The Digestive System and Body Metabolism Ch 14d

1. The Digestive System and Body MetabolismCh 14d

2. Metabolic Pathways Involved in Cellular Respiration • Glycolysis – energizes a glucose molecule so that it can be split into two pyruvic acid molecules and yield ATP • In cytoplasm

3. Metabolic Pathways Involved in Cellular Respiration Figure 14.18

4. Metabolic Pathways Involved in Cellular Respiration • Krebs cycle • Produces virtually all the carbon dioxide and water resulting from cell respiration • Yields a small amount of ATP • In mitochondria

5. Metabolic Pathways Involved in Cellular Respiration • Electron transport chain • Hydrogen atoms removed during glycolysis and the Krebs cycle are delivered to protein carriers Figure 14.19a

6. Metabolic Pathways Involved in Cellular Respiration • Electron transport chain (continued) • Hydrogen is split into hydrogen ions and electrons in the mitochondria Figure 14.19a

7. Metabolic Pathways Involved in Cellular Respiration • Electron transport chain (continued) • Electrons give off energy in a series of steps to enable the production of ATP • Also forms H2O Figure 14.19a

8. Hyperglycemia – increased blood glucose; excess stored in liver as glycogen & in body as fat • Hypoglycemia – decreased blood glucose; glycogen broken down

9. Fat Metabolism • Handled mostly by the liver • Use some fats to make ATP • Synthesize lipoproteins, thromboplastin (clotting factor), and cholesterol • Release breakdown products to the blood • Body cells remove fat and cholesterol to build membranes and steroid hormones • Used for myelin sheaths of neurons

10. Use of Fats for ATP Synthesis • Stored fats = energy • 9 kcal of energy in 1g of fat • 4 kcal of energy in 1g carbohydrates or proteins • Fats must first be broken down to acetic acid • Within mitochondria, acetic acid is completely oxidized to produce water, carbon dioxide, and ATP

11. When low glucose, use fat for ATP • Fat oxidation is fast, but incomplete • Produces acetoacetic acid and acetones → acidosis or ketosis • Atkin’s diet

12. Protein Metabolism • Proteins are conserved by body cells because they are used for most cellular structures • Ingested proteins are broken down to amino acids

13. Protein Metabolism • Cells remove amino acids to build proteins • Need 20 amino acids; 9 are essential (cannot be made by body) • Synthesized proteins are actively transported across cell membranes • Amino acids are used to make ATP only when proteins are overabundant or there is a shortage of other sources

14. Production of ATP from Protein • Amine groups are removed from proteins as ammonia • The rest of the protein molecule enters the Krebs cycle in mitochondria • The liver converts harmful ammonia to urea which can be eliminated in urine

15. Role of the Liver in Metabolism • Several roles in digestion • Makes bile • Detoxifies drugs and alcohol • Degrades hormones • Produce cholesterol, blood proteins (albumin and clotting proteins), lipoproteins • Albumin maintains osmotic pressure of blood; keeps fluids in • Plays a central role in metabolism • Process all nutrients

16. Removes amino acids, fatty acids & glucose for later use • Remove bacteria • Die within 24 hours of liver loss • Have excess liver tissue; it also regenerates • Hepatic portal circulation- • Brings nutrient-rich blood from digestive system to liver so liver can process it

17. Metabolic Functions of the Liver • Glycogenesis • Glucose molecules are converted to glycogen • Glycogen molecules are stored in the liver • Glycogenolysis • Glucose is released from the liver after conversion from glycogen • Gluconeogenesis • Glucose is produced from fats and proteins

18. Metabolic Functions of the Liver Figure 14.21

19. Metabolic Functions of the Liver • Fats and fatty acids are picked up by the liver • Some are oxidized to provide energy for liver cells • The rest are broken down into simpler compounds and released into the blood • Acetic acid & acetoacetic acid • Makes cholesterol

20. Cholesterol Metabolism • Functions of cholesterol • Serves as a structural basis of steroid hormones and vitamin D • Is a major building block of plasma membranes • Not used for energy • In bile salts • Most cholesterol is produced in the liver (85%) and is not from diet (15%)

