Nutrition and Digestion - Digestive System

Running head; NUTRITION AND DIGESTION
NUTRITION AND DIGESTION
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Introduction
Understanding the structure and function of the digestive system assists in understanding
how diet is closely associated with nutrient consumption and overall health outcomes (Gazouli
and Theodoropoulos 2019). The following paper will extensively and elaborately discuss on the
major structures and functions of the digestive system as well as how food tests can determine
the nutrient quality of specific food items in the diet.
Discussion
Structure and Function of Alimentary Canal
The alimentary canal comprises of a long tube which begins from the mouth and extends
till the rectum and comprises of a number of accessory glands and organs (Boland, Golding and
Singh 2014). The following are the key structures which can be found in the alimentary canal
along with their associated functions (Williams 2015). These have highlighted in Figure 1.
 Mouth and Oral Cavity: The digestion of food begins in the oral cavity or mouth which
comprises of structures like teeth, salivary glands and the tongue. The teeth masticates
food into small particles while the tongue mixes the food with salivary. Salivary glands
produce saliva which break down starches in the food by amylase enzyme. The tongue ad
epiglottis then pushes the bolus towards the throat down the esophagus.
 Esophagus: Longitudinal and circular muscular structures perform peristalsis by
constructing the esophageal structure front and behind of the food to push food further
towards the stomach.
 Stomach: The stomach comprises of three structural regions, known as the cardiac,
fundus and pylorus. Food enters the stomach through the cardiac sphincter. Food

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undergoes digestion by the stomach via secretion of gastrin from the fundus region while
the cardiac regions secret mucous to protect the stomach lining from being damaged by
acids. Once the food has been churned and mixed to form chime, it is then pushed
towards the intestines by the pyloric sphincter.
 Small Intestine: The small intestine contain structures like the duodenum, jejunum and
ileum. The duodenum receives bile salts and enzymes from the pancreas which break
down fats, carbohydrates and lipids in the food. Villi or small finger like structures lining
the small intestine absorb nutrients released from the food during digestion to be
transported via circulation to the cells and issues.
 Large Intestine: Food which remains undigested travels to the large intestine where
water is absorbed and undigested epithelial cells, bacteria and fiber undergo storage in the
rectum for excretion by the anus (Williams 2015).
Figure 1: Structure of the Digestive System

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Principles of Digestion
In addition to its various organs and associated structures, the function of the digestive
system can also be categorized and understood, in the form of mainly 5 processes, that is:
ingestion, digestion, absorption, assimilation and egestion. Each of these processes comprise of a
range of enzymatic and molecular function which collaborate together to form an efficient
digestive system (Michael, Michael and Grace 2000). These have been enlisted below:
 Ingestion: Ingestion is the process of ‘ingesting’ or consuming the food and is the first
process of the digestive system which directs foods to the rest of the organs of the
alimentary canal. Ingestion comprises of the process of mechanical digestion in the
mouth. The teeth chew and masticate to physically degrade the food into small, semi-
solid components or a bolus. Salivary glands release saliva which are then mixed by the
tongue to further facilitate bolus formation. Saliva contains the enzyme amylase which

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break down starches to form dextrin and sugars. Water and mucin from the saliva further
soften, lubricate and make it easy for the tongue and epiglottis to push or swallow the
food down the esophagus.
 Digestion: No form of chemical digestion takes place in the esophagus. However,
circular and longitudinal muscles perform peristalsis to push the food into the stomach
via the cardiac sphincter. The fundus or body of the stomach is lined with epithelial pits,
chief cells and parietal cells which release hydrochloric acid and pepsinogen. Pepsinogen
is converted to pepsin by the acid which then digests protein while the goblet cells release
mucous to protect the stomach from being damaged by the stomach. Antagonistic
muscles churn the food to form chyme which the pyloric sphincter begins to release in
small amounts into the duodenum of the small intestine.
 Absorption: Within the duodenum of the small intestine, bile is secreted from the gall
bladder whose main function is to neutralize the acid-rich chyme and emulsify fats to
facilitate the pancreatic enzymes to hydrolyze the food. The pancreas further releases
enzymes like pancreatic amylases, pancreatic lipases and trypsinogen which are
responsible for the digestion of carbohydrates, lipids and proteins in the chyme. Proteases
in the pancreas are comprised of either exopeptidases (Trypsisn, chymotrypsin) or
endopeptidase which either break down amino acids of the proteins or amino acid ends of
the peptide chains of the proteins (carboxypeptidases). As a result of pancreatic enzymes,
starches, nucleic acids, proteins and lipids are broken down to nutrients like
monosaccharide, amino acids, nitrogenous bases, glycerol and fatty acids.
 Assimilation: Assimilation is the process by which the above nutrients from the food are
absorbed by the cells and tissues of the body. This is done with help of villi – finger-like

