what are the four basic digestive systems of mammals and birds?
- simple system without caecum
- simple system with functional caecum
- ruminant system
- avian system
what are the main parts of the gi tract?
- mouth
- esophagus
- stomach
- small intestine
- large intestine
- caecum
- rectum
- anus
what is solubility?
ability of CHOs to dissolve in water
what is digestibility of CHOs?
the host organism has the enzymes necessary to digest CHOs
what is fermentability?
gut bacteria have the enzymes necessary to break down CHOs
what are the key features of a simple system without caecum?
- monogastric
- non functional caecum
- suited for a nutrient dense, low fibre diet
what is the function of the oral cavity?
- mechanical digestion via chewing
- chemical digestion via alpha amylase and lingual lipase which break down starch
what is the function of the stomach?
- turn bolus into chyme via gastric juice which contains water, electrolytes, HCl, and enzymes
- pH of 2
- some mechanical digestion
what is the function of the small intestine?
- main site for nutrient digestion and absorption via pancreatic juice and bile acids
- intestinal motility
- neutralize chyme acidity with pancreatic juice
what is the function of the large intestine?
- site of fermentation
- production of short chain fatty acids/volatile fatty acids
- water absorption
what is the importance of bacteria in the gut?
they ferment nondigestible CHOs, mostly through anaerobic fermentation
what are the key features of a simple system with a functional caecum?
- pseudo ruminant
- hindgut fermenter
- functional caecum
- suited for a diet with large amounts of fodder and foraging
what is the difference between hindgut and foregut fermenters?
- foregut: fermentation happens in the stomach and small intestine
- hindgut: fermentation happens after the small intestine
what is the purpose of a functional caecum?
- large hindgut filled with bacteria
- short chain fatty acids provide most energy needs for host
- produces vitamins
what is coprophagy?
when animals eat their feces, may be a sign of nutrient/energy deficiency, young animals do it to colonize their guts with bacteria as well
what are the key features of a ruminant system?
- large stomach divided into 4 regions: reticulum, rumen, omasum, abomasum
- highly suited for animals that eat a high quantity of fodder and forage
- foregut fermenters
- nutrients produced by bacteria then become available for digestion and absorption
- different in cows vs horses due to different lifestyle
what is the reticulum?
- honey comb appearance to capture nutrients and trap foreign materials
- rich in bacteria (fermentation vat)
what is the rumen?
- largest part of ruminant stomach
- rich in bacteria
- rumen papillae for increased surface area for absorption
- food is mixed, partially broken down, and temporarily stored
- most energy produced here as short chain fatty acids
what is the omasum?
- resorption of water and some electrolytes
- filters large particles
what is the abomasum?
- digestive enzymes secreted from gastric glands
- the true stomach, similar to that of monogastric animals
what are the pros and cons of a ruminant system?
- pros: vitamin synthesis, non protein nitrogen used for making protein
- cons: CHOs degraded into gases and lost through eructation (loss of energy), heat production
what are the key features of the avian digestive system?
- beaks and claws are important for breaking up food into small pieces that birds can swallow
- rapid digestion
what is the crop?
- enlarged part of esophagus
- temporary food storage
- softens food that can be regurgitated to feed offspring
what is the two chamber stomach?
- proventriculus: glandular portion, gastric enzymes and HCl are secreted
- gizzard: muscular portion, grinds and digests tough food
