The Digestive System

1. The Digestive System

2. 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

3. 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

4. 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: • Crown part of tooth above gums • Gums flesh around jaw bone • Enamel hard outer layer; easily scrubbed away if weakened • Dentine soft, bone-like middle of tooth • Root blood vessels/nerves keeping tooth alive • Cement strong material holding tooth to jaw

5. 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!

6. The War Against Plaque! • How can we reduce tooth decay? • Fluoride in water and toothpaste • Strengthens enamel of teeth by resisting bacteria acid • Not done in Asia…Thoughts? • 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 • Brush your gums • Bacteria can hide in space between gums and teeth

7. 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

8. 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”

9. 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

10. The Stomach: Chemical • Glands in stomach release Gastric juices (Pepsin andHCl) • 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

11. 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

12. 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

13. The Small Intestine: Mechanical • 6 m long but only 2.5 cm wide; covers 9m2How 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

14. You Ate It, Now Use It • After absorption, food molecules are assimilated • Assimilation to become a useful part of a cell or organ • Liver • Glycogen is made from excess blood glucose • Amino acids used to make proteins • Fatty acids/glycerols are made into fat • Form cholesterol from fat • Excess amino acids deaminated

15. 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

16. 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)