Lecture Nutrition & Metabolism PART 2

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Lecture Nutrition & Metabolism PART 2
2012-11-16 01:36:55
protein nutrients temperature regulation absorptive states glucagon lipoproteins energy balance obesity metabolic rate hypothalamus developmental aspects LCCC

for John Loughman's Exam III
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  1. What is protein metabolism?
    • When dietary protien is in excess, amino acids are
    • -oxidized for energy
    • -converted into fat for storage
  2. Describe the oxidation of amino acids during protein metabolism
    • First deaminated (NH2 amine group removed) then converted into:
    • -pyruvic acid
    • -a keto acid intermediate of the Krebs cycle

    • Events include:
    • 1. transamination
    • 2. oxidative deamination
    • 3. Keto acid  modification
  3. Describe protein synthesis?
    Its hormonally controlled

    it requires a complete set of amino acids that must be provided in the diet
  4. what is the catabolic-anabolic steady state?
    • a dynamic state in which
    • -organic molecules (except DNA) are continuously broken down and rebuilt
    • -organs have different fuel preferences
  5. What are nutrient pools?
    3 interconvertible pools

    • -amino acids
    • -carbohydrates
    • -fats
  6. What is the amino acid pool?
    Body's total supply of free amino acids

    • source for:
    • -resynthesizing body protiens
    • -forming amino acid derivatives
    • -gluconeogensis
  7. what are the carbohydrate and fate pools?
    easily interconverted through key intermediates

    • differ from amino acid pool in that:
    • 1. fats and carbs are oxidized directly to produce energy
    • 2. excess carbs and fat and can be stored
  8. What are absoptive and postabsorptive states?
    • Absorptive (fed) state:
    • -during and shortly after eating
    • -absoption of nutrients is occuring
    • -anabolism exceeds catabolism

    • Postabsoptive (fasting) state:
    • -when the GI tract is empty
    • -energy sources are supplied by breakdown of reserves
  9. Describe Carbohydrates during the absoptive state
    glucose is the major energy fuel

    glucose is converted into glycogen or fat (by the liver)
  10. Describe Fats during the absoptive state
    lipoprotein lipase hydrolyzes lipids of chylomicrons in muscle and fat tissues

    most glycerol and fatty acids are converted into triglycerides for storage

    triglycerides are used by adipose tissue, liver, and skeletal and cardiac muscle as a primary energy course
  11. Describe Proteins during the absoptive state
    excess amino acids are eaminated (to keto acids) abd ysed for ATP synthesis or stored as fat in the liver

    most amino acids are used in protetin synthesis
  12. What are the sources of blood glucose?
    1. Glycogenolysis in the liver metabolizes glucose quickly and efficiently

    2. Glycogenolysis in skeletal muscle to pyruvic acid in the liver

    • 3. lipolysis in adipose tissues and the liver
    • -glycerol is used for gluconeogenesis in the liver

    • 4. Catabolism of cellular protein during prolonged fasting
    • -amino acids are deaminated and used for gluconeogensis in the liver and later in the kidneys (for fasting that lasts several weeks)
  13. What are the hormonal controls of the postabsorptive state?
    glucagon release is stimulated by:

    • -declining blood glucose (dampening insulin release)
    • -rising amino acid levels
  14. what are the effects of glucagon?
    Glucagon is a hyperglycemic (sugar raising) hormone that promotes:

    • -glycogenolysis and gluconeogenesis in the liver
    • -liplysis in adipose tissue
    • -modulation of glucose effects after a high-protein, low carb meal (a counter balance for glucose)
  15. What are the neural controls of the postabsorptive state?
    • in response to low plasma glucose, or during the fight-or-flight response or exercise, the sympathetic nervous system and epinephrine from the adrenal medulla promote
    • -fat mobilization
    • -glycoenolysis
  16. What is the metabolix role of the liver?
    • Hepatocytes:
    • -process nearly every class of nutrient
    • -play a major role in regulating plasma cholesterol levels
    • -store vitamins and minerals
    • -metabolize alcohol, drugsm hormones, and bilirubin
  17. What is the purpose of cholesterol?
    *important dietary lipid

    structural basis of bile salts, sterooid hormones, and vitamin D

    major component of plasma membranes

    makes up part of the hedgehod singaling molecule that directs embryonic development

    transported in lipoprotein complexes containing triglycerides, phospholipids, cholesterol, and protein
  18. What are the 3 types of lipoproteins? Describe each of them
    • HDLs (high density lipoproteins)-have the highest protein content.  
    • *Transport excess cholesteral from peripheal tissues ot the liver to be broken down and secreted into bile.
    • *Also provide cholesteral to steroid-producing organs

    • LDLs (low density lipoproteins)-cholesterol-rich
    • transport cholesterol to peripheal tissues for membranes, storage, or hormone synthesis

