Chapter 23 Digestive physiology

Digestive system

•nutrition = food from environment to cells

•nutrition requires :

•getting nutrientsmusculo-skeletal

•digesting nutrientsdigestive system

•transporting nutrientscirculatory system

functions

•move food

–ingestion=stuffing your mouth

–propulsionmoving food thru tract

•swallowing

•peristalsis

–egestion defectation of wastes

•digest food

–mechanical digestionphysically breaking food

•chewingteeth, tongue

•churningstomach, intestines

–chemical digestionchemically breaking food

•digestive enzymes

•absorptionget nutrients into the body

Digestive organs

•alimentary canal~gastrointestinal tract (GI)

•accessory organsaid digestion

alimentary organs

•mouth

•pharynx

•esophagus

•stomach

•small intestine

•large intestine

accessory organs

•teeth

•tongue

•salivary glands

•liver

•gallbladder

•pancreas

goals of digestion

•proteinpolypeptide  peptide  amino acids

•CHOdisaccharides  glucose ; fructose ; galactose

•lipidsfatty acids + glycerol

•nucleic acids bases + pentose sugar + PO4

enzymes for protein digestion

•protein

–pepsinprotein to polypeptidestomach

–HCldenatures proteinsstomachactivates pepsinogen

–trypsinactivates other enzymespancreas

–chymotrypsin polypeptide to peptide “

–peptidasespeptide to AAsm. intest.

•aminopeptidase

•carboxypeptidase

•dipeptidase

enzymes for carbohydrate digestion

•carbohydrate

–amylaseCHO to disaccharides saliva pancreas

–disaccharidases disaccharides to monosaccharides sm. intest

•maltasemaltose  glucose

•lactaselactose  glucose + galactose

•sucrasesucrose  glucose + fructose

–dextrinase

enzymes for lipid and nucleic acid digestion

•lipids

–bileemulsifies lipidsliver

–lipaselipid to glycerol + fatty acidspancreas

•nucleic acid

–nucleases to nucleotides pancreas

–phosphotases removes phosphate

GI hormones

•gastrin gastric activitystomach

•serotonin churningstomach

•histamine HClstomach

•somatostatin most digestive functions stomach

•secretin pancreas, bile duodenum  gastric activity

•cholecystokinin pancreas , gall bladder duodenum

•vasoactive intestinal peptide blood supply duodenum  HCl

Salivary glands

•salivasalivary amylase IgA lysozyme ; defensins mucin

•salivary glandsparotid gland sublingual gland submandibular gland

•control

–sensory:chemoreceptors ; pressoreceptors sight ; smell ; thought

–P-ANSincrease

–S-ANSdecrease ; more mucin

swallowing = deglutition

•buccal phasevoluntary

–tongue forces bolus to pharynx

•pharyngeal-esophageal phaseinvoluntary

–peristalsispharyngeal muscles esophagus

stomach processes

•secretions

–digestivepepsinogen HCl

–hormonesgastrin  all actions histamine  HCl serotonin  smooth muscle somatostatin  all actions

•absorptionaspirin , alcohol

•compacting foodchyme

•storage

stomach anatomy

•cardiac sphincter

•fundus

•body

•rugae

•pylorus

•pyloric sphincter

cells of stomach mucosa

•chief cellspepsinogen

•parietal cellsHCl instrinsic factor

•G cellsgastrin

•ECL (enterochromaffin) cellshistamine serotonin

control of stomach actions

•cephalic phasereflex from brain

•gastric phaselocal (stomach) effects

•intestinal phasecontrol from small intestine

cephalic phase

•hunger center-hypothalamus

–stim:low glucose / AA see, smell, taste, think of food

•hypothalamus to medulla

•vagus n.stim gastric glands

–NT ???

