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Lecture 24, 25 Nov 2003 Chapter 15, Feeding and Digestion Chapter 16, Energy Expenditure?

Explore the complexities of feeding and digestion, energy expenditure, and gut physiology in vertebrates. From salivary glands to hindgut fermentation, uncover the intricacies of nutrient processing.

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Lecture 24, 25 Nov 2003 Chapter 15, Feeding and Digestion Chapter 16, Energy Expenditure?

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  1. 1 Lecture 24, 25 Nov 2003 Chapter 15, Feeding and Digestion Chapter 16, Energy Expenditure? Vertebrate Physiology ECOL 437 University of Arizona Fall 2003 instr: Kevin Bonine t.a.: Bret Pasch

  2. 2 Vertebrate Physiology 437 1. Feeding and Digestion (CH15) 2. ~Energy Expenditure (CH16)? 3. Announcements… - Exams returned Wed. - Term paper 04 Dec. - Seminar write-up 09 Dec. - Powerpoint practice (file to us on 09 Dec.) - Oral Presentations 10 Dec. - Wed assignment ~ 4 short questions on website Wed. midday (-25%? and extra question if absent) (15-36)

  3. REVIEW 3 Generalized Digestive System 1 1 Salivary glands (mucin) to lubricate Tongue for chemoreception 2 (incl. stomach) 2 3 3 4 4 (15-13)

  4. REVIEW 4 Foregut -Conducting, Storage, Digestion -Esophagus and Stomach Crop in some for storage/regurgitation e.g., Some birds use to grind with pebbles and sand Stomach - food storage - begins digestion (e.g., pepsin) - mechanical mixing (muscular walls) - Monogastric (1 chamber, carnivores and omnivores) - Digastric (> 1 chamber)

  5. REVIEW 5 Foregut Monogastric Stomach - strong muscular sac/tube - sphincters at both ends - mucus from goblet cells of gastric pit 1 - HCl from parietal cells of gastric gland 2 - pepsinogen from chief cells of gastric gland 3 1 2 3 (15-17)

  6. REVIEW 6 Foregut (15-18) Digastric Stomach - herbivores - regurgitation 3 1 2 4 - digestive enzymes Domestic cattle, 1L/min gas! (methane and CO2) - anaerobic fermentation by symbiotic bacteria and protozoans ( Carbohydrates -> sugars and gases ) sugars, amino acids, short FAs into blood

  7. 7 Midgut -Chemical digestion and Absorption (~ small intestine) -from stomach through pyloric sphincter into duodenum -alkaline 1-Duodenum(mucus + secretions from liver, pancreas) Bile duct from liver -Bile breaks up fats and neutralizes acids Pancreatic Juice -proteases, lipases, carbohydrases, antacid 2-Jejunum (digestion and absorption) 3-Ileum (mostly absorption) -Internal symbionts help digest, provide nutrition, vitamins -Gas exchange in some air-breathing fishes (15-31)

  8. 8 Midgut Anatomy: -longitudinal smooth muscle -circular smooth muscle -epithelium -submucosa (connective tissue) -mucosa (mucous membrane) Epithelial cells sloughed rapidly (2x1010 cells/day), lining replaced every few days (15-19)

  9. 9 Midgut -Intestinal Epithelium, SURFACE AREA -aids absorption of digested nutrients -epithelium arrangement: -circular folds -villi with blood vessels -central lacteal (lymph system) (15-19) -microvilli (2x105 per mm2) (15-20)

  10. 10 Midgut -Intestinal Epithelium, SURFACE AREA -surface of microvilli: -covered with glycocalyx -mucus and water mixed in -absorption through epithelial cells -intestinal chyme -microvilli with actin, interacts with myosin for movement (15-20)

  11. 11 Villi with microvilli (brush border) (15-20)

  12. 12 Hindgut -Water and Ion absorption; Defecation -reabsorb water and ions at end of small intestine (ilieum) and from large intestine/colon -feces into cloaca/rectum for excretion -cloaca can also be site of urine modification (e.g., birds) -bacterial digestion in hindgut fermenters (especially in cecum) -coprophagy/cecotrophy (e.g., rabbits)

  13. 13 Hindgut -Water and Ion absorption; defecation hindgut fermenters horse rabbit (15-22)

  14. 14 Gut Plasticity Alter gut size, activity (reversible) -Sustained increased metabolism can increase bird gut length by 1/5 -Mammals increase GI tract mass 3-4x post-hibernation (everted sleeve)

  15. 15 Gut Plasticity Alter gut size, activity (reversible) (15-23) -Some infrequently-feeding snakes: - intestine 2x larger within 2 days - microvilli length and area up 400% - glucose transport rate up as much as 22x - other transporters also up-regulated (e.g., a.a. absorption)

  16. 16 Motility Contraction of gut and movement of contents: 1. Propulsion, expulsion 2. Mixing and grinding (enzymes, mechanical digestion) 3. Stirring so brush border/epithelial lining gets nutrients Peristalsis -longitudinal muscle -circular muscle (15-24) Move food along...

