Transcript Comparative Digestive Physiology

Comparative Digestive Physiology
Why Do Animals Digest?
Food not ingested in suitable state
Physical nature of food determined by:
gathering apparatus for uptake
type of digestive system
Primary Functions of the
Digestive Tract
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Transport food – peristaltic contractions
Digestion
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Absorption
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Mechanical breakdown
Chemical breakdown
Passive diffusion and active transport
Synthesis - true protein, FA, starch, vitamins
Excretion – elimination of waste products
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Via bile (toxins, microbes etc)
Via rectum (Ca, Mg, P)
Regions of Alimentary Canal
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Foregut functions
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Midgut functions
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Ingestion and storage of feeds
Mechanical, chemical & enzymatic digestion of
feed
Nutrient absorption
Hindgut functions
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Water & ion re-absorption
Formation, storage, excretion of feces
Associated Structures
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Pancreas
Contribute to small
Liver
intestinal digestion
Gallbladder
Salivary glands
Primitive Gastrointestinal Tract
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Found in monotremes (egg-laying mammals),
insectivores (bats, shrews, moles), and dermopterans
(colugos)
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Simple stomach, little or no division between small intestines
and large intestines, large intestine simple, presence of
cecum, non-sacculated colon
Species-Dependent
Nutritional Adaptations
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Includes involvement of:
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Teeth
Jaws and jaw musculature
Alimentary canal
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Stomach - May be simple or become sacculated to
compartmentalize functions for prolonged storage of
feed and utilization of bacterial fermentation (langurs
and ruminants)
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May also become voluminous for storage of large amounts
of feed (vampire bats)
Large intestine - varies substantially in length,
compartmentalization, and complexity among species
Ruminants
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2.8 billion domesticated ruminants
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Cattle, sheep, deer, elk, bison
Pregastric fermentation
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Ability to chew cud at frequent intervals
distinguishes true ruminant from other foregut
fermenters
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Kangaroo, colobine monkey are not true ruminants
Four compartment stomach
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Reticulum
Rumen
Omasum
Abomasum
Ruminants vary in size and habitat
Classification of Ruminants by
Feeding Preference
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Classes of ruminants
 Concentrate selectors
 Intermediate feeders
 Roughage grazers
Concentrate Selecting Species
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Properties
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Evolved early
Small rumens
Poorly developed omasums
Large livers
Limited ability to digest fiber
Classes
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Fruit and forage selectors
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Very selective feeders
Duikers, sunis
Tree and shrub browsers
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Eat highly lignified plant tissues to extract cell solubles
Deer, giraffes, kudus
Intermediate Feeding Species
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Properties
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Seasonally adaptive
Feeding preference
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Prefer browsing
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Moose, goats, elands
Prefer grazing
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Sheep, impalas
Roughage Grazing Species
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Properties
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Most recently evolved
Larger rumens and longer retention times
Less selective
Digests fermentable cell wall carbohydrates
Classes
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Fresh grass grazers
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Roughage grazers
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Buffalo, cattle, gnus
Hartebeests, topis
Dry region grazers
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Camels, antelope, oryxes
Structures in Mouth
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Lips
Teeth
Tongue
Salivary glands
Mouth
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Functions
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Grasp food
Taste
Masticate food
Mix with saliva
Digestion in the Mouth
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Prehension
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Bringing the food to the mouth
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Upper limbs, head, beak, claws, mouth,
teeth and lips
Mastication or chewing
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To crush the food, increase surface
area and allow enzymes to act on
molecules
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Carnivores only to reduce the size of the
particle to a size small enough to swallow
Herbivores must chew continuously (4050,000 times a day) to increase surface
area
Prehension
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Seizing and conveying feed to mouth
Mechanisms vary with behavior and diet
 Forelimbs
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Snout
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Elephant, tapir
Tongue
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Primates, raccoon
Anteater, cow, sheep
Lips
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Horse, sheep, rhinoceros
Prehension
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Domestic mammals use lips, teeth and tongue
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Relative importance varies by species
Horses
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Cows and sheep have limited use of lips
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lips when eating from manger
teeth when grazing
Use long rough tongue to grasp forage
Pigs use snout to root in ground and pointed lower lip
to convey feed into mouth
Birds use beak and tongue
Drinking varies as well
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Most mammals use suction
Dogs and cats use tongue to form ladle
The Importance of Prehension
in Diet Formulation
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White Rhino (“wijd” = wide)
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Squared off upper lip used to
“crop” grass
Grazes on savannah
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Black Rhino
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Prehensile upper lip for
browsing
Consumes bushes and
shrubs in forest
Mastication
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Physical reduction of feed
Especially important in non-ruminant
herbivores
Adaptations with teeth
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Carnivores
