Digestive System, Enzymes, Absorption in the Small Intestine

Edited by Jamie (ScienceAid Editor), Jen Moreau, SmartyPants, Sim


Digestive System

the digestive tract or alimentary canal

The diagram above shows the digestive system of humans which is also known as The Alimentary Canal.

Types of Digestion:

  1. 1
    Mechanical Digestion:
    is a process that uses force to break down food into smaller elements. Such as, grinding and churning of food.
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  2. 2
    Chemical Digestion:
    is described as the use of chemicals, like enzymes (saliva, pepsin, renin, amylase, protease, lipase,..) in the digestion process.
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Process of Digestion

  • Once the food enters the mouth, it undergoes mechanical digestion to break the larger particles of food into smaller ones, then these small particles are mixed with saliva (digestive juice of the mouth) to form a bolus. At this level, starch (complex sugar also called polysaccharide) is broken down with the help of amylase enzyme into maltose (di-saccharide).
  • After being swallowed, the bolus travels down the oesophagus by a process called peristaltic movement to reach the stomach.
  • When food particles enter the stomach, they are mixed with the gastric juice (containing the enzymes of the stomach), and also churned to be digested properly. At this level, the proteins are broken down to peptides by the help of the proteases and then transported to the small intestine.
  • In the small intestine, the food particles are digested to their smallest elements called "nutrients". At this level, the peptides are broken down into amino acids, whereas the di-saccharides are broken down into simple sugars (mono-saccharides), and the fats are broken down to fatty acids and glycerol. All these processes happen with the help of the bile (a greenish liquid secreted by the liver that emulsifies the fats), the pancreatic juices (that secrete enzymes directly into the small intestine), and the intestinal juices.
  • Once the food is completely digested, the nutrients are absorbed by the blood through the intestinal villi (brush-like elements found on the walls of the small intestine)
  • The remaining food, that is deprived of nutrients, passes from the small intestine to the large intestine where water is retained, and then the rest of the molecules are exported out of the body as waste "feces" through the anus.

Below is a diagram that explains the peristaltic movement of the esophagus or the intestines.



For more information about enzymes see Enzymes.

Enzymes, also known as "biological catalysts", are chemical elements that catalyze, and speed up the breakdown of complex food into simple nutrients. Here are a few and what they do:

digestive enzymes.png

Enzymes are sensitive. Each enzyme acts at a specific temperature, specific pH, and on a specific substrate (food upon which the enzymes act). For example, salivary amylase (found in the saliva of the mouth) works best at neutral pH, whereas gastric enzymes work best in acidic medium, and the intestinal or pancreatic enzymes work best in basic medium. The Optimum Temperature of enzymes is 37 &degrees;C, which is the normal human body temperature. The enzymes become inactive at 0 &degrees;C and are destroyed at 60 &degrees;C.

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Human Gut Wall

Below is a diagram of the human gut wall showing the different layers.

The lumen is an empty space in the gut where nutrients are accumulated.

The first actual layer is the mucosa. It has a layer of epithelium, made of epithelial cells, which have projections called villi.

the human gut wall

In the diagram, you should also notice the capillaries, part of the blood network which absorbs the nutrients. And also, the lacteal ducts which are special tubes that carry fat molecules to the lymph.

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lymphatic system.

The Villi

By the time food reaches to the villi, it is already digested to small nutrients. These small nutrients can pass through the alimentary tract lining and can readily be absorbed by the blood.

The food products pass into the blood stream through villi, which are small folded structures that cover the internal surface of the small intestine.

diagram of a villus

It is important to know that there are a number of factors that improve the efficiency of absorption.

The villi on their own increase the surface area. However, the microvilli which are smaller projections (see diagram) further increase the surface area and speed up the absorption process.

Questions and Answers

How to remember the enzymes in the digestive system?

I am doing access course in biology about the digestive system. I have an exam on the digestive system and enzyme

ScienceAid QnA. There are several ways you can remember the names of enzymes.

1) Sometimes, the name of the enzyme shows what substrate it acts on. For example, protease and peptidase digest proteins and peptides respectively. Whereas, lipase digests lipids, and amylase acts on sugars.

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2) In the digestive system, each enzyme is secreted and acts in a different medium. For example, pepsin (for proteins) is an enzyme that acts in acidic medium (therefore it should act in the stomach). Trypsin is an enzyme that acts in basic medium therefore it should act in the small intestine.

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3) Third, by using logic. Remember, the sugar digestion starts in the mouth and continues in the small intestine, so the enzymes of the sugar molecules should be found in the mouth and the small intestine. The protein digestion starts in the stomach and continues to the small intestine therefore the proteases and the peptidases should be in the stomach and the small intestine. The lipid digestion starts in the small intestine, therefore lipases will be in the small intestine.

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I don't know how detailed your course is, If you have further questions do not hesitate to contact us.

Thank you

How can I write an essay question on enzymes in digestion?

I have to write an essay for my college course on the digestive system can you help me?

ScienceAid QnA. We can give you hints and help you find the source. However, you have to read and write on your own.

For example, you can first define digestion, then in the body paragraphs you can talk about the 2 types of digestion, and in each part mention where each type of digestion takes place and what are the enzymes involved. As a conclusion you can talk about the different enzymes and how specific they are.

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Do you have any names or dates I can use to reference this article?

Hi Jamie,. . I am referencing your article and not sure who to put as the author or the publication date, as this information I cannot find on the page. Thought I should contact you, any details would be greatly appreciated. Regards. (I'm not entirely certain what to put here, I haven't seen anybody ask this question already)

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ScienceAid QnA. To reference an article from the website please check the part: "Referencing this article" If you need further assistance please do not hesitate to contact us

Referencing this Article

If you need to reference this article in your work, you can copy-paste the following depending on your required format:

APA (American Psychological Association)
Digestive System, Enzymes, Absorption in the Small Intestine. (2017). In ScienceAid. Retrieved Mar 25, 2017, from https://scienceaid.net/biology/humans/digestion.html

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MLA (Modern Language Association) "Digestive System, Enzymes, Absorption in the Small Intestine." ScienceAid, scienceaid.net/biology/humans/digestion.html Accessed 25 Mar 2017.

Chicago / Turabian ScienceAid.net. "Digestive System, Enzymes, Absorption in the Small Intestine." Accessed Mar 25, 2017. https://scienceaid.net/biology/humans/digestion.html.

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Categories : Humans

Recent edits by: SmartyPants, Jen Moreau, Jamie (ScienceAid Editor)

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