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