carbohydrates digestion and absorption Flashcards
What is the primary goal of carbohydrate digestion?
To liberate monosaccharides (mainly glucose) from disaccharides and polysaccharides for absorption.
What are glycaemic carbohydrates?
Carbohydrates hydrolyzed and absorbed in the small intestine, including most sugars, α-glucan oligosaccharides, and starch (partially resistant).
What are non-glycaemic carbohydrates?
Carbohydrates that resist digestion in the small intestine and are fermented in the large intestine, including resistant starch and non-α-glucan polysaccharides.
Which enzyme begins carbohydrate digestion in the mouth?
Salivary α-amylase.
Why does α-amylase activity stop in the stomach?
The low pH in the stomach inhibits its activity.
Which enzymes complete carbohydrate digestion in the small intestine?
Enzymes at the brush border, such as sucrase, maltase, and lactase.
What are the primary monosaccharides absorbed in the small intestine?
Glucose, galactose, and fructose.
How are glucose and galactose transported across the apical membrane?
By active transport via the SGLT1 protein, along with sodium.
How is fructose absorbed in the small intestine?
Through facilitated diffusion via GLUT5 protein.
What happens to non-digested carbohydrates in the large intestine?
They are fermented by gut microbes into short-chain fatty acids, gases, and microbial biomass.
What are the by-products of carbohydrate fermentation in the large intestine?
Acetate, propionate, butyrate, hydrogen, carbon dioxide, methane, and microbial biomass.
How does carbohydrate digestion differ in ruminants?
In ruminants, carbohydrates are fermented in the rumen by microbes before exposure to host digestive enzymes, producing SCFAs for energy.
What role does particle size and transit time play in carbohydrate digestion?
They affect enzyme access and the rate of digestion.
What is the main energy source produced from fermentation in ruminants?
Short-chain fatty acids (SCFAs) such as acetate, propionate, and butyrate.
What limits the digestion of carbohydrates in the small intestine?
The lack of specific enzymes, enzyme inaccessibility, slow enzyme activity, or inadequate monosaccharide transport.
