Outline-2, BIO 3220, 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


1. Typhlosole – Spiral valve internally to increase surface area

2. Coils – Teleosts to increase surface area

3. Cecum/Ceca – Teleosts


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