Alimentary Canal

• ALIMENTARY CANAL: a long tube which runs from the mouth to the anus. It is part of the Digestive System. 
• MOUTH: Food is ingested using the teeth, lips, and tongue. The teeth then bite or grind the food into smaller pieces increasing the surface area.

  The tongue mixes the food with saliva and forms it into BOLUS. 
• Saliva is made in the salivary glands. It is a mixture of water, mucus and the enzyme AMYLASE.
• The water in saliva helps to dissolve substances in the food. The mucus helps bring together the chewed food to form BOLUS and lubricates it.
• AMYLASE in saliva begins to digest starch in the food to maltose.
• OESOPHAGUS: the tube behind the trachea which takes food down to the stomach. 
• EPIGLOTTIS: a piece of cartilage that covers entrance to the trachea. It stops food from going into the lungs.
• SPHINCTER MUSCLE: a ring of muscle which is the entrance to the stomach from the oesophagus. This muscle relaxes to let the food pass into the stomach. 
• STOMACH: it has strong, muscular walls. The muscles contract and relax to churn the food and mix it with the enzymes and mucus. The mixture is called CHYME.
• The stomach wall contains GOBLET CELLS which secrete mucus. It also contains other cells which produce PROTEASE and others which make HYDROCHLORIC ACID. 
• PEPSIN in the stomach digests proteins by breaking them down into POLYPEPTIDES. Pepsin works best in acidic conditions.
• HYDROCHLORIC ACID is useful in the stomach for 2 reasons:

  • helps to protect you from harmful microorganisms that may be in the food, by denaturing enzymes in them. (it kills bacteria)
  • creates an environment for the enzyme PEPSIN to work well
• The stomach can store food for one or two hours. 
• THE SMALL INTESTINE: the part of the Alimentary Canal which is between the stomach and colon. It is about 5m long.
• DUODENUM: part of the small intestine near the stomach
• ILEUM: part of the small intestine near the large intestine
• PANCREATIC JUICE: a fluid made by the pancreas that flows along the pancreatic duct to secrete to the small intestine.
• PANCREATIC JUICE contains many enzymes, including amylase, protease and lipase. Amylase breaks down starch to maltose. 
• TRYPSIN is a protease which breaks down proteins to polypeptides in pancreatic juice.
• LIPASE breaks down fats (lipids) to fatty acids and glycerol. 
• BILE: a yellowish green, alkaline, watery liquid, which helps to neutralise the acidic mixture from the stomach.
• BILE is made in the LIVER, and then stored in the GALL BLADDER.
• BILE: flows to the small intestine along the BILE DUCT.
• BILE does not contain any enzymes, but helps to digest fats. It does this by breaking down large drops of fats into small ones. 
• BILE increases the surface area of fats, making it easier for the lipase in the pancreatic juice to digest fats into fatty acids and glycerol. This is called EMULSIFICATION and it is done by the salts in the bile called BILE SALTS. 
• VILLI: tiny projections lining the inner walls of the small intestine. They also create enzymes.
• VILLI create these enzymes:

  • MALTASE: breaks down maltose to glucose
  • PROTEASE: finishes breaking down any polypeptides into amino acids
  • LIPASES: completes the breakdown of fats into fatty acids and glycerol
• ABSORPTION: once the enzymes are done breaking down the larger molecules, the smaller molecules are small enough to pass through the wall of the small intestine and into the blood. 
• VILLI help increase ABSORPTION as the tiny projections create a larger surface area to absorb the small molecules.
• THE LARGE INTESTINE: the undigested food which are not absorbed in the small intestine travels down the colon. In the colon, more water and salt are absorbed, but less water is absorbed in the large intestine compared to the small intestine.
• COLON: the upper part of the large intestine
• RECTUM: the lower part of the large intestine
• By the time the food reaches the last part of the large intestine called the RECTUM, most of the substances which can be absorbed have gone into the blood.

  All that remains is indigestible food, bacteria, and some dead cells from the inside of the alimentary canal called faeces.
• ASSIMILATION: after the small molecules have been absorbed into the blood in the villi, the nutrients are taken into the liver. The liver processes some of them, before they go any further. Some of these nutrients can be broken down, some converted into other substances, some stored and some unchanged. 
• ASSIMILATION: After the liver, the nutrients are dissolved in the blood plasma. They are then taken to other parts of the body where they may become assimilated as part of a cell.