Temperature Homeostasis & Diet Flashcards
HUMANS ARE HOMEOTHERMIC.
TRUE OR FALSE?
TRUE
Homeothermic= warm-blooded
WHY IS A WOMAN’S BASAL BODY TEMPERATURE HIGHER DURING THE SECOND HALF OF HER MENSTRUAL CYCLE?
Due to effects of progesterone
BODY TEMPERATURE BALANCE
- A dynamic equilibrium between heat input and output
- Heat input – internal production and external input
–internal: metabolism and muscle contraction
–external: from the environment via radiation or conduction
•Heat output - losses to the environment
–radiation, conduction, convection and evaporation
HEAT BALANCE IN THE BODY
BODY TEMPERATURE IS HOMEOSTATICALLY REGULATED
- Generally, body T > ambient (environmental) T
- Thermoneutral zone (TNZ): the range of ambient T over which the heat from basal metabolism is sufficient to maintain body core T (≈ 25-30 oC)
–above TNZ there is net bodily gain of heat
–below TNZ there is net bodily loss of heat
–in both cases homeostatic compensation is required
•A naked human can thermoregulate at ambient air T between 10-55 oC
–the main physiological thermoregulatory challenge is low T
ENVIRONMENTAL (AMBIENT) TEMPERATURE IS GENERALLY HIGHER THAN BODY TEMPERATURE.
TRUE OR FALSE?
False
Body temperature tends to be higher
WHAT IS THERMONEUTRAL ZONE (TNZ)?
The range of ambient T over which the heat from basal metabolism is sufficient to maintain body core T (≈ 25-30 oC)
WHERE IS THE THERMOREGULATORY CENTRE?
In the hypothalamus
THE THERMOREGULATORY CENTRE IS IN THE HYPOTHALAMUS
Integrates sensory input from thermoreceptors located in the core and periphery (skin).
–↑ blood T is detected in the anterior hypothalamus
–↓ blood T is detected in the posterior hypothalamus
- Input T is compared with the desired setpoint (37 oC)
- Appropriate regulatory response is output
–> 37 oC – sweating, cutaneous vasodilation
–< 37 oC – cutaneous vasoconstriction (and horripilation)
–< 37 oC – non-shivering thermogenesis (infants)
–< 37 oC – shivering
WHERE IS A DECREASE IN BLOOD TEMPERATURE DETECTED?
In the posterior hypothalamus
WHERE IS AN INCREASE IN BLOOD TEMPERATURE DETECTED?
In the anterior hypothalamus
THERMOREGULATORY REFLEXES 1
THERMOREGULATORY REFLEXES 2
THERMOREGULATORY RESPONSES: CUTANEOUS BLOOD FLOW VASOCONSTRICTION
THERMOREGULATORY RESPONSES: CUTANEOUS BLOOD FLOW VASODILATION
HOW MANY SWEAT GLANDS DO WE HAVE?
3-4 million
THERMOREGULATORY RESPONSES: SHIVERING
Voluntary (behavioural) & involuntary muscular thermogenesis
NON-SHIVERING THERMOGENESIS
Hormone-induced, uncoupling of mitochondrial oxidation from phosphorylation in brown adipose tissue.
Only of significance in infants
BODY TEMPERATURE RANGES
FEVER (PYREXIA), 38oC=
•Result of a chemical resetting (↑) of the thermal set point
–release of endogenous pyrogens (EPs) in response to infection
•EPs – cytokines released into the circulation include IL-1β, IL-6 and TNFα
–body triggers thermoregulatory responses
•↑ heat production and ↓ heat loss= core temperature rises
–body temperature stabilises at new (elevated) set point
Augmentation of the immune response (innate & adaptive)
•Body temperature remains elevated until fever ‘breaks’
WHAT IS ADEQUATE (HEALTHY) NUTRITION?
An integral part of daily life that contributes to the physiological, mental and social well-being of individuals.
A balanced diet that contains adequate amounts of nutrients in relation to bodily requirements.
WHAT IS MALNUTRITION?
