The Digestive System

Ch. 30.3

Feed Me!• Digestive system uses

mechanical and chemical energy to break organic material

• Material is absorbed into the cells of our bodies; used to make energy or other molecules

• Mechanical:– Grinding, smashing tearing,

crushing• Chemical:– Enzymes and Acidic solutions

The Mouth: Mechanical• Chewing:– Tearing and grinding food

into small lumps; increase surface area for enzyme activity

• Teeth:– Strongest bones in the body– Incisors; cutting food– Cuspids; tearing food– Molars; grinding food

• Tongue:– Strongest muscle in the body– Pushes food down esophagus

The Mouth: Chemical• Amylase:– Enzyme that breaks down starch

into di and monosaccharaides• Taste buds:– Alert us to nutrients we need to

consume– Sugar Sweet– Acids Sour– Toxins Bitter– Salts Salty– Protein Umami

• Tonsils:– Protect body from bacteria take

in through the mouth and nose

The Esophagus• Swallowing pushes food down the esophagus to the

stomach• Peristalsis:

– Contractions of muscle waves move food in one direction• Food has to pass by the trachea (entrance to the lungs) so a

small cartilage cover (epiglottis) blocks the opening• Eating too fast can send food “Down the Wrong Pipe”

The Stomach: Mechanical• Walls of stomach contract

to crush food and help mix food with digestive juices

The Stomach: Chemical• Glands in stomach

release Pepsin and HCl• Pepsin breaks down

proteins into amino acids• HCl keeps the stomach at

a pH 2!• Food can take up to 4

hours to digest• Why doesn’t HCl eat

through the stomach?– Lining of stomach makes

protective mucus

Heart Burn and Stomach Ulcers• “Heart Burn” is when

stomach acid gets into the esophagus and causes a burning feeling in the chest

• Caused by spicy food

• Stomach Ulcer is a hole in the stomach lining which can cause major health problems

• Caused by high acidic levels

The Small Intestine: Mechanical• 6 m long but only 2.5 cm wide• Peristaltic contractions move food through intestine and

continue to break down food• Food is absorbed into the blood through villus• Liver and Gallbladder release bile which physically breaks globs

of fat into smaller units

The Small Intestine: Chemical• 3 pronged attack in the Duodenum (first 25cm)– Pancreas releases enzymes to break down carbohydrates,

proteins, fats, and nucleic acids; also NaHCO3 to neutralize stomach acid

– Liver releases enzymes to break down organic material– Gallbladder release mild acids to help enzyme activity

The Large Intestine• Only 1.5m long but 6.5cm wide• Indigestible material is

compacted as much water as possible is absorbed back into the body

• Anaerobic bacteria produce vitamins B and K for us while digesting the material

• After 18-24 hours, waste is removed from the body as feces

• Passes through the last part of the digestive system, the rectum (the butt)