Digestion, Absorption, and Metabolism: Processes and Functions

1. Chapter 3 Digestion, Absorption, and Metabolism

2. Objectives • Describe processes of digestion, absorption, and metabolism • Name organs in digestive system and describe their functions • Name enzymes or digestive juices secreted by each organ and gland in digestive system • Calculate basal metabolic rate (BMR)

3. Digestion • Breakdown of food in body in preparation for absorption • Mechanical digestion • Food broken into smaller pieces by teeth and moved along gastrointestinal tract by peristalsis • Chemical digestion • Carbohydrates, proteins, and fats broken down into nutrients that tissues can absorb and use (continues)

4. Digestion • Chemical changes occur through hydrolysis • Enzymes act on food substances • Causing them to break down into simple compounds • Enzyme can act as catalyst • Speeds up chemical reactions without itself being changed in the process

5. Digestion in the Mouth • Teeth break up food • Food mixes with saliva • Forming bolus • Salivary amylase acts on starch • Food in mouth for brief length of time

6. Digestion in the Esophagus • Food travels through this muscular tube • Connects mouth to stomach • Peristalsis and gravity act to move bolus • Cardiac sphincter opens to allow passage of bolus into stomach

7. Stop and Share • Consider the following questions: • What symptom results when the cardiac sphincter does not close properly? • What is the name of this condition? • What prevents this condition from occurring? (continues)

8. Stop and Share • Indigestion or heartburn occurs as result of stomach acid flowing back into esophagus • Gastroesophageal reflux • Proper closing of cardiac sphincter prevents acidic content of stomach from flowing back into esophagus

9. Digestion in the Stomach • Temporary storage of food • Kneading and mixing of food with gastric juices • Regulation of slow, controlled emptying of chyme into intestine • Destruction of most bacteria consumed (continues)

10. Digestion in the Stomach • Secretion of intrinsic factor for vitamin B12 • Gastric juices contain hydrochloric acid, pepsin, and mucus • In children, two additional enzymes: • Rennin • Gastric lipase

11. Stop and Share • Consider the following scenario: • You are preparing a teaching plan for the nursing staff working on a gastrointestinal floor. You plan to review the anatomy and physiology of the stomach. (continues)

12. Stop and Share • Consider the following scenario: • Complete the following objectives to prepare for your class: • Identify the three parts of the stomach • Define chyme • Identify the condition that results from a lack of the intrinsic factor in the stomach (continues)

13. Stop and Share • Fundus • Upper portion of stomach • Body • Middle area of stomach • Pylorus • End of stomach near small intestines (continues)

14. Stop and Share • Chyme • Semiliquid mass of food and gastric juices • Pernicious anemia • Lack of intrinsic factor

15. Digestion in the Small Intestine • Hormones released • Secretin causes pancreas to release sodium bicarbonate to neutralize acidity of chyme • Cholecystokinin triggers gallbladder to release bile • Bile • Emulsifies fat after secreted into small intestine • Produced in liver • Stored in gallbladder (continues)

16. Digestion in the Small Intestine • Enzymes found in pancreatic juice secreted into small intestine • Pancreatic proteases • Splits proteins • E.g., trypsin, chymotrypsin, carboxypeptidases • Pancreatic amylase • Converts starches (polysaccharides) to simple sugars (continues)

17. Digestion in the Small Intestine • Enzymes found in pancreatic juice secreted into small intestine • Pancreatic lipase • Reduces fats to fatty acids and glycerol • Small intestine itself produces enzymes • Lactase, maltase, and sucrase convert lactose, maltose, and sucrose to simple sugars • Peptidases reduce proteins to amino acids

18. Stop and Share • Consider the following scenario: • A client with a duodenal ulcer asks you where the ulcer is located. How do you respond? (continues)

19. Stop and Share • Small intestine divided into three sections: • Duodenum • First section • Jejunum • Middle section • Ileum • Last section

20. Digestion in the Large Intestine • Consists of cecum, colon, and rectum • Major tasks of cecum: • Absorbs water and salts from undigested foods • Kneads content for enhanced absorption • Collects volatile fatty acids to be absorbed and used as sources of energy • Digested food progress through colon to anal canal

21. Stop and Share • Consider the following scenario: • You are providing preoperative teaching to a client who is going to have intestinal surgery. The client asks you to explain the structure of the large intestine. How do you respond? (continues)

22. Stop and Share • Cecum (blind pocket), colon, and rectum make up large intestine (continues)

23. Stop and Share • Contents travel through: • Ascending colon • Transverse colon • Descending colon • Sigmoid colon • Rectum • Anal canal

