physiology of absorption
Post on 06-Jan-2016
35 Views
Preview:
DESCRIPTION
TRANSCRIPT
© 2004, 2002 Elsevier Inc. All rights reserved.
Physiology Physiology of of
absorptionabsorption
Digestive SystemDigestive System
Reduces particle sizeReduces particle size Helps to absorb micronutrients Helps to absorb micronutrients
and trace elementsand trace elements Sets a physical and immunologic Sets a physical and immunologic
barrierbarrier
DigestionDigestion
Breaks downBreaks down Carbohydrates (starch and sugar) Carbohydrates (starch and sugar)
→→ single sugar molecules single sugar molecules Proteins Proteins → amino acids→ amino acids Fats → fatty acids, glycerolFats → fatty acids, glycerol
EnzymesEnzymes
Proteins Proteins that break that break bondsbonds
The Digestive SystemThe Digestive System
Is a long tube Is a long tube from the from the mouth to the mouth to the anusanus
Digestive SystemDigestive System
Mouth to anusMouth to anus– Epithelium lines the lumenEpithelium lines the lumen– Barrier to invadersBarrier to invaders– Submucosal layerSubmucosal layer– Muscularis Muscularis
Taste and smellTaste and smell
PeristalsisPeristalsis
Muscular Muscular contractions contractions that move food that move food along along throughout GI throughout GI tracttract
The MouthThe Mouth
Mastication: chewingMastication: chewing SalivaSaliva
– Salivary glands produce about 1.5 liters of Salivary glands produce about 1.5 liters of saliva dailysaliva daily
– Salivary amylase (ptyalin) begins to break Salivary amylase (ptyalin) begins to break down starch (inactivated in the stomach)down starch (inactivated in the stomach)
– Salivary lipase: begins fat digestion, but has Salivary lipase: begins fat digestion, but has minimal effectminimal effect
– Mucus to lubricate the food for easier Mucus to lubricate the food for easier swallowingswallowing
– Lysozyme to kill bacteria Lysozyme to kill bacteria
TongueTongue– Taste receptors: sweet, sour, salty, Taste receptors: sweet, sour, salty,
bitter, savorybitter, savory– Enzymes to help break down fatty acidsEnzymes to help break down fatty acids
SwallowingSwallowing Bolus is the food swallowed at one Bolus is the food swallowed at one
timetime Epiglottis blocks windpipe, prevents Epiglottis blocks windpipe, prevents
chokingchoking
The EsophagusThe Esophagus
Long tubeLong tube Connects pharynx Connects pharynx
to the stomachto the stomach Peristalsis, Peristalsis,
muscle muscle contractioncontraction
Lower esophageal Lower esophageal sphinctersphincter
HeartburnHeartburn
http://www.gerd.com/media/grossovw.gif
The StomachThe Stomach
Lower esophageal sphincter and Lower esophageal sphincter and pyloric sphincter control entry and exit pyloric sphincter control entry and exit from stomachfrom stomach
Storage capacity of ~4 cupsStorage capacity of ~4 cups Secretion of hydrochloric acid, Secretion of hydrochloric acid,
enzymes, including a protease, gastric enzymes, including a protease, gastric lipase; mucus, the hormone gastrin, lipase; mucus, the hormone gastrin, and intrinsic factor (B12)and intrinsic factor (B12)
Stomach secretes about 2000-2500 ml Stomach secretes about 2000-2500 ml of gastric juice dailyof gastric juice daily
StomachStomach
pH of stomach is low, 1 to 4; kills many pH of stomach is low, 1 to 4; kills many bacteria and micro-organismsbacteria and micro-organisms
Achlorhydria, gastrectomy, GI Achlorhydria, gastrectomy, GI dysfunction or disease dysfunction or disease ↑ risk of ↑ risk of bacterial overgrowth in the intestinesbacterial overgrowth in the intestines
Protein digestion begins with Protein digestion begins with pepsinogen which is converted to active pepsinogen which is converted to active pepsin in acidic stomach environmentpepsin in acidic stomach environment
Chief cells secrete acid-stable gastric Chief cells secrete acid-stable gastric lipase, which has minor effect on lipase, which has minor effect on shorter-chain triglyceridesshorter-chain triglycerides
StomachStomach
Most of a liquid meal exits in 1 to Most of a liquid meal exits in 1 to 2 hours and most of a solid meal 2 hours and most of a solid meal in 2 to 3 hoursin 2 to 3 hours
Formation of chymeFormation of chyme Mucus layer protects stomach Mucus layer protects stomach
from digestionfrom digestion Very little absorption of nutrientsVery little absorption of nutrients
Physiology of the Physiology of the Stomach Stomach