21. Cholesterol Transport • Cholesterol and fatty acids cannot freely circulate in the bloodstream • Not water soluble • They are transported by lipoproteins (made in liver) (lipid-protein complexes) • Low-density lipoproteins (LDLs) transport to body cells = Bad cholesterol • High-density lipoproteins (HDLs) transport from body cells to the liver = good cholesterol

22. Body Energy Balance • Energy intake = total energy output (heat + work + energy storage) • Energy intake is liberated during food oxidation • Glycolysis, Kreb’s cycle, electron transport • Energy output • Heat is usually about 60% of total • Storage energy is in the form of fat or glycogen

23. Regulation of Food Intake • Body weight is usually relatively stable • Energy intake and output remain about equal • Mechanisms that may regulate food intake • Levels of nutrients in the blood • Glucose, amino acids • Hormones – insulin, glucagon, leptin • Body temperature • Psychological factors

24. Metabolic Rate and Body Heat Production • Basic metabolic rate (BMR) – amount of heat produced by the body per unit of time at rest • = energy needed for essential life activities • Factors that influence BMR • Surface area – small body usually has higher BMR • Gender – males tend to have higher BMR • 70kg adult has BMR of 60-72 kcal/hr

25. Metabolic Rate and Body Heat Production • Factors that influence BMR (continued) • Age – children and adolescents have a higher BMR • The amount of thyroxin (from thyroid) produced is the most important control factor • More thyroxin means higher metabolic rate • Hyperthyroidism- lose weight • Hypothyroidism- gain weight

26. Total Metabolic Rate (TMR) • Total amount of kilocalories the body must consume to fuel ongoing activities • TMR increases with an increase in body activity • TMR must equal calories consumed to maintain homeostasis and maintain a constant weight • ↓ TMR leads to ↑ weight gain

27. Body Temperature Regulation • Most energy is released as foods are oxidized • Most energy escapes as heat • Less than 40% of food energy forms ATP

28. Body Temperature Regulation • The body has a narrow range of homeostatic temperature • Must remain between 35.6° to 37.8°C (96° to 100° F) • The body’s thermostat is in the hypothalamus • Initiates heat-loss or heat-promoting mechanisms

29. Heat Promoting Mechanisms • When cold: • Vasoconstriction of blood vessels • Blood is rerouted to deeper, more vital body organs • Skin becomes cold • Shivering – contraction of muscles produces heat • Hypothermia: • ↓ respiration rate, BP, heart rate, metabolism comes to a halt

30. Heat Loss Mechanisms • When hot: • Heat loss from the skin via radiation and evaporation • Skin blood vessels and capillaries are flushed with warm blood • Evaporation of perspiration cools the skin • Less evaporation if humidity is high

31. Hyperthermia: • ↑ T° depresses hypothalamus → positive feedback causing ↑ metabolism → ↑ T° → brain damage • = heat stroke; heat loss mechanism NOT working • Heat exhaustion: • From dehydration; ↓ BP, ↑ heart rate; cool, clammy skin, heat loss mechanisms still work

32. Fever: • Body T° reset high; heat promoting mechanisms = vasoconstriction, shivering (the chills), ↑ metabolic rate & inhibits bacterial growth • Too high a fever can lead to brain damage

33. Body Temperature Regulation Figure 14.22

34. Developmental Aspects of the Digestive System • The alimentary canal is a continuous tube by the fifth week of development • Digestive glands bud from the mucosa of the alimentary tube • The developing fetus receives all nutrients through the placenta • In newborns, feeding must be frequent (small stomach), peristalsis is inefficient, and vomiting is common

35. Rooting reflex – finding nipple • Sucking reflex – hold nipple and swallow

36. Congenital defects • Cleft lip/palate • Tracheoesophageal fistula • Inborn errors of metabolism • Cystic fibrosis – pancreatic duct blocked • No fat digestion • PKU – brain damage

37. Cleft lip

38. Cleft lip

39. Cleft lip & palate

40. Tracheoesophageal fistula

41. Developmental Aspects of the Digestive System • Teething begins around age six months • Metabolism decreases with old age • Metabolic rate ↓ by 5-8%/10 years • Middle age digestive problems • Ulcers • Gall bladder problems

42. Developmental Aspects of the Digestive System • Activity of digestive tract in old age • Fewer digestive juices • GI activity slows • Peristalsis slows • Diverticulosis and cancer (stomach & colon) are more common