Digestion And Absorption Flashcards
What does absorption of nutrients in small intestine depend on?
Intact Villous lining of small intestine
What isS on upper half of villi in small intestine?
Membrane-bound enzymes and site for absorption
What does the bottom half of villous lining do?
Secrete buffers and mucus
What is the unstirred water layer?
Slowing of laminar flow by edges of lumen with mixture of mucus secreted
What substrate does salivary amylase work on? What is its products?
Isomaltose
Maltose
What substrates do pepsin’s work on? Products?
Works on proteins and polypeptides to make smaller peptide chains (oligopeptides)
What substrate does pancreatic amylase work on? Products?
Starches to make isomaltose and maltose
What substate does enterokinase work on? Products?
Typsinogen—> trypsin
What substrate do peptidases work on? Products?
Polypeptides to make smaller peptides down to Amino acid, di and tri peptides
What substrate does maltase work on? Product?
Maltose down to glucose
What substrate does isomaltase work on? Products
Isomaltose—> glucose
What substrate does lactase work on?products
Lactose—> glu and galactose
What substrate does sucrose work on? Products?
SUCROSE—-> Glucose and fructose
What are the BB enzymes located in small intestine?
Enterokinase Peptidases Maltase Isomaltase Lactase Sucrose
Where are di and tri peptides converted to amino acids?
Inside cytoplasm of enterocyte by peptidases.
What type of carbohydrates can get into enterocyte?
Monosaccharides only!
Where does carbohydrate digestion begin?
Mouth with salivary alpha amylase Digests some carbohydrates to maltose/isomaltose (mainly maltose)
-stops digestion once food in stomach because of low pH
Where does carbohydate digestion continue after mouth?
In duodenum, pancreatic alpha amylase secreted by pancreas
-continue to break down starches to maltose/isomaltose
In small intestine, brush border enzymes continue breakdown of maltose, isomaltose, sucrose, lactose to monosaccharides (glucose, fructose, galactose)
What is absorbed via the SGLT-1 transporter on intestinal lumen?
Glucose, galactose absorbed via Glucose/Na cotransport, (also pulls in water)
What is absorbed via GLUT 5 facilitated transport on intestinal lumen?
Fructose
How are monosaccharides brought into capillaries from enterocytes?
Facilitated transport (GLUT -2)
All glucose absorption inside small intestine is ____ ____
Insulin-independent
Where does protein digestion begin?
Stomach with pepsinogen (secreted by chief cells)—> becomes pepsin by activation of HCl
What are the pancreatic proteases?
Trypsinogen
Chymotrypsinogen
Procardoxypeptidase
Typsinogen is converted to trypsin by enterokinase (BB enzyme)
Then trypsin converts chymotrypsinogen—> chymotrypsin, procarboxypeptidase—> carboxypeptidase
These break down protein—> oligopeptides
What do small intestine brush border enzymes do to proteins?
Break down oligopeptides into lots of Amino acids, di and tri peptides.
What proteins can be absorbed into enterocyte?
Amino acid, di, tri peptides
What proteins can go into capillary?
ONLY Amino acids.
Inside enterocyte, di and tri peptides are converted amino acids by peptidases in cytoplasm
How are di/tri peptides brought into enterocyte?
Facilitated transport
How are amino acids brought into enterocyte?
Facilitated transport as well as Na dependent transport
What is trypsin inhibitor?
Enzyme produced by pancrease that prevents trypsin form becoming activated in pancreas and ducts and damaging tissue.
Where does lipid digestion start?
- Mouth with lingual lipase (by von ebner’s glands)
- Begins hydrolysis of TG to diglycerides and FFA.
-This enzyme remains active in stomach
What happens to digestion of lipids in stomach?
Gastric lipase secreted by chief cells
-hydrolyzes TG to diglycerides and FFA
What happens to lipid digestion in small intestine?
Pancreatic lipase- hydrolyzes TG to monoglycerides and free fatty acids
BUT,
Needs help of colipase
Pro colipase secreted by duodenum and activated by trypsin to form colipase
What is role of micelle?
“Taxiing” lipids through unstirred water layer
What happens to lipids once inside enterocyte?
Enter smooth endoplasmic reticulum and re-esterified with FFA into TG, Phospholipids, and cholesterol esters
Form chylomicrons which exocytose from enterocyte and are absorbed into lymph
How is bile absorbed in terminal ileum?
Conjugated bile- Via secondary active transport with Na (also brings in water)
Unconjugated bile enters enterocyte through diffusion
How is Na absorbed in jejunum?
Na/K ATPase creates gradient needed for
-secondary active transport of Na into cell, either
-with sugars, amino acids.
- Na/H antiport
- NKCC-2 (Na-Cl-K cotransport)
How is iron absorbed in intestine?
Iron always has to be bound inside blood (otherwise toxic)
- Iron bound to protein can stay in cell (ferritin storage) or leave, and bind to transferrin in blood and go to liver for storage and bone marrow for use
Loose 3 mg iron everyday (from recycling enterocytes)
What does VItamin D do at enterocytes?
- Increase Ca channels at luminal wall
- Increase calbindin
- Increase Ca ATPase pump activity
What does calcium bind to once inside enterocyte?
Calbindin (this binding is increased by vitamin D)
What does binding of ca to calbindin allow?
Allows Ca gradient to continue, bringing more Ca into cell
Once in enterocyte, how does Ca go to capillary?
Ca ATPase or Ca/Na antiport
Once in blood, does calcium stay bound?
40% bound, 60% free
Not necessary to have everything bound in plasma but it is bound intracellularly
In what ways do we protect vitamin B12 as it’s going through GI system?
- In mouth, bound to TC-1 secreted by mouth. This protects B12 from pepsins in stomach
- In stomach, binds to intrinsic factor (forms B12-IF-TC-1 compounds
- TC-1 cleaved in small intestine by trypsin
- Left with B12-IF combo in small intestine. (Which is dimerized)
- This protects b12 from pancreatic lipases
- Goes to terminal ileum to be absorbed
How is b-12 absorbed at terminal ileum?
- Specific receptors that recognize B12-IF dimer and goes to transporters where absorbed
- Binds to TC-2 in enterocyte where it leaves, go to blood, goes to liver for storage or bone marrow for maturation of RBC
What stimulates Na absorption in colon?
Aldosterone
What happens if you eat a lot of fiber?
Less water will come out of chyme, softer stools
What does the increase in fluid and pressure in lower intestine from diarrhea, cause?
Increased motility and reduced absorption
What is the composition of feceS?
Water (75%)
SOlids (25%) - cellulose (variable), bacteria (30%), inorganic (15%), fat (5%)
Containers K AND HCO3