Stomach AcidStomach Acid
Activates digestive enzymesActivates digestive enzymes Partially digests dietary proteinPartially digests dietary protein Assists in calcium absorptionAssists in calcium absorption Makes dietary minerals soluble for Makes dietary minerals soluble for
absorptionabsorption
The Small IntestineThe Small Intestine
Most digestion and absorption Most digestion and absorption happens herehappens here
About 5-7 metersAbout 5-7 meters– Duodenum (.5 meters)Duodenum (.5 meters)– Jejunum (2-3 meters)Jejunum (2-3 meters)– Ileum (3-4 meters)Ileum (3-4 meters)
The Small IntestineThe Small Intestine
Folded walls with villi projectionsFolded walls with villi projections Absorptive cells are located on Absorptive cells are located on
the villithe villi Increases intestinal surface area Increases intestinal surface area
600x 600x Rapid cell turnoverRapid cell turnover
The Small IntestineThe Small Intestine
Nutrient AbsorptionNutrient Absorption Passive diffusion: driven by Passive diffusion: driven by
concentration; fats, water, some concentration; fats, water, some mineralsminerals
Active absorption: uses energy; Active absorption: uses energy; glucose and amino acidsglucose and amino acids
Phagocytosis and pinocytosis: Phagocytosis and pinocytosis: absorptive cells engulf compounds, absorptive cells engulf compounds, generally larger molecules, as in generally larger molecules, as in immune substances in breast milkimmune substances in breast milk
Determine of notion Determine of notion “absorption”“absorption” Absorption is a complex of Absorption is a complex of
processes, which are provide processes, which are provide transport of substances from transport of substances from digestive tract into internal digestive tract into internal surroundings of organism (blood, surroundings of organism (blood, lymph, intercellular substanceslymph, intercellular substances))
Nutrient AbsorptionNutrient Absorption
Site of AbsorptionSite of Absorption
AbsorptionAbsorption
Digestion Digestion → small particles→ small particles
End products of digestion:End products of digestion: Carbohydrates → Carbohydrates →
monosaccharidesmonosaccharides Proteins → amino acidsProteins → amino acids Fats → glycerol, fatty acidsFats → glycerol, fatty acids
AbsorptionAbsorption
Through small intestine wallsThrough small intestine walls
Absorbed intoAbsorbed into Blood – water soluble nutrientsBlood – water soluble nutrients Lymph – fat soluble nutrientsLymph – fat soluble nutrients
Blood Blood → liver → general circulation→ liver → general circulation– Liver detoxifies and repackagesLiver detoxifies and repackages
The Large IntestineThe Large Intestine
~3 1/2 feet in length~3 1/2 feet in length No villi or enzymes presentNo villi or enzymes present Little digestion occursLittle digestion occurs Absorption of water, some Absorption of water, some
minerals, vitaminsminerals, vitamins Bacteria break down fiber; produce Bacteria break down fiber; produce
Vitamin KVitamin K Formation of feces for eliminationFormation of feces for elimination
RectumRectum
Stool remainsStool remains Stimulates Stimulates
eliminationelimination Muscle Muscle
contractioncontraction Anal sphinctersAnal sphincters
– Voluntary controlVoluntary control– Opens for Opens for
eliminationelimination
Accessory OrgansAccessory Organs
Salivary glandsSalivary glands PancreasPancreas GallbladderGallbladder LiverLiver
Salivary GlandsSalivary Glands
SalivaSaliva Works in mouthWorks in mouth MoistensMoistens Salivary amylaseSalivary amylase
– Digests starchDigests starch
The PancreasThe Pancreas
Produces glucagon and insulin Produces glucagon and insulin (endocrine)(endocrine)
Manufactures digestive enzymesManufactures digestive enzymes→ → small intestinesmall intestine
Secretes pancreatic juicesSecretes pancreatic juices Bicarbonate needed to neutralize Bicarbonate needed to neutralize
chyme when it enters small chyme when it enters small intestineintestine
The LiverThe Liver
Produces bile (fat digestion)Produces bile (fat digestion) Enterohepatic circulationEnterohepatic circulation
The GallbladderThe Gallbladder
Stores bileStores bile Concentrates itConcentrates it Releases to Releases to
small intestine small intestine when neededwhen needed
The Digestive SystemThe Digestive System
Sites of Secretion, Digestion, Sites of Secretion, Digestion, and Absorptionand Absorption
