What happens in the alimentary canal?

Answer 1

The alimentary canal is the passage from the mouth to anus.... Digestion occurs in the alimentary canal.

Answer 2

The alimentary canal is also called the digestive tract and includes all organs and structures associated with digesting, and absorbing food, and eliminating undigestible materials . These structures and organs include the mouth, the pharynx, the esophagus, the stomach, the small intestine, the large intestine and the anus. Associated organs that help with digestion are the pancreas and the liver. Food is mashed up by the teeth in the mouth, then moves through the pharynx during swallowing into the esophagus, which then moves the bolus of food to the stomach. In the stomach the bolus of food is mixed with acids to kill bacteria. Then the material, now called chyme, is moved into the small intestine into which the pancreas secretes many digestive enzymes to break down the food into it's constituent parts and it also secretes sodium bicarbonate to neutralize the acid from the stomach. Carbohydrates are broken down to individual glucose molecules, proteins are broke down into individual amino acids, and fats are broken down to individual glycerol and fatty acid molecules. The liver is also involved here in that it secretes bile into the small intestine to emulsify fat molecules which allows them to be broken down by an enzyme secreted by the pancreas. As these substances move down the small intestine, they are absorbed through the wall of the small intestine. Glucose and amino acids move into capillaries in structures in the small intestine wall called villi. Glycerol and fatty acids however, are reconstructed into fats in the small intestine wall cells and are packaged into chylomicrons (a transport particle for fats) which move into lymphatic capillaries in the villi called lacteals. Since all of the venous drainage of the alimentary canal goes into the liver, the glucose and amino acids that enter the capillaries go into the liver first before they are released to the rest of the body. This circulatory set up is called the hepatic portal system and represents two capillary beds in series. This system insures that all incoming glucose and amino acids are regulated by the liver before they go out to the rest of the cells of the body. However, since the incoming fats go into the lacteals, they go directly into the venous blood (via the thoracic duct (the main lymphatic vessel) into the left subclavian vein) and are distributed to all cells of the body before they are secondarily dealt with by the liver. Any remaining undigestible material left in the small intestine will move into the large intestine where some remaining water and vitamins are reabsorbed. The remaining material is then packaged into feces and moved to the anus for elimination from the body.