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Digestion I
• Functions:
1) food procurement - method of capturing and ingesting food items
2) mechanical (physical) breakdown of food - breaking larger food items into
smaller pieces
to enhance chemical digestion
3) chemical breakdown of food - use of enzymes and other molecules to break
large molecules into smaller molecules
4) absorption - transport of smaller food molecules into body tissues for use
by body cells
5) additional processing - filtering of molecules to remove toxins
• Recall your embryology!
• Cleavage:
• Blastula:
• Blastocoele:
• Blastopore:
• Gastrulation:
• Gastrula:
• Archenteron:
• Protostome:
• Deuterostome:
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• Basic structure of the gut tube (eucoelomates):
• Formation of “accessory organs”:
• Liver
• Gall bladder
• Pancreas
• Cecum
• Gills
• Urinary bladder • Lungs
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• Basic breakdown of the digestive system (3 regions with different functions):
FUNCTION VERTEBRATE INVERTEBRATE
FOREGUT
MIDGUT
HINDGUT
THE FOREGUT:
• Food procurement – many examples of diversity:
• Molluskan radula for grazing, drilling, or
harpooning:
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• Crustacean modified legs for suspension feeding:
• Fish gill rakers for suspension feeding
• Whale baleen and crabeater seal teeth modified for
suspension feeding
• Fish cranial kinesis for suction feeding
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• Most vertebrates have homodonty for simple prey capture
• Mammals have heterodonty for complex mechanical
breakdown
• Selenodonty:
• Lophodonty:
• Bunodonty:
• Carnassials:
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• Similar diversity in bird beaks:
• FOREGUT (cont.):
1) Components (of tube): pharynx + esophagus
2) Function: transport via flushing with water (aquatic forms) or muscular
peristalsis (terrestrial forms)
3) Specializations in vertebrates:
• salivary glands produce venom (snakes, some shrews)
• salivary glands produce anticoagulant (vampire bats)
• birds with a crop for food storage
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• MIDGUT:
1) Components: stomach (including pyloris)
2) Function: absorption (proteins), storage,
transport, chemical breakdown (HCl +pepsinogen), mechanical breakdown
(muscular, rugae, gastroliths)
3) Specializations:
• birds have a proventriculus and gizzard
• ruminant mammals (foregut fermenters)
have a 4-chambered ruminant stomach
1. Food swallowed - passes to rumen
for fermentation
2. Regurgitate large pieces - the cud
3. After fermentation in rumen,
small pieces pass to
reticulum for absorption
4. Passage to omasum and then to abomasum for absorption
• Digestion slow but efficient - ruminant stomach limits food
intake
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• HINDGUT:
1) Components: intestines, liver, pancreas
2) Function: transport via muscular peristalsis; absorption
(water, sugars, amino acids, fatty acids, ions);fat emulsification (liver bile); starch breakdown
(pancreatic amylase)
3) Specializations:
• plica, villi, + microvilli (tetrapods)
• typhlosole (annelids)
• spiral intestine (sharks)
• long intestines (endotherms/herbivores)
• cecum (hind gut fermenting mammals, insects,
flatworms, … many others)
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