24. Absorption • Passage of nutrients into blood or lymphatic system (continues)

25. Absorption • Nutrients must be in simplest form • Carbohydrates • Simple sugars • Proteins • Amino acids • Fats • Fatty acids and glycerol

26. Absorption in the Small Intestine • Where most absorption occurs • Villi • Hairlike projections that increase surface area for maximum absorption • Absorb nutrients from chyme and transfer them to bloodstream • Water absorbed in stomach, small intestine, and large intestine

27. Absorption in the Large Intestine • Mucus protects colon from digestive juices • Major tasks of large intestine: • Absorbs water • Synthesizes vitamin B and vitamin K • Collects food residue • Undigested food excreted as feces

28. Metabolism • Transformation of nutrients into energy within cell • Occurs after digestion and absorption • Nutrients carried by blood to cells of body • Aerobic metabolism combines nutrients with oxygen within each cell • Also known as oxidation (continues)

29. Metabolism • Anaerobic metabolism reduces fats without use of oxygen • Krebs cycle • Complete oxidation of carbohydrates, proteins, and fats • Anabolism • Process of using energy from oxidation to create new compounds (continues)

30. Metabolism • Catabolism • Breakdown of compounds during metabolism • Controlled primarily by hormones secreted by thyroid gland • Triiodothyronine (T3) • Thyroxine (T4)

31. Stop and Share • Consider the following questions: • What condition is associated with too much thyroid hormone? • What condition is associated with too little thyroid hormone? (continues)

32. Stop and Share • Hyperthyroidism • Metabolism speeds up and body metabolizes food too quickly • Weight loss • Hypothyroidism • Metabolism slows down and body metabolizes food too slowly • Feeling of sluggishness and accumulation of fat

33. Energy • Needed for involuntary and voluntary activity • Involuntary activity • E.g., maintenance of body tissue, temperature, and growth • Voluntary activity • E.g., walking, swimming, eating, reading, typing (continues)

34. Energy • Three groups of nutrients provide energy: • Carbohydrates • Proteins • Fats • Carbohydrates should be primary source of energy (continues)

35. Energy • Kilocalorie • Unit used to measure energy value of foods • Also known as calorie • Calorie • Amount of heat needed to raise temperature of 1 kilogram (kg) of water 1 degree Celsius • Bomb calorimeter determines energy values of foods (continues)

36. Energy • 1 gram (g) of carbohydrate yields 4 calories • 1 g of protein yields 4 calories • 1 g of fat yields 9 calories • 1 g of alcohol yields 7 calories

37. Stop and Share • Consider the following question: • If you eat a dessert with 19 g of fat in it, how many calories from fat does it have? (continues)

38. Stop and Share • Fat contains 9 calories per gram • Dessert has 19 g of fat • 9 kilocalories per gram × 19 g of fat = 171 calories

39. BMR • Rate at which energy is needed for body maintenance • Energy necessary to carry on all involuntary vital processes while body at rest • Also known as resting energy expenditure (REE) (continues)

40. BMR • Affecting factors: • Lean body mass • Body size • Sex • Age • Heredity • Physical condition • Climate (continues)

41. BMR • Greater in males than females • Increases during growth and fever • Decreases with age and during starvation

42. Calculating BMR • Harris-Benedict equation • Used by dietitians for people over age 18 • Uses height, weight, and age • Female BMR • 655 + (9.6 × weight in kg) + (1.8 × height in centimeters [cm]) – (4.7 × age) • Male BMR • 66 + (13.7 × weight in kg) + (5 × height in cm) – (6.8 × age) (continues)

43. Calculating BMR • Another method used to estimate BMR: • Convert body weight from pounds to kg • Multiply kg by 24 (hours per day) • Multiply answer by 0.9 for females and by 1.0 for males

44. Stop and Share • Consider the following questions: • What is the BMR for a female weighing 110 pounds? • What is the BMR for a male weighing 170 pounds? (continues)

45. Stop and Share • 110-pound female • 110 pounds ÷ 2.2 (pounds per kg) = 50 kg • 50 kg × 24 hours = 1,200 calories • 1,200 calories × 0.9 = 1,080 calories (continues)

46. Stop and Share • 170-pound male • 170 pounds ÷ 2.2 (pounds per kg) = 77.27 kg • 77.27 kg × 24 hours = 1,854 calories • 1,854 calories × 1.0 = 1,854 calories

47. Conclusion • Food broken down through processes of mechanical and chemical digestion into nutrients that can be absorbed • Enzymes break down nutrients • Absorption occurs mostly in small intestines (continues)

48. Conclusion • During metabolism, carbohydrates and proteins combine with oxygen • Oxidation • Energy released during oxidation measured in calories • Person’s energy requirement can be measured in part by estimating BMR