Jan 4, 2010 AIM: How does the digestive system change food into usable nutrients? DN: WITHOUT using notes, books, or your classmates, draw and label the digestive system. Hand it in! HW: Finish the Homeostasis handout using p. 471-475. Also, read p. 480-481. Quiz Friday

Digestive System Converts (changes) food into nutrients that the body's cells can use These nutrients can be used for chemical reactions in the body or build new cells What are some nutrients and their purposes?

Two Types of Digestion Mechanical – physical change, large chunks of food is broken down into smaller pieces. Done by chewing, stomach churning Chemical – chemical change, the molecular bonds of food are changed, breaking them down into smaller molecules. Done with saliva, digestive juices and enzymes.

Digestion Begins in the Mouth Chewing Glands make saliva, that mix with food Saliva makes food easier to swallow Saliva has digestive enzyme amylase, which begins starch breakdown

Swallowing Muscles in mouth and tongue push food down the esophagus (food tube)‏ Epiglottis – flap that covers the trachea (windpipe) when swallowing, to prevent choking

Down the hatch! Peristalsis – involuntary muscular contractions that push food down the digestive system Think of the digestive system as one long tube starting at the mouth, and ending at the anus After swallowing, food travels from the mouth down the esophagus to the stomach

Stomach Muscular sac More mechanical digestion Chemical digestion: acids and enzymes (pepsin, which begins protein breakdown)‏ Valves (one way openings), aka sphincters, connect stomach to esophagus and small intestine

To the small intestine! Stomach churns food into a thick, soupy mixture called chyme Peristalsis pushes the chyme through stomach to small intestine

Small Intestine The MOST chemical digestion takes place here Several different enzymes break down food into its component nutrients Enzymes and juices from other glands (pancreas, liver) are sent here

Small intestine – site of absorption Villi line the small intestine, maximize nutrient absorption Nutrients pass through the villi Nutrients are absorbed into the bloodstream, are carried to cells

To the Large Intestine Undigested food is pushed to the large intestine (aka colon)‏ Any water, vitamins, minerals still in food absorbed Solid waste (feces) exit through the anus

Wrap-Up – To Hand In! Why can the digestive system be considered one long tube? Vomiting is also called “reverse peristalsis”. Explain why. Solid waste leaves the digestive system through the anus of the large intestine. How do you think liquid waste leaves the body?