Carbohydrate (CHO) Digestion and Absorption
Carbohydrates are broken down to provide glucose for energy. They are nutrients that provide your body with energy. Digestion predominantly occurs via enzymes lining the wall of the small intestine
Digestion is a physiological process by which complex food particles are broken down into a simple form which is suitable for absorption and subsequent utilization.
Absorption is the process by which the end products of digestion pass through the intestinal epithelium to enter the bloodstream.
Digestion of Carbohydrate (CHO)
CHO digestion starts in the mouth after taking foods by mouth.
Stages of CHO digestion
In the mouth: After mixing with saliva CHO is hydrolyzed by ptyalin (alfa-amylase) and form disaccharides like maltose and other small polymers of glucose that contain 3 to 9 glucose molecules. It continues in the body and fundus of the stomach for as long as 1 hr up to stomach pH 4.0.
Starch → Ptyalin → Erythrodextrin → Ptyalin → Maltose
In the stomach: The function of ptyalin (Salivary amylase) is lost in the acidic environment of the stomach. So no CHO is digested. HCl destroys the microorganism with food only.
In the duodenum: The more active pancreatic amylase digests all kinds of starch totally into maltose and other very small glucose polymers.
All forms of starch → pancreatic amylase → Maltose and very small glucose polymers.
In the small intestine: The CHO splitting enzymes are present in the enterocytes lining the villi of the small, intestine,
Lactose → Lactase → Glucose + Galactose
Maltose → maltase → Glucose + Glucose
Sucrose → Sucrase → Glucose + Fructose
A final product of CHO digestion
The final products of CHO digestion are all monosaccharides.
- Glucose → 80% of the total end product
- Galactose + fructose → 10% of the total end product.
Fig: Digestion of Carbohydrate.
Absorption of CHO
CHO’s are mainly absorbed as monosaccharides like glucose, fructose, and galactose
- Glucose and galactose → Na+ – glucose.
- Co-transport (2ndary active transport system)
- Fructose → By Facilitated diffusion from the intestinal lumen.
- Some fructose is converted into glucose and then it is absorbed by Na+ – glucose Co-transport.