Anatomy and Physiology of the Small Intestine and Associated Organs

Overview of the Small Intestine

• Parts of the Small Intestine

  • Duodenum: Also known as "the mixing bowl"; 10 inches long; receives chyme from the stomach and mixes with liver and pancreas secretions.
  • Jejunum: About 8 feet long; primary site for chemical digestion and nutrient absorption.
  • Ileum: Last section, about 11.5 feet long; continues absorption process.

• Functions

  • Responsible for 90% of nutrient absorption.
  • Increases surface area for absorption through structures:
    • Plicae Circulares: Permanent folds increasing surface area.
    • Villi: Finger-like projections that further increase surface area.
    • Microvilli: Tiny projections on individual cells, forming the "brush border."

Digestive Process in the Small Intestine

• Duodenum

  • Limited absorption; focuses on neutralizing stomach acid.
  • Receives digestive enzymes and bile from pancreas and liver.

• Jejunum

  • Primary site for nutrient absorption.

• Ileum

  • Continues absorption, finishing the process begun in the jejunum.

Role of the Pancreas

• Structure

  • Head, body, and tail.
  • Connects to the duodenum through the pancreatic duct.

• Functions

  • Exocrine: Produces digestive enzymes (proteases, amylase, lipase).
    • Proteolytic enzymes are vital for protein digestion.
  • Endocrine: Produces hormones (insulin and glucagon) for blood sugar regulation.

Liver and Bile Production

• Structure

  • Largest visceral organ located in the right abdomen.
  • Includes four lobes: right, left, caudate, and quadrate.

• Functions

  • Regulates blood composition, removes waste, and detoxifies substances.
  • Produces bile for fat emulsification.
  • Stores and releases nutrients as needed.

• Bile Flow

  • Produced in the liver, flows through the hepatic ducts, common hepatic duct, and into the common bile duct.
  • Bile emulsifies fats, increasing surface area for enzymes.

Gallbladder

• Structure and Function

  • Pear-shaped organ storing and concentrating bile.
  • Releases bile into the duodenum under hormonal control (cholecystokinin).

• Issues

  • Gallstones: Formed from concentrated bile leading to blockages and pain.

Summary

• The small intestine is crucial for nutrient absorption, aided by increased surface area from its structures.
• The pancreas and liver play vital roles in digestion by providing enzymes and bile.
• The gallbladder stores bile, releasing it to aid in fat digestion.
• Understanding these organs is essential for comprehending the digestive process and its regulation.