    • VLDLs (very low density lipoproteins)-mostly triglycerides
    • transport triglycerides to peripheral tissues (mostly adipose)
    • liver is the primary source of VLDLs

    • Chylomicrons: transport absorbed lipids in GI tract and have the lowest density of all lipoproteins
  19. What are good lipoproteins and what are bad lipoproteins?
    High levels of HDL are thought to protect against heart attack (good cholesterol) and a level of above 60 is desirable

    High levels of LDL, esp lipoprotein A increase the risk of heart attack.  Alevel of below 100 is desireable
  20. How/when does the liver produce cholesterol?
    At a basal leel regardless of dietary intake (about 85%)

    in reponse to saturated fatty acids
  21. Plasma Cholesteral Levels
    Saturated Fatty Acids
    Unsaturated Fatty Acids
    Trans Fat
    • Saturated fatty acids:
    • stimluate liver synthesis of cholesteral
    • inhibit cholesteral excretion from the body

    • Unsaturatred fatty acids:
    • enhance extcretion of cholesterl from body

    • Trans Fat
    • hardened by hydrogination (very bad!)
    • increases LDLs and reduces HDLs
  22. Plasma Cholesterol Levels
    Unsaturated omega-3 Fatty Acids 
    found in cold-water fish

    lower the proportions of saturated fats and cholesterol

    have an antiarrhythmic effect on the heart

    help prevent spontaneous clotting

    lower blood pressure
  23. What are the non-dietary factors affecting cholesterol?
    stress, cigarette smoking, and coffee lower HDL levels

    Aerobic exercise and sestrogen increase HDl levels and decrease LDL levels

    • body shape:
    • -"Apple": fat carried on the upper body is correlated with high cholesterol and LDL levels. more common in men
    • -"Pear": fat carried ont he hips and thighs is correlated with lower cholesterol and LDL levels. more common in women
  24. What is the importance of energy balance?
    Bond energy released from food must equal the total energy output

    energy intake=the energy liberated during food oxidation

    • energy output:
    • -immediately lose as heat (~60%)
    • -used to do work (driven by ATP)
    • -stored as fat or glycogen
  25. Why is heat energy important for energy balance?
    Eventually, nearly all energy derived from food is converted to heat!

    it cannot be used to do work

    it warms the tissues and the blood

    helps maintain the homeostatic body temperature

    allows matabolic reaction to occur efficiently
  26. What is obesity?
    • Measured by the body mass index (BMI)

    • considered overweight if BMI is 25-30
    • considered obese if BMI is over 30
    • -higher incidence of atherosclerosis, diabetes mellitus, hypertension, heart disease, and osteroarthritis
  27. What regulates food intake?
    • Two sets of distinct hypothalmic neurons
    • 1. LHA neurons promote hunger when stimulated by neuropeptides (e.g. NPY)

    2. VMN neurons cause satiety through release of CRH when stimulated by appetite-suppressing peptides (e.g. POMC and CART peptides)

    • Factors that affect brain thermoreceptors and chemoreceptors:
    • -neural signals from the digestive tract
    • -bloodborne signals erlated to body energy stores
    • -hormones
    • -to a lesster exten, body temperature and psychological factors
  28. What is the short-term regulation for food intake?
    • Neural signals:
    • *high protein content of meal increases and prolongs afferent vagal signals
    • *distenstion sends signals along the vagus nerve that suppress the hunger center

    • Nutrient Signals:
    • *increased nutrient levels in the blood depress eating
    • *blood glucose
    • *amino acids
    • *fatty acids

    • Hormones:
    • *gut hormones (e.g. insulin and CCK) depress hunger
    • *glucagon and epinephrine stimulate hunger
    • *Ghrelin (Ghr) from the stomach stimulates appetite just before a meal ("dinner bell")
  29. What is leptin and how does it contribute to the long term factors for food intake?
    • Leptin: hormone secreted by adipose cells in reponse to increased body fat mass
    • *indicator of total energy stores in the fat tissue (the fat-o-stat)
    • *protects against weight loss in times of nutritional deprivation

    Leptin acts on the ARC neurons in the hypothalamus

    • If too much fat, it suppresses the secretion of NPY, a potent appetite stimulant and it sitmulates the expression of appetite suppressants like CART peptides
  30. What are the additional factos for long term regulation of food intake?
    • Temperature
    • stress
    • psychological factors
    • adenovirus infetion
    • sleep deprivation
  31. What is the metabolic rate?
    Body's rate of energy output!

