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Chapter 41

Chapter 41. Animal Nutrition. Pages 884-890. Fig. 41-1. Concept 41.3: Organs specialized for sequential stages of food processing form the mammalian digestive system.

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Chapter 41

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  1. Chapter 41 Animal Nutrition Pages 884-890

  2. Fig. 41-1

  3. Concept 41.3: Organs specialized for sequential stages of food processing form the mammalian digestive system • The mammalian digestive system consists of an alimentary canal and accessory glands that secrete digestive juices through ducts • Mammalian accessory glands are the salivary glands, the pancreas, the liver, and the gallbladder

  4. Food is pushed along by peristalsis, rhythmic contractions of muscles in the wall of the canal • Valves called sphincters regulate the movement of material between compartments

  5. Fig. 41-10a Tongue Sphincter Oral cavity Salivary glands Pharynx Esophagus Sphincter Liver Stomach Ascendingportion oflarge intestine Gall-bladder Duodenum ofsmall intestine Pancreas Smallintestine Smallintestine Largeintestine Rectum Anus Appendix Cecum

  6. Fig. 41-10b Salivaryglands Mouth Esophagus Gall-bladder Stomach Smallintestine Liver Pancreas Largeintestine Rectum Anus A schematic diagram of thehuman digestive system

  7. The Oral Cavity, Pharynx, and Esophagus • The first stage of digestion is mechanical and takes place in the oral cavity • Salivary glands deliver saliva to lubricate food • Teeth chew food into smaller particles that are exposed to salivary amylase, initiating breakdown of glucose polymers

  8. The tongue shapes food into a bolus and provides help with swallowing • The region we call our throat is the pharynx, a junction that opens to both the esophagus and the trachea (windpipe) • The trachea leads to the lungs

  9. The esophagus conducts food from the pharynx down to the stomach by peristalsis • Swallowing causes the epiglottis to block entry to the trachea, and the bolus is guided by the larynx, the upper part of the respiratory tract • Coughing occurs when the swallowing reflex fails and food or liquids reach the windpipe

  10. Fig. 41-11-1 Food Epiglottisup Tongue Pharynx Esophagealsphinctercontracted Glottis Larynx Trachea Esophagus Tolungs Tostomach

  11. Fig. 41-11-2 Food Epiglottisup Tongue Pharynx Esophagealsphinctercontracted Epiglottisdown Glottis Larynx Trachea Esophagus Esophagealsphincterrelaxed Glottis upand closed Tolungs Tostomach

  12. Fig. 41-11-3 Food Epiglottisup Tongue Epiglottisup Pharynx Esophagealsphinctercontracted Epiglottisdown Glottis Glottisdownand open Esophagealsphinctercontracted Larynx Trachea Esophagus Esophagealsphincterrelaxed Glottis upand closed Relaxedmuscles Tolungs Tostomach Contractedmuscles Relaxedmuscles Sphincterrelaxed Stomach

  13. Digestion in the Stomach • The stomach stores food and secretes gastric juice, which converts a meal to acid chyme (ingested food and digestive juice)

  14. Chemical Digestion in the Stomach • Gastric juice is made up of hydrochloric acid and the enzyme pepsin ( a protease: an enzyme that digest proteins) • pH of gastric juice is highly acidic (~2) • The ingredients of gastric juice are kept inactive until released into the lumen (cavity of the stomach) • Parietal cells secrete hydrogen and chloride ions separately • Chief cells secrete inactive pepsinogen,which is activated to pepsin when mixed with hydrochloric acid in the stomach (by clipping off a small portion and exposing its active site) • Mucus: a viscous and slippery mixture of glycoproteins, cells, salts and water. • Mucus protects the stomach lining from gastric juice as well as to acid-tolerant pathogens in food

  15. Fig. 41-12a Esophagus Sphincter Stomach Sphincter 5 µm Small intestine Folds ofepithelialtissue Interior surfaceof stomach

  16. Fig. 41-12b Interior surfaceof stomach Epithelium 3 1 Pepsinogen and HClare secreted. Pepsinogen Pepsin 2 HCl Gastric gland 2 HCl convertspepsinogen to pepsin. 1 3 Pepsin activatesmore pepsinogen. Mucus cells H+ Cl– Chief cells Chief cell Parietal cells Parietal cell

  17. Barry Marshall and Robin Warren, 1982 • Gastric ulcers, lesions in the stomach lining, are caused mainly by the bacterium Helicobacter pylori • Nobel prize in 2005

  18. Stomach Dynamics • Coordinated contraction and relaxation of stomach muscle churn the stomach’s contents • Sphincters prevent chyme from entering the esophagus and regulate its entry into the small intestine • Acid reflux: a backflow of chyme from the stomach to lower end of esophagus.

  19. Digestion in the Small Intestine • Most enzymatic hydrolysis of macromolecules from food occurs in the small intestine • The small intestine is the longest section of the alimentary canal (> 6 m) • It is the major organ of digestion and absorption

  20. Fig. 41-13 Carbohydrate digestion Protein digestion Nucleic acid digestion Fat digestion Oral cavity,pharynx,esophagus Disaccharides Polysaccharides (starch, glycogen) (sucrose, lactose) Salivary amylase Smaller polysaccharides,maltose Stomach Proteins Pepsin Small polypeptides Lumen ofsmall intes-tine DNA, RNA Fat globules Polypeptides Polysaccharides Pancreatic amylases Pancreatic trypsin andchymotrypsin Pancreatic nucleases Bile salts Maltose and otherdisaccharides Fat droplets Nucleotides Smallerpolypeptides Pancreatic lipase Pancreatic carboxypeptidase Glycerol, fattyacids, monoglycerides Amino acids Epitheliumof smallintestine(brushborder) Small peptides Nucleotidases Nucleosides Disaccharidases Dipeptidases, carboxypeptidase,and aminopeptidase Nucleosidasesandphosphatases Nitrogenous bases,sugars, phosphates Monosaccharides Amino acids

