Lecture 24, 25 Nov 2003Chapter 15, Feeding and DigestionChapter 16, Energy Expenditure?Vertebrate PhysiologyECOL 437University of ArizonaFall 2003instr: Kevin Boninet.a.: Bret Pasch1Vertebrate Physiology 4371. 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)2(15-36)Generalized DigestiveSystem(15-13)123412 (incl. stomach)34Salivary glands(mucin) tolubricateTongue forchemoreception3REVIEWForegut-Conducting, Storage, Digestion-Esophagus and StomachCrop in some for storage/regurgitationStomach- begins digestion (e.g., pepsin)- food storage- mechanical mixing (muscular walls)- Monogastric (1 chamber, carnivores and omnivores)- Digastric (> 1 chamber)e.g., Some birds use to grind with pebbles and sand4REVIEWForegutMonogastric Stomach- strong muscular sac/tube- sphincters at both ends- mucus from goblet cells of gastric pit- HCl from parietal cells of gastric gland- pepsinogen from chief cells of gastric gland(15-17)5REVIEW112233ForegutDigastric Stomach- herbivores- anaerobic fermentation by symbiotic bacteria and protozoans(15-18)- regurgitation1234- digestive enzymes( Carbohydrates -> sugars and gases ) sugars, amino acids, short FAs into bloodDomestic cattle,1L/min gas!(methane and CO2)6REVIEWMidgut-Chemical digestion and Absorption (~ small intestine)-from stomach through pyloric sphincter into duodenum-alkaline1-Duodenum (mucus + secretions from liver, pancreas) Bile duct from liver-Bile breaks up fats and neutralizes acids Pancreatic Juice-proteases, lipases, carbohydrases, antacid2-Jejunum (digestion and absorption)3-Ileum (mostly absorption)-Internal symbionts help digest, provide nutrition, vitamins-Gas exchange in some air-breathing fishes7(15-31)MidgutAnatomy:-longitudinal smooth muscle-circular smooth muscle-epithelium -submucosa (connective tissue) -mucosa (mucous membrane)(15-19)Epithelial cellssloughed rapidly(2x1010 cells/day),lining replacedevery few days8Midgut-Intestinal Epithelium, SURFACE AREA-aids absorption of digested nutrients-epithelium arrangement: -circular folds -villi with blood vessels -central lacteal (lymph system)-microvilli (2x105 per mm2)(15-19)(15-20)9Midgut-Intestinal Epithelium, SURFACE AREA-intestinal chyme-surface of microvilli: -covered with glycocalyx -mucus and water mixed in -absorption through epithelial cells-microvilli with actin, interactswith myosin for movement(15-20)10(15-20)Villi withmicrovilli(brush border)11Hindgut-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)12Hindgut-Water and Ion absorption; defecationhorserabbithindgut fermenters(15-22)13Gut PlasticityAlter gut size, activity (reversible)-Sustained increased metabolism can increase bird gut length by 1/5-Mammals increase GI tract mass 3-4x post-hibernation14(everted sleeve)Gut PlasticityAlter gut size, activity (reversible)-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)(15-23)15MotilityContraction of gut and movement of contents:1. Propulsion, expulsion2. Mixing and grinding (enzymes, mechanical digestion)3. Stirring so brush border/epithelial lining gets nutrientsPeristalsis -longitudinal muscle -circular muscle(15-24)Move food along...16(15-25)Regurgitation, Vomiting?KneadingMovement17MotilityControl of smooth muscle contractionIntrinsic-pacemaker activity (basic electric rhythm = BER)-stretch-chemical signals from chymeExtrinsic-GI peptide hormones-autonomic NS(Myenteric and submucosal plexus)Sympathetic andParasympathetic innervation18Intrinsic-pacemaker activity (basic electric rhythm = BER)-cations and Ca2+(15-26)19ExtrinsicMyenteric and submucosal plexus(15-27)Parasympathetic (~ACh)-increased motility-increased secretionSympathetic (~norepi)-decreased motility-decreased secretionOther neurotransmitters also20Los SecretionsAlimentary canal is largest endocrine and exocrine glandSalivary glandSecretory cells of stomach and intestineSecretory cells of liver and pancreasWater, ions, mucus, enzymesBile (fat digestion) -created in liver, stored in gall bladder -also gets rid of some waste products metabolized by liver -Why is your poop brown?21(15-31)(proenzymes)Los Secretions22Los SecretionsDigestive Enzymes hydrolyze larger molecules:e.g., Sugars (glycosidic bonds) into monosaccharidesProteases (protein peptide bonds -> amino acids)-endopeptidases-exopeptidases~specialized (e.g., Trypsin cleaves arg. or lys.)Pepsin(from pepsinogen in acid, ~pH=2 envir.)23Los SecretionsCarbohydrasesa. Amylases -salivary glands, pancreas, stomachb. Glycosidases -absorptive cells, glycocalyx, disaccharides (midgut)Cellulase -symbiotic microorgansims(15-33)24Los SecretionsLipases• Break up insoluble fats using bile salts etc.• Formation of micelles (small lipid spheres)•Lipases cleave lipids into fatty acids plus mono- or diglycerides2526Control of Los SecretionsPresence of Food stimulates:Chemoreceptors lead to activation:1 Autonomic Efferent Neurons2 GI hormones into blood stream-stimulates liver, pancreas, gutMental influences-conscious decisions-learned smells, sounds-Pavlovian responseGastrointestinal secretions controlled by hormones:-endocrine cells of gastric and intestinal submucosa-complicated, varies in areas of gut2728Los Secretions (order and triggers)SalivaryWater, electrolytes, mucin, amylase, antimicrobialsDecreased salivation in response to sympathetic NSGastricHCl (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 microorganisms29(15-34)HCl(hydrochloricacid) fromparietal cellscarbonicanhydrase30Alkaline Tide…30bLos Secretions (order and triggers)GastricPepsin (pepsinogen) from chief cells-response to: 1 parasymp. stim. 2
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