Notes on The Digestive System

Functions 1. Breaks down food into molecules the body can use (digestion). 2 types: Mechanical (physical) – food broken down into smaller pieces Chemical – enzymes break foods into their smaller chemical building blocks 2. Molecules are absorbed into the blood and carried throughout the body (absorption) 3. Wastes are eliminated from the body

The Mouth Mechanical digestion – teeth break down food into smaller pieces, tongue mixes saliva with food, moistening them into a slippery mass Chemical Digestion – Enzymes speed up chemical reactions in the body Salivary gland produces amylase breaks down starch into sugar

Esophagus Epiglottis closes over the trachea so food doesn’t go “down the wrong pipe” Food travels down the esophagus, a muscular tube that connects the mouth to the stomach Lined with mucus to help food move along Peristalsis – waves of muscle contraction that move food through the digestive system

Stomach Expands to store food until it can be liquefied and proteins can be broken down Mechanical digestion – 3 layers of muscle contract to churn materials Chemical digestion – 3 secretions of the stomach Pepsin – digests proteins in your food HCl – activates pepsin, also kills bacteria to keep you healthy Mucus – coats and protects the lining of your stomach Food squirted into small intestine a little at a time

Word Bank Appendix Bile duct Duodenum Epiglottis Esophagus Gallbladder Large intestine Liver Pancreas Rectum Salivary glands Small intestine Stomach Teeth Tongue

Small Intestine Food leaves the stomach as chyme, a thick liquid Most chemical digestion takes place in the top 1/3 of the small intestine, called the duodenum Almost all chemical digestion and absorption of nutrients takes place here Small intestine produces enzymes that break down proteins, carbohydrates, and lipids Also receives secretions from the accessory organs

Accessory Organs Food does not actually travel through these organs Digestive juices are dumped into the top part of the small intestine 3 organs Liver – produces bile to break up fat particles (not an enzyme) Gallbladder – stores bile until it is needed, secretes it through the bile duct Pancreas – produces enzymes that break down proteins, lipids, and carbohydrates

Absorption in the Small Intestine Small nutrient molecules in the chyme are ready to be absorbed Inner surface of the small intestine looks hairy – covered in tiny finger-shaped structures called villi Villi have tiny capillaries inside where nutrients are absorbed Villi increase the surface area of the small intestine so more nutrients get absorbed more quickly

The Large Intestine The last section of digestive system Begins at the appendix, a vestigial organ Water is absorbed into the bloodstream Contain bacteria that feed on the material passing through (and give you vitamin K and outcompete bad bacteria) Waste is compacted and ready for elimination Last few inches of the large intestine is the rectum where waste is stored until it is eliminated Waste leaves through the anus, a muscular opening at the end of the rectum

Answers to Digestive System labeling 1. teeth/mouth 2. Epiglottis 3. Liver 4. Gallbladder 5. Bile duct 6. Large intestine 7. appendix 8. salivary glands 9. Tongue 10. Esophagus 11. Stomach 12. Duodenum 13. Pancreas 14. Small intestine 15. rectum