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DIGESTIVE SYSTEM and NUTRITION
Chapter 33
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Video: Homeostasis
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Overview: The Need to Feed
Food is taken in, taken apart, and taken up in the process of animal nutrition In general, animals fall into three categories Herbivores Carnivores Omnivores Most animals are also opportunistic feeders 3
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Figure 33.1. How does a fish help a bear make fat?
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Hominids, Hips and Hunger
IMPACTS, ISSUES VIDEO Hominids, Hips and Hunger
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Adipose cells are fat-storing cells
Adipose cells produce leptin helps to control hunger Ghrelin produced by stomach makes you feel hungry Obesity is overabundance of fat in adipose tissue Obese people do not have less leptin than normal, but leptin receptors may not work properly Cholecystokinin may promote appetite suppression
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Fighting Fat Fat-storing cells are an adaptation for survival in lean times Once formed, fat cells are forever Dieting decreases amount of fat in cells Dieting triggers metabolic slowdown
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BODY-MASS INDEX ----------------------------- Height (inches)2
An indicator of obesity-related health index BMI = Weight (lbs) X 700 Height (inches)2 BMI greater than or equal to 27 indicates health risk 8
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Body-Mass Index Body mass index 9
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Ideal Weights Fig , p.734 10
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Caloric requirements Caloric requirements 11
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Digestive System Functions
Ingestion Substrate feeders Fluid feeders Filter feeders Bulk feeders
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MAINTAINING WEIGHT Caloric input must equal caloric use
Calories burned depends upon Activity level Age Height and build 13
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Digestion Mechanical Chemical digestion mixing and propelling movements intracellular digestion food particles are engulfed by phagocytosis food vacuoles, containing food, fuse with lysosomes containing hydrolytic enzymes extracellular digestion breakdown of food particles outside of cells occurs in compartments reduce the risk of an animal digesting its own cells and tissues gastrovascualr cavity alimentary canal
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Crop Esophagus Gizzard Intestine Pharynx Anus Mouth (a) Earthworm
Foregut Midgut Hindgut Esophagus Crop Esophagus Rectum Stomach Figure 33.7 Variation in alimentary canals Gizzard Anus Intestine Mouth Anus Crop Mouth Gastric cecae (b) Grasshopper (c) Bird 15
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Small intestine Small intestine Stomach Cecum Colon (large Intestine)
Figure The alimentary canals of a carnivore (coyote) and herbivore (koala) Colon (large Intestine) Carnivore Herbivore 16
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Absorption Elimination
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Nutrient molecules enter body cells Mechanical digestion Chemical
(enzymatic hydrolysis) Undigested material Figure 33.4 The four stages of food processing 1 Ingestion 2 Digestion 3 Absorption 4 Elimination 18
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Incomplete digestive system One-way, saclike digestive cavity
TWO TYPES OF SYSTEMS Incomplete digestive system One-way, saclike digestive cavity Complete digestive system A tube with an opening at each end
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HUMAN DIGESTIVE SYSTEM
A complete system with many specialized organs About 6.5 to 9 meters long if extended Lined with mucus-secreting epithelium Movement is one way, from mouth to anus
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MAJOR COMPONENTS Mouth (oral cavity) Pharynx (throat) Esophagus Gut
Stomach Small intestine Large intestine Rectum Anus
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ACCESSORY ORGANS Salivary glands Pancreas Liver Gallbladder
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Duodenum of small intestine
Tongue Oral cavity Salivary glands Mouth Pharynx Salivary glands Esophagus Esophagus Stomach Liver Gallbladder Sphincter Small intestine Gall- bladder Liver Sphincter Pancreas Large intestine Pancreas Figure 33.8 The human digestive system Stomach Small intestine Rectum Anus Large intestine Duodenum of small intestine Rectum Anus 23
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Human digestive system
Human Digestion Human digestive system
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SALIVA Produced by salivary glands at back of mouth and under tongue
Saliva includes Salivary amylase Bicarbonate buffer Mucins bind food into bolus Water
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SWALLOWING Complex reflex Tongue forces food into pharynx
Epiglottis and vocal cords close off trachea breathing temporarily ceases Bolus moves into esophagus moves through esophagus by muscular contractions peristalsis then through esophageal / cardiac sphincter into stomach
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STRUCTURE OF THE STOMACH
J-shaped organ lies below the diaphragm Sphincters at both ends Outer serosa covers smooth muscle layers Inner layer of glandular epithelium faces lumen sphincters serosa muscle mucosa
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STOMACH SECRETIONS Secreted into lumen (gastric fluid)
Hydrochloric acid secreted from parietal cells Mucus protective Pepsinogen secreted from chief cells inactive form of a protein-digesting enzyme Stomach cells also secrete the hormone gastrin into the bloodstream stimulates HCL and pepsinogen secretion
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Production of gastric juice Pepsinogen Pepsinogen and
