Editing Gastrointestinal tract (section)

=====Small intestine=====
{{Main|Small intestine|Duodenum|Jejunum|Ileum}}
The [[small intestine]] is a tubular structure around 6 to 7 m long, that begins at the [[duodenum]], and ends at the [[ileum]].<ref name="GRAYS2005">{{cite book|title=Gray's anatomy for students|last=Drake|first=Richard L.|author2=Vogl, Wayne|author3=Tibbitts, Adam W.M. Mitchell|author4=illustrations by Richard|author5=Richardson, Paul|publisher=Elsevier/Churchill Livingstone|year=2015|isbn=978-0-8089-2306-0|edition=3rd|location=Philadelphia|page=312}}</ref> Its [[mucosal]] area in an adult human is about {{convert|30|m2|abbr=on}}.<ref name="ReferenceA">{{Cite journal|last1=Helander|first1=Herbert F.|last2= Fändriks|first2=Lars|date=2014-06-01|title=Surface area of the digestive tract - revisited|journal=Scandinavian Journal of Gastroenterology|volume=49|issue=6|pages=681–689|doi=10.3109/00365521.2014.898326|issn=1502-7708|pmid=24694282|s2cid=11094705}}</ref> The combination of the [[circular folds]], the villi, and the microvilli increases the absorptive area of the mucosa about 600-fold, making a total area of about {{convert|250|sqm|sqft|abbr=on}} for the entire small intestine.<ref name="Hall">{{cite book|last1=Hall|first1=John|title=Guyton and Hall textbook of medical physiology|date=2011|isbn=9781416045748|page=794|publisher=Saunders/Elsevier|edition=Twelfth}}</ref> Its main function is to absorb the products of digestion (including carbohydrates, proteins, lipids, and vitamins) into the bloodstream. There are three major divisions:
# [[Duodenum]]: A short structure (about 20–25&nbsp;cm long<ref name=GRAYS2005/>) that receives [[chyme]] from the stomach, together with [[pancreatic juice]] containing [[digestive enzymes]] and [[bile]] from the [[gall bladder]]. The digestive enzymes break down proteins, and bile [[emulsion|emulsifies]] fats into [[micelles]]. The [[duodenum]] contains [[Brunner's glands]] which produce a mucus-rich alkaline secretion containing [[bicarbonate]]. These secretions, in combination with bicarbonate from the pancreas, neutralize the stomach acids contained in the chyme.
# [[Jejunum]]: This is the midsection of the small intestine, connecting the duodenum to the ileum. It is about {{convert|2.5|m|ft|abbr=on}} long and contains the [[circular folds]] also known as plicae circulares and [[intestinal villus|villi]] that increase its surface area. Products of digestion (sugars, amino acids, and fatty acids) are absorbed into the bloodstream here.
# [[Ileum]]: The final section of the small intestine. It is about 3 m long, and contains [[intestinal villus|villi]] similar to the jejunum. It absorbs mainly [[vitamin B12]] and [[bile acids]], as well as any other remaining nutrients.