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76 Cards in this Set
- Front
- Back
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What are the major components of food?
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-Carbohydrates
-Fats -Proteins |
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What are the major and minor components carbohydrates?
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Major: Sucrose (dissacharide; cane sugar), Lactose, starches (large polysaccharides), cellulose (cannot be digested)
Minor: Amylose, glycogen, alcohol, lactic acid, pyruvic acid, pectins, and dextran |
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What are the major and minor components of fats?
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Major: Neutral Fats
Minor: Phospholipids, cholesterol, and cholesterol esters |
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What are proteins?
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Long chains of amino acids
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What is hydrolysis?
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The splitting of a compound into fragments by the addition of water, the hydroxyl group being incorporated in one fragment, and the hydrogen atom in the other.
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What does hydrolysis do?
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Takes larger molecules that are usually insoluble and too large for diffusion across membranes into the blood and breaks them down into products that are usually soluble and small enough for absorption into the blood and later assimilation into the tissues
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What are carbohydrates, proteins and fats broken down to?
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Carbohydrates --> monosaccharides
Proteins --> small peptides and amino acids Fats --> 2-monoglycerides (-->Glycerol + fatty acid) and fatty acids |
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Where does luminal digestion occur and what enzymes are involved?
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Occurs in lumen of GI tract
Enzymes from salivary glands, stomach, pancreas |
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What is membrane or contact digestion?
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Enzymes on brush border of enterocytes (intestinal absorption cell)
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What are villi?
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Epithelially covered, finger-like protrusions of the lamina propria
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What are the digestive enzymes found in the salivary glands?
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alpha-amylase
lingual lipase |
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What digestive enzymes are found in the stomach?
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Pepsin
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What enzymes are found in the pancreas?
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Amylase
Trypsin Chymotrypsin Carboxypeptidase Elastase Lipase-colipase Phospholipase A-2 Cholesterol esterase |
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What enzymes are found in the intestinal mucosa?
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Enterokinase
Sucrase Maltase Lactase alpha-dextrinase (isomaltase) amino-oligopeptidase dipeptidase |
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How is starch digested?
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-alpha-amylase in saliva
*5% in mouth *40% in stomach -pancreatic amylase in small intestine -Final digestion occurs at brush border |
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Where does lactose and sucrose absorption occur?
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Digestion only occurs at brush border
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What is ptyalin?
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Alpha-amylase (secreted by parotid glands) hydrolyzes starches into:
-disaccharide maltose -glucose polymers (3 to 9 long) |
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How long is ptyalin active in the stomach?
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Active for 1hr in stomach until pH<4
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What does pancreatic amylase do?
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Hydrolyzes starches in the duodenum, it is a heartier amylase; complete with 15-30 minutes
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What are digestion proteins called and where do they occur?
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Called proteases or peptidases
Occurs in 3 locations |
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What are the digestion proteins found in the stomach and small intestine?
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Stomach: Pepsin
Small intestine: Endopeptidases, exopeptidases |
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What are the digestion proteins found in the brush border?
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Oligopeptidases, dipeptidases
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What are the digestion proteins found in the cytoplasm of mucosal cells?
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Dipeptidases
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What is pepsin?
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Pepsin is the 1st proteolytic enzyme
Secreted by chief cells of the gastric gland Inactive above pH 5.0 Important for the digestion of collagen 10-20% of protein digestion |
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What activates and destroys proteases?
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Proteolytic enzymes are activated and destroyed very rapidly
-Enterokinase activates trypsinogen -Trypsin is autocatalytic -Trypsin activates other proenzymes -Proteolytic enzymes digest themselves |
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What is another name for enterokinase and what does it do?
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Enterokinase = enteropeptidase
Secreted from duodenum's glands, the crypts of Lieberkuhn. When food enters, activates trypsinogen to trypsin. NOT A KINASE!!!! |
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What does trypsin do?
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Converts Proenzymes to Active enzymes:
-Trypsinogen to Trypsin -Chymotrypsinoge to chymotrypsin -Proelastase to elastase -Procarboxypeptidase A to -Carboxypeptidase A -Procarboxypeptidase B to Carboxypeptidase B |
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What do endopeptidases do?
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-Cleaves the middle of the polypeptide chain
-Specific for certain amino acids |
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What do exopeptidases?
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-Removal of an amino acid from the end of the polypeptide chain.
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What does a trypsin inhibitor do?
What happens in the case of a damaged pancreas? |
Prevents activation of trypsinogen in secretory cells, acini and ducts of pancreas
A damaged pancreas overwhelms amount of inhibitor leading to acute pancreatitis |
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Where do the majority of protein digestion occur?
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In the upper small intestine
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What does elastase digest?
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Elastin fibers
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What are trypsin and chymotrypsin converted to?
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Small polypeptides
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What are carboxypeptides converted to?
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A.A. from carboxy ends of poplypeptides
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What occurs in the final stage of protein digestion?
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- Peptidases protrude through the membrane of microvilli
-Aminopolypeptidase, dipeptidases -Dipeptides, tripeptides and amino acids -Transported through membrane -Cytosolic peptidases -All amino acids within minutes pass through enterocyte and into blood |
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What are the 2 basic steps of lipid digestion?
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1) Emulsification
2) Enzymatic digestion |
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What is emulsification?
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large aggregates of dietary triglycerides are broken down
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What is enzymatic digestion?
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The yielding of monoglycerides and fatty acids - Both can diffuse into the enterocyte
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Where does essentially all fat digestion occur?
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In the small intestine
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How is fat transformed into emulsified fat?
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(Bile + agitation)
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How is emulsified fat transformed into 2-monoglycerides and fatty acids?
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Pancreatic lipase
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What doe bile salt micelles act as?
