OVERVIEW OF THE DIGESTIVE SYSTEM.

 


The digestive system includes

  • Thee accessory organs are not part of the tract but secrete substances into it via connecting ducts.
  • The GI tract is also known as the alimentary canal.
  •  Overall The overall function of the digestive system is to process ingested foods into molecular forms that are then transferred, along with salts and water, to the body's internal environment, where the circulatory system can distribute them to cells.
  • The digestive system is under the local neural control of the enteric nervous system and also of the central nervous system. 
  • pharynx, esophagus, stomach, small intestine, and large intestine. 
  • The length of the GI tract is about 5-7 meters (16.5-23 ft) in a living person when the muscles along the wall of the GI tract organs are in a state of tonus (sustained contraction). 
  •  It is longer in a cadaver (dead body) (about 7–9 meters or 23-29.5 ft) because of the loss of muscle tone after death.
  •  Teeth aid in the physical breakdown of food, and the tongue assists in chewing and swallowing.
  • The other accessory digestive organs, however, never come into direct contact with food. They produce or store secretions that flow into the GI tract through ducts; the secretions aid in the chemical breakdown of food.
  •  Muscular contractions in the wall of the GI tract physically break down the food by churning it and propel the food along the tract, from the esophagus to the anus.
  • The contraction also help to dissolve foods by mixing them with the fluids secerted into the tract.
  •  Enzymes secreted by accessory digestive organs and cells tract break down the food chemically.

 1. The gastrointestinal (GI) tract, consisting of the mouth, pharynx, esophagus, stomach, small intestine, and large intestine; and

 2. The accessory organs and tissues, consisting of the salivary glands, liver, gallbladder, and exocrine pancreas. 


STEPS OF DIGESTION.

  • Overall, the digestive system performs six basic processes:

 Ingestion. 

  • This process involves taking foods and liquids into the mouth (eating).

Secretion. 

  • Each day, cells within the walls of the GI tract and accessory digestive organs secrete a total of about 7 liters of water, acid, butfers, and enzymes into the lumen (interior space) of the tract.

 Mixing and propulsion. 

  • Alternating contractions and relaxations of smooth muscle in the walls of the GI tract mix food and secretions and move them towards the anus. This capability of the GI tract to mix and move material along its length is called motility. 
  • In some cases, muscular movements travel in a wavelike fashion in one direction along the length of a part of the tract, a process called peristalsis.

Digestion. 

  • Mechanical and chemical processes break down ingested food into small molecules. 

 1. MECHANICAL DIGESTION.

  • In mechanical digestion the teeth cut and grind food before it is swallowed, and then smooth muscles of the stomach and small intestine mix the food to further assist the process.
  • As a result, food molecules become dissolved and thoroughly mixed with digestive enzymes.

2. CHEMICAL DIGESTION.

  •  In chemical digestion the large carbohydrate, lipid, protein, and nucleic acid molecules in food are split into smaller molecules by hydrolysis.   
  • Digestive enzymes produced by the salivary glands, tongue, stomach, pancreas, and small intestine catalyze these catabolic reactions. 
 

Absorption

  •  A few substances in food can be absorbed without chemical digestion. These include vitamins, ions, cholesterol, and water.
  • secreted fluids, ions, and the products of digestion into the epithelial cells lining the lumen of the GI tract is called absorption. 
  • The absorbed substances pass into blood or lymph and circulate to cells throughout the body.

Defecation. 

  •  Wastes, indigestible substances, bacteria, cells from the lining of the GI tract, and digested materials that were not absorbed in their journey through the digestive tract leave the body through the anus in a process called defecation.
  • Thee eliminated material is termed as feces or stool.