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

1

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)

2

(15-36)

Generalized DigestiveSystem

(15-13)

1

2

3

4

1

2 (incl. stomach)

3

4

Salivary glands(mucin) tolubricate

Tongue forchemoreception

3REVIEW

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

4REVIEW

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)

5REVIEW

1

1

2

2

3

3

ForegutDigastric Stomach- herbivores

- anaerobic fermentation by symbiotic bacteria and protozoans

(15-18)

- regurgitation

12

3

4- digestive enzymes

( Carbohydrates -> sugars and gases ) sugars, amino acids, short FAs into blood

Domestic cattle,1L/min gas!(methane and CO2)

6REVIEW

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

7

(15-31)

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

8

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)

9

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)

10

(15-20)

Villi withmicrovilli

(brush border)

11

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)

12

Hindgut-Water and Ion absorption; defecation

horse rabbit

hindgut fermenters

(15-22)

13

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

14

(everted sleeve)

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)

15

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...

16

(15-25)

Regurgitation, Vomiting?

KneadingMovement

17

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

18

Intrinsic-pacemaker activity (basic electric rhythm = BER)-cations and Ca2+

(15-26)

19

ExtrinsicMyenteric and submucosal plexus

(15-27)

Parasympathetic (~ACh)-increased motility-increased secretion

Sympathetic (~norepi)-decreased motility-decreased secretion

Other neurotransmitters also

20

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?

21

(15-31)

(proenzymes)

Los Secretions22

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.)

23

Los Secretions

Carbohydrases

a. Amylases -salivary glands, pancreas, stomachb. Glycosidases -absorptive cells, glycocalyx, disaccharides (midgut)

Cellulase -symbiotic microorgansims

(15-33)

24

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

25

26

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

27

28

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

29

(15-34)

HCl(hydrochloricacid) from

parietal cells

carbonicanhydrase

30

Alkaline Tide…

30b

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)

31

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

32

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)

33

(15-36)

+

34

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)

35

(15-37)

36

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

(15-38)

Lipids38

END

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