Digestion and Absorption of Carbohydrates and Proteins Flashcards
What are the three classes of carbohydrates?
Monosaccharides (monomers)
Oligosaccharides (short polymers)
Polysaccharides (long polymers)
Fiber, pectin and cellulose are examples of?
Indigestible polysaccharides
What are the polysaccharides we can digest? (4)
- Starch
- Glycogen
- Amylose
- Amylopectin
What percent of dietary carbs in western society is from starch? Where is it primarily derived from?
45-60%
Primarily from plants
What is the primary source of dietary glycogen?
Animals
What type of structure of polysaccharide is amylose?
Straight
What type of polysaccharide structure does amylopectin have?
Branched
Identify the polymers
What are the two dietary oligosaccharides?
Sucrose and Lactose
What are the two dietary monosaccharides?
Glucose and Fructose
What kind of carbohydrates can the intestine absorb?
Monosaccharides
What are the two steps of carbohydrate digestion?
- Intraluminal hydrolisis
- Membrane digestion
What are the two types of amylases that participate in intraluminal hydrolysis of carbs?
In what form are these secreted?
Alpha-Amylases
- Salivary Amylase
- Pancreatic Amylase
Secreted in enzymatically active form
What does salivary amylase do? What inactivates it?
Initiates starch digestion
Inactivated by gastric acid
What does pancreatic Alpha amylase do?
Completes starch digestion in the lumen of the small intestine
What stimulates the secretion of pancreatic alpha amylase?
Cholecystokinin (CCK)
Pancreatic alpha-amylase cannot digest all linkages and the product is oligosaccharides. What structural components are ndigestible?
Terminal linkages and branch points
What is responsible for the membrane digestion?
Where does this happen?
Where does it definitely and specifically not happen?
Brush border oligosaccharidases
Mostly in the proximal jejunum.
Does not happen in the large intestine
What are the brush border oligosaccharidases? (3)
- Lactase
- Glucoamylase
- Sucrase-isomaltase
What is the action of lactase? When/how does expression change in humans?
- Digests lactose into glucose and galactose
- Expression decreases after weaning in the infant
What is glucoamylase also known as?
Maltase
Sucrase-isomaltase is two enzymes, what does it cleave?
•Cleaves sucrose and splits branch points
How is lactase downregulation determined? What can excess downregulation lead to?
Hereditarily determined
Lactase deficiency or Lactose intolerance
What are the symptoms of lactase deficiency/lactose intolerance?
–cramps
–diarrhea
–flatus
What are the symptoms of lactose intolerance determined by?
- Rate of peristalsis and gastric emptying
- Colonic bacteria
Colonic bacteria can metabolize undigested lactose into what? How do these contribute to the symptoms of lactose intolerance?
Short chain fatty acids (induces osmotic diarrhea)
CO2 (contributes to flatulence)
H2