Lecture 23: Mucosal Digestion Flashcards
Absorption refers to the…
Transfer of simple molecules across intestinal epithelium
Maldigestion is usually related to a ___ problem whereas malabsorption is related to a ___problem
Enzyme, epithelial
What is are four ways to increase surface area of GI
- GI tract elongation
- Plica circulars
- Villi
- Microvilli
What is the glycocalyx
Border of glycoproteins on apical membrane of enterocytes
What structures create the mucosal border
Microvilli, glycocalyx, mucus, unstirred water
What does enteritis do to the villi
Destroys villi resulting in loss of absorptive surface/malabsorption
What are the two phases of carbohydrate digestion
Luminal and membranous
What happens during luminal phase of carbohydrate digestion
- Breakdown facilitated by enzymes of salivary gland and pancreas
- Polysaccharides broken down to dimers and trimers
Where are enzymes bound during membranous phase
Glycocalyx (diffused through mucus layer)
What happens during membranous phase of carbohydrate digestion
Dimers and trimers are broken down by sugar specific enzymes to monomers and then absorbed
What enzyme hydrolyzes starches to smaller polysaccharides in the oral cavity
Alpha-amylase
In the stomach 30-40% of starches are converted to ___
Maltose
What enzyme further breaks down all starches to di or polysaccharides
Alpha-amylase
What di or polysaccharides are the result of carbohydrate digestion in SI
Maltose, isomaltose, dextrin and maltotriose
What are two forms of starches
Amylose and amylopectin
Carbohydrate polymers come as __, ___, ___ or ___
Fibers, starch, sugar, glycogen
T or F: fibers are indigestible by mammals
True
What bond makes fiber indigestible by mammals
Beta-acetal bond between carbons 1 and 4
How are fibers digested
Fermenting bacteria in hind or foregut depending on species
Where does fiber come from in plants
Cell wall
Where does sugar come from in plants
Vacuoles
Where does starch come from in plants
Endosperm
Fiber remains in the lumen and provides bulk to ___
Feces
Bacterial hydrolyzes in rumen and/pr cecum/colon ferment fiber to __
VFA’s
Describe the luminal phase of protein digestion
Broken down to peptides and amino acids, first in stomach via gastric enzymes and HCl and then by pancreatic enzymes in duodenum
Describe the membranous phase of protein digestion
Further breakdown to amino acids facilitated by peptidases
Proteins are hydrolyzed into __, ___ and ___
di, tripeptides and AS
Gastric pepsinogen is activated by __ and ___
HCl and pepsin
Trypsinogen is activated by ___ or ___
Enterokinase or trypsin
Trypsin activates __
Other pro enzymes
How does protein absorption differ from carbohydrate absorption
Proteins can be absorbed as di, tripeptides or amino acids whereas carbohydrates must be broken down to monomers
what cleave internal bonds in proteins
Endopeptidases
What cleaves terminal residue of polypeptide chain
Exopeptidases
What cleaves the N-terminal residue on proteins
Aminopeptidases
What cleaves the C terminal residue on proteins
Carboxypeptidases
During lipid digestion triglycerides are hydrolyzes into__ and ___
Monoglycerides and FFA
T or F: fats are water soluble
False
How does the stomach assist in fat digestion
- Initial emulsification (coat in bile acids)
- Fat globules liquify
- Lipid droplets
How does the small intestine participate in fat digestion
- Emulsification finalized
- Bile acids and phospholipids added
- Emulsified droplets are digested
- Co-lipase and lipase produce FFA and monoglycerides
What are the four steps of fat digestion in small intestine
- Emulsification
- Hydrolysis of triglycerides
- Micelle formation
- Micelle content can be absorbed in jejunum
What is emulsification
Coating lipids in bile acids to make them more hydrophilic
What are primary bile acids synthesized by
Liver
What are secondary bile acids a result of
Bacterial actions in the colon
What do small lipid droplets encoated in bile acids contain
Triglycerides, cholesterol, cholesterol esters, phospholipids
Describe the steps in hydrolysis of triglycerides
- Co-lipase clear bile from surface of droplets
- Lipase hydrolyzes triglycerides producing monoglycerides and FFA
What are Micelles
Small sized droplets that combine with bile salts and phospholipids to prepare for absorption
Micelles act as lipid ___ and increase ___ in chyme
Lipid shuttles, increase lipid solubility in chyme
What part of the small intestine are lipids exposed to bile and form droplets
Duodenum
What part of small intestine are does co-lipase and lipase act
Jejunum
What part of small intestines do Micelles diffuse through
Jejunum
What is exocrine pancreas insufficiency
Insufficient synthesis and secretion of pancreatic enzymes caused by pancreatic Acinar atrophy or tumor
How does exocrine pancreas insufficiency cause anorexia/exercise intolerance/weakness
Insufficient breakdown of nutrients and therefore prevents absorption
How does exocrine pancreas insufficiency cause abdominal pain
Bacterial gas production/ malfermentation in LI, inflammation
How can exocrine pancreas insufficiency cause vomiting
Delayed gastric emptying, SI distention due to increase gastric secretion, bacterial toxins in LI
How can exocrine pancreas insufficiency lead to diarrhea
Osmotic diarrhea
How can exocrine pancreas insufficiency lead to dehydration
Insufficient water reabsorption in LI
How can exocrine pancreas insufficiency lead to fever
Bacterial toxins; compromised immune defense
How can exocrine pancreas insufficiency cause arrhythmias
Electrolyte imbalance, acid-base imbalance
