Carbohydrate Digestion Overview

Carbohydrate Digestion in the Mouth

• Chewing breaks down carbohydrates into smaller pieces.
• Saliva contains salivary amylase, which breaks down starches into dextrins and maltose.
• Only about 5% of starches are broken down in the mouth, preventing excessive glucose and tooth decay.

Carbohydrate Digestion in the Stomach

• No further chemical breakdown occurs in the stomach due to the acidic environment.
• Mechanical breakdown continues with stomach contractions mixing carbohydrates into chyme.

Carbohydrate Digestion in the Small Intestine

• Pancreatic amylase in pancreatic juice further breaks down dextrins into shorter chains.
• Disaccharidases (sucrase, maltase, lactase) break down disaccharides into monosaccharides:
  • Sucrase breaks sucrose into glucose and fructose.
  • Maltase breaks maltose into two glucose units.
  • Lactase breaks lactose into galactose and glucose.
• Monosaccharides are absorbed into intestinal cells for transport to the bloodstream.

Lactose Intolerance

• Deficiency in lactase enzyme leads to undigested lactose.
• Undigested lactose is fermented by bacteria in the large intestine, producing gas and symptoms like diarrhea, bloating, and cramps.
• Common in adults, particularly those of African, Hispanic, Indigenous, and Asian descent.
• Severity depends on lactose intake and lactase deficiency level.

Glucose Absorption and Transport

• Monosaccharides (glucose, fructose, galactose) are transported to the liver.
• Liver converts galactose to glucose and breaks down fructose.
• Liver stores glucose as glycogen or releases it back into the bloodstream.

Blood Glucose Regulation

• Tightly controlled to prevent health issues from high or low glucose levels.
• Regulated by negative feedback mechanism, similar to a thermostat.
• Pancreas plays a key role in controlling blood glucose levels.

Insulin and Glucagon

• Insulin is released when blood glucose rises, promoting glucose uptake by cells.
• Insulin signals muscle and liver to store glucose as glycogen.
• Glucagon is released when blood glucose drops, stimulating glycogen breakdown and glucose release into the bloodstream.

Dietary Fiber and Resistant Starch

• Most carbohydrates are digested and absorbed, except for fiber and resistant starch.
• Some undigested carbohydrates are broken down by bacteria in the large intestine, producing short-chain fatty acids and gases.
• Short-chain fatty acids can be used by bacteria, eliminated, or absorbed by colon cells, with some going to the liver for metabolism.
• Dietary fiber yields about 2 kcal/gram, with soluble fiber and resistant starch offering more energy than insoluble fiber.
• Fiber slows down blood glucose rise, potentially reducing weight gain and chronic disease risk.

Explore the process of carbohydrate digestion from the mouth to the small intestine. Learn how various enzymes break down starches into sugars and the role of mechanical digestion. This quiz covers key topics essential for understanding human digestion.