1. Digestive Systems Functions of digestive system:
Break down food into organic molecules
Physically (teeth, gizzard)
Chemically (by hydrolysis in stomach, intestines)
polysaccharides HO H
H2O
fats
proteins H HO
Absorb subunits of organic molecules
Monosaccharides, amino acids, fatty acids

2. Digestive Systems Types of digestive systems:
None (intracellular digestion)
Phylum Porifera (sponges)

3. Digestive Systems Types of digestive systems:
Open ‘sac’ (gastrovascular cavity)
Phylum Cnidaria (jellyfish, sea anemone, Hydra)
Enzymes secreted from cells lining cavity
Two-way system (food and waste enter and leave mouth)
No specialization

4. Digestive Systems Types of digestive systems:
One-way digestive systems
Phylum Annelida (earthworm)
Phylum Arthropoda (grasshopper, crayfish)
Phylum Chordata (frog)
one-way system (food enters mouth, leaves anus)
Specialization of digestive tasks
Tube-within-tube body plan

5. Digestive Systems Specialization in vertebrate digestive systems:
Gastrointestinal tract
Mouth and structures to grind or break apart food
Mammals: teeth
Sharp, pointed canines to tear flesh
Large, flat teeth to grind plants
Birds: gizzard (swallow grit)
Saliva released in mouth -- moisten food and releases salivary amylase
Food swallowed and passes through pharynx to esophagus

6. Digestive Systems Specialization in vertebrate digestive systems:
Gastrointestinal tract
Esophagus
Muscular tube that connects pharynx to stomach
Successive waves of contractions (peristalsis)

7. Digestive Systems Specialization in vertebrate digestive systems:
Gastrointestinal tract
Stomach
Saclike portion of digestive tract
Inner surface convoluted (able to expand > 50x empty size)
Gastric glands release HCl (stomach pH=2)
Helps break down proteins
Kills most bacteria
Gastric glands also release pepsinogen (activated into protein-digesting enzyme called pepsin)
Partially digested food and gastric ‘juice’ passes into small intestine

8. Digestive Systems Specialization in vertebrate digestive systems:
Gastrointestinal tract
Small Intestine
Tube for chemical digestion and absorption of organic molecules
Small intestine receives:
Chyme from stomach
Digestive enzymes and bicarbonate from pancreas
Bile from liver
Inner surface of small intestine lined with fingerlike villi (and microvilli on cells)
Increases surface area for digestion (by enzymes in microvilli) and absorption (by epithelial cells)

9. Digestive Systems Specialization in vertebrate digestive systems:
Gastrointestinal tract
Large Intestine (colon)
Large diameter but short length
Some absorption of ions and vitamins, but main function is to concentrate digestive wastes (absorb water)
Many bacteria live within large intestine -- bacteria fermentation produces ‘gas’
Feces produced in large intestine passed to rectum and exit body through anus

10. Digestive Systems Specialization in vertebrate digestive systems:
Accessory organs
Pancreas
Liver
Gall bladder