Physiology of Carbohydrate and Protein Digestion and Absorption Flashcards
What type of digestion in the small intestine is mediated by pancreatic enzymes secreted into the duodenum?
Luminal
What kind og digestion in the small intestine is mediated by enzymes situated at the brush border of epithelial cells?
Membrane
Wat is the term for the overall process of digestion and absorption?
Assimilation
Give an example of luminal hydrolysis of polymer to monomers?
Protein to amino acids
Give and example of brushborder hydrolysis of oligomer to monomer?
Sucrose to glucose and fructose
Give an example of intracellular hydrolysis?
Peptide
Give an example of luminal hydrolysis followed by intracellular resynthesis?
Triacylglycerol to glycerol and fatty acids
Name two polymers of glucose?
Starch and glycogen
Name two oligosaccharides?
Sucrose and lactose
What does glucose + fructose give?
Sucrose
What does glucose + galactose give?
Lactose
What is more highly branched - amylopectin or glycogen?
Glycogen
What must all dietary carbohydrates be converted to for absorption?
Monosaccharides (glucose and fructose)
What is the process of starch being broken down to oligosaccharides?
Intraluminal hydrolysis
What are alpha-linit dextrins, maltotriose and maltose?
Oligosaccharides
What is the process for breaking down oligosaccharides to monosaccharides?
Membrane digestion (at brush border)
Name three oligosaccharidases?
Lactase
Maltase
Sucrase-isomaltase
What accomplishes starch by intraluminakl hydrolysis to oligosaccharides?
Alpha-amylase (salivary and pacnreatic)
What does a-amylase breakdown, and what does it not?
Breaks down linear internal alpha-1,4 linkages but not terminal alpha-1,4,linkages
Does the endoenzyme a-amylase produce glucose?
No
What enzyme, cannot cleave alpha-1,6 linkages at branch points (in amylopectin) ot alpha-1,4-linkages adjacent to branch points?
Alpha-amylase
What are the main class of products from a-amylase?
Oligosaccharides
What are integral membrane proteins with a catalytic domain that faces the lumen of the GI tract?
Oligosaccharidases
Ohter than lactase, which breaks down lactose to glucose and galactose, what do all other oligosaccharidases cleave?
The terminal alpha-1,4-linkages of maltose, maltotriose and alpha-limit dextrins
What oligosaccharidase is unique in that it is the only enzyme that can split the branching alpha-1,6,linkages of alpha-limit dextrins?
Isomaltase
Give an example of a disorder caused by impaired carbohydrate digestion?
Lactose intolerance
What insufficiency causes lactose intolerance?
Lactase deficiency
What is primary lactase deficiency (primary hypolactasia) due to?
Lack of the lactase persistence (LP) allele
What is secondary lactase deficiency due to?
Damage to/infection of/ the proximal small intestine
Name a rare, autosomal recessive disease with no ability to digest lactose from birth?
Congenital lactase deficiency
What are these produced in response to: short-chain fatty acids, hydrogen (can be detected in breath of lactase defiecient people), carbon dioxide and methane?
Produced by colonic microflora when lactose delivered to colon from ileum
What are three symptoms of lactase insufficiency?
Bloating
Abdominal Pain
Flatulence
What causes acidification of the colon and increased osmotic load - loose stools nad diarrhoea?
Undigested lactose
What are the three final products of carbohydrate digestion?
Glucose, galactose and fructose
Where does final product absorption occur?
In duodenum and jejunum
What is absorbed by secondary active transport mediated by SGLT1?
Glucose and galactose
What is absorbed by facilitated diffusion mediated by GLUT5?
Glucose and galactose
How is exit for all monosaccharides mediated?
By facilitated diffusion by GLUT2
For SGLT1 transport, what must the substrate be like?
A hexose in D conformation
Can form pyranose ring
What products do endopeptidases produce?
Oligopeptides (2-6 amino acids)
What products do exopeptidases produce?
Single amino acids
