assignment 3 - food and digestion.pdf

8/21/2019 Assignment 3 - food and digestion.pdf

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MONIQUE MAVRONICOLAS – FOOD AND DIGESTION

1. The importance of the major food classes

The human body requires energy to maintain its vital body processes. This energy is

derived from seven major types of food nutrient classes which fall into two main categories,

namely macronutrients and micronutrients. A nutrient is a source of nourishment derived

from an ingested substance which, once inside the human body, is then metabolised

(transformed from one form into another). The human body needs macronutrients in large

quantities whereas micronutrients are needed in smaller quantities. Of the macronutrients

needed by the body, these are further subdivided into energy macronutrients such as

carbohydrates, proteins and fats as well as other macronutrients which do not provide

energy such as fibre and water. Of the micronutrients needed by the human body, are

dietary minerals (chemical elements) and vitamins (organic compounds).

(http://www.medicalnewstoday.com/articles/160774.php)

A brief analysis of each nutrient is explored below, their importance to the human body

and the risk posed by either over or under-consumption of that nutrient. The nutrients have

been grouped according to their category referenced above, namely macronutrients and

micronutrients.

a. Macronutrients (providing energy)

Carbohydrates

On a molecular level, carbohydrates include monosaccharides (glucose, fructose,

glactose), polysaccharides (starch) and sisaccharides.


Polysaccharides, which are commonly known as starches, on a molecular level consist of

complex sugar chains, which are more favoured by the body as a source of fuel. Examples

of such starches are farmed organic foods such as rice, whole oats, beans and whole grain

wheat. Carbohydrates are important in the human diet because they provide fuel for bodilyfunctions and energy needed to maintain normal functioning of the organs. Carbohydrates

also contain important vitamins and minerals (micronutrients) needed by the body.

Additionally, they also provide the only form of energy used by the brain. Under-consumption

of complex carbohydrates (organic carbohydrates which are preferred by the body as they

provide long-term energy) can lead to muscle tissue breakdown, fatigue and the diminishing

of brain power. Over-consumption of carbohydrates can lead to weight gain which in turn

can lead to obesity. (http://www.eatingdisordersonline.com/nutritional/carbs.php)

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Protein

Proteins are examples of organic compounds and belong to the molecular class of

polyamides. They are commonly referred to as the building blocks of life simply because

they make up the structure of tissues and organs in the human body. However, more

accurately, they form one of the four basic categories for building life. Proteins are then

further made up of smaller units known as amino acids and as amino acids are organically

more plentiful in nature, they are therefore involved in just about every process of life.

(http://resources.schoolscience.co.uk/unilever/16-18/proteins/Protch1pg1.html)

(http://www.doublexscience.org/biology-explainer-the-big-4-building-blocks-of-life-

carbohydrates-fats-proteins-and-nucleic-acids/)

Meat and animal products such as eggs and dairy make up the most typical protein

dietary composition in human diets and are known as staple proteins, although in the case of

vegetarians and in poorer parts of the world, humans have to rely on plant-based proteins

such as legumes and nuts to substitute their diets. Dietary proteins, particularly those of

animals, contain important micronutrients for the human body. Under-consumption of dietary

protein results in a condition called Kwashiorkor which leads to diarrhoea, fatigue and

muscle loss. Over an extended period of time, if left untreated, this condition can lead to

permanent physical disabilities. The only consequence resulting from protein over-

consumption in humans, is over taxation of the liver and kidneys, which over time can lead to

organ failure in the most extreme circumstances. (http://healthyeating.sfgate.com/risks-

associated-overconsumption-underconsumption-protein-1862.html)

Fat

Fat is a dietary nutrient which forms one of the three energy providing macronutrients.

On a molecular level, fats are categorized as complex molecules known as triglycerides.