1 Pepsinogen and HCI secreted into lumen HCI Chief cell 1 H Cl− Parietal cell Figure 33.9b-1 The stomach and its secretions (part 2, step 1) 30
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Production of gastric juice Pepsinogen Pepsin (active enzyme)
2 1 Pepsinogen and HCI secreted into lumen HCI Chief cell 1 2 HCI converts pepsinogen to pepsin. H Cl− Parietal cell Figure 33.9b-2 The stomach and its secretions (part 2, step 2) 31
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Production of gastric juice Pepsinogen Pepsin (active enzyme)
3 Production of gastric juice Pepsinogen Pepsin (active enzyme) 2 1 Pepsinogen and HCI secreted into lumen HCI Chief cell 1 2 HCI converts pepsinogen to pepsin. H Cl− Parietal cell 3 Pepsin activates more pepsinogen, starting a chain reaction. Figure 33.9b-3 The stomach and its secretions (part 2, step 3) 32
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Digestive Enzymes
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MIXING CHYME A thick mixture of food and gastric fluid
High acidity kills many pathogens Mixed and moved by waves of stomach contractions Peristalsis
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INTO THE SMALL INTESTINE
Movement into duodenum controlled by pyloric sphincter Only a small amount of chyme passes through sphincter at a given time Fat content of chyme affects the rate of stomach emptying
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Small Intestine highly folded mucosa
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submucosa serosa blood vessels gut lumen circular muscle longitudinal muscle mesh of nerves (plexus)
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INTESTINAL SECRETIONS
Wall of the duodenum secretes Disaccharidases digest disaccharides to monosaccharides Peptidases break protein fragments down to amino acids Nucleases digest nucleotides down to nucleic acids and monosaccharides
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PANCREATIC ENZYMES Hormones Secretin
stimulates the pancreas to release bicarbonate Cholecystokinin (CCK) stimulates the pancreas to release enzymes Enzymes Secreted into duodenum Pancreatic amylase Trypsin and Chymotrypsin converts proteins to peptide Carboxypeptidase hydrolizes peptide bonds Lipase Pancreatic nucleases
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Fat Digestion Liver produces bile stored in gallbladder
Cholecystokinin (CCK) stimulates the gall bladder to form contractions to squirt bile into the small intestine bile emulsifies fats breaks them into small droplets this gives enzymes a greater surface area to work on
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triglycerides + proteins
FAT ABSORPTION bile salts bile salts + micelles fat globules (triglycerides) emulsification droplets fatty acids, monoglycerides triglycerides + proteins EPITHELIAL CELL chylomicrons INTERNAL ENVIRONMENT
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The hepatic portal vein carries nutrient-rich blood from the capillaries of the villi to the liver, then to the heart The liver regulates nutrient distribution, interconverts many organic molecules, and detoxifies many organic molecules 42
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Digestion and Absorption
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WALLS OF SMALL INTESTINE
Projections into the intestinal lumen increase the surface area available for absorption One villus
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ABSORPTION OF NUTRIENTS
Passage of molecules into internal environment Occurs mainly in jejunum and ileum of small intestine Segmentation mixes the lumen contents against wall and enhances absorption
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ABSORPTION MECHANISMS
INTESTINAL LUMEN ABSORPTION MECHANISMS carbohydrates monosaccharides Monosaccharides & amino acids are actively transported across plasma membrane of epithelial cells, then from cell into internal environment proteins amino acids EPITHELIAL CELL INTERNAL ENVIRONMENT
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INTO THE BLOOD Glucose and amino acids enter blood vessels directly
Triglycerides enter lymph vessels, which eventually drain into blood vessels
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Nucleic acid digestion Fat digestion Fat (triglycerides)
Carbohydrate digestion Oral cavity, pharynx, esophagus Polysaccharides Disaccharides (starch, glycogen) (sucrose, lactose) Salivary amylase Smaller polysaccharides Maltose Protein digestion Stomach Proteins Pepsin Nucleic acid digestion Small polypeptides Fat digestion Small intestine (enzymes from pancreas) DNA, RNA Fat (triglycerides) Pancreatic amylases Pancreatic trypsin and chymotrypsin Pancreatic nucleases Disaccharides Smaller polypeptides Nucleotides Pancreatic lipase Pancreatic carboxypeptidase Figure Chemical digestion in the human digestive system Glycerol, fatty acids, monoglycerides Small peptides Small intestine (enzymes from epithelium) Nucleotidases Dipeptidases, carboxypeptidase, and aminopeptidase Nucleosides Disaccharidases Nucleosidases and phosphatases Nitrogenous bases, sugars, phosphates Monosaccharides Amino acids 48
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LARGE INTESTINE (COLON)
Concentrates and stores feces Sodium ions are actively transported out of lumen and water follows Lining secretes mucus and bicarbonate ascending portion of large intestine appendix cecum
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Structure of the large intestine
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BACTERIA IN COLON Slow movement of material through colon allows growth of bacteria Harmless--unless they escape into abdominal cavity Some produce vitamin K, which is absorbed through intestinal wall Helps with blood clotting Helps elderly maintain strong bones
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MOVEMENT THROUGH THE COLON
During a meal, gastrin and autonomic signals trigger contraction of ascending and transverse colon Material moves along to make room for incoming food Feces is stored in last part of colon
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