Comparative Anatomy Digestive System Kardong Chapter 13 Part 11

Digestive System Agnatha - a straight digestive tube Coiled tube evolved with lengthening of tract Figure 11.1. Simple to complex digestive systems—lower verts and birds (book figure 13.27).

Figure 11.2. Simple to complex digestive systems—m ammals (book figure 13.28).

Digestive System Six major subdivisions Buccal cavity Pharynx Esophagus Stomach Small & large intestine Rectum

Buccal Cavity Begins at mouth, ends at pharynx Tongue in floor of cavity Palate in roof of cavity Primary palate Secondary palate Teeth Figure 11.3. Buccal cavity in monkey and shark.

Palates Primary palate in anamniotes- nasal passageways empty into buccal cavity Ex: Salamander Secondary palate of amniotes- extends to pharyngeal cavity Internal nares Figure 11.4. Buccal cavity of amphibian (a) and mammal (b).

Teeth Figure 11.5. Types of cusps (book figure13.15). On jaws normally Cheeks in mammals form pocket Acrodont teeth- fish Bicuspid- amphibians Tricuspid- lizards Pleurodont teeth- snakes Thecodont teeth- crocodilians Figure 11.5. Types of cusps (book figure13.15). Figure 11.6. Cross section of jaw (book figure 13.10).

Cheek and Jaw Teeth Used for storage- rodents and squirrels Modified placoid scales- sharks Polyphyodont- permanent replacement of teeth Diphyodont- two sets of teeth Monophyodont- one set of teeth

Reptilian Egg Tooth Egg tooth - reptiles and snakes Actual tooth Upper jaw To penetrate eggshell Figure 11.7. Monitor egg tooth.

Bird Egg Tooth Egg caruncle- all egg layers Not actual tooth Structure epidermal, horny, keratinized On tip of snout To penetrate eggshell Figure 11.8. Egg caruncle of 15 day old owlet.

Specialized Modifications of Snake Teeth Aglyphous- no modifications for venom delivery Solenoglyphous- retractable teeth, fangs Proteroglyphous- fangs in front of mouth - cobras Opisthoglyphous- fangs in back of mouth – rear-fanged species (hognose snake) Figure 11.9. Position, cross and longitudinal sections of aglyphous (1), opisthoglyphous (2), and solenoglyphous (3) fangs.

Mammalian Teeth Incisors Canines Premolars & Molars For cutting Ex: elephant tusks Canines For piercing Ex: walrus tusks Premolars & Molars To matriculate food Diastema- have incisors but no canines Figure 11.10. Mammalian teeth specializations (heterodont dentition).

Figure 11.11. Deciduous and permanent teeth (carnassials shaded). (book figure 13.7)

Dental Formula Catarrhines, including humans, have 2-1-2-3=16 x 2 = 32 total teeth Canids: 3-1-4-2 and 3-1-4-3 If 0 is present, diastema is present Figure 11.12. Dental formula for mammals.

Tongue Immobile in jawed fish Fleshy in higher vertebrates Frog- tongue shoots out and draws back Glandular field secretes sticky fluid Immobile tongue- turtles, corcs, and some birds Flexible tongue- nectar-feeding bats and snakes Forked tongue of snake Figure 11.13. Jacobson’s organ (sensing apparatus) of snake.

Oral Glands Named based on location Birds have few oral glands Labial- near the lips Palatal- near palate Internasal Sublingual- releases venom Parotid- salivary gland Submaxillary Birds have few oral glands Swifts Figure 11.14. Swift and nest.

Figure 11.15. Oral glands of reptiles

Pharynx In embryo, exhibits series of lateral pharyngeal pouches Gives rise to various glands Slits in pharyngeal region Figure 11.16. Embryonic pharyngeal arches and oral development. Figure 11.17. Adult regions of pharynx.

Pharynx Constant features in tetrapods Glottis-slit to larynx Covered by epiglottis Eustachian tube- opening Esohagus- opening Pharynx further subdivided for food and air passage Foramen cecum- groove on back of tongue Vestigial structure that leads to thyroid gland

Pharynx Figure 11.18. (a) Upper respiratory tract of human showing phayrnx regions and (b) hyoid and larynx.

Esophagus Muscular tube connecting pharynx and stomach Can be short Crop - specialization in birds Outpocketing of esophagus Used to store food Pigeon’s milk Figure 11.19. Esophagus, crop, and stomach of bird (see book figure 13.32).

Stomach Muscular chamber Secretes gastric juices Different lining of stomachs Esophageal-like epithelia Glandular epithelia Ruminant stomach 4 chambers: rumen, reticulum, omasum, abomasum Human stomach Cardiac sphincter- esophagus meets stomach Mostly lined with gastric epithelium Figure 11.20. Stomach of mammals with esophageal-like epithelia in gray and glandular epithelia in red.

Stomach Structure Greater and lesser curvature Messentaries Greater omentum Lesser omentum Cecum - increases surface area 2 parts in bird and croc stomach Proventiculus-granular Gizzard- grinding mill (gastroliths)

Four-chambered Stomachs Rumen - food enters Bacterial action Reticulum - forms a bolus Omasum - reswallowed gras Salivary action Abomasum- food worked out by gastric glands Figure 11.21. Stomach of calf (see book figure 13.43).

Small Intestine Duodenum - 1st portion Bile and pancreatic ducts Jejunum and ileum subdivisions Figure 11.22. Digestive tract showing regions of small intestine in humans.

Small Intestine Brunner’s Glands- mucous glands in duodenum Peyer’s patches- lymphatic nodules in ileum Crypts of Lieberkühn - intestinal glands at base of villi Lacteals- in villi within interior lymphatic vessels Transport fat molecules to circulatory system Valve of Kirckring- increases surface area

Small Intestine Figure 11.23. Histology of alimentary canal of a mammal showing various glands of small intestine.(book figure 13.26).

Large Intestine Fish and amphibians - straight and short Amniotes - divided into colon and rectum Ileocecal valve - allows passage from small intestine into large Sigmoid flexure - S shaped at rectum Cecum - aids in absorption Terminates at vermiform appendix Cloaca - common chamber for digestive, urinary, and reproductive products to empty Figure 11.24. Large intestine of human.

Liver Liver is endodermal diverticulum Liver produces bile Bile stored in gallbladder Common bile duct Ampulla of Vater - terminal portion of common bile duct Figure 11.25. Development of liver and pancreas (book figure 13.38).

Pancreas Pancreas is a diverticulum Most people have a single pancreatic duct Duct of Santorini - small, dorsal (accessory) Duct of Wirsung - large, ventral - functional duct after small, dorsal accessory duct disappears Exocrine and endocrine glands Islets of Langerhans- endocrine glands

Rectal gland- diverticulum in sharks “A Notable Duct” Duct of Cuvier or Common Cardinal Cuvier was founder of Comparative Anatomy and Paleontology 2 ducts of Cuvier in most vertebrates – See Circulatory System