Explain the structure and function of the duodenum. Name all substances, enzymes, substrates and products.
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  • Structure
The duodenum is located in your alimentary canal just past the stomach. Some textbooks describe it as being the first part of the small intestine, while others consider it to be a separate organ entirely. The duodenum is a small tube approximately ten inches long and not more than an inch or two in diameter. The duodenum is broken in to four parts. These four parts are somewhat unimportant. The entire duodenum is essentially a long tube. At the bottom of the stomach is a small valve known as the pyloric sphincter. Just pass this junction is the first part of the duodenum. The first part of the duodenum is located very close to the liver and pancreas.
Description: http://callmethedoctor.co.uk/wp-content/uploads/2012/09/Duodenum.jpg
Description: http://callmethedoctor.co.uk/wp-content/uploads/2012/09/Duodenum.jpg

  • Function
Its main function is to receive the partially digested foods from the stomach, and complete the process of digestion. In the stomach, foods are mixed with stomach acids and digested partially. This mixture of semi digested foods and stomach acids is known as chyme. It receives this chyme from the stomach, and then starts the breakdown foods with the help of enzymes and intestinal juice. It also receives bile from the liver and the gallbladder, and pancreatic juice from the pancreas. These chemicals are responsible for ensuring the proper digestion of foods in the duodenum.Along with digesting foods, it is responsible for regulating the rate of gastric emptying. Gastric emptying refers to the emptying of the stomach of chyme and allowing it to enter into the duodenum. These functions are facilitated by the hormones secreted from the duodenal epithelium. There is a small circular opening between the stomach and the duodenum, known as pylorus, which releases the chyme into the duodenum. The cells present in the epithelium of duodenum in turn, release two hormones known as secretin and cholecystokinin. Secretin is released in response to too much acid in the small intestine or duodenum, while secretion of cholecystokinin is stimulated by the presence of amino acids and fatty acids. These two hormones stimulate the liver and the gallbladder to release bile, as well as the pancreas to secrete enzymes (lipase, amylase and trypsin) into the duodenum.After the completion of digestion, it absorbs the nutrients, from where the nutrients enter the bloodstream.
To sum up, the duodenum's main functions in the digestive system are,

  1. controlling the rate of gastric emptying, and regulating hunger and the movement of food throughout the gastrointestinal tract.
  2. digestion of foods - (pancreatic amylase completes the digestion of starch here, trypsin continues the digestion of polypeptides and bile with lipase begin the digestion of fat)
absorption of nutrients, It has been found that more foods and nutrients are absorbed in duodenum than stomach. Gastric bypass surgery often involves the duodenum, due to its immense importance in the absorption of nutrients, and regulation of hunger and movement of food. In gastric bypass surgery, usually the duodenum is bypassed in an attempt to lower the absorption of nutrients and calories.

Definitions of the chemicals found :
Enzymes:Enzymes are large molecules responsible for the thousands of chemical conversions that sustain life. They are highly selective catalysts, greatly accelerating both the rate and specificity of metabolic reactions, from the digestion of food to the synthesis of DNA. Most enzymes are proteins, although some Catalytic RNA molecules have been identified. Enzymes adopt a specific three dimensional structure, and may employ organic (e.g. biotin) and inorganic (e.g. magnesium ion) confactors to assist in catalysis.
In enzymatic reactions, the molecules at the beginning of the process, called substrates, are converted into different molecules, called products. Almost all chemical reactions in a biological cell need enzymes in order to occur at rates sufficient for life. Since enzymes are selective for their substrates and speed up only a few reactions from among many possibilities, the set of enzymes made in a cell determines which metabolic pathways occur in that cell.

Description: http://4.bp.blogspot.com/-XEl5hWWQcBA/UAWV_qRHwDI/AAAAAAAACX4/byWxwBaUZTk/s1600/Digest3.gif
Description: http://4.bp.blogspot.com/-XEl5hWWQcBA/UAWV_qRHwDI/AAAAAAAACX4/byWxwBaUZTk/s1600/Digest3.gif

Substrates: Most food components are molecules. Food molecules are biological polymers (i.e., chains of repeating units of smaller molecules linked together) and are comprised of proteins, nucleic acids, carbohydrates (polysaccharides), and lipids. The repeating units forming molecules are called monomers, or building blocks. The monomers in proteins are amino acids, those in polysaccharides are sugar derivatives, (example: hexoses such as glucose or fructose, or pentoses such as ribose). Those in nucleic acids are nucleotides. Lipids as major food components are not organized as proteins, i.e., in a repeating manner of monomers. Instead they are made up by two two basic units fatty acids and glycerol. Proteins, carbohydrates, and lipids constitute the main substrates for digestive enzymes as well as the oral enzymes supplied as dietary supplements.
  1. 1. Proteins
  2. 2. Carbohydrates
  3. 3. Lipids

  1. The enzymes that operate as part of the digestive process, the subtrate and products obtained was not discussed as it relates to the function of the duodenum. the content above needs to be edited for easier reading,
  2. content needs to explain the specific role and processes of the duodenum
  3. it also need to relate the structures and organs associated with the duodenum and its function
  4. and what's going on with the diagrams??????
  5. the rest below should be deleted
p.s. fix it please
Mr Cooper
Proteins are essential molecules used in all types of cellular activity and life. Enzymes, antibodies, regulatory molecules, contractile molecules responsible for movement, hormones, cellular structural components are some of a few of the proteins needed to sustain life. Almost all proteins in the body are in continuous dynamic: breakdown (catabolism) and formation (anabolism). Thus, in order to maintain vitality, viability, and health the body must have a supply of building blocks to help replenish the proteins that are broken down. Considering that even the proteins involved in regulating and making other proteins need also to be made and replenished, protein in the diet (i.e., amino acids) is an obligatory demand by the body.

Carbohydrates: Carbohydrates also called polysaccharides are polymers of simple sugars such as glucose, fructose, and galactose in various combinations. The repeating units may be glucose, or fructose or a disaccharide of glucose plus another simple sugar. Carbohydrates are the main source of cellular energy important as energy sources, but also contribute in the synthesis of glycoproteins, proteoglycans, glycoplipids, and glycosaminoglycans.

Lipids:Lipids, commonly referred to as fats, constitute a heterogeneous group. The main classes of lipids are:
Simple lipids include fats and oils which are esters of glycerol and fatty acids (triglycerides) or esters of long chain alcohol and fatty acids (waxes);

Complex lipids are simple lipids conjugated with a non- lipid fraction such as phosphoric acid to form phospholipid or with a carbohydrate moiety to form glycolipid or with a protein to form lipoprotein;

Derived lipids are hydrolytic products of lipids and include fatty acids, sterols, carotenoids, and liposoluble vitamins.