Digestion in the Digestion in the StomachStomach Different nutrients leave the Different nutrients leave the
stomach at different rates: stomach at different rates: ——Carbohydrates first, followed by Carbohydrates first, followed by
protein, protein, fat, and fibrous foods fat, and fibrous foods
Summary of Enzymatic Summary of Enzymatic Digestion and Digestion and AbsorptionAbsorption
SecretioSecretionn
EnzymeEnzyme SubstratSubstratee
ActionAction Final Final ProducProductt
SalivaSaliva PtyalinPtyalin StarchStarch Hydrolysis Hydrolysis to form to form dextrinsdextrins
Gastric Gastric juicejuice
PepsinPepsin ProteinProtein Hydrolysis Hydrolysis of peptide of peptide bondsbonds
Gastric Gastric lipaselipase
FatsFats Hydrolysis Hydrolysis into free into free fatty acidsfatty acids
Summary of Enzymatic Summary of Enzymatic Digestion and Digestion and Absorption Absorption —cont’d—cont’d
SecretioSecretionn
EnzymeEnzyme SubstratSubstratee
ActionAction Final Final ProducProductt
Pancreatic Pancreatic exocrine exocrine secretionsecretion
LipaseLipase FatFat Hydrolysis Hydrolysis to mono-to mono-glyceridesglycerides
Fatty Fatty acidsacids
CholesterCholesterol ol esteraseesterase
CholesterolCholesterol Hydrolysis Hydrolysis to esters of to esters of cholesterol cholesterol and fatty and fatty acidsacids
Choles-Choles-terolterol
alpha-alpha-AmylaseAmylase
Starch, Starch, dextrinsdextrins
HydrolysisHydrolysis Dextrin, Dextrin, maltosemaltose
Summary of Enzymatic Summary of Enzymatic Digestion and Digestion and Absorption Absorption —cont’d—cont’d
SecretioSecretionn
EnzymeEnzyme SubstratSubstratee
ActionAction Final Final ProductProduct
Pancreatic Pancreatic exocrine exocrine secretionsecretion
TrypsinTrypsin ProteinProtein HydrolysHydrolysisis
PolypeptidPolypeptideses
ChymotrypChymotrypsinsin
ProteinProtein HydrolysHydrolysisis
PolypeptidPolypeptideses
Carboxy-Carboxy-peptidasepeptidase
Polypep-Polypep-tidestides
HydrolysHydrolysisis
Amino Amino acidsacids
RibonucleaRibonucleasese
Ribonu-Ribonu-cleic acidscleic acids
HydrolysHydrolysisis
Mono-Mono-nucleotidesnucleotides
ElastaseElastase Fibrous Fibrous proteinprotein
HydrolysHydrolysisis
Amino Amino acidsacids
Summary of Enzymatic Summary of Enzymatic Digestion and Digestion and Absorption Absorption —cont’d—cont’d
SecretionSecretion EnzymeEnzyme SubstratSubstratee
ActionAction Final Final ProductProduct
Brush Brush border border enzymesenzymes
Carboxy-Carboxy-peptidase; peptidase; aminopep-aminopep-tidase; tidase; dipeptidasdipeptidasee
Polypep-Polypep-tidestides
HydrolysiHydrolysiss
Amino Amino acidsacids
Entero-Entero-kinasekinase
Trypsino-Trypsino-gengen
Activates Activates to trypsinto trypsin
Polypep-Polypep-tidases tidases and and peptidespeptides
SucraseSucrase SucroseSucrose HydrolysiHydrolysiss
Glucose, Glucose, fructosefructose
Enzymatic Digestion and Enzymatic Digestion and AbsorptionAbsorption —cont’d—cont’d
SecretioSecretionn
EnzymeEnzyme SubstrateSubstrate ActionAction Final Final ProductProduct
Brush Brush border border enzymesenzymes
IsomaltaseIsomaltase DextrinDextrin HydrolysiHydrolysiss
GlucoseGlucose
MaltaseMaltase MaltoseMaltose HydrolysiHydrolysiss
GlucoseGlucose
LactaseLactase LactoseLactose HydrolysiHydrolysiss
Glucose, Glucose, galactosegalactose
NucleotidaseNucleotidasess
Nucleic acidNucleic acid HydrolysiHydrolysiss
NucleotideNucleotidess
NucleosidasNucleosidases and es and phosphorylaphosphorylasese
NucleosidasNucleosidaseses
HydrolysiHydrolysiss
Purine and Purine and pyrimidine pyrimidine basesbases
Features of Digestion Features of Digestion and Absorptionand Absorption 92% to 97% of the diet is 92% to 97% of the diet is
absorbedabsorbed Small intestine—key role in Small intestine—key role in
digestion and absorptiondigestion and absorption Intestines: 7 meters longIntestines: 7 meters long
——Villi and microvilli/brush borderVilli and microvilli/brush border
Villi of the Human IntestineVilli of the Human Intestine
Refeeding after Refeeding after StarvationStarvation GI tract compromised after GI tract compromised after
starvationstarvation Feeding results in cellular Feeding results in cellular
proliferation, which restores proliferation, which restores normal gastrointestinal normal gastrointestinal architecture and function after a architecture and function after a few daysfew days
LipidsLipids
