Comparative Digestive Physiology. Why Do Animals Digest? Food not ingested in suitable state...
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Transcript of Comparative Digestive Physiology. Why Do Animals Digest? Food not ingested in suitable state...
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Comparative Digestive Physiology
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Why Do Animals Digest?Food not ingested in suitable state
Physical nature of food determined by: gathering apparatus for uptake type of digestive system
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Primary Functions of the Digestive Tract
Transport food – peristaltic contractions Digestion
Mechanical breakdown Chemical breakdown
Absorption Passive diffusion and active transport
Synthesis - true protein, FA, starch, vitamins Excretion – elimination of waste products
Via bile (toxins, microbes etc) Via rectum (Ca, Mg, P)
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Regions of Alimentary Canal Foregut functions
Ingestion and storage of feeds Midgut functions
Mechanical, chemical & enzymatic digestion of feed
Nutrient absorption Hindgut functions
Water & ion re-absorption Formation, storage, excretion of feces
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Associated Structures Pancreas Liver Gallbladder Salivary glands
Contribute to small intestinal digestion
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Primitive Gastrointestinal Tract
Found in monotremes (egg-laying mammals), insectivores (bats, shrews, moles), and dermopterans (colugos)
Simple stomach, little or no division between small intestines and large intestines, large intestine simple, presence of cecum, non-sacculated colon
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Species-Dependent Nutritional Adaptations Includes involvement of:
Teeth Jaws and jaw musculature Alimentary canal
Stomach - May be simple or become sacculated to compartmentalize functions for prolonged storage of feed and utilization of bacterial fermentation (langurs and ruminants)
May also become voluminous for storage of large amounts of feed (vampire bats)
Large intestine - varies substantially in length, compartmentalization, and complexity among species
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Ruminants 2.8 billion domesticated ruminants
Cattle, sheep, deer, elk, bison Pregastric fermentation
Ability to chew cud at frequent intervals distinguishes true ruminant from other foregut fermenters
Kangaroo, colobine monkey are not true ruminants Four compartment stomach
Reticulum Rumen Omasum Abomasum
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Ruminants vary in size and habitat
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Classification of Ruminants by Feeding Preference
Classes of ruminants Concentrate selectors Intermediate feeders Roughage grazers
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Concentrate Selecting Species
Properties Evolved early Small rumens Poorly developed omasums Large livers Limited ability to digest fiber
Classes Fruit and forage selectors
Very selective feeders Duikers, sunis
Tree and shrub browsers Eat highly lignified plant tissues to extract cell
solubles Deer, giraffes, kudus
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Intermediate Feeding Species Properties
Seasonally adaptive Feeding preference
Prefer browsing Moose, goats, elands
Prefer grazing Sheep, impalas
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Roughage Grazing Species Properties
Most recently evolved Larger rumens and longer retention times Less selective Digests fermentable cell wall carbohydrates
Classes Fresh grass grazers
Buffalo, cattle, gnus Roughage grazers
Hartebeests, topis Dry region grazers
Camels, antelope, oryxes
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Structures in Mouth Lips Teeth Tongue Salivary glands
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Mouth Functions
Grasp food Taste Masticate food Mix with saliva
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Digestion in the Mouth Prehension
Bringing the food to the mouth Upper limbs, head, beak, claws,
mouth, teeth and lips Mastication or chewing
To crush the food, increase surface area and allow enzymes to act on molecules
Carnivores only to reduce the size of the particle to a size small enough to swallow
Herbivores must chew continuously (40-50,000 times a day) to increase surface area
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Prehension Seizing and conveying feed to mouth Mechanisms vary with behavior and diet
Forelimbs Primates, raccoon
Snout Elephant, tapir
Tongue Anteater, cow, sheep
Lips Horse, sheep, rhinoceros
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Prehension Domestic mammals use lips, teeth and tongue
Relative importance varies by species Horses
lips when eating from manger teeth when grazing
Cows and sheep have limited use of lips 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
Most mammals use suction Dogs and cats use tongue to form ladle
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The Importance of Prehension in Diet Formulation
White Rhino (“wijd” = wide) Squared off upper lip used to
“crop” grass Grazes on savannah
Black Rhino Prehensile upper lip for
browsing Consumes bushes and
shrubs in forest
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Mastication Physical reduction of feed Especially important in non-
ruminant herbivores Adaptations with teeth
Carnivores Herbivores Edentates (sloths, armadilloes, anteater)
Relative toothlessness
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Morphological Adaptations for Herbivory
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
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Monogastric Teeth Function:
Mechanically reduce particle size
Increase surface area
Four types: Incisors are used for
cutting Canine (fangs, eye teeth, tusks) are tearing teeth
Premolars and molars (cheek teeth) grind the food
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Ruminant Mouth - Teeth
Function: Reduce particle size
Anatomy: Upper dental pad Lower incisors Premolars Molars
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Teeth Specializations Carnivores
Canine teeth highly developed and used for tearing
Molars are pointed for bone crushing
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Teeth Specializations Omnivores
Grinding teeth patterns on posterior teeth (molars)
Piercing and ripping cusps on anterior teeth (incisors)
Tongue - used to move feed to teeth
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Jaw & Teeth Specializations Non-ruminant herbivores (horse)
Incisors for nipping, molars slightly angled, jaws move circularly (vertical and lateral)
Ruminants 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
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Ruminant Mouth
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
Needed to increase surface area of feed particles
Feed chewed primarily during rumination in grazing species
