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Understanding Small Intestine and Digestive Organs

Apr 2, 2025

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.