Some fats are liquids at room temperature, while others are solid. There are two common

sources of dietary fats, namely animal fats and vegetable fats. Examples of animal fats arebutter and cream while examples of vegetable fats are olive oil and peanut oil (although

there are many other derivatives of vegetable fats). Dietary fats essentially have an added

value over proteins and carbohydrates in that fats, apart from being essential to normal body

functions, also help other nutrients to do their jobs. Dietary fats are further classed as

saturated fat, monounsaturated fat, polyunsaturated fat (classed as healthy fats), and trans

fats. The most harmful of the list of fats are trans fats which are synthetically made fats and

do not naturally occur in nature. Consuming large quantities of dietary fats, as with other

nutrients not in moderation, can lead to disease. Under-consumption of “healthy” or naturally

http://www.doublexscience.org/biology-explainer-the-big-4-building-blocks-of-life-carbohydrates-fats-proteins-and-nucleic-acids/http://www.doublexscience.org/biology-explainer-the-big-4-building-blocks-of-life-carbohydrates-fats-proteins-and-nucleic-acids/http://www.doublexscience.org/biology-explainer-the-big-4-building-blocks-of-life-carbohydrates-fats-proteins-and-nucleic-acids/http://www.doublexscience.org/biology-explainer-the-big-4-building-blocks-of-life-carbohydrates-fats-proteins-and-nucleic-acids/


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occurring fats can cause vitamin deficiencies, low energy and poor growth in humans.


b. Macronutrients (not providing energy)

Fibre

Dietary fibre is found in carbohydrates and because fibre is largely indigestible, it has

limited absorption and thus passes through the digestive system. Dietary fibre is classed as

either soluble or insoluble and is present in all types of organic plant food. It is classed as a

nutrient, despite the fact that it does not provide absorbable nourishment and energy to the

body. It is essential to human health as it cleanses the digestive system and aids in regular

bowel movement. Benefits of soluble fibre include reducing cholesterol while benefits of

insoluble fibre are speeding up and elimination of toxic waste. Under-consumption of fibre

can thus lead to constipation, elevated cholesterol and toxicity of the blood. Over-

consumption can lead to an irritated bowel and diarrhoea. Good examples of dietary fibre

are seeds, plant cereals and whole grains.


Water

Believed to be the most important of the nutrients, water does not contain calories and is

therefore part of non-energy providing macronutrients essential to the human body. Because

the body cannot store water, regular intake is essential for normal metabolic functions in the

body such as maintaining the pH of the blood, eliminating by-products of cellular

metabolism, maintaining moisture in mucous membranes and regulating body temperature.

Under-consumption of fresh water will result in a disruption in body homeostasis and result

in dehydration. The human body cannot go for longer than three consecutive days without

water before vital body organs start to shut down. Over-consumption of water can flush too

much sodium from the body, negatively affect blood pH and cause hyponatraemia which is

water-intoxication.(http://sportsmedicine.about.com/od/hydrationandfluid/a/Hyponatremia.htm)

c. Micronutrients

Vitamins

These are classed as organic compounds and are needed by the body in much smaller

amounts relative to macronutrients. Vitamins are further divided into water-soluble and fat-

soluble. Fat-soluble vitamins are absorbed through the intestine with help from fats. An

example of a fat-soluble vitamin is Vitamin A. Under-consumption or a deficiency of this


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vitamin leads to night-blindness. Over-consumption leads to Keratomalacia (degeneration of

the cornea).

Minerals

Minerals, like vitamins, are derived from the food we eat. However, minerals are

inorganic compounds. They can be found in fruits, nuts, animal meats, dairy, vegetables and

grains. Examples of essential minerals are Calcium and Iron. Minerals are important to help

the body convert food into energy, to help strengthen teeth and bones and to help control

body fluids inside and outside of the cells. (http://www.nhs.uk/Conditions/vitamins-

minerals/Pages/vitamins-minerals.aspx) Calcium for example, iron is essential for the

formation of red blood cells. A deficiency or under consumption of iron results in anaemia

which is a deficiency or red blood cells or haemoglobin in the blood. This in turn results in

tiredness and lethargy. Excessive iron intake can result in blood toxicity.

(http://running.competitor.com/2014/04/nutrition/got-minerals_19500)

Addendum A contains a simplified illustration of food classes that includes certain vitamins

and minerals with examples of their sources, functions and deficiencies.

2. Process of Digestion

a. Introduction

As noted in the previous chapter, the human body requires energy to maintain its vital

processes. Energy is needed to fuel internal body functions, to build, repair and maintain

cells and body tissue and also externally, to enable humans to carry out functions in daily

activities. The energy which the body needs to do all of this, is derived from the calories

ingested on a regular basis and which are all necessary in a healthy human diet.

