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Digestion

This detailed guide covers the nutritional requirements for cells, including water, carbohydrates, lipids, proteins, nucleic acids, vitamins, and minerals. It delves into the steps of nutrition - ingestion, digestion, absorption, and distribution. The process of digestion involves mechanical and chemical breakdown of food for cell utilization. From the gut's anatomy to peristalsis, sphincters, and the functions of the oral cavity, pharynx, esophagus, stomach, small intestine, pancreas, liver, and large intestine, all aspects are explored. Learn about enzyme actions, bile production, absorption mechanisms, and waste elimination in the large intestine. Enhance your knowledge of the human digestive system with this resource.

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Digestion

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  1. Digestion Chapter 49

  2. 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

  3. Nutrition involves the following steps: • Ingestion • Digestion • Absorption • 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

  4. 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 • MuscularisExterna: muscle tissue (circular & longitudinal) • Serosa: outer covering of connective tissue

  5. 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

  6. 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)

  7. 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)

  8. The Stomach: Storage & Liquefaction …a collapsible, muscular, j-shaped bag with many folds and ridges • 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?

  9. Stomach acids, enzymes HCl: • 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

  10. The Small Intestine: Digestionand 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)

  11. Accessory Glands • neutralize stomach acids with alkaline secretions • produces several enzymes to chemically digest nutrients

  12. The Pancreas Enzymes made here enter the duodenum via the pancreatic duct • Amylase: continues starch digestion • Starchesdisaccharidesmonosaccharides • Trypsin: breaks down proteins  amino acids • Lipase: hydrolyzes fats

  13. 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)

  14. 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

  15. 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

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