  17. 17 Movement Kneading (15-25) Regurgitation, Vomiting?

  18. 18 Motility Control of smooth muscle contraction Intrinsic -pacemaker activity (basic electric rhythm = BER) -stretch -chemical signals from chyme Extrinsic -GI peptide hormones -autonomic NS Sympathetic and Parasympathetic innervation (Myenteric and submucosal plexus)

  19. 19 Intrinsic -pacemaker activity (basic electric rhythm = BER) -cations and Ca2+ (15-26)

  20. 20 Extrinsic Myenteric and submucosal plexus (15-27) Sympathetic (~norepi) -decreased motility -decreased secretion Parasympathetic (~ACh) -increased motility -increased secretion Other neurotransmitters also

  21. 21 Los Secretions Alimentary canal is largest endocrine and exocrine gland Salivary gland Secretory cells of stomach and intestine Secretory cells of liver and pancreas Water, ions, mucus, enzymes Bile (fat digestion) -created in liver, stored in gall bladder -also gets rid of some waste products metabolized by liver -Why is your poop brown?

  22. 22 Los Secretions (15-31) (proenzymes)

  23. 23 Los Secretions Digestive Enzymes hydrolyze larger molecules: e.g., Sugars (glycosidic bonds) into monosaccharides Proteases (protein peptide bonds -> amino acids) -endopeptidases -exopeptidases ~specialized (e.g., Trypsin cleaves arg. or lys.) Pepsin (from pepsinogen in acid, ~pH=2 envir.)

  24. 24 Los Secretions Carbohydrases a. Amylases -salivary glands, pancreas, stomach b. Glycosidases -absorptive cells, glycocalyx, disaccharides (midgut) Cellulase -symbiotic microorgansims (15-33)

  25. 25 Los Secretions Lipases • Break up insoluble fats using bile salts etc. • Formation of micelles (small lipid spheres) • Lipases cleave lipids into fatty acids plus • mono- or diglycerides

  26. 26

  27. 27 Control of Los Secretions Presence of Food stimulates: Chemoreceptors lead to activation: 1 Autonomic Efferent Neurons 2 GI hormones into blood stream -stimulates liver, pancreas, gut Mental influences -conscious decisions -learned smells, sounds -Pavlovian response Gastrointestinal secretions controlled by hormones: -endocrine cells of gastric and intestinal submucosa -complicated, varies in areas of gut

  28. 28

  29. 29 Los Secretions (order and triggers) Salivary Water, electrolytes, mucin, amylase, antimicrobials Decreased salivation in response to sympathetic NS Gastric HCl (hydrochloric acid) from parietal cells -carbonic anhydrase -response to: 1 parasymp. stimulation 2 gastrin 3 caffeine, alcohol, spices -breaks peptide bonds -activates some enzymes (pepsinogen) -kills microorganisms

  30. 30 HCl (hydrochloric acid) from parietal cells carbonic anhydrase (15-34)

  31. 30b Alkaline Tide…

  32. 31 Los Secretions (order and triggers) Gastric Pepsin (pepsinogen) from chief cells -response to: 1 parasymp. stim. 2 gastrin -breaks peptide bonds (15-35) Mucus from goblet cells -protects gut lining -works with alkaline electrolytes in glycocalyx

  33. 32 Los Secretions (order and triggers) Gastric Gastrin from endocrine cells of distal stomach mucosa -response to: 1 gastric chyme with proteins 2 stomach stretch (gastric distension) - binds to smooth muscle - stimulates stomach motility - stimulates HCl and pepsin release ~opposite effects Intestine Gastric Inhibitory Peptide (GIP) from duodenum -response to: 1 entry of fats and sugars - acts to stop gastric secretion and motility (also Enterogastric Reflex and sympathetic stimulation)

  34. 33 Los Secretions (order and triggers) Intestine Succus entericus from duodenum -alkaline and enzyme-rich Pancreatic Enzymes Several (amylase, trypsin, chymotrypsin, elastase, peptidases, lipases, nucleases) -alkaline fluid -controlled by hormones of small intestine -secretin -vasoactive intestinal peptide (VIP) -cholecystokinin (CCK; also stim. gallbladder)

  35. 34 + (15-36)

  36. 35 ABSORPTION: -Across epithelium of brush border (microvilli) -Glycocalyx has enzymes for final cleavage disaccharidases, aminopeptidases, phosphatases -Simple Diffusion 1 fat-soluble substances 2 small water soluble substances through regulated aquaporins 3 down concentration or electrochemical gradients -Facilitated Diffusion 1 monosaccharides and amino acids 2 transporter proteins 3 down conc. gradient or 4 coupled to Na+ gradient (Na/K-ATPase)

  37. 36 (15-37)

  38. 37 ABSORPTION -Active Transport -amino acids with ~specific transporters coupled to Na+ -Lipids -products cross into epithelial cells (monoglycerides, fatty acids, glycerol) -reconstructed into triglycerides -formed into chylomicrons using cholesterol and phospholipids -chylomicrons exocytosed -taken into central lacteal and into lymph system

  39. 38 Lipids (15-38)

  40. xx END

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