Digestion and absorption in itself, requires energy and nutrients in food account for 5 to10 percent of the daily energy stored by the body and required to complete the digestive

process. (http://healthyeating.sfgate.com/five-reasons-body-needs-energy-4673.htm)

b. What is digestion and absorption

Digestion is the breaking down of food into smaller particles so that it can better be

absorbed by the body and ultimately into the bloodstream where nutrients are needed and

can be circulated and used where required. Digestion can be further divided into mechanical

digestion and chemical digestion. Mechanical digestion is the primary point of digestion

http://www.nhs.uk/Conditions/vitamins-minerals/Pages/vitamins-minerals.aspxhttp://www.nhs.uk/Conditions/vitamins-minerals/Pages/vitamins-minerals.aspxhttp://www.nhs.uk/Conditions/vitamins-minerals/Pages/vitamins-minerals.aspxhttp://www.nhs.uk/Conditions/vitamins-minerals/Pages/vitamins-minerals.aspxhttp://www.nhs.uk/Conditions/vitamins-minerals/Pages/vitamins-minerals.aspxhttp://www.nhs.uk/Conditions/vitamins-minerals/Pages/vitamins-minerals.aspx


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where the food is broken down in the mouth into smaller pieces. Chemical digestion takes

place further down in the gastrointestinal tract where enzymes further break down the food

into small molecules (http://www.news-medical.net/health/What-is-Digestion.aspx). Digestion

also includes the movement of food through the digestive tract. The movement of the organ

walls are responsible for helping food move along downwards through the tract (also

referred to as hollow organs) and the term given to this action is peristalsis, which is an

involuntary action once it passes the oral cavity and pharynx.

Absorption (after mechanical digestion has taken place) is where food molecules pass

through the wall of the small intestine and into the bloodstream. For molecules to pass

through the intestinal wall, they have to be small enough and soluble, in other words, able to

be dissolved.

(http://www.bbc.co.uk/bitesize/ks3/science/organisms_behaviour_health/diet_drugs/revision/

6/)

3. Major subdivisions of the digestive system

In this section, a closer look will be given to the different subdivisions of the digestive

system. More specifically, the pathway that the food takes and how it is moved from the

mouth to the large intestine will be detailed and where necessary, how each organ

contributes to the process of digestion and absorption. In addition, reference will be made to

how and where each macro and micronutrient is digested and absorbed, which includes the

role of the different enzymes involved in the process of digestion and absorption.

Oral cavity

The oral cavity forms the initial part of the digestive path and its main purpose is to form

the entrance to the alimentary tract. The oral cavity or mouth as it is commonly termed, is the

beginning of the digestive system. It gets the digestive process underway through propulsionand salivation of the food which enters the oral cavity. Both mechanical and chemical

digestion (digestive enzyme called amylase) takes place at this stage. Through mastication

(also commonly referred to as chewing), the food then forms a rounded mass (which helps

take this form due to the fact that the oral cavity is oval in shape) which can more easily pass

into the pharynx in preparation to be swallowed.

(http://emedicine.medscape.com/article/1899122-overview)

Pharynx

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The pharynx is commonly referred to as the throat. Internally, the pharynx forms the part

of the digestive tract which receives the masticated food, in the form of a bolus, from the oral

cavity (mouth). Essentially, the pharynx forms a passageway for solids and liquids and

roughly takes the form of a funnel and the movement which enables these solids and liquids

to pass down from the oral cavity is enabled by the movement of the pharyngeal wall which

make up the sides of the pharynx. This movement process is known as swallowing or

deglutition. The muscles which make up the sides of the pharyngeal wall, take the form of

three pharyngeal constrictors, which help squeeze the food down in a peristaltic motion. The

pharynx is further divided into three parts: the oral pharynx, the nasal pharynx and the

laryngeal pharynx. For purposes of the discussion of digestion, the oral pharynx is the

operative part as it is shared by both the digestive and respiratory tracts, whereas the other

two are just airways. Diagram A below, illustrates the close proximity and connectedness of

the pharynx to the oral cavity (labelled “mouth” in the diagram).

Diagram A (http://www.britannica.com/EBchecked/topic/1081754/human-digestive-

system/45316/Pharynx)

Oesophagus

As indicated by Diagram A above, the oesophagus forms the longer part of the initial

part of the digestive tract and helps pass food from the pharynx to the stomach. The


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oesophagus is roughly 25 centimetres in length and consists of four layers: the mucosa,

submucosa, muscularis and tunica adventitia. The mucosa (also found in the mouth,

stomach and small intestine) contain tiny glands which secrete digestive enzymes which

help digest food, however no digestion takes place in the oesophagus. At the end of the

oesophagus, is a valve which closes the passage between the oesophagus and the

stomach. This is a sphincter valve which opens as a result of muscle relaxation once food

approaches the valve.

