PTA 106 Unit 2 Lecture 3. 25-2 Digestive Functions Ingestion intake of food Digestion breakdown of...
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Transcript of PTA 106 Unit 2 Lecture 3. 25-2 Digestive Functions Ingestion intake of food Digestion breakdown of...
![Page 1: PTA 106 Unit 2 Lecture 3. 25-2 Digestive Functions Ingestion intake of food Digestion breakdown of molecules Absorption uptake nutrients into blood/lymph.](https://reader031.fdocuments.us/reader031/viewer/2022032523/56649d845503460f94a6b560/html5/thumbnails/1.jpg)
PTA 106Unit 2 Lecture 3
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25-2
Digestive Functions
Ingestion intake of food
Digestion breakdown of molecules
Absorption uptake nutrients into blood/lymph
Defecation elimination of undigested material
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25-3
Stages of Digestion
• Mechanical digestion – physical breakdown of food into smaller particles– teeth and churning action of stomach and intestines
• Chemical digestion – series of hydrolysis reactions that break macromolecules into
their monomers– enzymes from saliva, stomach, pancreas and intestines– results
• polysaccharides into monosaccharides• proteins into amino acids• fats into glycerol and fatty acids
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Figure 25.1
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25-5
Subdivisions of Digestive System
• Digestive tract (GI tract)– 30 foot long tube
extending from mouth to anus
• Accessory organs– teeth, tongue, liver,
gallbladder, pancreas, salivary glands
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25-6
Lesser and Greater Omentum
• Lesser - attaches stomach to liver• Greater - covers small intestines like an apron
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25-8
Stomach
• Mechanically breaks up food, liquifies food and begins chemical digestion of protein and fat– resulting soupy mixture is called chyme
• Does not absorb significant amount of nutrients– absorbs aspirin and some lipid-soluble drugs
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25-9
Gross Anatomy of Stomach
• Muscular sac (internal volume from 50ml to 4L)– J - shaped organ with lesser and greater curvatures– regional differences• cardiac region just inside cardiac orifice• fundus - domed portion superior to esophageal opening• body - main portion of organ• pyloric region - narrow inferior end
– antrum and pyloric canal
• Pylorus - opening to duodenum– thick ring of smooth muscle forms a sphincter
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25-10
Gross Anatomy of Stomach
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25-11
Liver, Gallbladder and Pancreas
• All release important secretions into small intestine to continue digestion
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25-12
Gross Anatomy of Liver• 3 lb. organ located inferior to the diaphragm• 4 lobes - right, left, quadrate and caudate– falciform ligament separates left and right– round ligament, remnant of umbilical vein
• Gallbladder adheres to ventral surface between right and quadrate lobes
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25-13
Ducts of Gallbladder, Liver, Pancreas
• Bile passes from bile canaliculi between cells to bile ductules to right and left hepatic ducts
• Right and left ducts join outside liver to form common hepatic duct
• Cystic duct from gallbladder joins common hepatic duct to form bile duct
• Duct of pancreas and bile duct combine to form hepatopancreatic ampulla emptying into duodenum at major duodenal papilla– sphincter of Oddi (hepatopancreatic sphincter) regulates
release of bile and pancreatic juice
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25-14
Ducts of Gallbladder, Liver, Pancreas
• Bile passes from bile canaliculi between cells to bile ductules to right and left hepatic ducts
• Right and left ducts join outside liver to form common hepatic duct
• Cystic duct from gallbladder joins common hepatic duct to form bile duct
• Duct of pancreas and bile duct combine to form hepatopancreatic ampulla emptying into duodenum at major duodenal papilla– sphincter of Oddi (hepatopancreatic sphincter) regulates
release of bile and pancreatic juice
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25-15
Small Intestine
• Nearly all chemical digestion and nutrient absorption occurs in small intestine
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25-16
Small Intestine
• Duodenum curves around head of pancreas (10 in.)
– retroperitoneal along with pancreas– receives stomach contents, pancreatic juice and bile– neutralizes stomach acids, emulsifies fats, pepsin inactivated by
pH increase, pancreatic enzymes
• Jejunum - next 8 ft. (in upper abdomen)– has large tall circular folds; walls are thick, muscular– most digestion and nutrient absorption occur here
• Ileum - last 12 ft. (in lower abdomen)– has peyer’s patches – clusters of lymphatic nodules– ends at ileocecal junction with large intestine
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Water Balance
• Digestive tract receives about 9 L of water/day– .7 L in food, 1.6 L in drink, 6.7 L in secretions– 8 L is absorbed by small intestine and 0.8 L by large intestine
• Water is absorbed by osmosis following the absorption of salts and organic nutrients
• Diarrhea occurs when too little water is absorbed– feces pass through too quickly if irritated– feces contains high concentrations of a solute (lactose)
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25-18
Anatomy of Large Intestine
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Gross Anatomy of Large Intestine
• 5 feet long and 2.5 inches in diameter in cadaver• Begins as cecum and appendix in lower right
corner• Ascending, transverse and descending colon
frame the small intestine• Sigmoid colon is S-shaped portion leading down
into pelvis• Rectum - straight portion ending at anal canal
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Absorption and Motility
• Transit time is 12 to 24 hours– reabsorbs water and electrolytes
• Feces consist of water and solids (bacteria, mucus, undigested fiber, fat and sloughed epithelial cells
• Haustral contractions occur every 30 minutes– distension of a haustrum stimulates it to contract
• Mass movements occur 1 to 3 times a day– triggered by gastrocolic and duodenocolic reflexes
• filling of the stomach and duodenum stimulates motility• moves residue for several centimeters with each contraction
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25-21
Anatomy of Anal Canal
• Anal canal is 3 cm total length• Anal columns are longitudinal ridges separated by
mucus secreting anal sinuses• Hemorrhoids are permanently distended veins