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The structure and functions of the digestive system

The digestive system is made up of a group of organs
that work together to breakdown food into small substances that our body can
absorb and use in metabolic reactions, growth and repair in cells. Digestion
takes place in the alimentary canal starting at the mouth and ending at the
anus. (, n.d.). The alimentary canal is also known as
the    gastrointestinal (GI) tract, when
food is broken down the useful products are separated from the unusable
products. Useful products are transported to the body and the unusable products
are excreted from the body. The final product of digestion results in glucose,
amino acids and fatty acids. The five stages of food processing are, ingestion,
digestion, absorption, assimilation and egestion. (, n.d.).

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The mouth is the
cavity which food enters the GI tract, and is the location where the mechanical
and chemical digestion begins. Chewing food starts to break large chunks into
small chunks that are easier to manage and swallow. In the mouth, the food is
mixed with saliva secreted from salivary (paratoid, submandibular and
sublingual) glands that contains the enzyme, amylase. (Richardson, 2006). Amylase
is an extracellular enzyme as it works outside cells, it catalyses the
hydrolysis of starch into maltose. (Parsons, 2015). Once the food has been
chewed and in bolus form it is pushed the back of the mouth by the tongue and
into the oesophagus. Its function is to take food from the mouth to the stomach
for further digestion. It is specialised for this function by having a mucus
producing membrane and involuntary muscle contractions so that food slides
easily down it. (Richardson, 2006)




The stomach is a
muscular bag that can expand to hold up to a litre of food. The stomach is made
up of four layers that help in the digestion of food, the mucosa, produces
enzymes and acids, which help in digestion and protection of stomach lining.

The submucosa and muscularis that contact to churn the food. Finally, the
serosa, which is the strong membrane keeping the stomach together.

(, 2016). The food is then stored in the stomach with
hydrochloric acid for 30 – 60 minutes. (Taylor, n.d.)


The partially
digested food (chyme) leaves the stomach through pyloric sphincter and into the
duodenum, the C-shaped tube part of the small intestine. This is where the
pancreas, gallbladder, liver and some glands all deliver their digestive
enzymes and alkaline mucus too. Once all the secretions have mixed with the
chyme, the process of chemical digestion is complete. The carbohydrates, lipids
and proteins have now been broken down into their individual units and ready
for absorption. (Taylor, n.d.). Trypsin is one of the enzymes that is secreted
by the pancreas into the duodenum, it is responsible for the hydrolysis of
proteins into amino acids. (Hocking, S., Sochacki, F. and Winterbottom, M,


The ileum is the
final part of the long intestine and its soul function is the absorption of all
required nutrients needed by the body. The ileum is highly specialised for this
role as it is 3.5m in length, he walls have villi and then micro villi on them
so it has a very large surface area. The surface of the wall is moist, very
thin and has a rich blood supply. These help in maximising the amount of
nutrients absorbed. (Encyclopedia Britannica, 2018).



The remaining matter that was not absorbed in the ileum carries on
traveling through the GI tract and into the colon. Any remaining nutrients and
water is absorbed but waste feces carry on moving along the colon and passed
onto the rectum. The rectum stores feces until it passes out of the body
through the anus. (

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