(http://www.edinformatics.com/math_science/where_is_food_digested.htm)

Stomach

As noted above, the food will pass from the oesophagus into the stomach once the

valve which separates the two organs, relaxes and allows for the food to pass into the

stomach. In the stomach, digestion continues through the aid of digestive juices which are

released by glands situated in the stomach lining. The main function of the stomach is to

accept liquids and solids passing from the oesophagus and to digest proteins and

carbohydrates by converting the food particles into smaller and more soluble particles. The

enzyme pepsin is responsible for the digestion of protein into peptides. Through a series of

muscle contraction and relaxation, the stomach is mechanically able to perform three

functions: firstly, the upper region of the stomach relaxes to accommodate large volumes of

food and liquid, thus acting as a storage vessel for ingested material. Secondly, the stomach

acts as a mixer, being able to mix the solids, liquids and digestive juices (acids and

enzymes) together to form a chemical mixture referred to as chyme. Thirdly, the stomach

releases this mixture into the small intestine slowly when the chemical composition becomes

suitable for the next phase of digestion. The only absorption which takes place in the

stomach, is very small amounts of lipid-soluble compounds like aspirin, glucose and simple

sugars, since the acidic environment in the stomach, prevents absorption of much else.


In Diagram B above, the illustration best depicts the main stages of digestion and absorption

(on the left of the diagram) in the major subdivisions of the digestive system, namely the oral

cavity (mouth), oesophagus, stomach, small intestine and large intestine.

Small intestine

The longest part of the digestive tract, most of the chemical digestion which takes place in

the digestive system, does so in the small intestine. It is also one of the few places where

absorption takes place and ingested solid substances can be broken down into molecules

small enough to pass into the blood stream through the process of diffusion (briefly

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discussed under 2.1.1 above). After the food leaves the stomach and empties into the small

intestine at the junction known as the pylorus, two other organs help release juices and

enzymes which help with the chemical digestion. These two organs are the liver and the

pancreas (which will be discussed later). The walls of the small intestine contain glands

Diagram B

(www.boundless.com)

which also release enzymes which aid in digestion. It was noted above under the

subheading of the stomach, that the enzyme pepsin is responsible for the digestion of

protein into peptides. It should be noted that the digestion of protein which starts in the

stomach, is a multi-step process which is further continued in the small intestine where large

peptides are broken down into smaller peptides and then into individual amino acids. In

addition to protein digestion, lipid or fat digestion also begins in the stomach, but is

continued for the most part in the small intestine – bile acids are responsible for the digestion

of lipids (https://www.boundless.com/biology/textbooks/boundless-biology-textbook/animal-

nutrition-and-the-digestive-system-34/digestive-system-processes-197/digestion-and-


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absorption-754-11987/). In Table 1 below, a tabularized representation of the digestion of

nutrients which takes place in the small intestine and the corresponding enzyme responsible.

What it also in turn highlights, is the importance of the digestive function of this organ. A

point which can be added, and one which was discussed under 1.3 above, is the absorption

of vitamins which takes place in the intestine. Fat-soluble vitamins are absorbed in the same

way that fats are absorbed, while water-soluble vitamins are absorbed straight into the

bloodstream. Whatever molecules which are either too large and are therefore not absorbed

through the small intestinal wall, which includes waste products such as fibre, will then

further pass into the large intestine.

starting nutrient end product enzyme(s) responsible

proteins and peptides amino acids trypsin and chymotrypsin

Lipids fatty acids and glycerol

Pancreatic lipase with

help from bile (not an

enzyme)

Carbohydrates simple sugars (monsacharides) Pancreatic amylase

Table 1


Large intestine

The large intestine, otherwise commonly known as the colon, represents the final organ

involved in the stages of digestion as discussed under the heading of “major subdivisions of

the digestive system.” It is where undigested food material enters after it has passed through

the small intestine. The main function of the large intestine is to absorb water from the

indigestible waste material, thus helping to further solidify the waste for exit from the body.

