Digestive System

Overall FunctionIngestionDigestion (physical & chemical)AbsorptionWaste elimination

Development

Coelom forms from splitting of lateral plate mesoderm (hypomere)

This is the pleuroperitoneal cavity through reptiles

Parietal peritoneumVisceral peritoneumDorsal & Ventral mesentery are folds of

peritoneum

Endoderm

ForegutMidgutHindgut

General Morphology

Typical gut wall has MUCOSA, SUBMUCOSA, MUSCULARIS, SEROSA

Gut motility

PeristalsisSegmentation

Oral cavity/Oropharyngeal cavity

Tongue – can extend from mouth beginning with amphibians

Anchored by hyoidHelps to capture food, chew, swallow, taste

food

Glands

VenomSalivaIncluding several enzymesAnticoagulant in lampreysNutrients in catfishMucus

Snake venomsSnake venoms

Teeth

Dermal armor, dermal platesPlacoid scalesHomology 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, teleostsPleurodont – inner surface of jaws,

amphibians, lizardsThecodont – sockets, crocodiles, extinct

birds and mammals

Sets of teeth

Polyphydont – many sets, typical of most vertebrates

Diphydont – two sets, most mammalsMonophydont – one set, platypus

FeedingTeeth

New teeth forming

Shape of teeth

Homodont – fish, amphibians, most reptiles, some marine mammals

Shapes of teeth

Heterodont – later reptiles, most mammalsIncisors - cutting teeth, chisel shapedCanine teeth – pointed for piercing &

tearingPremolars – grinding teeth with 1-2 rootsMolars – grinding teeth with 3 roots

Dental formulas

Human: 2-1-2-3/2-1-2-3 = 32Cat: 3-1-3-1/3-1-2-1 = 30Cow: 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?

HerbivoreHerbivore

Pharynx

Fish – respiratory (gill) in functionTetrapods – throat, swallowing, location of

tonsils in mammals

Pharynx in Tetrapods

Common opening to airways via glottisOpening to middle ear via auditory tubesOpening 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 chambersPylorus, pyloric sphincterGreater & Lesser curvatureGreater omentum, mammals only

Stomach

Proventriculus – Contains digestive enzymes in birds (& crocodiles)

Gizzard –grinding mill in bird

Ruminant Stomachs

Rumen – cellulase & mucus releaseReticulum – bolus formation for

regurgitationOmasum – holding tankAbomasum – glandular portion

Stomach Physiology

Receives, stores, liquefies, mixes foodChymeZymogenic cells make pesinogen which

breaks down proteinParietal cells make HCl which breaks down

protein, activates pepsinogen & is anti-microbial

Stomach Physiology

Most gastric secretions come from the goblet cells which make mucus to protect the lining of the stomach from its contents

Intestine

FishStraightNo small & large intestine

Typhlosole = spiral valve

Coils

Cecum/cecal

Digestive systemStomach

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 digestionMost 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 amniotesColon is the majority of large intestineRectum is the terminal segment of large

intestineFunction 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 cellsJuice 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.