The Digestive System It’s a Wild Ride!
The Functions of the Digestive System 1.Ingests food! (Duh!) 2.Digests food while it is being forced along digestive tract. 3.Absorbs digested food into cells of body 4.Eliminates undigested materials from body
Some important terms: Mechanical digestion-the physical process of breaking food into smaller pieces Chemical digestion-the chemical process of structurally changing the food molecules with enzymes.
All Aboard-First Stop-The Mouth! ·Teeth-adapted for tearing and grinding food ·Tongue-manipulates food ·Saliva-1) Moistens and lubricates food 2) Contains salivary amylase which starts the breakdown ofstarch YOU PRODUCE 1-1.5 L OF SALIVA PER DAY!!!!!!
Second Stop-Throat and Esophagus! ·The mouth forms the chewed food into a ball (bolus) and moves it to the throat for swallowing. ·Swallowing forces the food into the esophagus. Swallowing is a reflex. ·The esophagus is like a busy expressway to the stomach! It has waves of muscle contractions that push the food down the body into the stomach! THIS HAPPENS IN 5-8 SECONDS!
Throat and Esophagus Peristalsis- Waves of muscle contraction that move the food down into the stomach Epiglottis- Covers the opening to the windpipe to prevent choking during swallowing.
Third Stop-The Almighty Stomach! Stomach-a muscular, pouch-like enlargement of the digestive tract Muscular Churning- three layers of muscle contract and mix food in the stomach (mechanical digestion)
Protection in the stomach… • Gastric juice-secreted by the stomach lining and contains hydrochloric acid (HCl) and enzyme pepsin. • Pepsin – enzyme that begins chemical digestion of protein; only works in an acidic environment--HCl (stomach pH is 2!) • Protective mucus prevents stomach from digesting itself!
Fourth Stop-The Small Intestine-Small, but Mighty! Small intestine-muscular tube about 6 m long That isn’t small! It is small in diameter, not length! Muscle contractions further breakdown the food mechanically Duodenum-section of the SI that secretes enzymes to digest food (SI is separated from stomach by pyloric sphincter)
Helpers Along the Route-Pancreas! Pancreas-soft, flattened gland that secretes enzymes and hormones Pancreatic juice is alkaline (pH>7) to neutralize acidic food and stops pepsin!
More Helpers!-Liver and Gall Bladder Liver-Produces bile Bile-breaks down fats Bile is stored in the gall bladder and then passes into the SI
Absorption of Food: • Liquid food stays in your stomach for 3-5 hours • Food moves through SI and passes over villi • Villi-fingerlike projections that absorb food • Villi increase surface area of SI • Villi have blood vessels and lymph ducts (linking immune and circulatory system!)
The Final Portal-The Large Intestine! Undigested material moves into LI LI-muscular tube, also called the colon LI-1.5 m long, but wider 6. 5 cm Appendix is an extension, but unnecessary organ! Water is absorbed by the LI Solid material is digested by bacteria in LI and some vitamins are made After 18-24 hours, indigestible material is eliminated.