The Small Intestine

  1. As chyme is pushed through the pyloric valve, it enters the duodenum, the first part of the small intestine.
  2. The small intestine performs three major functions on chyme that enters from the stomach.
  3. The small intestine digests carbohydrates and fats, completes the digestion of proteins, and absorbs digested nutrients.
  4. The small intestine is long (7m), but its diameter (2.5cm) is smaller than the large intestine.
  5. Some of the digestive fluids that contain enzyme activators and enzymes that digest food in the small intestine come from glands located in the small intestine.
  6. These glands produce enzymes that digest proteins and carbohydrates.
  7. The pancreas, an organ located behind the stomach, secretes pancreatic fluid into the small intestine.
  8. Pancreatic fluid contains enzymes that digest proteins, fats, and carbohydrates.
  9. Pancreatic fluid also contains sodium bicarbonate, which neutralizes the hydrochloric acid in chyme, protecting the small intestine.
  10. The liver is a large brownish organ that lies above the stomach in the abdomen. One of the functions of the liver is to secrete a yellow-brown liquid called bile.
  11. Bile is stored in a small sac called the gallbladder. The entrance of food into the small intestine stimulates the release of bile to the small intestine through a duct.
  12. Bile is produced by the liver and stored in the gallbladder until needed.
  13. Fats in the small intestine are broken down into smaller droplets by bile.
  14. One of the main functions of bile is to dissolve cholesterol. Bile is a salt containing detergent and if the amount of salt in the bile is insufficient, sharp, painful crystals can form, known as gallstones.
  15. Most nutrients are absorbed into the bloodstream through the cells that line the small intestine.
  16. The internal surface of the intestine is lined with fingerlike projections called villi.
  17. Villi increase the surface area of the lining of the small intestine, making absorption more efficient.
  18. Nutrients are absorbed through blood vessels and lymph vessels in the villi.
  19. Blood vessels absorb carbohydrates (sugars) and proteins (amino acids).
  20. Lymph vessels called lacteals absorb fats and fatty acids.
  21. Most of the nutrients used by the body are absorbed through the lining of the small intestine.
  22. Undigested material leaves the small intestine through a valve and enters the large intestine or colon.
  23. An organ called the appendix is located near the junction of the small and large intestine. The appendix is a finger-shaped pouch, which does not serve any known function. If the appendix becomes infected with bacteria, resulting in appendicitis, the appendix must be removed.

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