Carbohydrates that you eat are broken down to monosaccharides by enzymes in your digestive tract. In this lesson, you will learn about these digestive enzymes and how monosaccharides are absorbed out of the digestive tract.
Carbohydrates are nutrients that provide your body with energy. But, before carbohydrates can fuel your morning run, they must be broken down into their basic units, called monosaccharides, and absorbed out of your digestive tract and into your bloodstream. In this lesson, you will learn about the enzymes that break down carbohydrates and how this important nutrient is absorbed.
Carbohydrate digestion begins in the mouth with salivary amylase.
We previously learned that digestion of carbohydrates, and in particular starches, begins in the mouth with the action of salivary amylase. This enzyme catalyzes, or speeds along, the hydrolysis of the starch molecule. You may recall that hydrolysis is how nutrients that you eat are broken down, and it involves splitting bonds with water.
Even though carbohydrate digestion begins in your mouth, very few of us chew our food long enough for salivary amylase to have a significant effect on the carbohydrates that we eat. So, we swallow the carbohydrate somewhat intact. When you swallow the food mass, some of the salivary amylase travels along with it, and you would think that the enzyme would keep working to break down the carbohydrate. However, the enzyme is inactivated in the stomach because the environment of the stomach is too acidic.
Digestion of the carbohydrate does not resume until the food mass reaches the first part of the small intestine that we call the duodenum. There, the carbohydrate meets pancreatic amylase, which is similar to salivary amylase and continues the breakdown of the carbohydrate.
Brush Border Enzymes
Brush border enzymes in the small intestine complete the digestion of carbohydrates.
Any remaining sugars are acted upon by brush border enzymes. Brush border enzymes are special enzymes found on the microvilli of the small intestine that complete digestion. We previously learned that microvilli are tiny, hair-like projections that increase the surface area of the small intestine and therefore increase nutrient absorption. Because there are so many microvilli, the epithelial cells appear to be fuzzy, like the bristles of a paint brush, leading some anatomists to refer to them as the brush border, hence the name.
Now that all the carbohydrate molecules have been hydrolyzed into their simplest monosaccharide form, they can be absorbed out of the digestive tract and into your bloodstream. The digested sugars pass into the microvilli of the epithelial cells and then enter the capillaries found in the wall of the small intestine. The absorbed substances are now in the bloodstream, and with the exception of a quick detour to the liver, they are ready to be transported to your body cells.
Cells break down glucose and release energy in the form of ATP.
Carbohydrates, especially the monosaccharide glucose, provide your body cells with a ready and easy source of energy. When your body cells break down glucose, energy is released in the form of ATP, which your cells use to carry out most of their functions. Of course, if energy is not required, dietary carbohydrates can be processed and stored in the muscle or in fat cells. Those who eat a carbohydrate-rich diet know too well about the conversion of carbohydrates to fat.
Let's review. Enzymes, such as salivary amylase, pancreatic amylase, and brush border enzymes, catalyze, or speed up, hydrolysis of carbohydrates. The brush border enzymes are special enzymes found on the microvilli of the small intestine.
The monosaccharides, such as glucose, pass into the microvilli of the epithelial cells within the small intestine. From there, they enter the blood capillaries, and after a quick detour to the liver, travel to your body cells. When your body cells break down glucose, energy is released in the form of ATP, which your cells use to carry out most of their functions.
Following this video lesson, you will be able to:
- Trace the breakdown of carbohydrates from the mouth to absorption out of the digestive tract
- List the enzymes involved in the digestion of carbohydrates and the function of each
- Explain what happens to the broken down carbohydrates once they leave the digestive tract