mL of bile and is located under the liver.
• It concentrates bile by absorbing water, increasing bile salt concentration.
• Functions: stores and modifies bile.
• Bile flows from liver through right and left hepatic ducts → common hepatic duct; from gallbladder through cystic duct.
• Common hepatic duct and cystic duct merge to form the bile duct, which empties into the duodenum.

Regulation of Bile Release

• Release of bile into the duodenum is regulated by a sphincter at the end of the bile duct.
• When chyme enters the duodenum, enteroendocrine cells release cholecystokinin (CCK).
• CCK inhibits stomach contractions and stimulates gallbladder contraction, causing bile release into the duodenum.

Pancreas Anatomy and Functions

• The pancreas lies behind the stomach and has head, body, and tail regions.
• It has endocrine (hormone release: insulin, glucagon) and exocrine (digestive enzyme secretion) functions.
• Pancreatic acini secrete pancreatic juice into the main pancreatic duct, which drains into the duodenum.
• About 30% of people have a smaller accessory pancreatic duct.
• Pancreatic juice (1.2–1.5 L/day) contains water, bicarbonate (a base), and enzymes to digest lipids, carbs, proteins, and nucleic acids.
• Enzymes are stored in zymogen granules to prevent self-digestion.

Hormonal Control of Digestive Secretions

• CCK (from duodenum) triggers bile and pancreatic enzyme release and opens the hepatopancreatic sphincter.
• Secretin (from duodenum) stimulates pancreatic release of bicarbonate to neutralize acidic chyme.

Key Terms & Definitions

• Bile — a fluid produced by the liver that emulsifies fats.
• Cholecystokinin (CCK) — a hormone that promotes bile and pancreatic enzyme release.
• Secretin — a hormone that stimulates pancreatic bicarbonate secretion.
• Zymogen granules — storage vesicles for inactive digestive enzymes in the pancreas.
• Porta hepatis — area where vessels and ducts enter/exit the liver.

Action Items / Next Steps

• Review the structure and flow of bile and pancreatic ducts.
• Study the hormonal regulation of the accessory digestive organs.
• Prepare questions on the digestive system for any unclear topics.