Digestive System

Overall Function
 Ingestion
 Digestion (physical & chemical)
 Absorption
 Waste elimination
Development

Coelom forms from splitting of lateral plate
mesoderm (hypomere)
 This is the pleuroperitoneal cavity through
reptiles
 Parietal peritoneum
 Visceral peritoneum
 Dorsal & Ventral mesentery are folds of
peritoneum
Endoderm

Foregut
 Midgut
 Hindgut
General Morphology

Typical gut wall has MUCOSA,
SUBMUCOSA, MUSCULARIS, SEROSA
Gut motility

Peristalsis
 Segmentation
Oral cavity/Oropharyngeal cavity
Tongue – can extend from mouth beginning
with amphibians
 Anchored by hyoid
 Helps to capture food, chew, swallow, taste
food

Glands

Venom
 Saliva
 Including several enzymes
 Anticoagulant in lampreys
 Nutrients in catfish
 Mucus
Snake venoms
Teeth

Dermal armor, dermal plates
 Placoid scales
 Homology to teeth
Teeth

Dentin forms the majority of tooth and is a
bone-like material made by odontoblasts
Teeth

Enamel is the hardest substance in the body
due to mineral content and is made by
ameloblasts
Teeth

The pulp cavity of the tooth contains the
blood vessels and nerves
 The cementum covers the root of tooth and
is made of acellular bone
Tooth attachment
Acrodont – peak of jaws, teleosts
 Pleurodont – inner surface of jaws,
amphibians, lizards
 Thecodont – sockets, crocodiles, extinct
birds and mammals

Sets of teeth
Polyphydont – many sets, typical of most
vertebrates
 Diphydont – two sets, most mammals
 Monophydont – one set, platypus

Feeding
Teeth
New teeth forming
Shape of teeth

Homodont – fish, amphibians, most reptiles,
some marine mammals
Shapes of teeth
Heterodont – later reptiles, most mammals
 Incisors - cutting teeth, chisel shaped
 Canine teeth – pointed for piercing &
tearing
 Premolars – grinding teeth with 1-2 roots
 Molars – grinding teeth with 3 roots

Dental formulas

Human: 2-1-2-3/2-1-2-3 = 32
 Cat: 3-1-3-1/3-1-2-1 = 30
 Cow: 0-0-3-3/3-1-3-3 = 32
Key Points
What do you find unusual about the cow’s
dental formula?
 What does this tell you about their eating
habits?
 Can you think of another animal that would
have the same unusual feature?

Herbivore
Pharynx
Fish – respiratory (gill) in function
 Tetrapods – throat, swallowing, location of
tonsils in mammals

Pharynx in Tetrapods

Common opening to airways via glottis
 Opening to middle ear via auditory tubes
 Opening to esophagus
Esophagus
Can close in fish so stomach doesn’t
become filled with respiratory water
 Birds may have CROP – sometimes has
digestive enzymes & allows hoarding of
food
 Pigeon milk is an esophageal secretion in
doves for nestlings

Stomach

Gastr Anatomy – one or more chambers
 Pylorus, pyloric sphincter
 Greater & Lesser curvature
 Greater omentum, mammals only
Stomach
Proventriculus – Contains digestive
enzymes in birds (& crocodiles)
 Gizzard –grinding mill in bird

Ruminant Stomachs
Rumen – storage, cellulase & mucus release
(size 40 gallons in mature cow)
 Reticulum – bolus formation for
regurgitation
 Omasum – holding tank
 Abomasum – glandular portion

Stomach Physiology

Receives, stores, liquefies, mixes food
 Chyme
 Zymogenic cells make pepsinogen which
breaks down protein
 Parietal cells make HCl which breaks down
protein, activates pepsinogen & is antimicrobial
Stomach Physiology

Most gastric secretions come from the
goblet cells which make mucus to protect
the lining of the stomach from its contents
Intestine

Fish
 Straight
 No small & large intestine
Typhlosole = spiral valve
Coils
Cecum/cecal
Digestive system
Stomach
Spiral valve
Intestine in Tetrapods

Small Intestine
– Duodenum –mammals
– Jejunum –mammals
– Ileum –mammals
– Villi to increase surface area
– Blood vessels & lacteals for absorption
Small Intestine Function

Finish chemical digestion
 Most nutrient absorption occurs in small
intestine
Key Points

Name two anatomical features that supports
the function of the small intestine
Large Intestine in Tetrapods

Cecum/ceca may be present in amniotes
 Colon is the majority of the large intestine
 Rectum is the terminal segment of large
intestine
 Function is formation & storage of feces,
some water reabsorption, fermentation in
herbivores
Liver & Gall Bladder
Embryology – formed from diverticula of
foregut and midgut
 Lesser omentum supports ducts & vessels &
travels from lesser curvature of stomach to
liver
 Bile duct – Common Bile Duct is formed by
hepatic and cystic ducts & goes to
duodenum

Key Point

What are diverticula?
 What does the root “cyst-” mean?
Liver & Gall bladder
Falciform ligament – liver to ventral body
wall
 Function includes glucose storage, bile
secretion, amino acid deamination, clotting
factors, blood formation in fish
 Gall bladder store bile

Key Points

You are investigating why hundreds of
birds in a certain location died. You
primarily are interested in conducting tests
on the liver. Why? What would this tell
you?
Pancreas

Exocrine portion makes digestive juices that
travel through pancreatic duct
 Acinar cells are the exocrine cells
 Juice contains amylase, lipase, protease
Key Points

What does the pancreas make besides the
exocrine juices?
Cloaca

Receives digestive, urinary and genital
structures below placental mammals
Key Points

Name the four stomachs of the ruminant.