The Digestive System

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; 32 in a

normal mouth– Incisors cutting food; 8– Canines tearing food; 4– Premolars grinding food; 8– Molars grinding food ; 12

• Tongue:– Strongest muscle in the body– Pushes food down esophagus– Taste food– Wet area for chemical digestion

Smile!• How many sets of teeth do we have?

– 2; milk teeth (fall out) and permanent teeth• Wisdom teeth last molars to form (may never

form)– Ruins teeth placement in many people (mouth too

small)– Removed surgical

• Parts of a tooth:1) Crown part of tooth above gums2) Gums flesh around jaw bone3) Enamel hard outer layer; easily scrubbed

away if weakened4) Dentine soft, bone-like middle of tooth5) Root blood vessels/nerves keeping tooth

alive6) Cement strong material holding tooth to jaw

Tooth Pain is the WORST Pain• Why do we brush our teeth?– Reduce bad breath– Reduce tooth decay– Reduce gum disease

• What causes all these?– Bacteria living on our teeth; eating

mashed food– Bacteria produce acid as they eat;

slowly breakdown enamel• Plaque sticky layer of food and

bacteria• Cavity holes in teeth from tooth

decay• Pulp cavity decay reaches root;

extremely painful!

The War Against Plaque!• How can we reduce tooth decay?1) Fluoride in water and toothpaste– Strengthens enamel of teeth by

resisting bacteria acid– Not done in Asia…Thoughts?

2) Brush BEFORE meals, not after– After meals your mouth acidity is

much higher, so the enamel is weak; must wait 30 mins!

– Brushing after can make teeth decay faster

3) Brush your gums– Bacteria can hide in space between

gums and teeth

The Mouth: Chemical• Salivary glands:

– Hidden under tongue – Release mucus (watery solution) and

enzymes to help breakdown food• Amylase:

– Enzyme that breaks down starch into di and monosaccharaides

• Bolus:– Ball of mashed food

• Taste buds:– Alert us to nutrients we need to

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

The (O)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• Pyloric Sphincter muscular ring at exit of stomach that lets a

small amount of digested food (chyme) through at a time• Why?– Too much acidic liquid in the intestine at one time

will damage it

The Stomach: Chemical• Glands in stomach release

Gastric juices (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; become chyme

• 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: Chemical• Duodenum (first 25cm)– Pancreas releases enzymes to:• Amylase: Starch Maltose• Trypsin: Proteins Peptides• Lipase: Fats Fatty Acids• NaHCO3 to neutralize stomach

acid– Liver releases bile to:• Break apart fat globs

(emulsify)• Neutralize pH

– Gallbladder releases extra bile when needed

• Ileum second round of enzymes to finish digestion; absorption

The Small Intestine: Mechanical• 6 m long but only 2.5 cm wide; covers 9m2

How does this fit inside you?– Villi folds on the intestine membrane;

one cell thick so absorption can occur• Peristaltic contractions move food through

intestine and continue to break down food• Food is absorbed into the blood through

villus• Lacteals absorb fatty acids/glycerols into

lymph which carries it to blood in heart• Capillaries absorb sugars and amino

acids• Hepatic portal vein transfer food

molecules to liver

You Ate It, Now Use It• After absorption, food

molecules are assimilated• Assimilation to become a

useful part of a cell or organ• Liver1) Glycogen is made from excess

blood glucose2) Amino acids used to make

proteins3) Fatty acids/glycerols are made

into fat4) Form cholesterol from fat5) Excess amino acids

deaminated

Liquid Waste• Excess water, vitamins,

minerals, drugs and toxins are removed as urine

• Most of urine is Urea• Deamination excess amino

acids cannot be stored, so liver removes the amino group (NH2) to make sugars and fats– NH2 becomes ammonia (NH3)

– NH3 joins CO2 to make Urea– Urea is toxic, so it is filtered

from the blood by the kidneys

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)– Anus releases feces (egestion)