Comparison: The Digestive System

Unique among vertebrates, usually capped with enamel

Lacking teeth: turtle and birds

Homodont: teeth similar in appearance throughout mouth

Polyphyodont dentition: teeth are continuously replaced; ensures rejuvenation of teeth if worn/ broken

Heterodont- teeth differ in appearance throughout mouth

Polyphyodont- repitles

• diphyodont: two sets of teeth (mammalian)
• --> 1st set: deciduous dentition- milk/early teeth
• --> 2nd set= permanent dentition- adult/ mature teeth (includes molars)

• acrodont
• pleurodont
• thecodont

teeth attached in shallow sockets within the top surface of the jaw bone (weakest)

--> not very strong

--> allows for rapid replacement

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

• Teeth attached by roots that are firmly fixed into sockets within the jawbone
• - strongest vertebrate tooth attachment
• - Largest surface area of tooth to jawbone

most teleost fish--> teeth form abrasive surfaces used to scrape algae from rocks

--> acrodont tooth attachment

teeth have sharp, knifelike edges along sides to pierce the skin; acrodont tooth attachment

• 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)

display acrodont (snakes), thecodont (alligators), and pleurodont (lizards) tooth attachment

• 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 tooth: 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)

thecodont

four- incisors, canines, premolars, molars

brachydont-low crowns (humans, pigs)

hypsodont- high crowns (horses)

• -rounded peaks [omnivores])
• -lophodont (cusps drawn out into predominately straight edges [horses, rhinos])
• - selenodont (crescent-shaped cusps (camels, deer))

sectorial teeth

carnassials 

tusks

modified teeth with ridges on opposing teeth that slice by one another to cut tissue

used to cut sinew and muscle

• modified, elongated teeth
• --> elephants (incisors), Narqhals (spiraled upper left incisor), walrus (downward upper canines)

groupings of epithelial cells that line the buccal cavity and secrete mucous and serous fluids

fish- rarely present due to moistening from watery medium

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)

Amphibians: mucous glands on tonge and a large intermaxillary gland located within the palate

• 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

strips of glandular tissue (supralabial and infralabial glands) along upper and lower lips

• - lingual and sublingual glands (tongue)
• - premaxillary and nasal glands (snout)
• - palatine glands (roof of mouth)
• - Lacrimal and Hardesian glands
• - Duvernoy's gland (non-venomous snakes):
• - Venom gland (Duvernoy's homolog in venomous snakes)

release mucous to lubricate prey during swallowing

secretions bathe the eye and vomeronasal organ

Found along posterior upper lip and releases a serous secretion that may help in digestion

secretes toxic and digestive chemicals

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 zygomatic arch in dogs, cats, and other carnivores

release secretions into floor of buccal cavity

release secretions into floor of buccal cavity

release secretions into floor of buccal cavity

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

Liver is composed of multiple lobes

Snakes- elongated and narrow within the tubular body cavity

cecum from gut found near embryonic liver in vertebrate embryos, sometimes called the hepatic cecum

function: site of enzyme production and food absorption

function: bile storage and release during digestion

Absent in jawless fish, most birds, few mammals

Present in cartilaginous and bony fish, amphibians, reptiles, few birds, most mammals

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

have a dorsal and ventral pancreas with two distinct structures

distinct exocrine and endocrine pancreas with clearly delineated pancreatic islets

exocrine and endocrine pancreas always present as discrete organs near the duodenum