The Digestive System

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  1. Vertebrate Teeth
    Unique among vertebrates, usually capped with enamel 

    Lacking teeth: turtle and birds
  2. General characteristics of teeth in lower vertebrates
    Homodont: teeth similar in appearance throughout mouth

    Polyphyodont dentition: teeth are continuously replaced; ensures rejuvenation of teeth if worn/ broken
  3. General Characteristics of tetrapods
    • Heterodont- teeth differ in appearance throughout mouth
    • polyphyodont- reptiles
    • diphyodont- two sets of teeth (mammalian)
    • --> 1st set= deciduous dentition- milk/ early teeth
    • --> 2nd set= permanent dentition- adult/ mature teeth (includes molars)
  4. Vertebrate teeth attachment
    • acrodont
    • pleurodont
    • theocodont
  5. acrodont
    • teeth attached in shallow sockets within the top surface of the jaw bone (weakest)
    • --> not very strong--> allows for rapid replacement
  6. Pleurodont
    teeth attached on the inner side and upper side of the jawbone that increases jawbone attachment area--> still conducive to polyphodont, but not as much

    - stronger than acrodont, supports rapid replacement
  7. Thecodont
    • Teeth attached by roots that are firmly fixed into sockets within the jawbone
    • - strongest vertebrate tooth attachment
    • - Largest surface area of tooth to jawbone
  8. Specialized teeth of lower vertebrates: teleost fish
    • most teleost fish--> teeth form abrasive surfaces used to scrape algae from rocks
    • --> acrodont tooth attachment
  9. Specialized teeth of lower vertebrates: sharks
    teeth have sharp, knifelike edges along sides to pierce the skin; acrodont tooth attachment
  10. Specialized teeth of lower vertebrates: salamanders
    • Differences between larval and metamorphosed adults
    • - larval: pointed cone-shaped
    • - adults: specialized teeth are bicuspid (having 2 cusps) and crown sits upon a basal pedicel, attached by collagenous fibers
    • --> when tooth replaced, crown is lost and pedicel quickly resorbed for rapid tooth replacement (acrodont tooth attachment)
  11. Reptilian teeth
    display acrodont (snakes), thecodont (alligators), and pleurodont (lizards) tooth attachment
  12. Carnivorous reptiles
    teeth have sharply pointed cusps that penetrate skin and provide a firm hold on prey

    • - reverse curved teeth in front of mouth-tip of tooth inclined forward from the rest of the toot: better for grasping prey/ preventing escape
    • - maxillary teeth- open groves down which oral secretions flow during feeding
    • --> venomous snakes--> fangs- ends fuse to form a channel for venom from venom duct
    • --> polyphyodont (regular replacement)
  13. Mammalian teeth
    Attachment: thecodont

    Types of teeth: four- incisors, canines, premolars, molars

    Crown variations: brachydont- low crowns (humans, pigs); hypsodont- high crowns (horses)

    • Cusp variations:
    • - bunodont (cusps form rounded peaks [omnivores])
    • - lophodont (cusps drawn out into predominately straight edges [horses, rhinos])
    • - selenodont (crescent-shaped cusps (camels, deer))
  14. Specialized mammalian teeth
    • Sectorial teeth: modified teeth with ridges on opposing teeth that slice by one another to cut tissue
    • --> carnivores--> carnassials: used to cut sinew and muscle

    • Tusks- modified, elongated teeth
    • --> elephants (incisors), Narwhals (spiraled upper left incisor), walrus (downward upper canines)
  15. Orals glands
    • groupings of epithelial cells that line the buccal cavity and secrete mucous and serous fluids
    • Or
    • fish- rarely present  due to moistening from watery medium
    • tetrapods- prevalent
    • --> lack watery medium to moisten food
    • --> salivary glands- most common, form and secrete saliva
    • -----> saliva: contains mucous, salts, proteins, and enzymes such as amylase (starch digestion)
  16. Oral glands of amphibians
    Amphibians: mucous glands on tonge and a large intermaxillary gland located within the palate
  17. Oral glands of birds
    • birds: most birds, especially water feeding birds, lack oral glands
    • --> some passerine birds (perching birds with 3 toes and 1 toe back) use mucous oral secretions to aid in nest building
  18. Oral glands of reptiles
    strips of glandular tissue (supralabial and infralabial glands) along upper and lower lips

    • Types of glands: 
    • - lingual and sublingual glands (tongue), premaxillary and nasal glands (snout) and palatine glands (roof of mouth): release mucous to lubricate prey during swallowing

    - Lacrimal and Hardesian glands: secretions bathe the eye and vomeronasal organ

    - Duvernoy's gland (non-venomous snakes): Found along posterior upper lip and releases a serous secretion that may help in digestion

    - Venom gland (Duvernoy's homolog in venomous snakes): secretes toxic and digestive chemicals
  19. Oral glands in mammals
    most common oral gland= salivary glands to produce saliva for lubrication and digestion

    Found in three major pairs: mandibular, sublingual, parotid

    Zygomatic gland can be found below zygomatci arch in dogs, cats, and other carnivores
  20. Mandibular
    release secretions into floor of buccal cavity
  21. Sublingual
    release secretions into floor of buccal cavity
  22. parotid
    release secretions into roof of buccal cavity
  23. Liver
    • All vertebrates possess a liver that has the same basic microscopic structure
    • - composed of sheets of hepatocytes separated by blood sinuses where courses of venous blood returning from intestines and arterial blood from the hepatic artery are filtered through
    • Snakes- elongated and narrow within the tubular body cavity
    • Liver is composed of multiple lobes
  24. Liver: Protochordates/ Amphioxus
    cecum from gut found near embryonic liver in vertebrate embryos, sometimes called the hepatic cecum

    function: site of enzyme production and food absorption
  25. The gallbladder
    function: bile storage and release during digestion
  26. The pancreas
    present throughout vertebrates as an exocrine (pancreatic cells-digestive enzymes) and endocrine (pancreatic islets- blood glucose regulation) gland, although distinction may not always be discrete

    Jawless fish: exocrine pancreas dispersed throughout submucosa and on the liver; Endocrine pancreas distinct, near bile duct; has a diffuse pancreas

    Sharks: forms discrete gland with associated exocrine and endocrine components
  27. Sharks
    have a dorsal and ventral pancreas with two distinct structures
  28. Pancreas: bony fish
    distinct exocrine and endocrine pancreas with clearly delineated pancreatic islets
  29. Pancreas: tetrapods
    exocrine and endocrine pancreas always present as discrete organs near the duodenum
Card Set
The Digestive System
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