    Total heat produced by chemical reactions and mechanical work of the body

    meaured directlt with a calorimeter or indirectly with a respirometer (masures O2 consumption that is in drect proportion to heat production)
  32. What is the Basal metabolic Rate? What are the factors that influence BMR?
    Reflects the energy the body needs to perform its most essential activities, like breathing

    this is measured under controlled confitions

    • Factors influencing BMR:
    • -as the ration of body surface are to volume increases, BMR increases
    • -decreases with age (highest in children using energy to grow)
    • -increases with temperature or stress
    • -males have disproportionately higher BMR due to more muscle mass
    • -thyroxine increases O2 consumption, cellular respiration, and BMR (the metabolic hormone produced by thyroid gland)
  33. What is the total metabolic rate (TMR)?
    BMR is a large part of the TMR

    rate of kilocalorie consumption to fuel all ongoing activities

    increases with skeletal muscle activity and food ingestion
  34. Describe the regulation of body temperature
    body temperature reflects the balance between heat production and heat loss

    at rest: the liver, heart, brain, kidneys, and endocrine organs generate the most heat

    during exercise: heat production from skeletal muscles increases dramatically

    • normal body temp= 37C + - 5C (98.6F)
    • (optimal enzyme activity occurs at this temperature)

    • increased temperature denatures proteins and depresses neurons
  35. Describe the relationship between core and shell body temperatures
    organs in teh core have the highest temperature

    blood is the major agent of heat exchange between the core and the shell

    core temperature is regulated and remains relatively constance, while the shell temp fluctuates substantially (20C-40C)
  36. What are the four mechanisms of heat exchange?

    • 1. Radiation (thermal energy)is the loss of heat in the form of infared rays.
    • -accounts for about 1/2 of the body's heat loss in normal circumstances

    2.  Conduction is the transfer of heat by direct contact

    3. Convection is the transfer of heat to the surrounding air

    4.  Evaporation is the heat loss due to evaporation of water from body surfaces
  37. What is insensible heat loss and what is sensible heat loss?
    Insensible heat loss accompanies insensible water loss from lungs, oral mucosa, and skin (this is unnoticable)

    evaporative heat loss becomes sensible (active) when body temperature ruses and sweating increases water vaporization
  38. What is the role of the hyporthalamus in heat regulation?
    The hypothalamus is the main integrating center for thermoregulation!!

    • Preoptic region og the hypothalamus contains the two thermoregulatory centers
    • -heat-loss center
    • -heat-promoting center

    • the Hypothalamus receives afferent input from:
    • -peripheal thermoreceptors int he skin
    • -central thermoreceptors (some in hypothalamus)

    initiates appropriate heat-loss or heat-promoting activities, acting must like a thermostat!
  39. What are the heat-promoting mechanisms of the hypothalamus?
    1. contriction of cutaneous blood vessels

    2. shivering

    3. increased metabolic rate via epinephrine and norepinephrine (nonshivering thermogensis provein in infants but controversial in adults)

    4. enhances thyroxine release (in infants only)

    • Voluntary measures include:
    • -putting on more clothing
    • -drinking hot fluids
    • -changing posture or increasing physical activity
  40. What are the heat-loss mechanisms of the hypothalamus?
    Dilation of the cutaneous blood vessels

    Enhanced sweating

    • Voluntary measures include:
    • -reduced activity and seeking a cooler enviornment
    • -wearing light colored and loose fitting clothing
  41. What is hyperthermia?
    elevated body temperature depresses the hypothalamus

    positive feedback system (heat stroke) begins at a core temp of 41C

    can be fatal if not corrected with ice bath and fluids
  42. What is heat exhaustion?
    heat-associated collapse after vigorous exercise

    due to dehydration and low blood pressure

    heat-loss mechanisms are still functional

    may progress to heat stroke
  43. What is Hypothermia?
    low body temperature where vital signs decrease

    shivering stops at core temp of 30-32C

    can progress to coma and deat by cardiac arrect at 21C
  44. What is a fever and what is its purpose?
    Fever is controlled hyperthermia

    it can be due to infection (also cancer, allergies, or CNS injuries)

    macrophages release interleuns (pyrogens) that cause the release of prostaglandins from the hypothalamus

    prostaglandins rese thte hypothalamic thermostat higher (heat promoting mechanisms kick in, which is why you can still shiver with chills!)

    natural body defenses or antibiotics reverse the diesease process; crygens reset the thermostat to a normal level
  45. What are some  developmental aspects of metabolism and nutrition?
    lack of proteins in utero and the first three years can lead to mental deficites and learning disorders

    insulin-dependent diabetes mellitus and genetic disorders can lead to metabolic problems in children

    non-insulin dependent diabetes mellitus may occur in middle and old age, especially in the obese

    metabolic rate declines with age throughout the life span

    nonenzymatic binding of glucose to proteins increases with age, leading to lens clouding and general tissue stiffening in elderly
  46. What are the effects of medications for age related problems and how do they influence nutrition?
    Diuretics for heart failure and hypertension increase the risk of potassium loss

    some antibiotics interfere with digestion and absorption and lead to dehydration by diarrhea

    mineral oil (laxative) decreases absoprtion of fat-soluable vitamins

    excessive alcohol consumption may lead to malabsorption, vitmain and mineral deficiencies, deranged metabolism, and damage to liver and pancreas