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144 Cards in this Set
- Front
- Back
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TQ: Define Digestion
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Process in which ingested molecules are cleaved into smaller molecules by enzymes
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TQ: Define Absorption
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Transport of the molecules thru the spithelial cells of the GI tract into blood or lymph
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TQ: What organ is the MAJOR site of digestion and absorption?
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Small intestine
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What is the gross area of SI?
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2.5 m2
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What increases the absorptive surface area if SI and maximizes the ezposure of chyme to digestive enzymes and absorptive cells?
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villi and microvilli brush borders
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True of false:
Intestinal epithelial cell turnover is rapid (3-6 days) because of stem cells located in villus crypst that produce new enterocytes (digestion, absorption, secretion) and mucus secreting goblet cells |
TRUE
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List the 3 different sites of digestion
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Luminal (Cavital) Digestion
Membrane (Contact) Digestion Cytoplasmic Digestion |
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Which digestion is perfomed by digestive enzymes secreted into the GI lumen and ainly by pancreas but also stomach and salivary glands?
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Luminal (Cavital) Digestion
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Which digestion is performed by digestive enzymes bound to apical microvilli that comprise "brush border" of small intestine enterocytes?
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Membrane (Contact) Digestion
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Which digestion is performed by digestive enzymes located within the cytoplasm of small intestine enterocytes and mainly relevant to protein digestion?
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Cytoplasmic Digestion
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Enterocytes are involved which digestion?
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Both membrane and cytoplasmic digestion
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What is the primary source calories?
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Carbohydrates
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List Carbohydrates
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Plant starch
Animal Starch Dietary sugars |
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List examples of plant starch
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Amlyopectin
Amylose Cellulose |
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TQ What is Cellulose compose of?
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a B-1,3 linked glucose polymer. We cannot hydrolyze B-glycosidic linkages so cellulose remains undigested (DIETARY FIBER)
is a B 1,4 linked glucose REMAIN UNDIGESTED |
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What is Amylopectin composed of?
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large branched polymer of glucose units
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What is Amylose composed of?
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smaller version of polymer
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What is a example of animal starch?
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glycogen (animal type of sugar)
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List teh dietary sugars
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Disaccharides
Monosaccharide |
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Disachharides are composed of?
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Sucrose and lactose
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Monosaccharde is composed of?
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Glucose
Fructose Galactose |
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TQ: Starch digestion (Carbs) begins with what step?
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Starch begins with a-amylase in saliva
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Action of amylase ends with?
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LOW pH of stomach
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Where is pancreatic amylase secreted into?
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duodenum continues starch digestion and continues with brush border enzymes on the intestinal lumen of duodenum and jejunum
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TQ: Sucrose is composed of?
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glucose and fructose
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TQ: Lactose is composed of?
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glucose and galactose
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TQ: Maltase is composed of?
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2 glucose
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What carbohydrate is the ONLY one absorbed?
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Monosaccharides
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Which transport system is specific for fructose?
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GLUT 5
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Which part of the stomach has the highes absorption, and dereases progressively as we move down the intestinal tract?
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Duodenum and upper jejunum
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Which transporter system takes in Na+ and Glucose?
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SGLT1
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Which transport system takes in glucose, galactose and fructose? any of the monosaccharides
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GLUT 2
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TQ: WHAT IS the RATE limiting step for carbohydrate?
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Absorption
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What is the secondary active transport for carbs?
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Glucose and galactose
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What transport system uses facilitated diffusion- doe snot require energy BUT requires concentration gradient?
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Fructose
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What does PROTEIN provode?
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essential amino acids
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GI tract of typical American diet must process ______gm of protein per day
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90-170
Note: Most from diet, 10-30 gm from GI secretion, 10-30 from exfoliated intestinal cells |
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TQ: List what is needed for the digestion of proteins
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Endopeptidases
Exopeptidases |
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What is Endopeptidases?
