Lecture Nutrition & Metabolism PART 2
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What is protein metabolism?
- When dietary protien is in excess, amino acids are
- -oxidized for energy
- -converted into fat for storage
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
Describe protein synthesis?
Its hormonally controlled
it requires a complete set of amino acids that must be provided in the diet
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
What are nutrient pools?
3 interconvertible pools
- -amino acids
What is the amino acid pool?
Body's total supply of free amino acids
- source for:
- -resynthesizing body protiens
- -forming amino acid derivatives
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
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
Describe Carbohydrates during the absoptive state
glucose is the major energy fuel
glucose is converted into glycogen or fat (by the liver)
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
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
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)
What are the hormonal controls of the postabsorptive state?
glucagon release is stimulated by:
- -declining blood glucose (dampening insulin release)
- -rising amino acid levels
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)
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
What is the metabolix role of the liver?
- -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
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
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
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
How/when does the liver produce cholesterol?
At a basal leel regardless of dietary intake (about 85%)
in reponse to saturated fatty acids
Plasma Cholesteral Levels
Saturated Fatty Acids
Unsaturated Fatty Acids
- 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
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
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
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
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
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
What regulates food intake?
2. VMN neurons
- Two sets of distinct hypothalmic neurons1. LHA neurons promote hunger when stimulated by neuropeptides (e.g. NPY)
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
- -to a lesster exten, body temperature and psychological factors
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
- *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")
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
What are the additional factos for long term regulation of food intake?
- psychological factors
- adenovirus infetion
- sleep deprivation
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)
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)
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
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
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)
What are the four mechanisms of heat exchange?
HEAT ALWAYS TRAVELS DOWN THE GRADIENT
- 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
is the transfer of heat by direct contact
is the transfer of heat to the surrounding air
is the heat loss due to evaporation of water from body surfaces
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
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!
What are the heat-promoting mechanisms of the hypothalamus?
1. contriction of cutaneous blood vessels
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
What are the heat-loss mechanisms of the hypothalamus?
Dilation of the cutaneous blood vessels
- Voluntary measures include:
- -reduced activity and seeking a cooler enviornment
- -wearing light colored and loose fitting clothing
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
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
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
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
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
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
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