Digestive system

• Digestive system Involves?

  • digestive tract (DT)
  • Gastrointestinal tract (GIT)
  • the gut
• Autonomic nervous system controls DS:

  • parasympathetic = stimulates DS - increased salivation, motility
  • sympathetic = inhibits DS
• components of digestive tract:

  • mouth + oral cavity
  • fore gut
  • mid gut
  • hind gut
• components of digestive tract - mouth and oral cavity:

  • bite, chew, grind, lubricate
  • pharynx - facilitates food passage
• components of digestive system: foregut:

  • oesophagus - pushes + transports
  • stomach - degrades, digests, absorbs
  • part of duodenum
• components of digestive tract: mid gut:

  • last part of duodenum
  • small intestine - degrades, digests, absorbs
  • appendix
  • part of caecum - colon
• components of digestive tract: hind gut:

  • colon
  • rectum
  • anal canal
  • ferments and expels
• Mouth and lip function:

  Select, bite, gather and grasp food

  • Move food to the oral cavity
  • Taste or select or reject food
  • Salivate to neutralise & lubricate food
  • Prehensile and Masticate food to form bolus
• prehension:

  moving food into oral cavity
• importance of chewing:

  • Increases surface area for good mixing of buffers, saliva and enzyme with food
  • Reduces particle size for safe swallowing
  • Exposes food for microbial colonisation
• mastication:

  grinding to reduce particle size
• teeth and jaws: carnivores

  carnivores:

  • use canine teeth for tearing
  • use pointed molars for crushing bones
• Teeth and jaws: Omnivores

  Omnivores

  • molars for grinding
  • incisors for piercing & ripping
  • tongue to move food into teeth
• teeth & jaws: Pseudo-ruminants

  Pseudo-ruminants:

  • incisors for biting
  • angled molars
  • circular jaw movements = help grinding
• teeth & jaws: ruminants:

  • no upper incisors
  • strong dental pad
  • molars with tongue and jaw movements = help chew food
• salivation:

  • soften & lubricates food
  • buffering - pH
• foregut - stomach in mammals

  Mono - gastric = simple stomach - single part

  Multi - gastric = four parts (ruminants)
• multi - gastric stomach: 4 parts:

  • reticulum
  • rumen
  • omasum
  • adomasum
• front vs hind gut fermenters:

  • both use microbes
  • degrade & digest high fibre diets
  • cellulose rich
• Mid-gut:

  • short in carnivores
  • long in herbivores
  • no sucrose in ruminants
  • no lactase in adult pigs
• post gastric fermenters: Caecal fermenters:

  • rodents, rabbits, small herbivores
  • use coprophagy
• post gastric fermenters: colonic fermenters

  • true herbivores - horse
  • omnivores - humans, pigs
  • carnivores - cats & dogs
• foregut fermentation:

  • more efficient per unit of food
  • slow digestion
  • size reduction
• hind gut fermentation:

  • more efficient over time
  • faster turnover but less effective
  • coprophagy = food passes though DS twice
• ruminant stomach: 4 compartments

  1. rumen
  2. reticulum
  3. omasum
  4. abomasum
• ruminant digestion:

  • rapid swallowing of food with no chewing
  • ingested feed moves directly to rumen
  • solid parts stay in rumen
  • liquid and solubles move to reticulum then omasum then abomasum
• rumination:

  chewing the cud while standing or sitting
• regurgitation:

  feed is forced back into mouth for chewing
• rumen microbes:

  • bacteria
  • protozoa
  • fungi
• rumen bacteria: main that occupy RR

  • streptococci
  • lactobacilli
  • cellulolytic
  • proteolytic
  • amylolytic
  • lipolytic
• rumen function:

  • receives, breaks + moves food
  • fermentation vessel
  • saliva helps maintain rumen pH
• rumen: papillae

  • has papillae that increase surface area for:
  • microbial attachment
  • absorption of fermented products via rumen wall
• rumen fermentation:

  • has by-products: including gases
  • remove gases via eructation = belching
  • small amounts absorbed into blood stream and removed by lungs
  • if not - can cause bloat
• functions of reticulum:

  • microbe population
  • honeycomb like projections
  • solid particles can be trapped
  • regurgitation starts here
  • helps move food backwards & forwards - help disintegration + fermentation
• functions of omasum:

  • muscular with piles
  • grinds & squeezes food
  • little digestion
  • removes water from food
  • absorption of VFAS
• functions of abomasum:

  • true stomach - similar to monogastrics
  • gastric juices added to undegraded feed - pepsin, HC1, mucous
  • pH = 3
  • food turns into slurry before entering small intestine
• abomasum, why is pH 3?

  • dismantles protein molecules
  • denatures bacteria, pathogens & toxins
  • dissolves minerals
  • promotes gastric digestion
• pancreatic secretions:


  enzymes:

  • amylase
  • lipase
  • proteases
  • trypsinogen converted to trypsin
  • chymotrypsinogen converted to chymotrypsin
  • procarboxipeptidase converted to carboxypeptidase
• bile:

  • secreted via bile duct
• bile: factors affecting secretion:

  • food as slurry in duodenum
  • HC1 in duodenum
  • salts in duodenum
  • fat molecules in duodenum