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INTERIOR peptide bonds, cannot break # 1 and # 15, only break in middle
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What is EXOPEPTIDASES?
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Exterior peptide bond, can break #1 only take off end parts
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Protein digestion is ingested as large complexes (polypeptides and peptides) that must be hydrolyzed to absobable molecules by proteolytic enzyme
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TRUE
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TQ: What are the three sites of break down of large molecules?
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Luminal Digestion
Membrane Digestion Cytoplasmic Digestion |
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In luminal digestion, dietary protein digestion begins where? by denaturing actions of gastric acid and proteolytic actions of pepsin (not considered physiologically essential for protein digestion)
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stomach
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In luminal digestion, Digestion of protein into absorbable molecules occurs maily through the actions of __________________ secreted into the small intestine lumen
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PANCREATIC PEPTIDASES
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What doe the action of PANCREATIC PEPTIDASES do?
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Large peptides 4-8 AA stay
End product free AA and smal Di and Tri Peptides go across brush border membrane |
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Pancreatic Proteolytic Enzyme Activation is iniated by brush border enzyme_______
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ENTEROKINASE (also called ENTEROPEPTIDASE)
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Enterokinase first cleaves________ from the pancreatic precursor trypsinogen and forms proteolytic active trypsin.
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Hexapeptide
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Trypsin is ______________ and also converts other pancreatic protease precursors
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AUTOCATALYTIC
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How is pancreatic protease inactivation occcur?
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thorugh autodigestion or cross digestion
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Membrane Digestion are located where?
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Brush border peptidases (analogous to brush border disachhridases) are located at enterocyte apical membrane
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What does the Brush border peptidases in membrane digestion do?
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digest LARGER peptides into free amino acids and di/Tri peptides
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Where is the final product in membrane digestion processed?
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final products absorbed through membrane carriers into enterocyte
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Which digestion is intracellular and complete the protein digestion process (absent with carbohydrate digestion) by further hydrolyzing more absorbed Di/Tri Peptides into Amino Acids?
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Cytoplasmic Digestion
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What is the end product of Cytoplasmic Digestion?
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Free Amino Acids (75%)
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Free Amino Acids leave the cell and blood across the_____
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BLM, Basal lateral membrane
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True or False:
MIXTURES or Free amino acids and Di & Tripeptides are absorbed faster than either form alone? |
TRUE
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List the fats
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Dietary lipid
Triglycerideas Cholesterol Esters Phospholipids |
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What the major component of fat?
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Triglycerides
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Which type of fat is from 10-40% daily intake, fat signifcantly calorie source and largely insoluable in aqueous fluids of GI tract?
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Dietary lipid
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Which fat is comprised of three FAs esterified to glycerol and digested by pancreatic lipase into 2 FFAs and 2 minoglyceride?
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Triglycerides
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Cholesterol Esters is Cholesterol esterified to____________
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Fatty Acids
hydrolyzed by cholesterol ester hydrolase to cholesterol and FFAs. Completes TG breakdown by hydrolyzing 2 monoglyceride to glycerol and FFA |
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Which fat involve: glycerol esterided to 2 FAs and either choline (phosphatidylcholine) or inositol (phosphatidylinositol). Phosphlipiase A2 release FFAs to yield lysopholipids (Lysolecithin)
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Phosolipids (Lecithin)
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Where does lipid digestion and absorption mainly occur?
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duodenum and jejunum
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When does lipid digestion and absorption decrease?
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decrease further along jejunum
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Lipid digestion and absorption is primarily which type of fat?
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triglycerides because
NOt very soluable Must be emulsfied with bile salts in small intestine and increase the surface area available for digestion |
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TQ: What lipase is found in Oral cavity (Saliva)?
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Lingual lipase
(non esstential) |
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TQ: What lipase is found in the stomach?
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Gastric lipase
(non-essential) |
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What is the indirect action of the stomach (for lipid digestion and absorption)?
