vertebrate physiology ecol 437 university of arizona fall 2003vertebrate physiology 437 1. feeding...
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Lecture 24, 25 Nov 2003Chapter 15, Feeding and DigestionChapter 16, Energy Expenditure?
Vertebrate PhysiologyECOL 437
University of ArizonaFall 2003
instr: Kevin Boninet.a.: Bret Pasch
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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)
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(15-36)
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Generalized DigestiveSystem
(15-13)
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2 (incl. stomach)
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4
Salivary glands(mucin) tolubricate
Tongue forchemoreception
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Foregut
-Conducting, Storage, Digestion-Esophagus and Stomach
Crop in some for storage/regurgitation
Stomach
- 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 sand
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ForegutMonogastric 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)
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ForegutDigastric Stomach- herbivores
- anaerobic fermentation by symbiotic bacteria and protozoans
(15-18)
- regurgitation
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3
4- digestive enzymes
( Carbohydrates -> sugars and gases ) sugars, amino acids, short FAs into blood
Domestic cattle,1L/min gas!(methane and CO2)
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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
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(15-31)
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Midgut
Anatomy:-longitudinal smooth muscle-circular smooth muscle-epithelium -submucosa (connective tissue) -mucosa (mucous membrane)
(15-19)
Epithelial cellssloughed rapidly(2x1010 cells/day),lining replacedevery few days
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Midgut-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)
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Midgut-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)
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(15-20)
Villi withmicrovilli
(brush border)
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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)
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Hindgut-Water and Ion absorption; defecation
horse rabbit
hindgut fermenters
(15-22)
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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
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(everted sleeve)
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Gut Plasticity
Alter 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)
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MotilityContraction of gut and movement of contents:1. Propulsion, expulsion2. 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...
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(15-25)
Regurgitation, Vomiting?
KneadingMovement
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MotilityControl of smooth muscle contractionIntrinsic
-pacemaker activity (basic electric rhythm = BER)-stretch-chemical signals from chyme
Extrinsic-GI peptide hormones-autonomic NS
(Myenteric and submucosal plexus)
Sympathetic andParasympathetic innervation
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Intrinsic-pacemaker activity (basic electric rhythm = BER)-cations and Ca2+
(15-26)
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ExtrinsicMyenteric and submucosal plexus
(15-27)
Parasympathetic (~ACh)-increased motility-increased secretion
Sympathetic (~norepi)-decreased motility-decreased secretion
Other neurotransmitters also
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Los SecretionsAlimentary canal is largest endocrine and exocrine gland
Salivary glandSecretory cells of stomach and intestineSecretory 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?
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(15-31)
(proenzymes)
Los Secretions22
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Los SecretionsDigestive 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.)
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Los Secretions
Carbohydrases
a. Amylases -salivary glands, pancreas, stomachb. Glycosidases -absorptive cells, glycocalyx, disaccharides (midgut)
Cellulase -symbiotic microorgansims
(15-33)
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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
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Control of Los SecretionsPresence of Food stimulates:
Chemoreceptors lead to activation:1 Autonomic Efferent Neurons2 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
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Los Secretions (order and triggers)
SalivaryWater, electrolytes, mucin, amylase, antimicrobialsDecreased salivation in response to sympathetic NS
GastricHCl (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
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(15-34)
HCl(hydrochloricacid) from
parietal cells
carbonicanhydrase
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Alkaline Tide…
30b
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Los Secretions (order and triggers)Gastric
Pepsin (pepsinogen) from chief cells-response to: 1 parasymp. stim. 2 gastrin-breaks peptide bonds
Mucus from goblet cells-protects gut lining-works with alkaline electrolytes in glycocalyx
(15-35)
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Los Secretions (order and triggers)
GastricGastrin 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
IntestineGastric 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)
~oppositeeffects
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Los Secretions (order and triggers)IntestineSuccus entericus from duodenum
-alkaline and enzyme-rich
Pancreatic EnzymesSeveral (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)
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(15-36)
+
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ABSORPTION:
-Across epithelium of brush border (microvilli)-Glycocalyx has enzymes for final cleavage disaccharidases, aminopeptidases, phosphatases
-Simple Diffusion1 fat-soluble substances2 small water soluble substances through
regulated aquaporins3 down concentration or electrochemical gradients
-Facilitated Diffusion1 monosaccharides and amino acids2 transporter proteins3 down conc. gradient or4 coupled to Na+ gradient (Na/K-ATPase)
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(15-37)
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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
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(15-38)
Lipids38
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