  21. Fig. 41-13a Carbohydrate digestion Polysaccharides Disaccharides (sucrose, lactose) (starch, glycogen) Oral cavity,pharynx,esophagus Salivary amylase Smaller polysaccharides,maltose Stomach Polysaccharides Lumen ofsmall intestine Pancreatic amylases Maltose and otherdisaccharides Disaccharidases Epitheliumof smallintestine(brushborder) Monosaccharides

  22. Fig. 41-13b Protein digestion Proteins Pepsin Stomach Small polypeptides Polypeptides Pancreatic trypsin andchymotrypsin Lumen ofsmall intestine Smallerpolypeptides Pancreatic carboxypeptidase Amino acids Small peptides Epitheliumof smallintestine(brushborder) Dipeptidases, carboxypeptidase,and aminopeptidase Monosaccharides Amino acids

  23. Fig. 41-13c Nucleic acid digestion DNA, RNA Pancreaticnucleases Lumen ofsmall intestine Nucleotides Nucleotidases Nucleosides Epitheliumof smallintestine(brushborder) Nucleosidasesandphosphatases Nitrogenous bases,sugars, phosphates

  24. Fig. 41-13d Fat digestion Fat globules Bile salts Lumen ofsmall intestine Fat droplets Pancreatic lipase Glycerol, fattyacids, monoglycerides

  25. The first portion of the small intestine is the duodenum, where acid chyme from the stomach mixes with digestive juices from the pancreas, liver, gallbladder, and the small intestine itself

  26. Fig. 41-14 Liver When chyme rich in fats enters the Duodenum , secretin and CCK inhibit peristalsis and acid secretion thereby slowing digestion Gallbladder Bile Stomach Circulates back to the stomach and stimulates production of gastric juices Secretinand CCK – Gastrin + CCK + Pancreas Secretin stimulates the pancreas to release sodium bicarbonate which neutralizes chyme, act as a buffer Duodenum ofsmall intestine Secretin + Amino acids or fatty acids trigger the release of cholecytokinin (CCK) which stimulates the release of enzymes from the pancreas and of bile from the gallbladder Key StimulationInhibition CCK + + –

  27. Pancreatic Secretions • The pancreas produces proteases trypsin and chymotrypsin, protein-digesting enzymes that are activated after entering the duodenum • Its solution is alkaline (rich in bicarbonate) and neutralizes the acidic chyme

  28. Bile Production by the Liver • Bile is contains bile salts which act as detergents that aid in digestion and absorption of lipids in small intestine. • Bile is made in the liver and stored and concentrated in the gallbladder • Liver breaks down toxins and helps balance nutrient utilization • Bile is important in the liver in destruction of red blood cells that are no longer functional

  29. Secretions of the Small Intestine • The epithelial lining of the duodenum, called the brush border, produces several digestive enzymes • Enzymatic digestion is completed as peristalsis moves the chyme and digestive juices along the small intestine • Most digestion occurs in the duodenum; the jejunum and ileum function mainly in absorption of nutrients and water

  30. Absorption in the Small Intestine • The small intestine has a huge surface area, due to villi (finger-like projections) and microvilli that are exposed to the intestinal lumen • The enormous microvillar surface greatly increases the rate of nutrient absorption • Surface area ~ 300 m2.

  31. Fig. 41-15a Vein carrying bloodto hepatic portal vein Muscle layers Largecircularfolds Villi Key Nutrientabsorption Intestinal wall

  32. Fig. 41-15b Microvilli (brushborder) at apical(lumenal) surface Lumen Bloodcapillaries Epithelialcells Basal surface Epithelial cells Lacteal Lymphvessel Villi Key Nutrientabsorption

  33. Each villus contains a network of blood vessels and a small lymphatic vessel called a lacteal • After glycerol and fatty acids are absorbed by epithelial cells, they are recombined into fats within these cells • These fats are mixed with cholesterol and coated with protein, forming molecules called chylomicrons, which are transported into lacteals

  34. Fig. 41-16 Triglycerides Lumenof small intestine 1. In the lumen, bile salts keep fat droplets from coalescing. Within the droplets, fats are broken down by the enzyme lipase Fatty acids Monoglycerides Epithelialcell 2. After diffusing into epithelial cells, monoglycerides and fatty acids are reformed into fats Triglycerides Phospholipids,cholesterol,and proteins 3. Triglycerides are incorporated into water-soluble globules called chylomicrons Chylomicron 4. Chylomicrons leave epithelial cells by exocytosis and enter lacteals, where they are carried away by the lymph and later pass into large veins Lacteal

  35. Amino acids and sugars pass through the epithelium of the small intestine and enter the bloodstream (by active transport) • Capillaries and veins from the lacteals converge in the hepatic portal vein and deliver blood to the liver and then on to the heart

  36. Absorption in the Large Intestine • The colon of the large intestine is connected to the small intestine • The cecum aids in the fermentation of plant material and connects where the small and large intestines meet • The human cecum has an extension called the appendix,which plays a very minor role in immunity

  37. Fig. 41-17

  38. A major function of the colon is to recover water that has entered the alimentary canal • Wastes of the digestive tract, the feces, become more solid as they move through the colon • Feces pass through the rectum and exit via the anus

  39. The colon houses strains of the bacterium Escherichia coli, some of which produce vitamins • Feces are stored in the rectum until they can be eliminated • Two sphincters between the rectum and anus control bowel movements

  40. The END

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