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Fat breakdown and mixing
Emulsification and increased surface area |
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What lipase is found in the Duodenum?
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Pancreatic Lipase and the stabilizer Colipase
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What is Colipase?
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No direct digestive action, "Anchors" lipase to emulsfied fat droplet
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In the duodenum, what type of fat is found 90% and is ESSENTIAL?
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FAT HYDROLYSIS
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Emulsification involves:
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Lipase digests TG (Triglycerides) to MG (Monoglyceride), FFA (free fatty acids) and glycerol
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What is Glycerol?
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small and water soluable
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where does Glycerol enter?
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eneter enterocyte and exit into blood by diffusion
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What happens to remaining products of water insoluable?
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they are slubilized and emulsified with bile satls into micelles
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How much is fat absorption?
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150-200 gms fat/day
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How much is fat excreted in the stool/day?
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3-5 excreted.
derived from unabsorbed fat and colonic bacteria and mucosal cells |
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Tryglycerides resynthesis occurs through what 2 pathways?
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monoglyceride aclation and phosphatidic acid pathways
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Resynthesizes TG is combined with: _____ to form ______________
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1) proteins
phospholipid cholesterol 2) chylomicrons |
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Chylomicrons exit enterocytes through basal membranes and enter lymph via the central lacteals present in villi.
Chylomicrons reach systemic circulation via throacic ducts. |
NOTE
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What is the Passive process driven by?
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Osmotic forces of absorbed electrolytes and other solutes
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In the GI system, water absorption is largely dependent upon what?
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water permeability of epithelial membranes and/or tight junctions along the tract.
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Water and Elctrolytes in the GI system is absorbed across the epithelia through two routes:
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Transcellular Route
Paracellular Route |
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What is the primary route used for water or electrolyte absorption and determines the relative "leakiness" or tightness of junctions. Functionally, this separate the fluid and substrate environemnts across the apical and basolateral membranes.
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Tight junctions
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How much is fluid ingested or secreted?
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9L fluid is ingested or secreted
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Where is most fluid absorbed?
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duodenum
jejunum ileum |
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Maxmimum absorptive capacity of colon _____ is larger than the fluid reabsorbed _____
Reabsorbtive capacity |
5-7 L, 1.4L
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What is the reserve absorptive capacity?
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Protects against excessive fluid and electrolytes loss when SI function is impaired.
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What is the colon incapable of absorbing?
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most nutrients (except short Free fatty acid)
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TQ: Passive Process driven by:
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Osmotic forces of absorbed electrolytes and other solutes
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Where is leaky epithelia mainly found? and which is highly permeable to water and small ions
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Small intestine
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Which route (Transcellular or Paracellular) involves solute absorption across membranes results in solute )ions) deposition whitin intercellular and subepithelial spaces, creating an osmotic driving force for water absorption
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Transcellular
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Which route (Transcellular or Paracelular) involves absorption of water also contributes to solute movement into the regions by solvent drag of small ions across the highly permeable leaky junctions
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Paracellular
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TQ: Semi-tight epithelia are mainly found in which intestine? And which are signficantly less permeable to water than leaky epithelial, resulting in almost exclusive transcellular water absorption
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Colon
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Where is all remaining sodium and chloride absorbed?
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in proximal half of colon and water follows
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SODIUM and CHLORIDE absorption occurs in what part of the intestine?
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Jejunum and ilium
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In the Basolateral membrane, what transporter will you find?
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Na+/K+ ATPase
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In the Apical Membrane, what transporter will you find?
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Na+ and Cl- transport
Nutrient Co-transport Na+/Cl- Co-transport Na+/H+ anti-porter Cl-/HCO3- anti-porter |
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Where in the intersine will you find NaCl absorption and K secretion?
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In colon
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Where is HCO3 secretion ilocated inthe stomach?
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duodenum and also lower part of intestine
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TQ: Where is K+ Absorption found?
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Small Intestine
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How is K+ absorption in Small Intestine transported?
