Human Gastrointestinal Tract - Lower Gastrointestinal Tract

Lower Gastrointestinal Tract

The lower gastrointestinal tract includes most of the small intestine and all of the large intestine. According to some sources, it also includes the anus.

• Bowel or intestine
  • Small Intestine: Has three parts:
    • Duodenum: Here the digestive juices from the pancreas (digestive enzymes) and hormones and the gallbladder (bile) mix. The digestive enzymes break down proteins and bile and emulsify fats into micelles. The duodenum contains Brunner's glands which produce bicarbonate. In combination with bicarbonate from pancreatic juice, this neutralizes HCl of the stomach.
    • Jejunum: This is the midsection of the intestine, connecting the duodenum to the ileum. It contains the plicae circulares, and villi to increase the surface area of that part of the GI Tract. Products of digestion (sugars, amino acids, fatty acids) are absorbed into the bloodstream.
    • Ileum: Has villi and absorbs mainly vitamin B12 and bile acids, as well as any other remaining nutrients.
  • Large Intestine: Has three parts:
    • Cecum: The Vermiform appendix is attached to the cecum.
    • Colon: Includes the ascending colon, transverse colon, descending colon and sigmoid Flexure: The main function of the Colon is to absorb water, but it also contains bacteria that produce beneficial vitamins like vitamin K.
    • Rectum
• Anus

The Ligament of Treitz is sometimes used to divide the upper and lower GI tracts.