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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
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)
REVIEW
Generalized Digestive
System
Salivary glands
(mucin) to
lubricate
Tongue for
chemoreception
3
1
1
2
2
(incl. stomach)
3
3
4
4
(15-13)
Foregut
REVIEW
-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)
4
REVIEW
5
Foregut
Monogastric Stomach
- strong muscular sac/tube
- sphincters at both ends
1 - mucus from goblet
cells of gastric pit
2 - HCl from parietal cells
of gastric gland
3 - pepsinogen from chief
cells of gastric gland
1
2
3
(15-17)
Foregut
Digastric Stomach
- herbivores
REVIEW
6
(15-18)
- regurgitation
3
4
2
1
- 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
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
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
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)
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
Villi with
microvilli
(brush border)
(15-20)
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
Hindgut
-Water and Ion absorption; defecation
hindgut fermenters
horse
rabbit
(15-22)
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
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)
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...
16
17
Movement
Kneading
(15-25)
Regurgitation, Vomiting?
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)
18
19
Intrinsic
-pacemaker activity (basic electric rhythm = BER)
-cations and Ca2+
(15-26)
20
Extrinsic
Myenteric and submucosal plexus
(15-27)
Sympathetic (~norepi)
-decreased motility
-decreased secretion
Parasympathetic (~ACh)
-increased motility
-increased secretion
Other neurotransmitters also
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
Los Secretions
(15-31)
(proenzymes)
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.)
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Los Secretions
Carbohydrases
a. Amylases
-salivary glands, pancreas, stomach
b. Glycosidases
-absorptive cells, glycocalyx, disaccharides (midgut)
Cellulase
-symbiotic microorgansims
(15-33)
25
Los Secretions
Lipases
1. Break up insoluble fats using bile salts etc.
2. Formation of micelles (small lipid spheres)
3. Lipases cleave lipids into fatty acids plus
mono- or diglycerides
26
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
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
HCl
(hydrochloric
acid) from
parietal cells
carbonic
anhydrase
(15-34)
30b
Alkaline Tide…
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
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
~opposite
- stimulates HCl and pepsin release
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)
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)
34
+
(15-36)
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)
35
36
(15-37)
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
37
38
Lipids
(15-38)
xx
END