1. Chapter 24 – Nutrition, Metabolism and Thermoregulation
Use the video clip, CH 24 Nutrition for a review of general nutrition
G.R. Pitts, J.R. Schiller, and
James F. Thompson, Ph.D.

2. Nutrition We eat, we digest, we absorb, then what?
3 fates for food = nutrients
Most are used to supply energy for life
Some are used to synthesize structural or functional molecules
The rest are stored for future use – love handles!

3. Nutrition for College Students
Four Groups:
Grease
Salt
Sugar
Alcohol

4. Weight Management
If energy consumption (food intake) equals energy utilized (activity), then body weight will remain constant
Activity and consumption levels vary day to day, but individuals keep relatively constant weight for long periods of time
Many individuals in affluent nations have an imbalance between intake and use  obesity

5. Regulation of Food Intake
Hypothalamus - complex integrating center receiving sensory information from all parts of the body
Two hypothalamic centers control eating
Feeding (hunger) center
located in lateral hypothalamus
when stimulated, it initiates feeding, even if one is “full”
Satiety center
ventromedial nuclei
when stimulated, they cause cessation of eating, even if one has been starved for days
Controls for their set points are unknown!

6. Regulation of Food Intake (cont.)
Feeding center is always active; but the satiety center can inhibit it
May be driven by changes in blood composition
glucostatic theory – blood glucose levels vary
lipostatic theory - blood lipid levels vary; fat released from adipose tissue between meals
Other influences
blood amino acid levels
temperature - high temp decreases appetite
GI tract distension (a slow and variable reflex)
social and psychological factors
hormones (CCK), neurotransmitters, ions (Zn+)

7. Metabolism All biochemical reactions in the body
Balance between synthesis (anabolic) and breakdown (catabolic) reactions
Anabolism
chemical reactions that combine simple, smaller molecules into more complex molecules
uses energy
protein formation from amino acids
carbohydrate formation from simple sugars
etc.
Catabolism
chemical reactions that break down complex organic molecules into simpler ones
releases energy
proteins are broken down by various proteases

8. Relationship of Catabolism to Anabolism

9. Adenosine Tri-Phosphate
ATP is the link between anabolism and catabolism
ATP energy is the “currency” used in most cellular energy exchanges
catabolic reactions provide the ATP energy that most anabolic reactions require
only about 10-30% of the energy released by catabolic reactions can be used
most chemical energy is lost as “waste heat”
“waste heat” is not wasted; it is essential in maintaining a constant body temperature
3 Phosphates

10. ATP Metabolism
Allows for transfer of small but useful amounts of energy from one molecule to another
Cell's entire amount of ATP is recycled approximately every minute
ATP is NOT for long term energy storage
too reactive in the cell
other molecules available for energy storage (neutral fats, glycogen, creatine phosphate, etc.)
About 8kg (17 lb) of ATP is produced every hour in an average male
Total amount of ATP present in the body at any time is only about 50g

11. ATP Metabolism (cont.)
energy is released by breaking the third phosphate group’s bond
ATP  ADP + Pi
a reversible reaction
the energy released is enough to drive anabolic reactions
ATP  ADP + CrP
creatine provides energy storage in skeletal muscle
allows for more ATP to be formed when O2 is less readily available during skeletal muscle contraction

12. Energy Production Energy is stored in chemical bonds
Oxidation-Reduction (Redox) reactions:
Oxidation component:
also known as dehydrogenation reactions
remove electrons from molecules
decreases the energy remaining in the oxidized molecule
generally, 2e- (and 2H+) are removed simultaneously
Can also be the gain of oxygen

13. Energy Production (cont.)
Oxidation-Reduction reactions (cont.)
Reduction component:
addition of electrons to a molecule
increases the energy of the reduced molecule
These 2 component reactions are always coupled: oxidation-reduction reactions