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Jaw Muscles and Mastication
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)
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Monogastric Tongue
Function: Comprised of three muscles Maneuvers food in the mouth
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
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Ruminant Mouth - Tongue
Drinking, chewing and forming boluses Prehension of feed
Covered with rough, hook-like papillae that assist in grasping feed
Important in nonselective grazing species Taste buds
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
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Monogastric Salivary Glands
Types of Glands:
Parotid
Sublingual
Mandibular
Zygomatic
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Functions of Saliva Moisten feed (salt and water) Lubrication (aids swallowing) Starch and(or) lipid digestion
(amylase and(or) lipase)
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Salivary GlandsGland Type of
secretionMain 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
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Monogastric Salivary Glands Flow rate affected by:
Parasympathetic nervous system Increased tone = Increased flow Increased flow = Increased dilution
Sympathetic nervous system Increased tone = Decreased flow Decreased flow = Increased
concentration
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Ruminant Mouth - Saliva From at least three paired glands
Submaxillary, sublingual, parotid (50% of secretions)
Aids in mastication, swallowing, forming bolus No digestive enzymes in the saliva of
mature ruminants Provides N, P, S and Na for rumen
microoganisms Buffering compounds to maintain rumen pH
and mucin to prevent bloat
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Salivation Quantity and composition of saliva
varies considerably between species Quantity related to level of chewing activity
Amount of secretion Dogs minimal (lubrication, no
enzymes) Sheep 3-10 liters/d Horse 10-12 liters/d Cattle 130-180 liters/d
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Deglutition (Swallowing) Reflex initiated by presence of
food in pharnyx Propulsion of food to stomach by
esophageal peristalsis
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Monogastric Esophagus Horse/Pig:
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
MOST horses cannot belch out gas or vomit Dog:
Striated muscles throughout allow GREAT control of digesta movement both directions
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Ruminant Esophagus
Involved in rumination Different from monogastric
esophagus Striated muscle along the entire length
Provides greater strength Allows some voluntary control
Funnel shaped Contains three sphincters active in
rumination and eructation
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Esophagus
Species adaptations Ability to control
peristaltic contractions
◆ Reverse peristalsis ◆ Amount and location
of skeletal muscle◆ Regurgitation vs.
vomiting
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Foregut in Birds
Crop Bottom of the
esophagus forms a sac called crop
◆ Stores undigested food.
◆ Birds with crop gorge when food is available, store it in crop, and slowly digest it later
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Stomach Monogastric
One compartment Varies in size by species
Ruminant Four compartments
Reticulum Rumen Omasum Abomasum
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Gastric Digestion Functions
Reservoir for controlled release of digesta to small intestine
Horse has small capacity – requires increased number of smaller sized meals
Mixing food Mechanical breakdown of feed Hydrolytic digestion by acid and enzymes
Mainly protein Kill bacteria Secrete intrinsic factor: needed for vitamin B12
absorption Hormone production
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Stomach Regions Esophageal
Non-glandular Cardiac
Secretes mucus
Fundic Parietal cells Chief cells
Pyloric Mucus
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Gastric Pits Formed by numerous
folds in the epithelium Glands empty into the
gastric pit Many types of glands
may empty into one gastric pit
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Gastric Glands
Gland Type of secretion
Main constituents
Cardia Mucous Mucin
Pylorus or Antrum
Mucous Mucin
Fundus Chief cells Parietal cells
EnzymeAcid
acid
Pepsinogen PepsinHCl, intrinsic factor
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Stomach Secretions HCl
Decreases pH (~2-3) Denatures protein Kills bacteria Activates pepsinogen
Mucus Protects lining from
acid and enzymes No
“autodigestion” Lubricant
Pepsinogen Activated form is
pepsin Hydrolyzes protein
Rennin (abomasum) Clots milk
Lipase Some species
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Gastric Motility and Emptying Motility aids mixing, mechanical
and hydrolytic reduction of feed to chyme acid pulp
Emptying is stimulated by distension of antral wall and presence of liquid chyme
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Control of Gastric Secretions and Gastric Motility Cephalic phase Gastric phase Intestinal phase
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Cephalic Phase Vagal reflex
Parasympathetic innervation Increases gastric motility, enzyme
secretion Small increase in HCl secretion
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Gastric Phase Local reflex, depends on presence
of feed in stomach Mainly mediated by gastrin
Increases HCl secretion
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Intestinal Phase Stimulated by duodenal distension,
pH, osmolarity, nutrients (fat) Cholecystokinin (CCK) is released
by the small intestine Decreases HCl secretion and gastric
motility
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Gastrointestinal Hormones Gastrin
Origin: Stomach, Abomasum Stimulus: Food in stomach Function: Stimulates HCl & pepsinogen
secretion, increases stomach motility Secretin
Origin: Duodenum Stimulus: Acid Function: Stimulates pancreatic secretions.
Slows stomach motility and acid production
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Gastrointestinal Hormones Cholecystokinin (CCK)
Origin: Duodenum Stimulus: Fat & protein in duodenum Function: Stimulates bile and pancreatic
secretions Also regulates appetite and feed intake
Gastric Inhibitory Protein (GIP) Origin: Duodenum Stimulus: Fats and bile Function: Inhibit stomach motility and
secretion of acid and enzymes
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Ruminant Stomach
Anatomy: Reticulum
Rumen
Omasum
Abomasum
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Reticulo-rumen
Although structurally they appear as a single continuous compartment, functionally they are distinctly different
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Reticulum
Honeycomb lining No secretions
Formation of food bolus
Regurgitation initiated here
Collects hardware (nails, wire)