Another function of the large intestine is to compact faecal matter and then to store it further

down in the rectum, which is the end part of the large intestine and leads to the anus. The

gut bacteria which is present in the large intestine, helps to digest substances in the chyme

(discussed briefly under the sub-heading of the stomach), thus converting the chime into

faeces and at the same time releasing important vitamins, such as vitamin K and numerous

B-vitamins. A by-product of this final digestion process is the release of gasses and carbon

dioxide. (http://www.innerbody.com/anatomy/digestive/large-intestine)


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4. Accessory organs of the digestive system

In this section, the function of each of the accessory organs will be outlined. As with the

major digestive organs discussed in the previous section, the roll and process of the

accessory organs will be discussed in terms of digestion and absorption.

Accessory organs are ones that assist in the process of digestion, but do not form part

of the digestive tract. These accessory organs include the salivary glands, the gallbladder,

the liver and the pancreas. Below, a breakdown description of each accessory organ during

the stages these organs assist in the process of digestion.

Salivary Glands

The salivary glands release saliva into the oral cavity. Saliva contains water, mucus and

the digestive enzyme amylase. As a result of this enzyme, the chemical digestion process

starts in the oral cavity. The saliva itself functions as a lubricant to aid in swallowing, while

the enzyme it contains, breaks down carbohydrates into polysaccharides and disaccharides.

(http://training.seer.cancer.gov/anatomy/digestive/regions/accessory.html)

Gallbladder

The gallbladder, attached to the visceral surface of the liver, aids in digestion by

releasing bile. Bile in turn is produced by the liver cells, although this is stored in the

gallbladder when there is no food in the small intestine. One of the principal ingredients of

bile is bile salts (conjugated bile acids) which are involved in digestion and absorption of fats.

Under the subheading of the small intestine listed above, it was noted that bile acids are

responsible for the digestion of lipids. Lipids are essentially any organic compound which

has fatty acids. Fats, or lipids are not water soluble and as fat breakdown takes place in the

small intestine, bile acids help with this breakdown which would otherwise not be possible.

(http://training.seer.cancer.gov/anatomy/digestive/regions/accessory.html)

Liver

Located just below the diaphragm, the liver serves as a large gland. It serves multiple

roles in the body, but in terms of digestion and as an accessory organ, its main role involves

the production of bile. Below in Diagram C , an illustration of the liver and the gallbladder.


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Diagram C

(http://education-portal.com/academy/lesson/the-gallbladder-liver-function-role-in-

digestion.html#lesson)

Pancreas

The pancreas, like the liver, is a gland. It has two functions, an exocrine function and an

endocrine function. As an accessory organ, it is the exocrine function which aids in digestion.

The exocrine cells which form the larger part of the organ, produce enzymes which help with

digestion. A series of ducts join together in which these digestive enzymes find their way

from the pancreas via a main pancreatic duct into the duodenum which is the beginning part

of the small intestine. It is in the duodenum that the digestive enzymes from the pancreas

and the bile produced by the liver, enter the digestive system to help assist in digestion of

chime, which is partially digested food. The composition of pancreatic enzymes includeanylase, trypsin, lipase and peptidase. As noted earlier and is evident in Diagram B, the

nutrients which are digested in the small intestine include carbohydrates, proteins and fats

(lipids).

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(http://www.edinformatics.com/math_science/where_is_food_digested.htm) accessed on

06/01/2015

Digestion and Absorption, available at: (www.boundless.com/biology/textbooks/boundless-

biology-textbook/animal-nutrition-and-the-digestive-system-34/digestive-system-processes-

197/digestion-and-absorption-754-11987/), accessed on 06/01/2015

Large Intestine, available at: (http://www.innerbody.com/anatomy/digestive/large-intestine),

accessed on 07/01/2015

Accessory Organs, available at:

(http://training.seer.cancer.gov/anatomy/digestive/regions/accessory.html), accessed on