The major portion of fat digestion The major portion of fat digestion takes place in the small intestine takes place in the small intestine as a result of pancreatic lipaseas a result of pancreatic lipase
Summary of Fat AbsorptionSummary of Fat Absorption
Transport Pathways through the Cell Transport Pathways through the Cell MembraneMembrane
Large IntestineLarge Intestine
5 feet long5 feet long Bacterial action to produce gases Bacterial action to produce gases
and organic acidsand organic acids Nutrients formed here—vitamin K, Nutrients formed here—vitamin K,
thiamin, vitamin B12, riboflavinthiamin, vitamin B12, riboflavin
The Gradual Breakdown of The Gradual Breakdown of Large Starch MoleculesLarge Starch MoleculesThe Gradual Breakdown of The Gradual Breakdown of Large Starch MoleculesLarge Starch Molecules
Process of Digestion of Process of Digestion of CarbohydrateCarbohydrate
Sites of Secretion and Absorption Sites of Secretion and Absorption into Gastrointestinal Tractinto Gastrointestinal Tract
NeurotransmittersNeurotransmitters
Alpha-aminobutyric acid: relaxes LESAlpha-aminobutyric acid: relaxes LES Norepinephrine: decreases motility, Norepinephrine: decreases motility,
increases contractions of sphincters, increases contractions of sphincters, inhibits secretionsinhibits secretions
Acetylcholine: increases motility, Acetylcholine: increases motility, relaxes sphincters, stimulates secretionsrelaxes sphincters, stimulates secretions
Neurotensin: inhibits release of gastric Neurotensin: inhibits release of gastric emptying and acid secretionemptying and acid secretion
Neuropeptide-Y: stimulates feeding Neuropeptide-Y: stimulates feeding behaviorbehavior
Hormones and GI Hormones and GI Function: GastrinFunction: Gastrin Released from gastric mucosa Released from gastric mucosa
and duodenum in presence of and duodenum in presence of peptides and amino acids; peptides and amino acids; stimulates secretion of stimulates secretion of hydrochloric acid and hydrochloric acid and pepsinogen; increases gastric pepsinogen; increases gastric antral motility, increases LES antral motility, increases LES tonetone
Hormones and GI Hormones and GI function: Secretinfunction: Secretin Secretin: from duodenal mucosa Secretin: from duodenal mucosa
in presence of acid in small in presence of acid in small intestine; stimulates pancreas to intestine; stimulates pancreas to secrete water and bicarb; also secrete water and bicarb; also insulin and pancreatic enzymesinsulin and pancreatic enzymes
Hormones and GI Hormones and GI function: Cholecystokinin function: Cholecystokinin (CCK)(CCK) Released from proximal small Released from proximal small
bowel in presence of peptices, bowel in presence of peptices, amino acids, fat, HCL, stimulates amino acids, fat, HCL, stimulates pancreas to release pancreatic pancreas to release pancreatic enzymesenzymes
Hormones and GI Hormones and GI function: Gastric function: Gastric Inhibitory Polypeptide Inhibitory Polypeptide (GIP)(GIP) Released from small intestine in Released from small intestine in
presence of glucose and fat; presence of glucose and fat; inhibits gastrin-stimulated release inhibits gastrin-stimulated release of gastric acidof gastric acid
Hormones and GI Hormones and GI Function (Motilin)Function (Motilin) Released from stomach and small Released from stomach and small
and large intestine in presence of and large intestine in presence of biliary and pancreatic secretions; biliary and pancreatic secretions; promotes gastric emptying and promotes gastric emptying and increases GI motility increases GI motility
Hormones and GI Hormones and GI function: Somatostatinfunction: Somatostatin Released from stomach, Released from stomach,
pancreas, and upper small pancreas, and upper small intestine in presence of acidity intestine in presence of acidity and products of protein and fat and products of protein and fat digestion; inhibits release of digestion; inhibits release of gastrin, motilin, and pancreatic gastrin, motilin, and pancreatic secretions; decreases motility of secretions; decreases motility of GI tractGI tract
Digestion and Digestion and AbsorptionAbsorption It’s important to know the It’s important to know the
physiology and function of the GI physiology and function of the GI tract in order to understand the tract in order to understand the implications of pathophysiologyimplications of pathophysiology
top related