Functions of digestive system:

1
Digestive Systems

• Functions of digestive system

• Break down food into organic molecules

• Physically (teeth, gizzard)

• Chemically (by hydrolysis in stomach, intestines)

• polysaccharides

• fats

• proteins

• 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)

• Specialization of digestive tasks

• one-way system (food enters mouth, leaves anus)

• 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 gt 50x
  empty size)

• Gastric glands release HCl (stomach pH2)

• 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