07/01/2015

Addendum A Classes of food – published by Ng Lay Hoon

http://healthyeating.sfgate.com/five-reasons-body-needs-energy-4673.htmlhttp://healthyeating.sfgate.com/five-reasons-body-needs-energy-4673.htmlhttp://healthyeating.sfgate.com/five-reasons-body-needs-energy-4673.htmlhttp://healthyeating.sfgate.com/five-reasons-body-needs-energy-4673.htmlhttp://www.news-medical.net/health/What-is-Digestion.aspxhttp://www.news-medical.net/health/What-is-Digestion.aspxhttp://www.news-medical.net/health/What-is-Digestion.aspxhttp://www.news-medical.net/health/What-is-Digestion.aspxhttp://www.bbc.co.uk/bitesize/ks3/science/organisms_behaviour_health/diet_drugs/revision/6/http://www.bbc.co.uk/bitesize/ks3/science/organisms_behaviour_health/diet_drugs/revision/6/http://www.bbc.co.uk/bitesize/ks3/science/organisms_behaviour_health/diet_drugs/revision/6/http://www.bbc.co.uk/bitesize/ks3/science/organisms_behaviour_health/diet_drugs/revision/6/http://emedicine.medscape.com/article/1899122-overviewhttp://emedicine.medscape.com/article/1899122-overviewhttp://emedicine.medscape.com/article/1899122-overviewhttp://www.britannica.com/EBchecked/topic/1081754/human-digestive-system/45316/Pharynxhttp://www.britannica.com/EBchecked/topic/1081754/human-digestive-system/45316/Pharynxhttp://www.britannica.com/EBchecked/topic/1081754/human-digestive-system/45316/Pharynxhttp://www.britannica.com/EBchecked/topic/1081754/human-digestive-system/45316/Pharynxhttp://www.edinformatics.com/math_science/where_is_food_digested.htmhttp://www.edinformatics.com/math_science/where_is_food_digested.htmhttp://www.edinformatics.com/math_science/where_is_food_digested.htmhttp://www.boundless.com/biology/textbooks/boundless-biology-textbook/animal-nutrition-and-the-digestive-system-34/digestive-system-processes-197/digestion-and-absorption-754-11987/http://www.boundless.com/biology/textbooks/boundless-biology-textbook/animal-nutrition-and-the-digestive-system-34/digestive-system-processes-197/digestion-and-absorption-754-11987/http://www.boundless.com/biology/textbooks/boundless-biology-textbook/animal-nutrition-and-the-digestive-system-34/digestive-system-processes-197/digestion-and-absorption-754-11987/http://www.boundless.com/biology/textbooks/boundless-biology-textbook/animal-nutrition-and-the-digestive-system-34/digestive-system-processes-197/digestion-and-absorption-754-11987/http://www.boundless.com/biology/textbooks/boundless-biology-textbook/animal-nutrition-and-the-digestive-system-34/digestive-system-processes-197/digestion-and-absorption-754-11987/http://www.innerbody.com/anatomy/digestive/large-intestinehttp://www.innerbody.com/anatomy/digestive/large-intestinehttp://www.innerbody.com/anatomy/digestive/large-intestinehttp://training.seer.cancer.gov/anatomy/digestive/regions/accessory.htmlhttp://training.seer.cancer.gov/anatomy/digestive/regions/accessory.htmlhttp://training.seer.cancer.gov/anatomy/digestive/regions/accessory.htmlhttps://www.scribd.com/isaxkhttps://www.scribd.com/isaxkhttps://www.scribd.com/isaxkhttp://training.seer.cancer.gov/anatomy/digestive/regions/accessory.htmlhttp://www.innerbody.com/anatomy/digestive/large-intestinehttp://www.boundless.com/biology/textbooks/boundless-biology-textbook/animal-nutrition-and-the-digestive-system-34/digestive-system-processes-197/digestion-and-absorption-754-11987/http://www.boundless.com/biology/textbooks/boundless-biology-textbook/animal-nutrition-and-the-digestive-system-34/digestive-system-processes-197/digestion-and-absorption-754-11987/http://www.boundless.com/biology/textbooks/boundless-biology-textbook/animal-nutrition-and-the-digestive-system-34/digestive-system-processes-197/digestion-and-absorption-754-11987/http://www.edinformatics.com/math_science/where_is_food_digested.htmhttp://www.britannica.com/EBchecked/topic/1081754/human-digestive-system/45316/Pharynxhttp://www.britannica.com/EBchecked/topic/1081754/human-digestive-system/45316/Pharynxhttp://emedicine.medscape.com/article/1899122-overviewhttp://www.bbc.co.uk/bitesize/ks3/science/organisms_behaviour_health/diet_drugs/revision/6/http://www.bbc.co.uk/bitesize/ks3/science/organisms_behaviour_health/diet_drugs/revision/6/http://www.news-medical.net/health/What-is-Digestion.aspxhttp://www.news-medical.net/health/What-is-Digestion.aspxhttp://healthyeating.sfgate.com/five-reasons-body-needs-energy-4673.htmlhttp://healthyeating.sfgate.com/five-reasons-body-needs-energy-4673.html


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Addendum A


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assignment 3 - food and digestion.pdf

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