Digestion and Absorption the Carbohydrates

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

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

What species of carbohydrates would certainly you find in that bite?

Lactose from the cheese

Sucrose, glucose, and also fructose from the naturally-occurring sugars in the tomatoes, and also sugar that may have actually been included to the sauce

Starch in the flour supplied to make the crust

Fiber in the flour, tomatoes, and basil.

In stimulate to usage these food carbohydrates in your body, you an initial need come digest them. Last week, us explored the gastrointestinal system and the basic process of digestion. Now that girlfriend know around the different species of carbohydrates, we"ll take it a closer look at exactly how these molecules are digested as they travel v the GI system.

In the picture below, monitor the numbers to check out what wake up to carbohydrate at each site of digestion.


Fig. 4.1. The cradle system

1 - Mouth or dental Cavity

As you chew her bite of pizza, you"re making use of mechanical digestion to start to break it right into smaller pieces and also mix it through saliva, produced by several salivary glands in the dental cavity.

Some enzymatic digestion of starch occurs in the mouth, because of the activity of the enzyme outstanding amylase. This enzyme start to rest the long glucose chain of starch into shorter chains, some as little as maltose. (The various other carbohydrates in the bread don"t undergo any type of enzymatic digestion in the mouth.)


Fig. 4.2. The enzyme salivary amylase division starch right into smaller polysaccharides and also maltose.

2 - Stomach

The short pH in the stomach inactivates salivary amylase, so it no longer works when it arrives at the stomach. Back there"s more mechanical cradle in the stomach, there"s little chemical digestion of carbohydrate here.

3 - small intestine

Most carbohydrate digestion wake up in the little intestine, many thanks to a suite the enzymes. Pancreatic amylase is secreted native the pancreas into the tiny intestine, and like outstanding amylase, it division starch under to small oligosaccharides (containing 3 come 10 glucose molecules) and maltose.


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

The remainder of the work-related of carbohydrate digestion is done by enzymes produced by the enterocytes, the cells lining the small intestine. Once it pertains to digesting your part of pizza, this enzymes will break down the maltase developed in the process of strength digestion, the lactose from the cheese, and the sucrose present in the sauce.

Maltose is spend by maltase, creating 2 glucose molecules


Lactose is digested by lactase, creating glucose and galactose


Sucrose is digested by sucrase, forming glucose and fructose


Fig. 4.4. Action of the enzyme maltase, lactase, and sucrase.

(Recall that if a human being is lactose intolerant, castle don"t make sufficient lactase enzyme to digest lactose adequately. Therefore, lactose overcome to the huge intestine. There it paint, etc water in through osmosis and also is fermented through bacteria, leading to symptoms such as flatulence, bloating, and diarrhea.)

By the end of this process of enzymatic digestion, we"re left with 3 monosaccharides: glucose, fructose, and galactose. These can now be soaked up across the enterocytes of the tiny intestine and also into the bloodstream to it is in transported come the liver.

Digestion and absorption of carbohydrate in the small intestine are portrayed in a an extremely simplified schematic below. (Remember that the inner wall of the little intestine is actually created of large circular folds, inside wall with many villi, the surface of i beg your pardon are consisted of of microvilli. Every one of this provides the small intestine a vast surface area for absorption.)


Fig. 4.5. Digestion and also absorption of carbohydrates in the small intestine.

Fructose and also galactose are converted come glucose in the liver. Once took in carbohydrates pass with the liver, glucose is the main type of carbohydrate circulating in the bloodstream.

4 - large Intestine or Colon

Any carbohydrates that weren"t spend in the little intestine -- mostly fiber -- pass right into the large intestine, however there"s no enzymatic digestion of these carbohydrates here. Instead, bacteria living in the huge intestine, sometimes called our gut microbiota, ferment these carbohydrates to feeding themselves. Fermentation causes gas production, and that"s why we might experience bloating and flatulence after a an especially fibrous meal. Fermentation likewise produces short-chain fatty acids, i beg your pardon our large intestine cells can use as an power source. Over the last decade or so, an ext and more research has displayed that our gut microbiota are incredibly important to ours health, playing crucial roles in the function of our immune response, nutrition, and also risk the disease. A diet high in whole food resources of fiber help to keep a populace of healthy and balanced gut microbes.

Summary the Carbohydrate Digestion:

The primary goal of carbohydrate digestion is to break polysaccharides and also disaccharides into monosaccharides, which have the right to be soaked up into the bloodstream.

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

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

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

4. Fiber in food is no enzymatically digested in the cradle tract, because humans don"t have enzymes to do this. However, part dietary fiber is fermented in the large intestine by gut microbes.

Table 4.1. An overview of Enzymatic digestion of Carbohydrate

Macronutrients in Food

Is this Macronutrient Enzymatically Digested?

(enzyme name)

What Is soaked up Into the Villi after Digestion?







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

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Galactose. It is then transported come 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 enzyme to failure fiber, however some is fermented by gut microbes in the large intestine.)


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

This video clip will help you determine carbohydrates in foods, what carbohydrates should be enzymatically digested, and also what is absorbed: https://youtu.be/XcIInk32nn4