The Digestive System

1
The Digestive System

• Chapter 45

2
Animals are heterotrophs

• Require fuel
• Chemical energy is obtained from the oxidation of
  complex organic molecules
• Require essential nutrients
• Chemicals an animal requires but cannot
  synthesize varies from species to species
• Essential amino acids human adults can produce
  12 of the 20, making 8 essential
• Essential fatty acids deficiencies are very
  rare
• Vitamins and minerals (required in small amounts)

3
Food Processing

• Ingestion
• The act of eating
• Digestion
• Breaking down food into smaller molecules
• Polymers ? monomers
• Mechanical digestion physically breaks food up
  and increases its surface area
• Chemical digestion enzymatic hydrolysis uses
  water to break bonds in polymers
• Absorption
• The uptake of small molecules into the body
• Elimination
• Undigested material passes out of the body

4
The Mammalian Digestive System

• The oral cavity
• Begins both physical and chemical digestion
• Teeth saliva produce bolus
• The pharynx
• Epiglottis helps prevent food in trachea
• The esophagus
• Peristalsis rhythmic contractions that move
  food starts as voluntary and changes to
  involuntary

5
The Mammalian Digestive System

• The stomach
• Stores food and performs preliminary digestion
• Churning to mix food into chyme
• Gastric juice works mainly on proteins
• The small intestine
• Most enzymatic hydrolysis of food and absorption
  of nutrients
• Also involved pancreas, liver, gall bladder
• Huge surface area provided by villi and
  microvilli
• Nutrients cross into bloodstream by diffusion and
  active transport
• The large intestine
• Reclaiming water from feces is the major job
• Intestinal bacteria live on organic material
  produce vitamin K