GI - Pt 4 Digestion Flashcards
T/F
Gastrin is a great digestive enzyme
False
Gastrin does not digest anything. It is an endocrine hormone.
Histological Enterocyte function
- Contains Folds of []
- [] - which are longest in the dueodenum and shortest in the ileum
- Structure
- [] Cells
- [] cells produce mucus
- Apical surface contains [] brush b order
- Contains Folds of Kerkring
- Villi - which are longest in the dueodenum and shortest in the ileum
- Structure
- Columnar Cells
- Goblet cells produce mucus
- Apical surface contains microvilli brush border
The tips of enterocytes are borderline [] and are easily [] off.
The tips of enterocytes are borderline ischemic and are easily abraided off.
T/F
Gastrectomy has a greater effect on gastric stomach digestion than on intestinal digestion/absorption
False
gastrectomy often has a greater indirect effect by causing defective intestinal digestion and absorption.
The most absorption occurs in the [] []
small intestine
Usually the principle source of calories in the diet = []
carbohydrates
[] and [] are indigestible due to [] glycosidic linkages
Fiber and Cellulose are indigestible due to B-1,4 glycosidic linkages
The greatest amount of carbohydrate ingested is in the form of [].
starch
- [] are long, unbranched chains of glucose with à-1,4 linkages
- [] have multiple à-1,4 linkages with branches at []
- Amylose are long, unbranched chains of glucose with à-1,4 linkages
- Amylopectin have multiple à-1,4 linkages with branches at à-1,6
T/F
We need à-amylase for digestion?
False
It is not essential, for digestion.
Salivary à-amylase
- Secreted by the [] gland
- converts starch to [] and []
- not required, but ends up being [] of carbohydrate digestion
- Continues to work in somach fundus until []
- Secreted by the parotid gland
- converts starch to maltose and oligosaccharides
- not required, but ends up being 50% of carbohydrate digestion
- Continues to work in stomach fundus until acidified
Pancreatic à-amylase
- Identical to [] amylase
- Completes activity within 10 minuyutes after chyme enters the []
Intestinal amylase - identical to [] amylase
- Identical to salivary amylase
- Completes activity within 10 minutes after chyme enters the duodenum
Intestinal amylase - identical to salivary amylase
à-Amylase
- hydrolyzes [] linkages
- Spares [] linkages and terminal [] linkages
- hydrolyzes à 1-4 linkages
- Spares à 1-6 linkages and terminal à 1-4 linkages
- Digestion by à-Amylase results in [], [] and []-[]
Digestion by à-Amylase results in maltose, maltotriose and à-limit-dextrans
Many brush border enzymes have []-[] [] - indicating that they may hve more than one giestive activity.
Cross Over Activity
[] (or []) on the brush border only goes after à 1-6 linkages
Isomaltase (or à-dextrinase) on the brush border only goes after à 1-6 linkages
Sucrase converts Sucrose into [] and []
Sucrase converts Sucrose into glucose and Fructose
Isomaltase (à-Dextrinase) - converts [] and other branch point residues to Glucose by acting on [] glycosidic linkages…highest activity is in the [] and []
Isomaltase (à-Dextrinase) - converts Isomaltose and other branch point residues to Glucose by acting on à-1,6 glycosidic linkages…..highest activity is in the jejunum and ileum
Any enzyme that produce free glucose is considered to have [] activity
Maltase
- Maltase converts [] or [] to glucose by actin on [] glycosidic linkages
- Maltotriase converts [] to glucose by acting on (terminal) [] glycosidic linkages
- Maltase converts maltose or maltotriose to glucose by actin on à-1,4 glycosidic linkages
- Maltotriase converts maltotriose to glucose by acting on (terminal) à-1,4 glycosidic linkages
Maltase-Glucoamylase Complex
- Primarily an [] enzyme
- 2 different enzymes
- Digest either [] or [] linkages
- Exhibits [] activity
- Highest activity in the []
- Considered to be an [] (acts on terminal 1-4 linkages)
- Primarily an à-Glucosidase enzyme
- 2 different enzymes
- Digest either à 1-4 or à 1-6 linkages
- Exhibits Maltase activity
- Highest activity in the ileum
- Considered to be an exoglucosidase (acts on terminal 1-4 linkages)
B-Galactosidase (or []) acts on [] linkages, converting [] to [] and []
B-Galactosidase (or lactase) acts on B-1-4 linkages, converting lactose to glucose and galactose
- Only monosaccharides may be absorbed [] (minor component)
- Most monosaccharide absorption occurs via [] [] Trnasport mechanisms coupled thorugh the movements of []
- Only monosaccharides may be absorbed passively (minor component)
- Most monosaccharide absorption occurs via Secondary Active Trnasport mechanisms coupled through the movements of Na+
Monosaccharide Absorption
- [] and [] compete for the same active uptake system
- []/[] carriers bring in Na+ and Glucose from the lumen into the enterocyte.
