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Comparative Anatomy Digestive System Note Set 11 Chapter 13 Digestive System Six major subdivisions Oral cavity Pharynx Esophagus Stomach Small & large intestine Rectum Digestive System Agnatha - straight digestive tube Coiled tube evolved with lengthening of tract Figure 11.1: Simple to complex digestive systems. Oral Cavity Begins at mouth, ends at pharynx Tongue in floor of cavity Palate in roof of cavity Primary palate Secondary palate Teeth Figure 11.2: Human oral cavity. Palates Primary palate in anamniotes- nasal passageways empty into oral cavity Ex: Salamander Secondary palate of amniotes- extends to pharyngeal cavity Internal nares Figure 11.3: Oral cavity of amphibian (a) and mammal (b). Teeth On jaws normally Cheeks in mammals form pocket Acrodont teeth- fish and snakes Bicuspid- amphibians Tricuspid- lizards Pleurodont teeth- snakes Thecodont teethcrocodilians Figure 11.4- Cross section of jaw. Figure 11.5- Types of cusps. Jaw Teeth and Cheek Used for storage- rodents and squirrels Modified placoid scales- sharks Polyhyodont- permanent replacement of teeth Diphyodont- two sets of teeth Monophyodont- one set of teeth Bird Teeth Egg caruncle- all egg layers Not actual tooth Structure epidermal, horny, keratinized On tip of snout To penetrate egg shell Figure 11.6: Egg caruncle of 15 day old owlet. Reptilian Teeth Egg tooth- lizards and snakes Actual tooth Upper jaw To penetrate egg shell Figure 11.7: Monitor egg tooth.. Modifications of Snake Teeth Aglyphous- no modifications for venom delivery Solenoglyphous- retractable teeth, fangs Proteroglyphous- fangs in front of mouth Opisthoglyphous- fangs in back of mouth Figure 11.8: Position, cross and longitudinal sections of aglyphous (1), opisthoglyphous (2), and solenoglyphous (3) fangs. Mammalian Teeth Incisors Canines For piercing Ex: walrus tusks Premolars & Molars For cutting Ex: elephant tusks To matriculate food Diastema- space without teeth; e.g., no canines Figure 11.9: Mammalian teeth specializations. Mammalian Teeth Heterodont dentition Other varieties Homodont- all teeth the same Bunodont- all teeth on single plain Sectorial teeth – carnassials; e.g., upper premolar and lower molar in carnivores Dental Formula Catarrhines and humans have 2-1-2-3=16 x 2 = 32 total teeth Canines: 3-1-4-2 and 3-1-4-3 If 0 is present, diastema is present Figure 11.10: Dental formulae. Tongue Immobile in jawed fish Fleshy in higher vertebrates Frog- tongue shoots out and draws back Glandular field secretes sticky fluid Immobile tongue- turtles, crocs, and some birds Flexible tongue- nectar feeding bats and snakes Forked tongue of snake Figure 11.11: Jacobson’s organ (sensing apparatus) of snake and forked tongue. Oral Glands Named based on location Labial- near the lips Palatal- near palate Internasal Sublingual- releases venom Parotid- salivary gland Submaxillary Birds have few oral glands Swifts Figure 11.12: Swift and nest. Pharynx In embryo, exhibits series of lateral pharyngeal pouches Gives rise to various glands Slits in pharyngeal region Figure 11.13: Embryonic pharyngeal arches and oral development. Figure 11.14: Adult regions of pharynx. Pharynx Constant Features in Tetrapods Glottis-slit to larynx Covered by epiglottis Eustachian tube- opening Esophagus- opening Pharynx further subdivided for food and air passage Foramen cecum- groove on back of tongue Vestigial structure the leads to embryonic thyroid gland Pharynx Figure 11.15: (a) Upper respiratory tract of human showing pharynx 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 11.16: Esophagus and crop of bird. Stomach Muscular chamber Secretes gastric juices Different lining of stomachs Ruminant stomach Esophageal-like epithelia Glandular epithelia 4 chambers: rumen, reticulum, omasum, abomasum Human stomach Figure 11.17: Stomach of mammals with esophageal-like epithelia in gray and glandular epithelia in red. Cardiac sphincter- esophagus meets stomach Mostly lined with gastric epithelium Stomach Structure Greater and lesser curvature Messentaries Greater omentum – attaches along greater curvature Lesser omentum – attaches along lesser curvature Cecum- increases surface area 2 parts in bird and crocodile stomach Proventiculus-glandular Gizzard- grinding mill (gastroliths) 4-Chambered Stomachs Rumen- food enters Reticulum- forms a bolus Omasum- reswallowed grass Bacterial action Salivary action Abomasum- food worked out by gastric glands Figure 11.18: Stomach of calf. Small Intestine Duodenum- 1st segment Bile and pancreatic ducts Jejunum and Ileum subdivisions Figure 11.19: Digestive tract showing regions of small intestine. Small Intestine Brunner’s Glands- mucous glands in duodenum and jejunum Peyer’s Patches- lymphatic nodules in ileum Crypts of Lieberkühns- intestinal glands at base of villi Lacteals- within villi—interior lymphatic vessels Transport fat molecules to circulatory system Valve of Kirckring- increases surface area Small Intestine Figure 11.20: Histology of alimentary canal of a mammal showing various glands of small intestine. 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 region at rectum Cecum- aids in absorption Terminates at vermiform appendix Cloaca- common chamber for digestive, urinary, and reproductive products to empty (includes monotremes) Figure 11.21: Large intestine of human. Liver Liver is diverticulum of primitive gut Liver produces bile Bile stored in gallbladder Common bile duct Ampulla of Vater- terminal portion Figure 11.22: Development of liver and pancreas. Pancreas Pancreas – diverticulum of gut Duct of Santorini- small, dorsal pancreas Duct of Wirsung- large, ventral pancreas Accessory duct- large duct after small, dorsal duct disappears Exocrine and endocrine glands Islets of Langerhans- endocrine glands Rectal gland- diverticulum in sharks Literature Cited Figure 11.1, 11.3, 11.4, 11.5, 11.10, 11.15, 11.16, 11.17, 11.18 & 11.22- Kent, George C. and Robert K. Carr. Comparative Anatomy of the Vertebrates. 9th ed. McGraw-Hill, 2001. Figure 11.2- http://www.mouth-cancer-symptoms.com/ Figure 11.6- http://gargravarr.cc.utexas.edu/owl/2002/ Figure 11.7- http://www.proexotics.com/collection_nonPE9.html Figure 11.8- http://www.kingsnake.com/reptilia-italia/My_HomePage_file/snakesgeneral.htm Figure 11.9- http://www.okc.cc.ok.us/biologylabs/Documents/zoology/22 Figure 11.11- http://www2.worldbook.com/features/reptiles/html/body_senorg.html Figure 11.12- http://www.rspb.org.uk/birds/whatyoucando/attracthousemartins/index.asp Figure 11.13- http://people.eku.edu/ritchisong/342notes7.html Figure 11.14- http://www.cortexity.com:8080/nicksblog/ Figure 11.19- http://www.yoursurgery.com/ProcedureDetails.cfm?BR=1&Proc=49 Figure 11.20- Kardong, K. Vertebrates: Comparative Anatomy, Function, Evolution. McGraw Hill, 2002. Figure 11.21- http://www.becomehealthynow.com/popups/lrg_intest.htm