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A transport medium
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What volume does the small intestine absorb every day?
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8-9 L of fluid
30 - 35 g sodium 0.5 kg of carbs and proteins 1.0 kg of fat The majority of absorption each day occurs in the small intestine |
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What volume does the colon absorb each day?
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400 ml/day
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How much doe the folds of kerckring increase the surface area by?
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3-fold
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How much do the villi increase the surface area by?
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10-fold
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How much do the microvilli increase the surface area by?
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20-fold
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What is the increase in surface area as aided by the folds of kerckring, villi, and microvilli?
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1000-fold increase in surface area
About the size of a tennis court |
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How does water move in the small intestine?
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Water moves into or out of the gut lumen by diffusion in accordance with osmotic forces
-Hypotonic chyme (dilute) - water is absorbed -Hypertonic chyme - water enters intestinal lumen |
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How much water is needed for digestion and what are the two processes that establish an osmotic gradient?
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-Lots of water needed for digestion
-Two process establish an osmotic gradient: 1. Increased osmotic pressure resulting from digestion of foodstuffs 2. Crypt of Lieberkuhn cells actively secrete electrolytes, leading to water secretion |
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What drives the water secretion by the crypt cells?
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Chloride secretion
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What activates the Cl- channels?
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cAMP
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What follows the electrical gradient?
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Na+
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What moves along the osmotic gradient?
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Water (H2O)
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What is another name for cyclic AMP-dependent chloride channel?
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Cystic fibrosis transmembrane conductance regulator or CFTR
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What results in cystic fibrosis and what are the symptoms?
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Mutations in gene for ion channel (CFTR) result in cystic fibrosis. Failure to produce sweat, digestive juices, and mucous result
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What is sodium absorption?
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-Need to recover Sodium from intestinal secretions (30 g/day)
-Rapidly absorbed -Helps absorb sugars and a.a. |
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What are the steps of sodium absorption?
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1. Sodium actively transported across basal and basolateral membranes
2.Intracellular level falls 3. Sodium moves in through brush border 4. Osmotic gradient brings water through epithelial junctions |
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What stimulates the Na transport mechanism?
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Aldosterone (during dehydration)
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What "follows" the sodium absorption?
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Cl- absorption by diffusion
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What is digestion?
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The break down of large food molecules into smaller molecules
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What is absorption?
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The uptake of small molecules into the blood
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What happens to the absorbed molecules once the are in the blood?
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They are carried to the tissues where they are assimilated - taken in to be used.
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How are the different carbohydrates absorbed?
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-Active Transport System
-Absorbed as monosaccharides *Glucose 80% *Galactose 10% *Fructose *10% -Glucose and Galactose - Sodium co-transport -Fructose - Facilitated diffusion |
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What is the processes of carbohydrate absorption?
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-Active transporte of Na+ across the basolateral membrane depletes Na+ inside
-Na+ coupled to transport protein and glucose moves across apical membrane -REMEMBER that solute and water movements are coupled -Galactose transported identically -Fructose by diffusion; converted into glucose intracellularly |
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What is lactose intolerance?
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-Symptoms: abdominal cramps, bloating, diarrhea, and flatulence
-Diagnosis: food lactose - look for glucose in plasma -Cause: absence of brush border lactase |
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What is the treatment if there is a lack of glucose/galactose carriers?
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-Rare
-Diagnosed at birth -Feed fructose |
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How are amino acids absorbed?
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-Secondary active transport (Na+ dependent)
-Facilitated diffusion |
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How are di- and tri- peptides absorbed?
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-Different carrier system than amino acids
-Absorbed faster than amino acids -Hydrolyzed to amino acids in the cytoplasm |
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How are sugars, amino acids, electrolytes and water that are absorbed across the small intestine and colon carried to the liver?
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By the hepatic portal circulation
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What is the process of lipid absorption?
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1. Monoglycerides and fatty acids diffuse passively into enterocyte
2. Enter the smooth endoplasmic reticulum 3. Reconstituted into triglycerides 4. Transferred to Golgi; aggregate with cholesterol and phospholipids to form chylomicrons 5.Excreted by exocytosis into basolateral space 6. Pass into lacteal and into lymphatic vessels 7. Short chain fatty acids (<12 carbons), slightly soluble, diffuse across basolateral membrane into capillaries and progress to the liver for processing |
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What absorption occurs in the large intestine?
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-Reabsorbs NaCl and water
-Occurs in proximal 1/2 (absorbing colon) -Distal 1/2 (storage colon) |
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What is diarrhea?
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-The third leading cause of death by disease worldwide
-5-8 million children per year worldwide -250,000 hospital visits in US -8 million office visits in US |
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What are the common causes of diarrhea?
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-Increased secretion and/or increased motility of large or small intestine
-Infectious diarrhea - viruses, bacteria, protozoa -Ulcerative colitis -Drug related |
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What is cholera?
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-Cause - cholera toxin stimulates secretion of water and electrolytes from crypt cells - lose 10 L or more fluid per day
-Prognosis: untreated 50% will die, treated, <1% will die -Treatment: Oral rehydration solutions (glucose and electrolytes), glucose facilitated absorption of sodium and water remains intact |
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What are the mechanisms of action of the cholera toxin?
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-Cholera toxin binds GM1 ganglioside receptor triggereing endocytosis of the toxin
-Toxin cleaved -Activates the G proteins Gsalpha through an ADP-ribosylation reaction -Locks the G protein in its GTP-bound form -Continually stimulating adenylate cyclase to produced cAMP -High cAMP levels activate the cystic fibrosis transmembrane conductance regulator (CFTR) -Causing a dramatic efflux of ions and water -Result: watery diarrhea |
