Final answer:
The small intestine is the major site of digestion, extending approximately 20 ft., where the bicarbonate and enzymes from the pancreas, along with bile, break down food over 7-8 hours.
Step-by-step explanation:
The Major Site of Digestion
The major site of digestion is the small intestine, which extends to about 20 ft. long. This is where most of the chemical digestion and almost all absorption of nutrients occur. The pancreas plays a crucial role in this process by producing enzyme- and bicarbonate-rich pancreatic juice. This juice is channeled to the small intestine through the pancreatic duct. In the small intestine, the bicarbonate from the pancreas neutralizes acidic stomach contents, making an environment conducive for the pancreatic and small intestine enzymes to effectively digest carbohydrates (CHO), protein, and fat. Moreover, bile, which is produced by the liver and stored in the gallbladder, is secreted into the duodenum where it emulsifies fats to assist their digestion.
The small intestine is divided into three parts: the duodenum, the jejunum, and the ileum. The duodenum is where the chyme, mixed with pancreatic juices and bile, undergoes significant chemical digestion. The contents of a meal usually complete their transit through the stomach and reach the duodenum within 2 to 4 hours, and can stay in the small intestine for about 7-8 hours as part of the larger digestion process which can take in total from 24 to 72 hours.