Herbivores
Edentates (sloths, armadilloes, anteater)
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Relative toothlessness
Morphological Adaptations
for Herbivory
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All related to finding, ingesting, masticating, and
digesting plant cell walls
Dental adaptations for herbivory include changes
to incisors, molar occlusal surfaces, & masseter
Solution for digestive problems is to provide a
place in digestive tract for anaerobic bacteria &
protozoans (microflora) to colonize
Monogastric Teeth
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Function:
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Mechanically reduce particle
size
Increase surface area
Four types:
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Incisors are used for cutting
Canine (fangs, eye teeth,
tusks) are tearing teeth
Premolars and molars (cheek
teeth) grind the food
Ruminant Mouth - Teeth
Function:
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Reduce particle size
Anatomy:
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Upper dental pad
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Lower incisors
Premolars
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Molars
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Teeth Specializations
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Carnivores
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Canine teeth
highly
developed
and used for
tearing
Molars are
pointed for
bone crushing
Teeth Specializations
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Omnivores
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Grinding teeth
patterns on
posterior teeth
(molars)
Piercing and ripping
cusps on anterior
teeth (incisors)
Tongue - used to
move feed to teeth
Jaw & Teeth Specializations
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Non-ruminant herbivores (horse)
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Incisors for nipping, molars slightly angled,
jaws move circularly (vertical and lateral)
Ruminants
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No upper incisors, have dental pad, molars
allow only lateral movements
Different classes - roughage eaters,
transition types, selective eaters all differ in
tongue mobility and cleft palate
Ruminant Mouth
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Lips range from short,
relatively immobile in
nonselective grazing species to
very mobile (prehensile) in
selective grazing or
concentrate selecting species
Chew in a lateral (grinding)
motion on one side of mouth at
a time
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Needed to increase surface area
of feed particles
Feed chewed primarily during
rumination in grazing species
Jaw Muscles and Mastication
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Temporalis muscle - develops maximum force on anterior portion
of jaw (largest muscle in carnivores and smallest muscle in
herbivores)
Masseter and medial pterogoid - maximum force for crushing and
grinding
Lateral pterogoid - allows lateral movement which is important
for grinding (highly important in herbivores, but carnivores and
many omnivores have almost no lateral movement of jaws)
Monogastric Tongue
Function:
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Comprised of three muscles
Maneuvers food in the mouth
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Moves feed to teeth for grinding and to the
back of the mouth for swallowing
Can distinguish between feed and toxins by
papillae or taste buds
Ruminant Mouth - Tongue
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Drinking, chewing and forming boluses
Prehension of feed
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Covered with rough, hook-like papillae that assist
in grasping feed
Important in nonselective grazing species
Taste buds
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More numerous than monogastric species
More numerous on nonselective grazing species
Believed that taste is primarily used for food
avoidance by grazing species while concentrate
selecting species select on the basis of smell
Monogastric Salivary Glands
Types of Glands:
Zygomatic
Parotid
Sublingual
Mandibular
Functions of Saliva
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Moisten feed (salt and water)
Lubrication (aids swallowing)
Starch and(or) lipid digestion (amylase
and(or) lipase)
Salivary Glands
Gland
Type of secretion
Main constituents
Parotid
Serous
Water, enzymes, ions
Submaxillary
Mucous or mixed
Mucin (mucous), mucin
plus enzymes (mixed),
water
Sublingual
Mucous or mixed
Mucin (mucous), mucin
plus enzymes (mixed),
water
Monogastric Salivary Glands
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Flow rate affected by:
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Parasympathetic nervous system
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Increased tone = Increased flow
Increased flow = Increased dilution
Sympathetic nervous system
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Increased tone = Decreased flow
Decreased flow = Increased concentration
Ruminant Mouth - Saliva
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From at least three paired glands
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Submaxillary, sublingual, parotid (50% of
secretions)
Aids in mastication, swallowing, forming bolus
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No digestive enzymes in the saliva of mature
ruminants
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Provides N, P, S and Na for rumen microoganisms
Buffering compounds to maintain rumen pH and
mucin to prevent bloat
Salivation
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Quantity and composition of saliva varies
considerably between species
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Quantity related to level of chewing activity
Amount of secretion
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Dogs
Sheep
Horse
Cattle
minimal (lubrication, no enzymes)
3-10 liters/d
10-12 liters/d
130-180 liters/d
Deglutition (Swallowing)
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Reflex initiated by presence of food in
pharnyx
Propulsion of food to stomach by
esophageal peristalsis
Monogastric Esophagus
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Horse/Pig:
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Striated muscles for first 2/3
Smooth muscles for last 1/3
In horse, esophagus joins stomach at an oblique angle and
cardiac sphincter (the valve between the stomach and
esophagus) only allows one-way flow
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MOST horses cannot belch out gas or vomit
Dog:
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Striated muscles throughout allow GREAT control of digesta
movement both directions
Ruminant Esophagus
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Involved in rumination
Different from monogastric esophagus
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Striated muscle along the entire length
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Provides greater strength
Allows some voluntary control
Funnel shaped
Contains three sphincters active in
rumination and eructation
Esophagus
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Species adaptations
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Ability to control
peristaltic contractions
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Reverse peristalsis
Amount and location of
skeletal muscle
Regurgitation vs.