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structures and folds which line the small intestine, which are further lined with microvilli.
The digested nutrients are absorbed by the epithelium of the villi which then transports
them to the hepatic portal pain via blood circulation, either to be used by cells or tissues
or for storage and excretion of excess by the liver and kidneys.
 Egestion: Egestion is the process by which undigested food is excreted by the body.
Food which does not undergo digestion are transported to the large intestine where water
is absorbed. The remaining undigested fiber, bacterial cells and epithelial cells are stored
in the rectum till they undergo evacuation by the anus (Michael, Michael and Grace 2000,
Williams 2015).
Daily Needs
Considering the context of an individual who is a vegetarian and is free from any chronic
disease, the daily needs of a balanced diet as per the Eatwell Guide (Food and Agricultural
Organization 2017) would be as follows:
 The individual must consume at least 5 portions or servings of colorful whole vegetables
and fruits on a daily basis.
 The individual must consume 6 to 7 portions of whole grains such as whole wheat rice,
pasta, multigrain bread and oats along with a combination of starchy vegetables like
potatoes.
 The individual must consume 2 portions of vegetarian sources of proteins like soy, soy
products, legumes and pulses.
 The individual must consume 2 to 3 portions of low fat dairy products like skimmed
milk, yoghurt and cheese and also non-dairy alternatives like soy, seeds and nuts.

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 For a balanced diet, the individual must consume 6 to 8 glasses of water and limit the
intake of saturated fats. Unsaturated fats like vegetable oils, seeds and nuts must be
considered.
The following three food items have been considered for analysis (Fulgoni III and Bailey
2017):
 Pasta: Pasta is rich in carbohydrates, fiber and proteins and is useful for meeting
macronutrients requirements in a balanced diet. Whole wheat varieties are preferred due
to their higher fiber content.
 Broccoli: Broccoli is a good source of fiber as well as micronutrients like vitamin A, C
and B vitamins. Additionally, broccoli is low in macronutrients like carbohydrates,
proteins and fat and thus, can be supplemented with pasta in a vegetarian diet to improve
macro and micro nutrient intake.
 Apple: Apples are a good source of carbohydrate, soluble fibers and sugars as well as
micronutrients like vitamin A and potassium. They can be used to supplement the
vegetarian diet with fiber and micronutrients in addition to pasta and broccoli (Fulgoni III
and Bailey 2017).
Food Tests
The following food tests were used to determine the nutrients of the above foods in a
vegetarian diet of the individual (Aston 2017). The results have been summarized in Table 1.
While each test proved to be useful in determining key ingredients, a key limitation was that
these tests were not sensitive enough to detect small amount of nutrients in food. For example:
pasta also contains proteins but were not detected in the biuret. Thus, higher quality, sensitive
tests are needed (Fleischer 2019).

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 Iodine test: Iodine solution was added to each of the three food samples using a dropper.
No changes were observed in the broccoli and apple while in pasta, the brown iodine
solution turned blue indicating that it is rich in starch.
 Biuret test: The chopped food samples were shaken with potassium hydroxide and
copper sulphate. None of three samples of apple, broccoli and pasta turned purple thus
implying the absence of sufficient protein in each of them.
 Emulsion: All foods were ground with ethanol, filtered and mixed with water. None of
the samples turned cloudy hence implying the absence of fat.
 Benedict’s reducing test: All chopped samples of food were boiled with water and
added with Benedicts reducing solution. Only apply changed to orange reflecting high
glucose content.
Table 1: Food Tests and Results
Type of Test
Food Iodine Biuret Emulsion Benedicts Reducing
Benedicts Non-
Reducing
Pasta
Colour change to blue-
black
no
change
no
change no change no change
Broccol
i no change
no
change
no
change no change no change
Apple no change
no
change
no
change
colour change to
orange
colour change to
green
 Benedict’s non-Reducing test: All chopped food sample were diluted with hydrochloric
acid, neutralized with sodium hydrogen carbonate. The above test was repeated again
where only apple turned to green implying high sugar content (Aston 2017; Fleischer
2019).

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Conclusion
Simple food tests can be useful in determining the nutrient composition of specific foods
and overall quality of a diet consumed by an individual. To conclude, a single food test may not
be sensitive enough to accurately determine all nutrients in food, which is why, multiple food
tests must be considered.

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References
Aston, T.A., 2017. The Really Useful Book of Secondary Science Experiments: 101 Essential
Activities to Support Teaching and Learning. Routledge.
Boland, M., Golding, M. and Singh, H. eds., 2014. Food structures, digestion and health.
Academic Press.
Fleischer, H., 2019. The Iodine Test for Reducing Sugars–A Safe, Quick and Easy Alternative to
Copper (II) and Silver (I) Based Reagents. World Journal of CHEMICAL Education, 7(2), p.45.
Food and Agriculture Organization, 2017. United Kingdom. [online] Food and Agriculture
Organization of the United Nations. Available at: <http://www.fao.org/nutrition/education/food-
dietary-guidelines/regions/countries/united-kingdom/en/> [Accessed 10 April 2020].
Fulgoni III, V.L. and Bailey, R., 2017. Association of Pasta Consumption with Diet Quality and
Nutrients of Public Health Concern in Adults: National Health and Nutrition Examination
Survey 2009–2012. Current Developments in Nutrition, 1(10), p.e001271.
Gazouli, M. and Theodoropoulos, G.E., 2019. Digestive System Diseases. Springer International
Publishing.
Michael, K., Michael, R. and Grace, M., 2000. Advanced biology. Cheltenham, United
Kingdom: Nelson Thornes.
Williams, G., 2015. Advanced Biology for you. Oxford University Press-Children.