The Digestive System

• An autotrophic organism can produce its own food while a heterotrophic organism cannot.
• Digestion is the process of breaking down food into smaller particles.
• Digestion allows for food to be absorbed into the bloodstream.
• The alimentary canal starts at the mouth and ends at the anus.
• The first step in digestion is ingestion where the food enters the mouth. The food is then broken down in digestion. The food is absorbed into the blood and waste is removed via egestion.
• An example of mechanical digestion is chewing.
• Incisors can cut, slice, and bite food. Canines tear and grip food while premolars and molars crush and chew.
• This is the human dental formula.

  
• An example of chemical digestion is the enzyme amylase found in saliva breaking down the food in the mouth.
• Amylase turns starch into maltose.
• The esophagus carries the food from the mouth to the stomach. This is aided by a process called peristalsis. This helps break down food mechanically.
• Fiber helps stimulate peristalsis. It is found in cereals and vegetables and helps absorb water from the large intestine.
• The stomach is a muscular bag that stores and digests food. It mechanically churns food creating chyme.
• Food enters and leaves the stomach through the sphincter muscle. The stomach lining releases gastric juices, containing mucous to prevent self-digestion of the stomach, and pepsinogen which is converted to active pepsin when reacting with acid.
• Hydrochloric acid in the stomach has a pH of 1-2. This acid can kill any bacteria that may cause harm to the body. HCl activates pepsinogen to form pepsin, which digests proteins.
• The pancreas secretes pancreatic juice containing sodium bicarbonate which neutralizes the chyme in the stomach. It also contains the enzymes amylase and lipase which are secreted into the duodenum to aid digestion.
• The liver produces bile and breaks down excess amino acids to form urea.
• Bile is a yellow liquid formed from dead red blood cells. It is made in the liver and stored in the gall bladder. It enters the duodenum through the bile duct.
• The small intestine is lined with villi, which increase the surface area for absorption.
• The duodenum, the first part of the small intestine, carries out the digestion of food. The ileum absorbs nutrients into the body via passive transport. This does not require energy.
• The villi are only one cell thick and have a rich supply of blood to carry products away.
• Deamination is the process in which excess amino acids are broken down in the liver to form urea.
• Nutrients are carried from the small intestine to the liver by the hepatic portal vein.
• The large intestine is only 1.5 meters long and holds food from ten hours to a few days.
• The colon is used to reabsorb water and contains feces. This is stored in the rectum.