vomiting
Foregut
in Birds
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Crop
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Bottom of the
esophagus forms a sac
called crop
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Stores undigested food.
◆ Birds
with crop
gorge when food is
available, store it in
crop, and slowly digest
it later
Stomach
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Monogastric
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One compartment
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Varies in size by species
Ruminant
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Four compartments
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Reticulum
Rumen
Omasum
Abomasum
Gastric Digestion
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Functions
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Reservoir for controlled release of digesta to small
intestine
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Mixing food
Mechanical breakdown of feed
Hydrolytic digestion by acid and enzymes
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Horse has small capacity – requires increased number of
smaller sized meals
Mainly protein
Kill bacteria
Secrete intrinsic factor: needed for vitamin B12
absorption
Hormone production
Stomach Regions
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Esophageal
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Cardiac
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Secretes mucus
Fundic
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Non-glandular
Parietal cells
Chief cells
Pyloric
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Mucus
Gastric Pits
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Formed by numerous folds
in the epithelium
Glands empty into the
gastric pit
Many types of glands may
empty into one gastric pit
Gastric Glands
Gland
Type of
secretion
Main constituents
Cardia
Mucous
Mucin
Pylorus or Antrum
Mucous
Mucin
Fundus
Chief cells
Parietal cells
Enzyme
Acid
acid
Pepsinogen Pepsin
HCl, intrinsic factor
Stomach Secretions
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HCl
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Decreases pH (~2-3)
Denatures protein
Kills bacteria
Activates pepsinogen
Mucus
 Protects lining from
acid and enzymes
 No “autodigestion”
 Lubricant
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Pepsinogen
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Rennin (abomasum)
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Activated form is
pepsin
Hydrolyzes protein
Clots milk
Lipase
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Some species
Gastric Motility and Emptying
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Motility aids mixing, mechanical and
hydrolytic reduction of feed to chyme
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acid pulp
Emptying is stimulated by distension of
antral wall and presence of liquid
chyme
Control of Gastric Secretions
and Gastric Motility
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Cephalic phase
Gastric phase
Intestinal phase
Cephalic Phase
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Vagal reflex
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Parasympathetic innervation
Increases gastric motility, enzyme
secretion
Small increase in HCl secretion
Gastric Phase
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Local reflex, depends on presence of
feed in stomach
Mainly mediated by gastrin
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Increases HCl secretion
Intestinal Phase
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Stimulated by duodenal distension, pH,
osmolarity, nutrients (fat)
Cholecystokinin (CCK) is released by the
small intestine
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Decreases HCl secretion and gastric
motility
Gastrointestinal Hormones
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Gastrin
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Origin: Stomach, Abomasum
Stimulus: Food in stomach
Function: Stimulates HCl & pepsinogen secretion,
increases stomach motility
Secretin
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Origin: Duodenum
Stimulus: Acid
Function: Stimulates pancreatic secretions. Slows
stomach motility and acid production
Gastrointestinal Hormones
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Cholecystokinin (CCK)
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Origin: Duodenum
Stimulus: Fat & protein in duodenum
Function: Stimulates bile and pancreatic secretions
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Also regulates appetite and feed intake
Gastric Inhibitory Protein (GIP)
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Origin: Duodenum
Stimulus: Fats and bile
Function: Inhibit stomach motility and secretion of
acid and enzymes
Ruminant Stomach
Anatomy:
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Reticulum
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Rumen
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Omasum
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Abomasum
Reticulorumen
Although
structurally they
appear as a single
continuous
compartment,
functionally they
are distinctly
different
Reticulum
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Honeycomb lining
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No secretions
Formation of food
bolus
Regurgitation
initiated here
Collects hardware
(nails, wire)