Any physical condition resulting either from an inappropriate or inadequate diet that either provides too much or too little of necessary nutrient
Negatively affects the quality of life and learning as well as death and disease status.
HOW DO YOU CALCULATE TOTAL BODY ENERGY?
Total body energy= Energy stored + Energy Intake - Energy output
ENERGY BALANCE
HOW DO YOU CALCULATE ENERGY OUTPUT?
Total energy output= work + heat
NUTRITION AND ENERGY BALANCE
Energy output= work + heat
- In the human body at least 50% of the energy released in chemical reactions is thermal and not available for _.
- Active transport of molecules
–into/out of the body, between compartments, across membranes
•Mechanical
–voluntary and involuntary movement of muscles
•Chemical
–synthesis for growth and maintenance (tissues & cells)
–short-/long-term energy _ (ATP, glycogen, fat)
Work
Storage
WHAT IS BASAL METABOLIC RATE (BMR)?
The minimum level of energy required to sustain vital functions
MEASURING ENERGY CONSUMPTION
Basal Metabolic Rate
• Minimum level of energy required to sustain vital functions
–Measured at rest in a fasted state in a thermo-neutral environment
–Measured as the heat produced or oxygen consumed per unit time
–Expressed as the calories released/kg of body mass or /m2 of BSA/h
Total Energy Expenditure (TEE)
BMR + dietary-induced thermogenesis + physical activity
- Estimated from an individuals BMR & Physical Activity Level (PAL)
- PAL – a 24h index of energy expenditure due to physical activity
- BMR x PAL = Estimated Average Requirement (EAR) for energy
HOW DO YOU ESTIMATE TOTAL ENERGY EXPENDITURE?
Estimated from BMR and and the individuals phyiscal activity level (PAL)
WHAT IS PHYSICAL ACTIVITY LEVEL (PAL)?
A 24h index of energy expenditure due to physical activity
WHEN WOULD YOU MEASURE BMR?
When an individual is at rest in a fasted state in a thermo-neutral environment
THE DIFFERENT CATEGORIES OF NUTRIENTS
Macronutrients (daily requirements tens of grams)
- Proteins- energy content of 3.75 kcal/16 kJ per g
- Fats- energy content of 9 kcal/37 kJ per g
- Carbohydrates- energy content of 4 kcal/17 kJ per g
Micronutrients (daily requirements are a less)
•Vitamins (organic) - water soluble (not stored) and fat soluble (stored)
Minerals (inorganic)
Macrominerals – Na, K, Ca, Mg, Cl and P
Trace elements – Fe, Zn, Se, Cu, Se, Mn, Mo…
WHAT CATEGORIES OF FOOD ARE MACRONUTRIENTS?
Proteins
Fats
Carbohydrates
WHAT CATEGORIES OF FOOD ARE MICRONUTRIENTS?
Vitamins
Minerals
IN A HEALTHY BODY CARBOHYDRATE IS THE PREFERRED, SHORT-TERM ENERGY SOURCE
NON-ENERGY-RELATED FUNCTIONS OF PROTEINS
•Dietary proteins are the source of amino acids (aa)
–essential (I, L, V, F, W, H, K, T and M)
–non-essential (A, G, P, Y, D, E, R, S, C, N, Q)
•Amino acids are required for the synthesis of proteins
–structural (e.g. collagens, elastins, keratins)
–functional (e.g. enzymes, antibodies, receptors, hormones)
•Amino acids are precursors for other biomolecules
–nucleotides (purines and pyrimidines; E, R, D and Q)
–catecholamines (e.g. dopamine, (nor)epinephrine; Y, F)
–neurotransmitters (e.g. serotonin, melatonin; W)
–some amino acids function as neurotransmitters (e.g. E, G)
NON-ENERGY-RELATED FUNCTIONS OF CARBOHYDRATES
•Dietary carbohydrates provides monosaccharides for the biosynthesis and modification of macromolecules
–glycoproteins (secreted and integral membrane proteins)
–membrane glycolipids (e.g. blood group antigens)
–glycosaminoglycans (GAGs; e.g. hyaluronan)
–proteoglycans (GAGs linked to a protein core; e.g. aggrecan)
•Dietary carbohydrate is a source of fibre
–indigestible, structural polysaccharides derived from plants
•e.g. cellulose, hemicellulose, pectin and resistant starch
–add bulk and thicken the contents of the GI tract
–slows the digestion and absorption carbohydrates and fats
-production of beneficial, short-chain fatty acids by colonic microbiota
WHAT ARE THE TWO NON-ENERGY RELATED FUNCTIONS OF CARBOHYDRATES?