- 2 Na+/[] cross the apical membrane
- [] transporter moves glucose across the basolateral membrane
- Glucose and galactose compete for the same active uptake system
-
SGLT-1/2 carriers bring in Na+ and Glucose from the lumen into the enterocyte.
- 2 Na+/glucose cross the apical membrane
- Glut-2 transporter moves glucose across the basolateral membrane
Fructose uses the [] carrier protein to cross the apical membrane of an enterocyte
GLUT-5
Exopeptidases remove one [] [] at a time from the C-terminal end
amino acid
- Pepsin is an []
- hydrolyzes [] peptide bonds
- Pepsin is an endopeptidase
- hydrolyzes interior peptide bonds
Pancreatic Proteases
- released from pancrease as inactive [] precursor
- Trypsinogen is converted to [] by [] in the brush border
- Trypsin then converts the following
- Chymotrypsinogen –> []
- Proelastase –> []
- Procarboxypeptidase –> []
- proteases [] each other as their route of inactivation
- released from pancrease as inactive zymogen precursor
- Trypsinogen is converted to trypsin by enteropeptidase in the brush border
- Trypsin then converts the following
- Chymotrypsinogen –> chymotrypsin
- Proelastase –> Elastase
- Procarboxypeptidase –> Carboxypeptidase
- proteases digest each other as their route of inactivation
Trypsin, Chymotrypsin, and Elastase are all []
endopeptidases
What are the 3 exopeptidase pancreatic enzymes?
Aminopeptidase
Carboxypeptidase A
Carboxypeptidase B
How are all amino acids absorbed through the basolateral membrane of an enterocyte?
Through some unknown carrier protein
What structure/mechanism breaks down amino acids even further once they cross the apical membrane into the enterocyte?
Lysozymes as Cytoplasmic Peptidases
- How many amino acid transporters do we find on the apical membrane of enterocytes, that need require specific “types” of amino acids?
- What molecule is coupled with amino acids for transport?
- What are the different “types” of transporters?
- 4
- Na+
- Basic Amino Acids, Neutral Amino acids, acidic amino acids, Imino Acids
- Non specific amino acids transport, located on the apical membrane of enterocytes, are coupled with [] for transport
Na+
Di and Tri peptides croos the enterocyte apical membrane through the [] transporter
Pep T1
[] is a proton and amino acid transporter located on the [] membrane of eneterocytes
hPAT-1 is a proton and amino acid transporter located on the apical membrane of eneterocytes
Duodenal receptors respond to fat by activating release of[] and neural reflex slows [] []
Duodenal receptors respond to fat by activating release of CCK and a neural reflex that slows gastric emptying
- 10% of fats within the stomach are hydrolyzed by [] []
- Its optimum pH is around [] +/- 1
- 10% of fats within the stomach are hydrolyzed by Lingual lipase
- Its optimum pH is around 5 +/- 1
Bile [] fats and lipid within the intestine
emulsifies
- Pancreatic Secretions act as detergents and enzymes in fat digestion
- [] - acts in intestine and cells
- [] & [] [] - water soluble
- Pancreatic Co-Lipase - has []activity with Pancreatic Lipase
- Pancreatic Secretions act as detergents and enzymes in fat digestion
- Phospholipase A2 - acts in intestine and cells
- Pancreatic & Intestinal Lipase - water soluble
- Pancreatic Co-Lipase - has potentiation activity with Pancreatic Lipase
Micelles
- surface covered with [] []
- Fuse with lipid bilayer of enterocyte and [] their contents into cell cytoplasma
- surface covered with bile salt
- Fuse with lipid bilayer of enterocyte and release their contents into cell cytoplasma
- Bile Salts are [] reabsorbed in the Proximal intestine
- Bile Salts are [] reabsorbed in the distal intestine
- Bile Salts are passively reabsorbed in the Proximal intestine
- Bile Salts are actively reabsorbed in the distal intestine
Steatorrhea
- Causes:
- [] deficiency - leading to a failure to emulsify fats
- Absence of pancreatic secretions like []
- [] disease
Steatorrhea
- Causes:
- Bile deficiency - leading to a failure to emulsify fats
- Absence of pancreatic secretions like lipase
- Whipples disease