•inhibit :S-ANS (fear, anxiety, excitement)  gastric activity

•emotions ; learned behaviors

gastric phase

•stim:distension protein high pH

•controls:

–gastrin pepsinogen  HCl

–histamine HCl

–Ach  HCl(enteric ns ; vagal reflex)

•protein + pH -  gastrin -  HCl -  pH + protein

•high protein foodsincrease gastrin and HCl

•lipidsdecrease gastrin and HCl

•glucoseno effect

HCl production

•stim by :gastrinG cells Ach (vagus and enteric) histamine local mast cells

•H+CO2 + H2O  H2CO3 HCO3- + H+

•Cl-from blood

•H+H+/K+ ATPase to lumen

•Cl-diffuse to lumen

•HCO3-to blood

•alkaline tideblood from stomach is alkaline

intestinal phase

•small intestine limits gastric activity (intermittent)

•enterogastric reflexinhibits gastric activity

–inhibit P-ANS

–enterogastronesinhibit gastric secretions , motility

•secretin gastric action

•vasoactive intestinal peptide (VIP) HCl

gastric motility

•initial response to filling

–plasticitystretch-relaxation of smooth muscle

•contraction

–basic electrical rhythm (BER)3 / min

•pacemaker cells

•gap junctions

•emptying

–gastrinspeeds emptying

–enterogastronesinhibit emptying

•variesCHO empty faster than lipids or proteins

pancreas

•bicarbonatepH 8

•digestive enzymes

–trypsinogen

–chymotrypsinogen

–procarboxypeptidase

–pancreatic amylase

–lipases

–nucleases

•regulation of functions:

–secretinstim bicarbonate

–CCKstim enzymes

–vagalstim enzymes

liver and gallbladder

•bile“emulsify fats”

–bile saltscholic acid (cholesterol derivative)

–bilirubinwaste product of heme

•excreted as urobilinogen ( feces , urine)

–toxin, drug byproducts

•enterohepatic circulation

•stim by secretin

•gallbladderstores bile

–CCKgallbladder contraction relaxes hepatopancreatic sphincter

small intestine anatomy

•duodenum

–hepatopancreatic ampulla

•jejunum

•ileum

–ileocecal valve

•brush border

small intestine digestion

•most digestion and absorption occurs here

•brush border enzymes

–disaccharidasesmaltase, sucrase, lactase

–dextrinase

–glucoamylase

–peptidasesaminopeptidase, carboxypeptidase

–nucleases , phosphotases

–enteropeptidase

•pancreatic juice

•bile

small intestine – other processes

•hormonessecretin CCK somatostatin VIP

•peristalsis

•segmentationpacemaker cells ANS

•gastroileal reflexgastrin relaxes ileocecal valve

large intestine anatomy

• = colon

•ascending colon

–cecum

–appendix

•transverse colon

•descending colon

•sigmoid colon

•rectum

large intestine

•absorption

–water

–vitamins

–electrolytes

•bacterial florae. coli

–Vitamin K

–folic acid

•peristalsis

•gastrocolic reflex

•defecation

digestion review:

•know:

•digestion by area

–what enzyme is made where

–location of action

•digestion by food type

•absorption

absorption

•lumen to bloodtransepithelial transport

•stomachaspirin, alcohol, small peptides?

•small intestineall biochemicals most water electrolytes vitamins bile salts , urobilinogen

•large intestineremaining water electrolytes Vitamin K, folic acid

absorption of CHO

•monosaccharides

•into epithelium

–facilitated diffusion

–secondary active transport

•to blood

–facilitated diffusion

absorption of proteins

•amino acids

–into epithelium

•secondary active transport

–to blood

•active transport

•dipeptides

•secondary active transportcarrier facilitated

•whole peptidesendocytosisinfants only

absorption of lipids

•products of digestionglycerol fatty acids cholesterol fat soluble vitamins

•into epitheliumdiffusion

•chylomicronsreassembled TRIGs

•into lactealsdiffusion

•lipoproteinsfor transport in blood

–LDLto organs, blood vessels

–HDLto liver

absorption of nucleic acids

•products of digestionnitrogenous bases

•into epitheliumactive transport

•to blooddiffusion

absorption of Vitamins

•water solubleB, C,

–diffusion

•vitamin B12endocytosis requires intrinsic factor

•to blooddiffusion

absorption of electrolytes

•Na+diffusion ; active transport

–Na / K pumps

–also stim by Aldosterone

•K+diffusion

•Cl-diffusion

•Ca++diffusion

–Vitamin Dincrease absorption

– PTHincrease absorption

•Fe++active transport

–ferritin dependent

•anionsdiffusion

absorption of water

•9 L enter small intestine daily

•3 L gastric juices

•1-2 L pancreas

•1-2 L small intestine

•3-5 L food and drinks

•95% absorbed in small intestine

•osmosis

–after Na active transport