The Digestive System

Chapter 45

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)

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

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

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