1. Chapter 3: Digestion

3. The Digestive System (also known as the Gastrointestinal System) A collection of organs whose purpose is to break down foods into compounds that are small enough to be taken up into the body Gastrointestinal (GI) Tract Organs Food and nutrients pass through these organs Accessory Organs that AID in Digestion Chemicals necessary for digestion are supplied by these organs MouthSalivary glands EsophagusLiver StomachGallbladder Small IntestinePancreas Large Intestine

5. “Involuntary” photo

6. Sphincters! Sphincter – a ring-like muscle that relaxes or contracts to open or close bodily passageways Regulate the rate at which food and nutrients pass from one organ to the next Four important sphincters in the digestive process Upperesophageal sphincter Loweresophageal sphincter Pyloric sphincter Ileocecal valve

7. The Digestive Process The Digestive Process has 4 basic steps: 1.Food is ingested – taken into the gastrointestinal (GI) tract via the mouth 2.Food is digested – broken down into smaller units 3.Small units of nutrients are absorbed – they pass from the GI tract into the blood stream 4.Anything leftover is excreted – eliminated through the anus

8. The Gastrointestinal Tract A tubular channel extending from the mouth to the anus; digestion and absorption occur here. Includes what 5 organs? Intestinal Lumen - the inner space of the GI tract. This space is lined with mucosal cells, which produce mucus, a viscous solution that lubricates and protects the GI tract

9. Digestion Mechanical Digestion – Physical breakdown of food into small particles Mastication and mixing Chemical Digestion – breaks chemical bonds to turn large molecules into smaller ones Involves chemicals from the salivary glands, stomach, pancreas, liver, and gallbladder

10. Mechanical Digestion Peristalsis – rhythmic, wavelike contractions of smooth muscle to propel food through the GI tract Gastric Peristalsis

11. Mechanical Digestion Segmentation – Circular muscles in the small & large intestine contract so that fluid contents slosh back and forth between the segments. Helps mix intestinal contents

12. Chemical Digestion Enzymes – Protein molecules that catalyze (speed up) chemical reactions. Without enzymes, digestion could not occur Produced by the salivary glands, stomach, pancreas, and small intestine. Only work for specific molecules Hormones – Chemicals that serve as messengers and help to control and regulate body processes Regulate appetite, secretions, and physical digestion

13. The Path of Digestion: The Mouth The mouth is the beginning of both physical and chemical digestion Saliva – fluid secreted from the salivary glands to moisten the food and provide lubrication Salivary Amylase – Enzyme that starts the digestion of carbohydrates Lingual Lipase – Enzyme that starts the digestion of lipids The tongue helps mix the saliva with food

14. The Path of Digestion: The Esophagus After being swallowed, food is pushed through (1)_______________________ into the esophagus and then through the (2)________________________ into the stomach. A.Loweresophageal sphincter B.Ileocecal valve C.Upperesophageal sphincter D.Pyloric sphincter E.None of the above

15. The Path of Digestion: The Stomach The stomach churns food to help break it down. The stomach cells release chemicals to break bonds between nutrients GASTRIC JUICE Hydrochloric acid (HCl) – dentatures (unravels) protein Protease – enzyme that helps digest protein Gastric Lipase – enzyme that helps digest lipids Mucus – protects lining of the stomach from HCl Chyme – partially digested, liquefied food that leaves the stomach through the ___________?

16. The Path of Digestion: The Small Intestine Main site of digestion & absorption of nutrients Specialized structures to increase surface area and increase absorption Carbohydrates, protein, fats, and other nutrients (like what??) are digested & absorbed in the small intestine

17. Digestion in the Small Intestine Mechanical Digestion – does it happen here? Chemical Digestion Three organs provide enzymes needed (Hint: these are the accessory organs that aid in digestion)

18. Pancreas Pancreas releases a liquid solution called Pancreatic Juice Pancreatic Juice moves from the pancreas into the small intestine where it digests nutrients by breaking down chemical bonds Amylase – digests carbohydrates Protease – digests proteins Pancreatic Lipase – digests lipids Bicarbonate – neutralizes HCl

19. Liver and Gallbladder Liver produces Bile Bile – a substance necessary for digestion of lipids. It works with the enzyme ____________ to maximize lipid digestion. Gallbladder – storage facility for bile In what organ along the gastrointestinal tract does bile interact with lipids to assist in digestion?

20. Absorption After food and nutrients are small enough, nutrients move out of the lumen of the small intestine into either the blood vessels OR the lymph vessels Blood vessels: proteins (amino acids), carbohydrates, minerals, water-soluble vitamins Lymph vessels: lipids, fat-soluble vitamins The blood and lymph vessels are like highways that transport nutrients to the organs and tissues in the body

24. Simple Diffusion – movement of a substance down a concentration gradient Facilitated Diffusion – movement of a substance down a concentration gradient with the help of a transport protein Diffusion in the Small Intestine

25. Active Transport – movement of a substance against a concentration gradient; requires both a transport protein and energy Diffusion in the Small Intestine

26. The Path of Digestion: The Large Intestine Waste products move from the small intestine through the __________________ into the large intestine Remaining nutrients are absorbed Water is absorbed into the body Over 1000 different species of bacteria feed on undigested fiber Produces gas! Produces short chain fatty acids, which either feed the bacteria or are absorbed into the body

27. The final step of the Digestive Process Excretion Waste products are excreted via the rectum and anus Takes 24-72 hours for foods to pass through the digestive system