14. Energy Production (cont.)
ATP Generation
Addition of phosphate to a chemical compound is phosphorylation
3 mechanisms for this:
(1) substrate-level phosphorylation – a high-energy phosphate group is transferred directly from a molecule to ADP to make ATP
For example, when the energy stored on a high-energy phosphate group on creatine phosphate is transferred to ADP to make ATP in skeletal muscles
CK transfers its high energy phosphate to ADP

15. Energy Production (cont.)
ATP Generation
Adding a phosphate ion to a molecule is phosphorylation
3 mechanisms:
(2) oxidative phosphorylation
electrons (H+) removed from molecules
enzymes combine H+ with O2 releasing enough energy for ATP formation
(3) photo-phosphorylation - photosynthesis

16. Carbohydrate Metabolism
General
80% of carbohydrates ingested contain glucose; remainder: fructose, galactose
glucose is the body's preferred carbohydrate energy source
Fate of carbohydrates -- depends on needs of body cells
ATP production
Amino acid synthesis
Glycogenesis
Lipogenesis
Excretion in urine (minimal)

17. Carbohydrate Metabolism (cont.)
Glucose movement into cells
facilitated diffusion - insulin controls () rate
glucose is immediately phosphorylated upon entry (glucose-6-phosphate)
maintains the diffusion (concentration) gradient
traps glucose inside the cell

18. Carbohydrate Metabolism (cont.)
Glucose anabolism
Glucose storage: glycogenesis
glycogen formation is stimulated by insulin
glucose not needed immediately is stored in the liver (25%) and in skeletal muscle (75%)
Glucose release: glycogenolysis
converts glycogen to glucose
occurs between meals, stimulated by glucagon and epinephrine

19. Carbohydrate Metabolism (cont.)
Glucose anabolism (cont.)
Formation of glucose from proteins, fats: gluconeogenesis
when blood glucose level is low, you eat; if glucose remains low, body catabolizes some proteins and fats
stimulated by cortisol and thyroid hormone
cortisol (glucocorticoids) mobilizes proteins, making AA's available
thyroid hormone mobilizes proteins (AA's) and may mobilize lipids
epinephrine, glucagon, hGH also stimulate
These five hormones are often referred to as the “insulin antagonists.”

20. Glucose Metabolism Glucose Catabolism
glucose oxidation is known as cellular respiration
complete catabolism of each molecule of glucose to CO2, H2O
maximum yield of 36 ATP molecules/glucose
38% of the energy present in a glucose
excellent efficiency for a biological system
the rest of the energy is “waste heat”
2 linked enzymatic pathways are involved in glucose catabolism
glycolysis
Kreb’s cycle

21. Glucose Metabolism (cont.)
Glycolysis - Overview
Occurs in cytosol
1 glucose 2 pyruvates (pyruvic acid)
net gain 2 ATP’s
2 ATP’s used
4 ATP’s made
net gain 2 NADH + 2H+ (aerobic conditions)

22. Glucose Metabolism (cont.)
Fate of pyruvate (pyruvic acid) - depends on availability of O2
without O2: NADH + H+ + pyruvate  lactic acid
with O2 available to the cell
pyruvate converted to acetyl coenzyme A (acetyl CoA)
this reaction couples glycolysis to the Krebs cycle

23. Glucose Metabolism (cont.)
Pyruvic acid - formation of acetyl coenzyme A (Acetyl CoA) + CO2
lose one carbon from pyruvate to form CO2 (waste)
the remaining two carbons, the acetyl group, join with CoA, to generate NADH + H+ (1 from each pyruvate = NADH + 2H+ total from one glucose)

24. Glucose Metabolism (cont.)
Krebs cycle (Citric Acid Cycle or Tricarboxylic Acid Cycle (TCA)
oxidation of acetyl Coenzyme A
reduction of coenzymes (NAD+, FAD+)
Oxidative phosphorylation
uses NADH2‘s and FADH2‘s to make additional ATPs

25. Glucose Metabolism (cont.)
Glycolysis and
Krebs Cycle combined total:
6 CO2 (waste) + 6 H2O
10 NADH2 + 2 FADH2 +
4 ATP (energy harvest)

