Chapter 29: Nutrition and Digestion (pg 634 – 651)

1. Chapter 29: Nutrition and Digestion (pg 634 – 651) Section 1: Nutrition depends on digestion and absorption Section 2: Each region of the digestive tube is specialized Section 3: A healthful diet provides both fuel and building materials Section 4: Nutritional disorders damage health

2. Section 1: Nutrition depends on digestion and absorption • Food is a source of energy derived from complex polymers • Polymers can not be used directly by the body but must be simplified into universal monomers • Cells take up these monomers and convert them into useful products • Amino acids  protein

3. Stages of Food Processing • Nutrition – how your body gets raw material from food • 4 Stages • Ingestion • Digestion • Absorption • Elimination

4. Ingestion and Digestion • Ingestion • Eating or drinking • Mouth acts as an organ for ingestion and digestion • Digestion • Breaking down food into small particles for the body to absorb • Polysaccharides  monosaccharides • Two Steps • Mechanical • Chewing to decrease the size of food and increase surface area of food for the next step • Chemical • Breaking chemical bonds in the food to produce monomers

5. Absorption and Elimination • Absorption • Cells take up the monomers produced from chemical digestion • Blood can transport some of the monomers to other parts of the body • Elimination • Removal of undigested food

6. Section 2: Each region of the digestive tube is specialized • Digestion occurs in a specialized tube, the alimentary canal • Food moves only in one direction • The alimentary canal (complete digestive tract) has many loops to increase absorption time of monomers • Lined by epithelial tissue which secretes a protective mucus • Stomach acid has a pH of 2 • Your stomach lining is replaced every 3 days

7. Organs of the Digestive System • Six main organs • Mouth • Pharynx • Esophagus • Stomach • Small Intestine • Large Intestine • Accessory glands • Salivary glands, pancreas, liver, and gallbladder

9. Mouth (Oral Cavity) • Food triggers nervous reflex that causes salivary glands to deliver saliva to mouth. • Saliva contains • Mucin: • Protects and lubricates mouth • Amylase: • Enzyme that hydrolyzes starch and glycogen Tongue: tastes foods, manipulates it during chewing, and shapes food into bolus

10. Throat (pharynx) • Pharynx – junction between esophogus and airway • Epiglottis temporarily seals off the airway to direct food down into the stomach • Esophagus – connect pharynx to the stomach • Food pushed viaperistalsis(rhythmic contraction of smooth muscle in one direction) • Contraction is a wave - like motion

11. Stomach (upper abdominal cavity) • Elastic muscular sac (stretch 2 L) • Gastric juice is secreted to break down food into chyme • Mixture of mucus, HCl, and enzymes • Pepsin: hydrolysis of proteins* • Stomach muscles contract pushing the chyme to the small intestine • Both ends of the stomach are generally sealed off • Heartburn and vomit

12. *Secretion of gastric juice • Pepsin: secreted in an inactive form: pepsinogen • Comes from chief cells located in gastric pits • HCl is also in pits • Secreted by parietal cells • Acid coverts pepsinogen into active pepsin • Positive feedback: once some is activated the rate increases.

13. *Secretion of gastric juice

14. Small Intestine, Liver, and Pancreas • Small intestine completes digestion (1st portion) and begins absorption of nutrients (rest of intestine) • 1st portion = duodenum (first 25 cm) • Chyme mixes with bile produced by the liver • Bile is stored in the gallbladder & contains no digestive enzymes • Bile contains salts that act as detergents that aid in the digestion and absorbtion of fats. • Pancreas • Produces several hydrolytic enzymes and an alkaline solution rich in bicarbonate • Acts as a buffer and to neutralize acidic chyme • Digestion results in individual amino acids

15. Enzymatic Action

16. Small intestine • Large circular folds in the lining • Lined with finger like projections called villi. • Villi have microscopic appendages call microvilli • Projections increase surface area and increase rate of absorption.

17. Small intestine • Each villus is a net of microscopic blood vessels and a vessel of the lymphatic system (lacteal). • Nutrients are absorbed across the intestinal epithelium of the blood vessels and lacteals. • Sometimes passive (fructose) • Sometimes pumped across concentration gradient (amino acids, peptides, vitamins, glucose) • Lacteals converge into larger vessels of the lymphatic system. • Blood vessels converge into the hepatic portal vessel.

18. Hepatic Portal Vessel • Leads directly to the liver. • Why the liver? • Metabolic versatility to interconvert various organic molecules • Ensues first access to amino acids and sugars. • Important to control sugar levels in the body. • From the liver blood travels to the heart, which pumps nutrients all over the body.

19. Small intestine

20. Large Intestine (colon) • Food moves from the small intestine past the colon into the large intestine • Connected to small intestine in T shape • Sphincter controls movement of material • Pouch called the cecum • Main branch is upside-down U shape (1.5 m long). • Appendix: contributes to body defenses

21. Large Intestine (colon) • Focus is absorption of water • 7 L of fluid used daily • Most is reclaimed in small intestine • Together small & large reabsorb 90% of water • Undigested food is passed as feces • Absorbed water makes feces more compact and solid • 12-24 hours before material travels the length of the digestive system. • Terminal part of colon is called rectum. • Between the rectum and anus are two sphicters.