Physiology of Digestive System.ppt by ZubairLatif


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									Digestive System
 Three (3) basic types of digestive systems:

  ► Monogastric – simple stomach.

  ► Ruminant (cranial fermentor) – multi-compartmented

  ► Hind gut (caudal) fermentor – simple stomach, but
    very large and complex large intestine
           Monogastric         Ruminants                     Hind fermentor

Chickens          Pigs   Beef Cattle          Dairy Cattle

Turkeys           Dogs     Goats                Sheep

           Cats                        Deer                          Ostrich
• 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
    Primary Functions of the Digestive Tract

•   Transport food – peristaltic contractions

•   Digestion - reduce feed particles to molecules that can be absorbed
              the blood
              mechanical breakdown by chewing
              chemical breakdown by HCl and digestive enzymes

•   Absorption - allows nutrients to pass through membranes of GIT to
              the blood stream
               passive diffusion and active transport

•   Synthesis - true protein, FA, vitamins

•   Excretion – elimination of waste products
                bile (toxins, microbes etc)
– Grasp food
– Taste
– Masticate food
– Mix with saliva
Myenteric plexus (Auerbach)
   Located between the longitudinal and circular layers of muscle in
   the tunica muscularis
   Controls tonic and rhythmic contractions
   Exerts control primarily over digestive tract motility

Submucosal plexus (Meissner)
   Buried in the submucosa
   Senses the environment within the lumen
   Regulates GI blood flow
   Controls epithelial cell function (local intestinal secretion and
   May be sparse or missing in some parts of GI tract

Partially controlled by autonomic nervous system
3 types of neurons in enteric system
  1. Sensory neurons (5 types)
         Chemoreceptors sensitive to acid, glucose and amino acids have
            been demonstrated which, in essence, allows "tasting" of
            lumenal contents. Sensory receptors in muscle respond to
            stretch and tension
  2. Motor neurons
     Control GI motility and secretion, and possibly absorption
  3. Interneurons
     Largely responsible for integrating information from sensory neurons
         and providing it to motor neurons
          Digestion in 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 need only to reduce the size of the particle
     • Herbivores must chew continuously (40-50,000 times a day)
• Seizing and conveying feed to mouth
• Mechanisms vary with behavior and diet
  – Forelimbs
     • Primates,
  – Snout
     • Elephant, Tongue
     • cow, sheep
  – Lips
     • Horse, sheep
• Domestic mammals use lips, teeth and
  – 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

• 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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