26. Electron Transport
Electrons Source: NADH2/FADH2 from glycolysis and Krebs cycle
High‑energy electrons enter the system, and low‑energy electrons leave
Animal Physiology, Hill et al., 2004

27. Electron Transport System
Oxidative phosphorylation
O2 is the final electron acceptor for low‑energy electrons from last of the carrier molecules
NADH2  3 ATP
FADH2  2 ATP
Enzyme cytochrome oxidase splits apart O2 molecules
Combines each O atom with 2 H+ ions to makes H2O = water
Animal Physiology, Hill et al., 2004

28. Glucose Metabolism Overview
C6H12O6 + 6 O2 
6 CO2 (waste) H2O ATP (useful energy)

29. Lipids
Beta oxidation breaks down fatty acids to form acetyl Coenzyme A.
Lipids are more reduced (have fewer oxygens); therefore, they have more potential chemical energy and can be more fully oxidized as an energy fuel.
Therefore, we gain more energy, gram for gram, from fats than from carbohydrates.

30. Protein Metabolism
Amino acids may be deaminated and the resulting “carbon skeletons” of whatever composition, can be entered into the glycolytic or Krebs cycle pathways to yield an energy harvest of ATPS. The amino groups will be joined with CO2 molecules to form the nitrogenous waste urea.

31. Nutrient Catabolism Pathways Are All Interconnected
Ketone bodies result from excessive lipolysis and fat catabolism; a symptom of diabetes mellitus

32. The Daily Metabolic Cycle
The body shifts back and forth physiologically between the absorptive state and the postabsorptive state.
The absorptive state occurs for approximately 4 hours after each regular meal.
The postabsorptive state takes over until the next meal can be absorbed.

33. All Cells Rely on Glucose from the Meal for Energy
The Absorptive State
Insulin
Dominates the
Absorptive State
All Cells Rely on Glucose from the Meal for Energy

34. The Post-Absorptive State
Glucagon dominates the post-absorptive state and is assisted by the “insulin antagonists (glucocorticoids, thyroid hormones, epinephrine, and hGH).
Only Brain and Spinal Cord Cells Rely on Glucose for Energy; Most Other Body Cells Rely on Fatty Acids for Energy.

35. The Post-Absorptive State
Glycogenolysis provides glucose fuel for skeletal muscle.
Glycogenolysis and gluconeogenesis in the liver provide plasma glucose for nervous tissue.
Lipolysis supplies lipids to fuel all other cells.

36. Lipid Transport by Lipoproteins
Lipoproteins transport hydrophobic lipids in a droplet which is emulsified by an external layer of phospholipids and proteins which make the surface water soluble.

37. Lipid Transport by Lipoproteins
Chylomicrons carry absorbed fat from the meal to adipose tissue via lymph
VLDL and LDL carry cholesterol synthesized in the liver and fat stored in the liver to body tissues
HDL carries excess cholesterol back to the liver for catabolism and excretion
Increased total cholesterol and increased LDL are linked to vessel and heart disease

38. Thermogenesis

39. Heat Loss to the Environment
radiation away of infrared radiation
convection and conduction of heat to air or water surrounding the body
evaporation from sweating and from ventilating respiratory membranes
vasodilation of cutaneous capillary beds
decreased hormonal activity leading to decreased basal metabolic rate (BMR)
behavioral: stop exercising; move to the shade, take off clothes, turn on a/c, etc.

40. Heat Production/Conservation
increased hormone activity (thyroxine, epinephrine) leading to increased (BMR)
increased sympathetic ANS activity leading to increased (BMR)
shivering of skeletal muscles
vasoconstriction of dermal capillary beds
behavioral: start exercising, huddle together, use clothing and shelter, use fire or other means of heating the surroundings

41. Thermogenesis (cont.)
A complex regulation involving negative feedback control through endocrine and autonomic pathways:

42. Pathology of Temperature Control
fever
heat cramps, heat exhaustion, heat stroke
heat-induced dehydration
burns
hypothermia
alcohol-induced hypothermia

43. End Chapter 24