Digestion and Absorption that Carbohydrates

Imagine acquisition a bite of pizza. The tastes amazing, but it"s also full of fuel for your body, much of the in the kind of carbohydrates.

You are watching: Where does starch digestion begin?

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

Lactose indigenous the cheese

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

Starch in the flour supplied to do the crust

Fiber in the flour, tomatoes, and also basil.

In order to use these food carbohydrate in her body, you first need to digest them. Critical week, we explored the gastrointestinal system and also the basic procedure of digestion. Now that girlfriend know about the different types of carbohydrates, we"ll take a closer look at at just how these molecules are digested together they travel with the GI system.

In the photo below, monitor the number to watch what wake up to carbohydrates at each website of digestion.


Fig. 4.1. The cradle system

1 - Mouth or dental Cavity

As girlfriend chew your bite that pizza, you"re using mechanical digestion to begin to break it right into smaller pieces and mix it with saliva, developed by numerous salivary glands in the dental cavity.

Some enzymatic cradle of starch occurs in the mouth, due to the activity of the enzyme outstanding amylase. This enzyme beginning to break the lengthy glucose chain of starch into shorter chains, some as small as maltose. (The various other carbohydrates in the bread don"t undergo any enzymatic digestion in the mouth.)


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

2 - Stomach

The low pH in the stomach inactivates salivary amylase, so it no longer works as soon as it arrives at the stomach. Although there"s an ext mechanical digestion in the stomach, there"s tiny chemical cradle of carbohydrates here.

3 - tiny intestine

Most carbohydrate digestion occurs in the small intestine, thanks to a suite that enzymes. Pancreatic amylase is secreted from the pancreas into the tiny intestine, and also like salivary amylase, it division starch under to tiny oligosaccharides (containing 3 come 10 glucose molecules) and maltose.


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

The rest of the work-related of carbohydrate cradle is excellent by enzymes created by the enterocytes, the cells lining the little intestine. As soon as it pertains to digesting your part of pizza, this enzymes will breakdown the maltase developed in the procedure of starch digestion, the lactose from the cheese, and also the sucrose existing in the sauce.

Maltose is digested by maltase, developing 2 glucose molecules


Lactose is digested by lactase, developing glucose and galactose


Sucrose is digested by sucrase, forming glucose and fructose


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

(Recall the if a person is lactose intolerant, lock don"t make enough lactase enzyme to digest lactose adequately. Therefore, lactose passes to the large intestine. There it paint, etc water in by osmosis and also is fermented through bacteria, causing symptoms such as flatulence, bloating, and also diarrhea.)

By the end of this procedure of enzymatic digestion, we"re left with three monosaccharides: glucose, fructose, and galactose. These deserve to now be absorbed across the enterocytes of the tiny intestine and into the bloodstream to it is in transported come the liver.

Digestion and also absorption of carbohydrate in the tiny intestine are shown in a really simplified schematic below. (Remember that the inner wall of the small intestine is actually composed of big circular folds, lined with numerous villi, the surface ar of i beg your pardon are consisted of of microvilli. All of this offers the tiny intestine a huge surface area because that absorption.)


Fig. 4.5. Digestion and absorption of carbohydrate in the small intestine.

Fructose and also galactose room converted to glucose in the liver. Once absorbed carbohydrates pass v the liver, glucose is the main kind of carbohydrate circulating in the bloodstream.

4 - big Intestine or Colon

Any carbohydrates that weren"t digested in the small intestine -- mostly fiber -- pass into the big intestine, yet there"s no enzymatic digestion of these carbohydrates here. Instead, bacteria life in the large intestine, sometimes dubbed our gut microbiota, ferment these carbohydrates to feed themselves. Fermentation reasons gas production, and also that"s why we might experience bloating and also flatulence after ~ a an especially fibrous meal. Fermentation also produces short-chain fatty acids, which our huge intestine cells can use as an energy source. Over the last decade or so, an ext and more research has presented that our gut microbiota space incredibly important to ours health, playing essential roles in the duty of our immune response, nutrition, and risk the disease. A diet high in totality food sources of fiber help to preserve a populace of healthy gut microbes.

Summary of Carbohydrate Digestion:

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

1. After ~ eating, nothing needs to happen in the digestive street to the monosaccharides in a food choose grapes, since they are already small enough come be absorbed as is.

2. Disaccharides in the grape or in a food prefer milk are broken down (enzymatically digested) in the digestive tract to monosaccharides (glucose, galactose, and 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, due to the fact that humans don"t have enzymes to carry out this. However, part dietary fiber is fermented in the big intestine by gut microbes.

Table 4.1. Summary of Enzymatic cradle of Carbohydrate

Macronutrients in Food

Is this Macronutrient Enzymatically Digested?

(enzyme name)

What Is took in Into the Villi ~ Digestion?







Fructose. It is climate transported come the liver wherein it is convert to glucose.

See more: How Long Can Fleas Hold Their Breath, Do Fleas Drown In Water



Galactose. That is climate transported come the liver where it is converted 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 through gut microbes in the big intestine.)


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

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