Digestive System

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Digestive System

• Overall Function
• Ingestion
• Digestion (physical chemical)
• Absorption
• Waste elimination

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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

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Endoderm

• Foregut
• Midgut
• Hindgut

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General Morphology

• Typical gut wall has MUCOSA, SUBMUCOSA,
  MUSCULARIS, SEROSA

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Gut motility

• Peristalsis
• Segmentation

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Oral cavity/Oropharyngeal cavity

• Tongue can extend from mouth beginning with
  amphibians
• Anchored by hyoid
• Helps to capture food, chew, swallow, taste food

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Glands

• Venom
• Saliva
• Including several enzymes
• Anticoagulant in lampreys
• Nutrients in catfish
• Mucus

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Snake venoms
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Teeth

• Dermal armor, dermal plates
• Placoid scales
• Homology to teeth

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Teeth

• Dentin forms the majority of tooth and is a
  bone-like material made by odontoblasts

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Teeth

• Enamel is the hardest substance in the body due
  to mineral content and is made by ameloblasts

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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

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Tooth attachment

• Acrodont peak of jaws, teleosts
• Pleurodont inner surface of jaws, amphibians,
  lizards
• Thecodont sockets, crocodiles, extinct birds
  and mammals

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Sets of teeth

• Polyphydont many sets, typical of most
  vertebrates
• Diphydont two sets, most mammals
• Monophydont one set, platypus

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Feeding
Teeth
New teeth forming
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Shape of teeth

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

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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

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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

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Key Points

• What do you find unusual about the cows dental
  formula?
• What does this tell you about their eating
  habits?
• Can you think of another animal that would have
  the same unusual feature?

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Herbivore
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Pharynx

• Fish respiratory (gill) in function
• Tetrapods throat, swallowing, location of
  tonsils in mammals

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Pharynx in Tetrapods

• Common opening to airways via glottis
• Opening to middle ear via auditory tubes
• Opening to esophagus

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Esophagus

• Can close in fish so stomach doesnt 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

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Stomach

• Gastr-
• Anatomy one or more chambers
• Pylorus, pyloric sphincter
• Greater Lesser curvature
• Greater omentum, mammals only

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Stomach

• Proventriculus Contains digestive enzymes in
  birds ( crocodiles)
• Gizzard grinding mill in bird

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Ruminant Stomachs

• Rumen cellulase mucus release
• Reticulum bolus formation for regurgitation
• Omasum holding tank
• Abomasum glandular portion

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Stomach Physiology

• Receives, stores, liquefies, mixes food
• Chyme
• Zymogenic cells make pesinogen which breaks down
  protein
• Parietal cells make HCl which breaks down
  protein, activates pepsinogen is anti-microbial

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Stomach Physiology

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

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Intestine

• Fish
• Straight
• No small large intestine
• Typhlosole spiral valve
• Coils
• Cecum/cecal

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Digestive system
Stomach
Spiral valve
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Intestine in Tetrapods

• Small Intestine
• Duodenum mammals
• Jejunum mammals
• Ileum mammals
• Villi to increase surface area
• Blood vessels lacteals for absorption

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Small Intestine Function

• Finish chemical digestion
• Most nutrient absorption occurs in small intestine

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Key Points

• Name two anatomical features that supports the
  function of the small intestine

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Large Intestine in Tetrapods

• Cecum/ceca may be present in amniotes
• Colon is the majority of large intestine
• Rectum is the terminal segment of large intestine
• Function is formation storage of feces, some
  water reabsorption, fermentation in herbivores

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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

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Key Point

• What are diverticula?
• What does the root cyst- mean?

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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

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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?

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Pancreas

• Exocrine portion makes digestive juices that
  travel through pancreatic duct
• Acinar cells are the exocrine cells
• Juice contains amylase, lipase, protease

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Key Points

• What does the pancreas make besides the exocrine
  juices?

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Cloaca

• Receives digestive, urinary and genital
  structures below placental mammals

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Key Points

• Name the four stomachs of the ruminant.