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paracellular diffusion
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Where does K+ secretion occur?
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Colon
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Calcium Absorption Absorbed daily
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400 mg/day
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Absorption of Calcium is regulated by which hormone?
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Vita D3 and PTH
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Apical Calcium Entry
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Ca++ absorption into enterocytes by diffusion
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Basolateral Calcium Exit into body
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Active transport Ca++ ATPAse and Na+/Ca++ Exchanger
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What is the amount of Iron absorption from GI tract?
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a mg/day
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What are the two absorptive dietary forms absorbed in duodenum and upper jejunum?
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Heme Fe
Free Fe (ionized) |
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After Iron enter enterocyte, Heme Fe is bound by which enzyme?
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Heme Oxygenase
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What is the funciton of Heme Oxygenase?
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release Free Fe
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Can Vitamins be synthesized by the human body?
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No, needs to get fro diet.
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Does Vitamine require digestion by GI tract?
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No, absorbed intact, mainly in the Small intestine
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Fal Soluable Vitamins (ADEK) transport mechanism
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PAssive diffusion
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Ca+ transport mechanism
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Active
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Fe transport mechanism
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Facilitated diffusion
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Water soluable vitamins that require Na+ coupled/2 active (secondary transport)
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Vit C
Thiamin B 1 Riboflavin B2 Biotin Vit B12 Pyridoxine |
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Vit B12 use what transport system?
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Facilitated diffusion
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Pyridoxine B6 require what type of transport mechanism?
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Passive diffusion
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List the element that absorbs in teh duodenum and jejunum
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Ca+
Fe+ |
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Which Water Soluable Vitamin absorb in the ileum?
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Vit C, Vit B12
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Which Water Soluable Vitamin absorb in the Jejunum?
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Thiamin B1
Riboflavin B2 Biotin |
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Which Water Soluable Vitamin is absorbed in the Jejunum and ileum?
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Passive diffusion
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Fat Soluable Vitamins are absorbed where?
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Jejunum and ileum
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Water Soulable Vitamins are soluable where?
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Soluable in aqueous GI fluid
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Cobalamin (CBL) Vit B12 is made where?
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synthesized by microorganisms, so source is animal products (not in veggies)
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Where is CBL bound?
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CBL bound to proteins in food
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How is CBL released from proteins?
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The LOW pH of stomach causes its release from proteins
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How is CBL carried into the duodenum?
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Stomach gastric cells release HAPTOCORRIN and INTRINSIC factor (IF). CBL binds to HAPTOCORRIN which carries into duodenum.
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What can cause degradation of haptocorrin? and leads CBL to form with IF-- intrinsice factor
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Proteases from pancreas and CBL forms complex with IF
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Where is the CBL -If absorbed?
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CBL-IF travels to ileal anterocyte where it is absorbed.
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What type of molecule is fat soluable vitamins
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Hydrophobic polar molecules
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How does fat soluable vitamins delivered to the absorbing surface of intestine?
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Sequestered in micelles and delivered to surface of intestine
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Where are the largest proportion of fat soluable vitamins absorbed?
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lymph within chylomicrons
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What are the other portion of fat soluable vitamins transported as?
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intact molecules or percursor molecules
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TQ: Where is Vit K absorbed?
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intestine
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TQ: What is the transport system that Vit K use?
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active transport
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Which Vitamin is a rentinol?
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Vit A
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Vit A is ingested as what precursor?
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precursor B carotene
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What type of transport system does Vit A use?
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Concentration dependent and passive.
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Once Vit A is inside a enterocyte, what is cleaved into two vitamin A molecules?
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Once inside enterocyte, B caotene is cleaved into two vitamin A molecules.
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Vit D is similar to what other vitamin?
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Vit A
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Which Vitamin is consumed as esters that are cleaved non-specifically by cholesterol ester hydrolast prior to micelle formation or specific membrane transport
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Via D
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What is Vit E consumed as?
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esters
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