digestion chapter 41 campbell & reece. 49-1: nutritional requirements cells need: water...
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DigestionChapter 41
Campbell & Reece
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49-1: Nutritional Requirements
Cells need:• Water • Carbohydrates • Lipids • Proteins • Nucleic acids • Vitamins-- Study Table 49-1 pg. 980 • Minerals - Table 49-2 pg. 981
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Nutrition involves the following steps:1. Ingestion2. Digestion3. Absorption4. Distribution
Digestion: the breakdown of ingested food materials into molecules that can be delivered to and utilized by the individual cells.
• Can be both mechanical and chemical.• human anatomy tutorials, labeled with explanations (all systems) link
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The “Gut” (Gastrointestinal Tract): Fig.49-2 pg. 983
• Made of 4 layers (see pictures on page 985)
• Mucosa: (innermost) -epithelial, connective, some smooth muscle
• Submucosa: connective, nerve fibers, blood & lymph vessels
• Muscularis Externa: muscle tissue (circular & longitudinal)
• Serosa: outer covering of connective tissue
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• Peristalsis: coordinated contractions of circular muscles along digestive tract which move food along
• Sphincters: thickened, heavy bands of muscle along tract that act as valves by contracting (closing) and relaxing (opening) to control of materials
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The Oral Cavity: Initial Processing:Mechanical Digestion• Tongue - swallowing (microscopic picture)• Teeth: “mastication” (chewing)
– incisors- cutting, clipping– canines- tearing, stabbing– premolars- "bicuspids" 2 cusps (points)– molars- 4 or 5 cusps (for grinding)
• Other Animals lack teeth, have alternatives:– rasping tongue: ex- snails, lamprey, frogs – grinding organ (gizzard): ex- birds, earthworms
Chemical Digestion (enzymatic hydrolysis): saliva, mucous• 3 pairs of salivary glands and buccal glands in jaw: lubricates, softens food• Enzyme- salivary amylase for hydrolysis of starch into smaller sugar
molecules; slightly alkaline (sodium bicarbonate)
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The Pharynx & Esophagus: Swallowing
Swallowing: passage of food to the esophagus ----> stomach
• begins as voluntary action (striated muscles in upper part of esophagus) lower portion involuntary (smooth muscle)= "peristalsis" Esophagus opens into Stomach
• Abdominal cavity lined with peritonium / organs are suspended by mesentaries
(animation)
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The Stomach: Storage & Liquefaction
• mucosal lining folds into gastric pits (microscopic picture)
• lined with mucous-secreting epithelial cells
• gastric glands secrete HCl and pepsinogen (precurser to pepsin)
• pH between 1.5 & 2.5 (mucous barrier between acids + stomach lining )- ulcers?
…a collapsible, muscular, j-shaped bag with many folds and ridges
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Stomach acids, enzymesHCl: • kills bacteria loosens tissues for digestion converts
pepsinogen to pepsin Pepsin: breaks down proteins into smaller peptides• Semi-liquid mass "Chyme" moves to lower end of
stomach => Pyloric Sphincter (takes about 4 hrs.)• Rate of leaving stomach = H2O,carbs, proteins, fat,
protein/fat combo• The three phases of gastric secretion animation
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The Small Intestine: Digestion and absorption
• lined with VILLI ( microscopic fingerlike projections) and tiny microvilli on surface of epithelial cells
• about 21 feet long (adult), total surface area about 300 m2
Digestion:• Duodenum- 1st 25 cm (10
inches)• most digestion takes place here;• receives several digestive
juices/enzymes from ducts leading from ACCESSORY GLANDS (liver pancreas, gall bladder)
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Accessory Glands
• neutralize stomach acids with alkaline secretions• produces several enzymes to chemically digest nutrients
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The Pancreas
Enzymes made here enter the duodenum via the pancreatic duct
• Amylase: continues starch digestion– Starchesdisaccharidesmonosaccharides
• Trypsin: breaks down proteins amino acids
• Lipase: hydrolyzes fats
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The Liver: an accessory gland
Bile- • produced by liver• stored in gall bladder• contains salts (emulsify fats)• sodium bicarbonate (neutralize pH to
optimum 7 or 8)
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Absorption of Nutrients:
• food is absorbed through epithelial cells of intestinal mucosa into the bloodstream, for distribution to all cells
• Active Transport: Monosaccharides, Dipeptides, Amino Acids
• Diffusion: fatty acids• Lipids resynthesize into triglycerides,
phospholipids (blood & lymph vessels), Cholesterol
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The Large Intestine: Water Absorption & Elimination
The Large Intestine (colon)continues absorption of water, sodium, and other minerals (which begins in small intestine)
• E. coli bacteria: makes Vit.K, amino acid synthesis• Appendix: vestigial organ (gastric caecum?)• Waste: "fecal matter"
– water, bacteria, dead cells, indigestible matter (cellulose)
– lubricated with mucus– temporary storage in rectum