Bile is necessary to emulsify fats. Proteases break down proteins, not fat. Fiber is broken down by bacteria in the large intestine. The stomach does not release bile. Note that the liver synthesizes bile, but it is stored in and released from the gallbladder.

The small intestine receives stomach contents and continues to digest them by using various enzymes, it also absorbs small nutrient molecules. The large intestine produces waste by removing water from undigested material. The liver produces bile for the gallbladder and also processes and stores nutrients. The gallbladder stores bile and assists in the breakdown of fats in the small intestine. 

The correct pathway for food to travel through the gastrointestinal tract after ingestion is the following: esophagus, stomach, duodenum, jejunum, ileum, cecum, ascending colon, transverse colon, descending colon, sigmoid colon, rectum.

CCK is a gastrointestinal hormone that acts to decrease gastric emptying when stimulated by the presence of fat and protein. This hormone also has a direct effect on the brain centers responsible for hunger to reduce further eating. The majority of other gastrointestinal hormones are stimulated by the presence of fat.

The duodenum is responsible for the absorption of iron and calcium. Without it, individuals will be iron deficient (anemia) and hypocalcemia (soft bones and etc.). B9 and B12 are both absorbed in the small intestine. 

The large intestine is responsible for the absorption of water and electrolytes. Most digestion and nutrient absorption occurs in the small intestine, leaving water and insoluble wastes for the large intestine. Once absorption takes place, the wastes become more solid and the body is able to retain water. Loss of this large intestine function can lead to severe dehydration.

Fat digestion is primarily a function of lipase and bile. Lipase helps cleave lipid molecules and bile helps emulsify particles for transport into the lymphatic system via lacteals.

The digestive system is responsible for the breakdown of food as it moves from the mouth, down through the stomach and the intestines. The food is mechanically broken down into small pieces in the mouth, and then further digested by the gastric secretions and contractions of the stomach. The small intestine is the site of chemical digestion due to the presence of pancreatic secretions. Once digested, the nutrients are absorbed in the jejunum and ileum of the small intestine. The large intestine is responsible for absorption of water and electrolytes, after which the remaining products are carried to the rectum for elimination.

If the water is not absorbed due to an infection or anatomical abnormality the feces will retain the water content, resulting in diarrhea.

The kidneys are responsible for the excretion of fluid wastes from the blood and help to maintain water balance and blood pressure. They are not involved in the digestive tract.

Amino acids, sugars, and fats are absorbed in the small intestine, but water is absorbed in the large intestine.

All enzymes released into the lumen of the small intestine by the pancreas are zymogens. Enterokinase is an enzyme that activates trypsin in the lumen. Once trypsin is activated, it is capable of activating every other enzyme found in the lumen of the small intestine, even other trypsin enzymes.

Bile is produced by the liver and released from the gall bladder into the small intestine. It has the function of emulsifying fat, increasing its surface area by forming micelles. This allows the protein lipase to break down and digest the fat in the small intestine much more quickly.

The pancreas secretes bicarbonate to neutralize the acidity of chyme and pancreatic amylase to aid in the digestion of carbohydrates.