The Human Digestive Tract

1. The Human Digestive Tract Unit 2A: Internal Systems – Digestion Lesson 1

2. Digestion: 4 Easy Steps!

3. Physical and Chemical Digestion 1) Mechanical (Physical) Digestion • Involves chewing the food into small pieces and mixing it with liquids • No enzymes are necessary and no energy is released 2) Chemical Digestion • Digestive enzymes split specific chemical bonds holding the food molecules together. • Once split up, molecules must be small enough to be absorbed into the bloodstream and, in turn, into the cells of the body.

4. The Mouth: Mechanical and Chemical! Mechanical: chewing and wetting with saliva Chemical: salivary amylase (digestive enzyme) breaks down starches in the mouth Food bolus is pushed to the back of the throat (pharynx) Epiglottis prevents food and liquids from entering the larynx (and subsequently the “windpipe”) during the swallowing reflex

6. Esophagus: Neither Mechanical nor Chemical! Esophagus secretes mucous to lubricate the bolus Esophagus has circular and longitudinal muscles to help with peristalsis (waves of muscular contraction and relaxation that move the food bolus towards the stomach)

7. Stomach: Mechanical and Chemical! Mechanical: contractions of the muscular stomach walls break down food into smaller particles Chemical: hydrochloric acid (HCl) and digestive enzymes pepsin and lipase are secreted by the gastric glands The stomach protects itself from being digested with copious amounts of mucous secreted by the pyloric glands! Food mass + gastric juice = chyme.

9. Real Stomach Muscles!

10. Small Intestine: Chemical and Absorption Small intestine is about 6 m long and consists of 3 parts: duodenum, jejunum, ileum 1st stop out of the pyloric sphincter is the duodenum! In the duodenum, the chymeis neutralized and mixed with digestive juices: bile from liver and gallbladder, pancreatic juice, and intestinal juice Peristalsis continues – mixes mechanically and improves contact with intestinal wall, speeding absorption

11. Surface Area!!!! Intestinal lining has folds [3x area] The folds have villi(finger-like projections) [30x area] The cells lining the villi have projections called microvilli [600x area] During absorption, nutrients pass through the microvilli of the cells and enter capillaries (sugars, vitamins, minerals, etc.) or lacteals (fatty acids and glycerols)

13. Large Intestine: Absorption 1.5 metres long Reabsorption of water Absorption of vitamins B and K produced by live bacteria in the large intestine Elimination of feces (undigested material, bacteria, mucous, bile, old cells, etc.) Fecal matter stored in the rectum and eliminated through the anus

14. Accessory Organs Liver, gallbladder, and pancreas Produce and secrete digestive juices into the duodenum Bile salts made from cholesterol (made by liver; stored in gallbladder) break down lipid globules Pancreatic juice helps to neutralize the pH of the chyme and contains additional enzymes that act on carbohydrates, fats, and protein

19. The End!  Read p. 338-341 and 350-351 in your text. Add/integrate any new information into your notes!