- Dietary carbohydrates provides monosaccharides for the biosynthesis and modification of macromolecules
- Dietary carbohydrate is a source of fibre
NON-ENERGY-RELATED FUNCTIONS OF FAT
•Dietary fats are the source of the essential fatty acids
–alpha linoleic acid (ALA) and linoleic acid (LA)
•Dietary fats are required for membrane biosynthesis
–phospholipids, glycolipids, sphingolipids and cholesterol
- Act as ‘carriers’ for the fat soluble vitamins
- Required for the biosynthesis of steroid hormones
- Required for the biosynthesis of lipid mediators
–eicosanoids, phosphoinositides, sphingosine-1-phosphate
•Required for the biosynthesis of proteolipids
–glycosylphosphatidylinositol(GPI)-anchored proteins
(e.g. enzymes, receptors, cell adhesion molecules)
DIFFERENT TYPES OF FATS
MACRONUTRIENTS METABOLISM: FED VS FASTED STATES
MICRONUTRIENTS: VITAMINS AND TRACE ELEMENTS
•Essential for growth, maintenance and repair
–no utilisable energy content per se
–required for intermediary metabolism
•Required in small quantities
–typically in the µg – mg range
–cannot be synthesised de-novo
•Participate in many metabolic/regulatory processes
–endocrine signalling (hormones)
–intermediary metabolism (coenzymes and cofactors)
–many function as antioxidants (scavengers of free radicals)
•highly reactive - capable of damaging cellular macromolecules
WHAT ARE THE THREE FUNCTIONS OF MICRONUTRIENTS?
Essential for growth, maintenence and repair
Required in small quantities
Participate in many metabolic and regulatory processes
THE CHEMICAL STRUCTURES OF VITAMINS
MICRONUTRIENTS: MINERALS
ANAEMIA
•Symptoms and signs
–pallor
–tachycardia (abnormally rapid heart rate)
–fatigue, tiredness and headache
–breathlessness
–angina (chest pain)
–intermittent claudication (pain/cramps in lower limbs)
•Multiple causes including
–Iron deficiency (microcytic anaemia)
–vitamin B12 (cobalamin) deficiency (macrocytic anaemia)
NUTRIENT INTAKE: DEFINING THE RIGHT AMOUNT
•Dietary Reference Values (DRVs)
–population-based estimates of energy and nutritional requirements for different groups of healthy individuals (men, women, infants, children, teenagers, adults, the elderly)
•There are four DRVs
–Estimated Average Requirement (EARs)
–Reference Nutrient Intakes (RNIs)
–Lower Reference Nutrient Intake (LRNIs)
–Safe Intake (none of the above yet defined)
•The RNI is used when issuing nutritional guidance
–replaces the RDAs/RDIs used previously
WHAT ARE DIETARY REFERENCE VALUES (DRVs)?
Population-based estimates of energy and nutritional requirements for different groups of healthy individuals (e.g. men, women, children, elderly etc).
WHAT ARE THE FOUR DIETARY REFERENCE VALUES?
–Estimated Average Requirement (EARs)
–Reference Nutrient Intakes (RNIs)
–Lower Reference Nutrient Intake (LRNIs)
–Safe Intake (none of the above yet defined)
HOW MUCH PROTEIN WOULD THE STANDARD UK ADULT REQUIRE PER DAY?
0.75g per kg of body weight (e.g. 70kg person = 0.75 x 70)
DAILY PROTEIN REQUIREMENTS INCREASE DURING PREGNANCY AND LACTATION.
TRUE OR FALSE?
TRUE
