II. DIGESTIVE SYSTEM
A. Overall function
1. Ingestion
2. Digestion
3. Absorption
4. Waste elimination
B. Development
1. Coelom, Pleuroperitoneal cavity through reptiles
2. Parietal peritoneum – From somatic mesoderm
3. Visceral peritoneum – From splanchnic mesoderm
4. Dorsal and Ventral Mesentery – Folds of peritoneum
5. Foregut – Embryonic region giving rise to organs to the small intestine, liver, pancreas, bile duct…
6. Midgut – Embryonic region giving rise to small intestine & part of large intestine
7. Hindgut – Embryonic region giving rise to large intestine & cloaca
C. Morphology
1. Overview of gut wall (Mucosa, Submucosa, Muscularis, Serosa)
2. Peristalsis and Segmentation – Wave like contraction and stationary mixing contraction
3. Oral cavity; Oropharyngeal cavity
a. Tongue – Can extend from mouth beginning with amphibians; anchored by hyoid
b. Glands – Examples include venom, saliva, enzymes, anticoagulant in lampreys, nutrients for young in catfish, mucus
c. Teeth
1. Dermal armor, dermal plates, placoid scales
2. Parts of tooth
a. Dentin – Odontoblasts
b. Enamel – Ameloblasts
c. Pulp cavity
d. Cementum – Acellular bone
3. Attachment classification
a. Acrodont – Peak of jaws; e.g. teleosts
b. Pleurodont – Inner surface of jaws; e.g. frogs, urodeles, lizards
c. Thecodont – Roots in sockets; e.g. crocodiles, extinct birds, mammals
4. # Sets
a. Polyphydont – Typical of most vertebrates
b. Diphydont – Many mammals
c. Monophydont – Platypus
5. Shape
a. Homodont – Fish, amphibians, most reptiles, some marine mammals
b. Heterodont – later reptiles, most mammals
1. Incisors – Flat, chisel-shaped
2. Canine – Pointed for piercing & tearing
3. Premolars – Grinding teeth with 1-2 roots
4. Molars – Grinding teeth with 3 roots
6. Dental formulas
a. Human: 2-1-2-3/2-1-2-3 = 32
b. Cat: 3-1-3-1/3-1-2-1 = 30
c. Cow: 0-0-3-3 /3-1-3-3= 32
4. Pharynx
a. FISH – Respiratory in function
b. TETRAPODS – Throat; swallowing, location of tonsils in mammals
1. Glottis – Opening into airways
2. Auditory tubes – Connect pharynx with middle ear to equalize ear pressure
3. Esophageal opening
5. Esophagus – Capable of closing in fish
a. Crop – 1-2 present in some birds, sometimes contains digestive enzymes, allows for hoarding of food
b. Pigeon milk – In doves; regurgitated for nestlings
6. Stomach
a. Anatomy – 1 or more chambers
1. Pylorus/Pyloric sphincter
2. Greater & Lesser Curvature
3. Greater omentum – Mammals only
4. Proventriculus – Contains digestive enzymes; in birds and crocodiles
5. Gizzard – Grinding mill in birds
6. a. Rumen, b. Reticulum, c. Omasum, d. Abomasum – a. Cellulase & mucus release, b. Formation of bolus for regurgitation, c. Holding tank, d. Glandular portion
Found in Ruminants that regurgitate & rechew/reswallow food – such as deer, cattle
b. Physiology
1. Overall – Receives, stores, liquefies, and mixes food
2. Chyme – Liquefied food
3. Zymogenic cells – Pepsinogen – Breakdown of protein
4. Parietal cells – HCl – Protein breakdown, pepsinogen activation, antimicrobial
5. Goblet Cells – Mucus – Stomach lining protection
7. Intestine
a. FISH
1. Typhlosole – Spiral valve internally to increase surface area
2. Coils – Teleosts to increase surface area
3. Cecum/Ceca – Teleosts
b. TETRAPODS
1. Small Intestine
a. Duodenum – Mammals
b. Jejunum- Mammals
c. Ileum- Mammals
d. Villi – Increases surface area
e. Blood vessels & Lacteals – For absorption of nutrients
f. Function – Chemical digestion & most nutrient absorption occurs in small intestine
2. Large Intestine
a. Cecum/Ceca – Pouches, common in amniotes
b. Colon – Majority of Large intestine
c. Rectum – Terminal segment of large intestine
d. Function – Formation & storage of feces; some water absorption, fermentation in some herbivores
8. Liver & Gall Bladder
a. Embryology – Foregut & Midgut Diverticula
b. Lesser omentum – Supports ducts & vessels; Lesser curvature of stomach to liver
c. Bile duct – Hepatic & Cystic ducts combine to form Common Bile Duct which dumps into the duodenum/or beginning of intestine
d. Falciform ligament – Liver to ventral body wall
e. Function – Glucose storage, form bile, amino acid deamination (ammonia, uric acid, urea), clotting factors, blood formation in fish, gall bladder stores bile
9. Pancreas [exocrine-makes digestive juices that travel through the pancreatic duct into the intestine (duodenum)]
a. Acinar cells – Produce pancreatic juice
b. Amylase, lipase, protease
10. Cloaca – Receives digestive, urinary, genital structures below placental mammals