The Small Intestine
By Alex & Bella
Where is the Small Intestine Located?
Function of the Small Intestine
90% of digestion and absorption takes place in the small intestine. The main function is to absorb the nutrients from our food and drink into the blood stream to be transported to the cells to be used for energy (...). The small intestine is divided into three parts, the duodenum, jejunum and the ileum (Wikimedia Foundation, 2014).
- All four macromolecules carbohydrates, lipids, proteins and nucleic acid are digested in the small intestine.
- These nutrients are then absorbed into the blood stream to be transported around the body to be used for various functions.
Figure 3: Wake Gastroenterology, 2014
Parts of the Small Intestine
This is the first part of the small intestine and it is 25 cm long and 5 cm wide. The function of this is to absorb iron. It is also where the majority of chemical digestion takes place.
The lining of the jejunum is specialised for the absorption of small nutrient particles which have previously been digested by enzymes in the duodenum.
The function of this is to absorb vitamin B 12 and bile salt, as well as any products of digestion that were not previously absorbed. This is where the villi are located.
Mechanical & Chemical Digestion
Mechanical digestion involves the physical digestion of food. This process occurs before the nutrients in the food reach the small intestine and therefore does not occur in this organ.
Chemical digestion is the chemical breakdown of food into smaller parts that are able to be more easily absorbed into the blood stream, this digestion has been discussed in the macromolecule section of the flyer but here is some more information:
- The digestive enzymes enter the small intestine in response to the cholecystokinin, which is a hormone released by the body due to nutrients entering the small intestine.
- This cholecytokinin hormone not only causes the enzymes to enter the small intestine but also causes bicarbonate to be released, which works to neutralise any harmful acid that may be coming from the stomach.
Digestive Enzymes Present in the Small Intestine
- Nuclease: Any of a group of enzymes that split nucleic acids into nucleotides and other products.
- Protease: Any of various enzymes, including the proteinases and peptidases, that catalyze the hydrolytic breakdown of proteins.
- Collagenase: Any of various enzymes that catalyze the hydrolysis of collagen and gelatin.
- Lipase: Any of a group of lipolytic enzymes that cleave a fatty acid residue from the glycerol residue in a neutral fat or a phospholipid.
- Amylase: Any of a group of enzymes that catalyze the hydrolysis of starch to sugar to produce carbohydrate derivatives.
- Elastase: An enzyme capable of catalyzing the digestion of elastic tissue.
- Trypsin: A proteolytic digestive enzyme produced by the exocrine pancreas that catalyzes in the small intestine the breakdown of dietary proteins to peptones, peptides, and amino acids.
- Chymotrypsin: A proteolytic enzyme produced by the pancreas that catalyzes the hydrolysis of casein and gelatin.
Source (Online Medical Dictionary)
These enzymes allow the particles of food and nutrients to be broken down and consequently absorbed in to the blood stream.
What are the Villi? How do they Help with Digestion?
Villi are finger shaped and are covered in tiny hairs called microvilli.
Thousands of villi are attached to the muscular wall of the small intestine, which greatly increase the surface area to volume ratio that aids absorption. The microvilli located on the villi aid in increasing the surface area. Inside the villi there are many blood capillaries that absorb the food.
The Small and Large Intestines n.d., Illustration, OpenStax CNX, accessed 9 September 2014, <http://cnx.org/contents/430d8e5a-f699-4949-9849-5b4ca1125fa2@4>.
Mechanical Digestion 2011, Illustration, Human Anatomy and Physiology, accessed 9 September 2014, <http://andreeasanatomy.blogspot.com.au/2011_05_01_archive.html>.
Carbohydrate Digestion 2001, myDr.com.au, accessed 9 September 2014, <http://www.mydr.com.au/nutrition-weight/animation-carbohydrate-digestion>.
Chemical Digestion of Carbohydrates, Proteins, Lipids, Nucleic Acids n.d.,Boundless, accessed 9 September 2014, <https://www.boundless.com/physiology/textbooks/boundless-anatomy-and-physiology-textbook/the-digestive-system-23/chemical-digestion-224/chemical-digestion-of-carbohydrates-proteins-lipids-nucleic-acids-1104-1171/>.
Digestion 2004, Biology Mad, accessed 9 September 2014, <http://www.biologymad.com/master.html?http://www.biologymad.com/digestion/digestion.htm>.
Wikipedia 2014, Small Intestine Cancer, Wikimedia Foundation, accessed 9 September 2014, <http://en.wikipedia.org/wiki/Small_intestine#Digestion>.
The Intestines 2014, Illustration, BBC, accessed 9 September 2014, <http://www.bbc.co.uk/schools/gcsebitesize/science/add_edexcel/common_systems/digestionrev5.shtml>.
The Digestive System 2010, Illustration, Unknown, accessed 9 September 2014, <http://www2.estrellamountain.edu/faculty/farabee/BIOBK/biobookdigest.html>.
Absorption in Small Intestine n.d., Illustration, Bio-662, accessed 9 September 2014, <http://bio662.dyndns.info/s3b/b3n/b3n01FoodNutrition/b3n01eFdN442AbsorptionInSmallIntestine.htm>.
Human Digestive System 2014, Diagram, Competition Affairs, accessed 10 September 2014, <http://competitionaffairs.blogspot.com.au/2010/11/human-digestive-system.html>.
Absorption of Lipids by Cells in the Small Intestine n.d., Diagram, Unknown, accessed 10 September 2014, <http://www.uic.edu/classes/bios/bios100/lectf03am/fats.htm>.
Pancreatitis Symptoms & Treatment 2014, Diagram, Wake Gastroenterology, accessed 13 September 2014, <http://www.wakegastro.com/pancreatitis/>.