CHAPTER 21 Nutrition and Digestion

1. CHAPTER 21Nutrition and Digestion Nutrition->life process by which an organism obtains and utilizes food

2. OBTAINING AND PROCESSING FOOD • Animals ingest their food in a variety of ways • Animal diets are highly varied • Herbivores are plant-eaters • Carnivores are meat-eaters • Omnivores eat both plants and other animals

3. Overview: Food processing occurs in four stages • Ingestion: taking in food • Digestion: mechanical and chemical breakdown of food so that it can be absorbed by the cells • Absorption: cells lining the digestive tract take up (absorb) small nutrient molecules • Elimination: undigested material passes out of the digestive tract

4. HUMAN DIGESTIVE SYSTEM • consists of 1. alimentary canal (GI gastrointestinal tract) ~ continuous one way food tube (mouth to anus) 2.accessory glands ~pancreas, liver, & gallbladder

5. HUMAN DIGESTIVE SYSTEM • When food is swallowed, it is moved through the alimentary canal by peristalsis • Peristalsis is rhythmic muscle contraction in the walls of the digestive tract • Ringlike sphincter muscles regulate the passage of food

6. Digestion begins in the oral cavity • The teeth break up food (mechanical digestion) • Saliva moistens it • Salivary enzymes begin the hydrolysis of starch (amylase) (chemical digestion) • The tongue pushes the chewed food into the pharynx (throat)

7. The food and breathing passages both open into the pharynx • The swallowing reflex moves food from the pharynx into the esophagus • At the same time, food is kept out of the trachea; epiglottis is a flap that prevents choking • Food is now in the form of a bolus

8. The esophagus squeezes food along to the stomach • Peristalsis in the esophagus moves food boluses into the stomach

9. The stomach mechanically churns food into liquid and further chemically digests some of the food by secreting gastric juice • The stomach mixes food with gastric juice: 1. water-solvent 2. mucus-lubrication 3. pepsin- enzyme that begins chemical digestion of protein 4. Hydrochloric acid ( HCl) - makes food acidic, (pH=2) activates pepsin Food now in liquid form –chyme NOT all digestion has occurred

10. Connection: Bacterial infections can cause ulcers • evidence suggests that a spiral-shaped prokaryote causes many ulcers • Helicobacter pylori growth erodes protective mucus and damages the stomach lining

11. The small intestine is the major organ of chemical digestion and nutrient absorption • Alkaline pancreatic juice neutralizes stomach acids • Its enzymes digest polysaccharides, proteins, nucleic acids, and fats • Bileemulsifies fat droplets for attack by pancreatic enzymes • It is made in the liver and stored in the gall bladder

12. Enzymes from the walls of the small intestine complete the digestion of many nutrients

13. Absorption • The lining of the small intestine is folded and covered with tiny, fingerlike villi • Villi increase the absorptive surface • Nutrients pass through the epithelium of the villi and into the blood • The blood flows to the liver • The liver can store nutrients and convert them to other substances the body can use • Center of villi contains lymph vessel called lactealswhich absorb fatty acids

14. The large intestine reclaims water • Undigested material passes to the large intestine, or colon • Water is absorbed • Feces are produced • Absorption of vitamins produced by bacteria that live in LI • Storage and elimination of feces • rectum-last part of GI, feces eliminated through anus Largeintestine(colon) Small intestine Endof smallintestine Rectum Anus Nutrientflow Cecum

15. SomeDigestive Homeostasis Disorders • 1. Constipation– person has uncomfortable or infrequent bowel movements results from sluggish peristalsis that allows excess water to be removed from feces (fecal matter hardens)- may result from insufficient fiber in diet • 2. Diarrhea– opposite of constipation– associated with intestinal disturbances caused by infections or stress– prolonged diarrhea may result in severe dehydration • 3. Gall stones– small hard particles made of cholesterol which form & collect in gall bladder- may block the bile duct and cause pain • 4. acid reflux -backflow of stomach contents upward into esophagus • 5. appendicitis- inflammation of appendix

16. NUTRITION • Overview: A healthful diet satisfies three needs • fuel for its activities • raw materials for making the body’s own molecules • essential nutrients that the body cannot make

17. Chemical energy powers the body • Once nutrients are inside cells, they can be oxidized by cellular metabolism to generate energy • This energy is in the form of ATP

18. Chemical energy powers the body • The energy a resting animal requires each day to stay alive is its basal metabolic rate (BMR)

19. Chemical energy powers the body • More energy is required for an active life • Excess energy is stored as glycogen or fat

20. Connection: Body fat and fad diets • The human body tends to store excess fat molecules instead of using them for fuel • A balanced diet includes adequate amounts of all nutrients • Fad diets are often ineffective and can be harmful

21. Connection: Vegetarians must be sure to obtain all eight essential amino acids • The eight essential amino acids that adults require must be obtained from food • They are easily obtained from animal protein • They can also be obtained from the proper combination of plant foods

22. A healthful diet • includes 13 vitamins • Most of these vitamins function as coenzymes • Essential minerals are required for many body functions • A sound diet supplies • enough raw materials to make all the macromolecules we need • the proper amounts of prefabricated essential nutrients • enough kilocalories to satisfy our energy needs

23. Diet can influence cardiovascular disease and cancer