leky-latky/enzymy/sacharidasy

Sacharidy v GIT

• Predominantly absorbed within the proximal small intestine
• Complex carbohydrates need to be hydrolyzed by salivary and pancreatic amylases to glucose, maltose, maltotriose, and oligosaccharides
• Brush border enzymes monosaccharide production
• Maltase
• Sucrose-isomaltase
• Lactase

Ústa

• Salivary alpha-amylase
• Hydrolyzes the alpha-1,4 bonds in starch
• Maltose
• Maltriose
• Small dextrins [12]

Pancreatic alpha-amylase

Enzymes in the brush border of the small intestine

• Disaccharidases or alpha-glucosidases
• Maltase
• Sucrase
• Lactase
• Monosaccharides
• Glucose
• Fructose
• Galactose [12]

Glucose and galactose transported from GIT

• Up to 50% of this transport is an active process
• Depends on a sodium ion gradient
• Main sodium-glucose cotransporter in the human intestine is SGLT-1 [5]
• Five functional mammalian facilitated hexose carriers (GLUTs)
• High-affinity transporters
• GLUT-1, GLUT-3, and GLUT-4
• Low-affinity transporter
• GLUT-2 for glucose
• GLUT-5 is primarily a fructose carrier
• Expression is regulated by glucose and several hormones
• In the intestine are
• GLUT-2 and GLUT-5
• Support facilitated rather than active transport [5]

Malabsorption of complex carbohydrates

• May thus occur due to pancreatic exocrine insufficiency
• But is less likely to play a major clinical role because of compensatory mechanisms
• Salivary amylase
• Brush border enzymes
• Complete experimental inhibition of amylase activity
• Only about 20% of a carbohydrate meal reach the terminal ileum [5]
• Significant proportion of calories from carbohydrates entering the colon
• Can still be absorbed
• Contributes markedly to energy supply after bacterial metabolism to short-chain fatty acids [5]

Defects of brush border enzymes

• Associated with maldigestion and malabsorption of disaccharides
• (relative) GLUT deficiencies
• Can lead to malabsorption of monosaccharides
• Lactase deficiency
• Lactose intolerance
• Normal in non-Caucasian adults
• Intact lactose cannot be absorbed from the small bowel
• May bind water osmotically
• Will be metabolized by colonic bacteria
• Production of gas in the large bowel [5]
• Relative deficiency of GLUT-5
• Leading to intestinal fructose malabsorption
• Prevalence of fructose malabsorption is not well known
• Appears to depend largely on dietary habits [5]

Main end products of carbohydrate fermentation

• Short-chain fatty acids
• Acetate
• Propionate
• Butyrate
• Gases
• Carbon dioxide
• Hydrogen
• Methane [12]

• Absorbed in the large intestine (providing energy)
• Used as a bacterial substrate
• Released as flatus
• Excreted as biomass in the feces [12]