Digestive systemFunctions of the digestive systemGastrointestinal tract- Smooth muscleVisceral/parietal peritoneum: in-folding that suspend organs Salivary glandsTeethesophagusSmall intestinesvalvesLiverCirculation thru the digestive system Release of bilePancreasDigestive systemFunctions of the digestive system• Digestion--mechanical and chemical breakdown of material• Motility--movement of material from the oral cavity to the anus-swallowing / peristalsis• Secretion--exocrine release of enzymes into the lumen of the digestive tract for chemical digestion• Absorption--movement of material from the lumen into the blood stream• Alimentary canal or GI-tract- a continuous tube – about 30 feet in length– oral cavityÆesophagusÆstomachÆsmall intestinesÆlarge int.Æ rectum• Accessory organs- digestive organs outside of canal– communicate with GI tract via ducts– salivary glands, pancreas, liver, gallbladder, teeth, tongueGastrointestinal tract-Four layers:Tunica mucosaTunica submucosaTunica muscularis externaTunica serosa-visceral peritoneummucosasubmucosamuscularis externaserosaFig25.2• Tunica mucosa-mucus membrane= moist epithelial tissue (different types) + loose connective tissue– Folding increases surface area• Tunica submucosa-areolar connective tissue usually contains glands• Tunica muscularis externa -2 or 3 layers of smooth muscle (3 in stomach only)• Tunica serosa-connective tissue serous membrane NOT in esophagus/rectum-adventitiaSmooth muscle• No sarcomere arrangement, No striations• Many have no efferent innervation• Gap junctions, Arranged in sheets• Ability to stretch• Two forms of contraction:– Peristalsis– segmentationFig25.3PeristalsisNet movement of material towards the rectumSegmentationNo net movement of material, mixing and churningEnteric nervous system-nerves network that control digestive reflexesVisceral/parietal peritoneum: in-folding that suspend organs• Falciform ligament– connect liver to diaphragm and anterior wall• Greater omentum– fold laying over large intestines– connects the greater curvature of stomach to transverse colon– filled with fat globules and lymph nodules• lesser omentum– from liver to lesser curvature of stomach• mesentery proper– sm. intestines to posterior abdominal wall• mesocolon– suspends lg. intestines from posterior abdominal wallFig25.4Fig25.1Digestive tract & accessory organsFig25.5Fig25.5Salivary glands• Slightly different secretions• Stimulated by parasympathetic• Release enzymes• Lubrication oral cavity• Submandibular S.G.-release majority of saliva, 70%Fig25.6Teeth• Dentin of teeth is similar to the inorganic portion of bone• Only example ofgomphosis joint• Incisors-clipping/cutting• Canines-tearing/slashing• Premolars-mashing/grinding• Molars mashing/grindingFig25.7Fig25.7• 20 Deciduous teeth-baby teeth• Permanent dentition-32 adult teeth (molars)• Wisdom teeth-posterior molarsFig25.7Epiglottis closes over larynxVoluntary controlesophagus• Tunica muscularis-superior 1/3 skeletal muscle• No serosa, instead adventitiaFig25.11Tunica muscularishas three layers of muscleTunica mucosa has folds, rugaewhen emptyFig25.13Tunica mucosaTunica submucosaTunica externaTunica serosaMucous layer protects epithelia of stomach from stomach acidsG cells release hormone, GastrinFluid leaving stomach is acid chymeSmall intestines• 90 percent of nutrient absorption (most in jejunum)• Contains plicae, villi, microvilli to increase surface area• Releases hormones CCK & secretin• Lacteal absorption of lipids• mucus and buffers (neutralize acid chyme)Fig25.14Duodenum is 10 in long, Receives digestive juices from liver/pancreasjejunum is 8 ft longileum is 12 ft longPeyers patch more commonFig25.15Peyer’spatchesiliocecalvalveFig25.175 ft longLarger diameterAbsorption of vitaminsReabsorptionof water & electrolytesCompaction & storage of fecesFig25.19Tunica mucosaTunica serosaFig25.17valves• Valves regulate passage of material from segment to segment• pharynx/esophagus• Esophagus/stomach-cardiac sphincter• Stomach/small intestines-pyloric sphincter• Small/large intestines-iliocecal valve • Anus/environmentFig25.1Digestive tract & accessory organsLiver• Metabolic regulation– absorbed nutrients are further metabolized in the liver– Toxins break down – Fat soluble vitamins stored in liver• Hematological regulation– Liver receives 25% of blood from aorta – breakdown of old/damaged blood cells– Makes plasma proteins• Synthesis of bile/bile salts– Bile-pH buffer neutralize stomach acid– Bile salts-aids in breakdown of lipidsCirculation thru the digestive systemFig25.20Fig25.20Fig25.22Stores and increases the concentration of bileRelease of bile• Liver Gallbladder•Common hepatic duct Cystic duct•Common bile duct• DuodenumPancreasFig25.23Majority of pancreas has digestive (exocrine) functionReleases pancreatic juice to the duodenum via pancreatic ductMajority of chemical digestionFig25.10• <- point of release enzyme name = organ secreting enzymes• Oral cavity <--Amylase, Lipase = Salivary Glands• Oropharynx• Laryngopharynx• Esophagus• Stomach <--Pepsinogen = Chief Cells, HCL = Parietal Cells• Duodenum <--Pancreatic Juice = Pancreas• Jejunum Brush-border Enzymes = Absorptive Cells• Ileum Bile = Liver & Gallbladder• Ascending Colon• Transverse Colon• Descending Colon• Sigmoid Colon•Rectum• Anus• Inside the stomach:• Pepsinogen (inactive precursor) + HCL = Pepsin (active form)• Pancreatic Juice, Brush-border Enzymes, & Bile are released into the duodenum.FYICentral vein Sinusoid hepatic platePancreatic aciniTunica mucosaTunica submucosaTunica muscularisexternaTunica