Digestion and Absorption of Carbohydrates

Imagine taking a bite that pizza. That tastes amazing, yet it"s additionally full the fuel for her body, lot of it in the form of carbohydrates.

You are watching: Which of the following describes the process of starch digestion

What types of carbohydrates would certainly you discover in the bite?

Lactose native the cheese

Sucrose, glucose, and also fructose from the naturally-occurring street in the tomatoes, as well as sugar that may have been added to the sauce

Starch in the flour used to do the crust

Fiber in the flour, tomatoes, and also basil.

In stimulate to usage these food carbohydrates in her body, you first need come digest them. Critical week, us explored the cradle system and also the basic process of digestion. Now that friend know around the different types of carbohydrates, we"ll take a closer look at at exactly how these molecules room digested together they travel with the GI system.

In the image below, monitor the numbers to check out what happens to carbohydrates at each website of digestion.


Fig. 4.1. The digestive system

1 - Mouth or oral Cavity

As you chew her bite the pizza, you"re utilizing mechanical digestion to begin to rest it into smaller pieces and also mix it through saliva, produced by numerous salivary glands in the dental cavity.

Some enzymatic cradle of starch occurs in the mouth, as result of the activity of the enzyme outstanding amylase. This enzyme starts to rest the long glucose chains of starch into shorter chains, part as tiny as maltose. (The various other carbohydrates in the bread don"t undergo any enzymatic digestion in the mouth.)


Fig. 4.2. The enzyme salient amylase breaks starch right into smaller polysaccharides and also maltose.

2 - Stomach

The low pH in the stomach inactivates outstanding amylase, so that no much longer works when it come at the stomach. Back there"s more mechanical digestion in the stomach, there"s tiny chemical digestion of carbohydrates here.

3 - tiny intestine

Most carbohydrate digestion occurs in the little intestine, thanks to a suite of enzymes. Pancreatic amylase is secreted native the pancreas right into the small intestine, and like salivary amylase, it division starch down to little oligosaccharides (containing 3 come 10 glucose molecules) and maltose.


Fig. 4.3. The enzyme pancreatic amylase division starch into smaller polysaccharides and maltose.

The remainder of the occupational of carbohydrate cradle is done by enzymes developed by the enterocytes, the cells lining the small intestine. As soon as it comes to digesting your slice of pizza, these enzymes will breakdown the maltase created in the process of starch digestion, the lactose indigenous the cheese, and the sucrose present in the sauce.

Maltose is digested by maltase, creating 2 glucose molecules


Lactose is digested by lactase, developing glucose and also galactose


Sucrose is digested by sucrase, creating glucose and fructose


Fig. 4.4. Activity of the enzymes maltase, lactase, and also sucrase.

(Recall that if a human is lactose intolerant, castle don"t make sufficient lactase enzyme come digest lactose adequately. Therefore, lactose overcome to the big intestine. Over there it color etc water in by osmosis and is fermented through bacteria, bring about symptoms such as flatulence, bloating, and also diarrhea.)

By the end of this process of enzymatic digestion, we"re left with 3 monosaccharides: glucose, fructose, and galactose. These have the right to now be took in across the enterocytes that the tiny intestine and also into the bloodstream to be transported to the liver.

Digestion and also absorption of carbohydrate in the small intestine are shown in a really simplified schematic below. (Remember that the inner wall of the little intestine is actually composed of big circular folds, lined with plenty of villi, the surface of i beg your pardon are made up of microvilli. All of this gives the little intestine a vast surface area because that absorption.)


Fig. 4.5. Digestion and absorption of carbohydrates in the little intestine.

Fructose and also galactose are converted come glucose in the liver. Once absorbed carbohydrates pass through the liver, glucose is the main kind of carbohydrate turn in the bloodstream.

4 - large Intestine or Colon

Any carbohydrates that weren"t spend in the little intestine -- largely fiber -- pass right into the huge intestine, however there"s no enzymatic digestion of these carbohydrates here. Instead, bacteria living in the large intestine, sometimes called our gut microbiota, ferment this carbohydrates to feeding themselves. Fermentation reasons gas production, and that"s why we might experience bloating and flatulence after a particularly fibrous meal. Fermentation additionally produces short-chain fatty acids, i beg your pardon our large intestine cells can use as an power source. End the last te or so, an ext and an ext research has displayed that ours gut microbiota room incredibly vital to our health, playing vital roles in the duty of our immune response, nutrition, and risk the disease. A diet high in entirety food sources of fiber help to maintain a population of healthy gut microbes.

Summary the Carbohydrate Digestion:

The primary goal the carbohydrate digestion is to rest polysaccharides and disaccharides right into monosaccharides, which deserve to be took in into the bloodstream.

1. After ~ eating, nothing demands to take place in the digestive tract to the monosaccharides in a food prefer grapes, due to the fact that they space already small enough to be soaked up as is.

2. Disaccharides in the grape or in a food choose milk are damaged down (enzymatically digested) in the digestive street to monosaccharides (glucose, galactose, and also fructose).

3. Starch in food is damaged down (enzymatically digested) in the digestive street to glucose molecules.

4. Fiber in food is not enzymatically digested in the cradle tract, since humans don"t have actually enzymes to carry out this. However, part dietary fiber is fermented in the large intestine by gut microbes.

Table 4.1. An introduction of Enzymatic digestion of Carbohydrate

Macronutrients in Food

Is this Macronutrient Enzymatically Digested?

(enzyme name)

What Is took in Into the Villi after ~ Digestion?







Fructose. The is climate transported to the liver where it is converted to glucose.

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Galactose. The is then transported to the liver whereby it is convert to glucose.



Yes (maltase)



Yes (sucrase)

Glucose, Fructose


Yes (lactase)

Glucose, Galactose




(amylase, maltase)



No (Humans don"t have the digestive enzymes to break down fiber, yet some is fermented by gut microbes in the huge intestine.)


This video reviews the process of carbohydrate digestion: https://www.wiley.com/college/grosvenor/0470197587/animations/dig3a/

This video will help you identify carbohydrates in foods, what carbohydrates need to be enzymatically digested, and what is absorbed: https://youtu.be/XcIInk32nn4