Lecture 11 pt 2: Body temp regulation Flashcards
True or false: Temperature extremes injure tissues.
True
How do heat and cold damage tissues?
1) Heat: Denatures proteins
2) Cold: Ice crystals form
Are increases in body temp necessary? Why or why not?
Some increases are necessary for specialized functions to increase reaction rate.
1) Increasing temp by 10°C increases the reaction rate by a factor of ___ or ___
2) Ratio between these: ______
1) 2 or 3
2) Q10
What are 5 sites for monitoring body temperature?
1) Oral
2) Axillary
3) Rectal
4) Tympanic membrane
5) Temporal scanner
1) What two body temperatures are 98.6F?
2) What temperature is typically 1F warmer?
1) Oral and axillary
2) Rectal
1) Devices can measure heat generated by tympanic membrane and convert to an _____ equivalent reading
2) How are temporal scanners used?
1) oral
2) Stroked across forehead to measure blood in temporal artery, which is near the surface
1) All heat exchange must ultimately occur between the body and what?
2) What organ plays a major role in heat exchange
3) Heat moves _______ its thermal gradient from a ___________ to a ___________ region
1) external environment
2) Skin
3) down; warmer; cooler
What 4 mechanisms allow for temperature balance?
1) Radiation
2) Conduction
3) Convection
4) Evaporation
1) Define radiation
2) How much of heat loss does it make up?
1) Emission of thermal energy from body surface in the form of heat waves (electromagnetic waves). Incl. emission from the sun or a fire.
2) Half of heat loss
1) Define conduction
2) What does the rate of heat transfer depend on?
3) Heat exchange occurs between skin and what?
1) Transfer of heat between objects that are in direct contact
2) Magnitude of temperature difference and the thermal conductivity of the substances
3) The air that directly contacts it
1) Is a lot of heat exchanged via conduction? Why?
2) Why will water feel cooler than air of the same temperature?
1) Minimal heat is exchanged this way because air has poor thermal conductivity
2) Because water has higher thermal conductivity and heat is lost more rapidly from body surface
1) Define convection
2) How is convection achieved?
3) What can enhance convection? Give 2 examples
1) Transfer of heat energy by currents (air or water)
2) Convection currents
3) Forced movement; like air from a fan, riding a bike
How do convection currents work?
1) Skin in direct contact with cooler air will warm the air
2) Warm air rises and replaced by cooler air, which is also heated
3) Repeated process creates a current that carries heat away (otherwise the layer of air in contact with skin would immediately equilibrate with skin temperature)
What would happen if the convection current process didn’t repeat?
The layer of air in contact with skin would immediately equilibrate with skin temperature
1) Describe evaporation in the context of the human body
2) What does this do?
3) Evaporative heat is lost from what 2 places?
1) Heat required to transform water from liquid to a gas is absorbed from the skin
2) Cools the body
3) Respiratory linings and the skin surface
1) How is water lost via evaporation in the airways?
2) What about via evaporation through the skin?
3) Can we control evaporation through the skin? What about in cold weather?
1) Air is humidified in airways
2) Skin is not perfectly waterproof, water molecules diffuse through and evaporate
3) Passive baseline diffusion not subject to physiologic control, even with very cold weather
1) What is the body’s thermostat? What is it also called?
2) Does it receive or send afferent information about temperature?
3) Does it send efferent signals? If so, why?
4) How many centers for temperature regulation does it have?
1) Hypothalamus; Thermoregulatory integration center
2) Receives afferent information
3) Sends efferent signals to initiate counter-mechanisms
4) Two
What are the two centers for temperature regulation within the hypothalamus?
1) Anterior: activated by warmth
2) Posterior: activated by cold
What are the two ways the hypothalamus receives afferent information about temperature?
1) Peripheral thermoreceptors in skin
2) Central thermoreceptors in hypothalamus and organs
1) Chronic cold exposure stimulates what?
2) What is this abundant in? (2 things) What does this do?
3) What idea is this relevant to?
1) Brown adipose tissue (“brown fat”)
2) In mitochondria and iron; gives red/brown appearance
3) Thermogenesis
What is brown adipose tissue?
Adipocyte specialized at converting energy to heat
-Used in non-shivering (chemical) thermogenesis
Why do newborns have large deposits of brown fat?
Non-shivering (chemical) thermogenesis; they cannot shiver
Each cell in the body needs ____________ to perform essential functions
energy
List 4 essential body functions that require energy
1) Active transport
2) Cellular repair
3) Gland secretion
4) Muscle contraction
Heat storage is a balance between net ____________________ and net ____________________
heat production; heat loss
1) Large amounts of body heat can be dissipated through what?
2) What can lead to overheating? What can this also lead to?
3) What else augments heat loss?
1) Sweat evaporation
2) Sweat Gland “fatigue” ; depletion of glycogen
3) Increased vasodilation of the skin
What are the two main types of sweat glands? Which is dominant?
1) Eccrine: Dominant.
2) Apocrine
1) Sweat glands involve mostly what 2 ions?
2) What type of sweat gland appears in puberty?
1) Na+ and Cl-
2) Apoeccrine
1) The sympathetic fibers of what type of gland release ACh?
2) Does this type of gland have an odor?
3) If so, what creates odor? If not, explain why.
1) Sweat
2) No, odorless
3) Mixes with flora on the skin and creates odor
1) What type of glands are viscous and in smaller amounts?
2) What is a subtype of this type? When does it appear?
1) Apocrine
2) Apoeccrine; appears during puberty
1) What are the nutritional needs of the skin?
2) How is blood flow to the skin controlled? What does this operate in tandem with?
3) What is dependent on sympathetic nerve signals?
1) Nutritional needs of the skin are low
2) Blood flow is controlled by reflexes or changes in temperature; in tandem with sweating
3) Vasodilation
Give an example of sympathetic control of skin circulation. What fibers is this mostly through?
Reflex Vasoconstriction; adrenergic fibers
What is your default body temperature called? What can affect it?
Set point; exercise
Circadian Rhythm and temperature:
1) When does minimum temperature happen?
2) What about maximum temperature?
1) At night hours before waking
2) Late afternoon/evening
Regarding the menstrual cycle and temperature, when does lowest temperature occur?
Just before ovulation
1) What makes up energy input?
2) What type of energy is it? What is it released from?
3) What two things can happen with this energy?
1) Ingested food
2) Chemical energy; released from bonds of nutrient molecules
3) Used immediately to perform biological work or stored for later use
Energy output falls into two categories; what are they? Define them.
1) External work: Energy used when skeletal muscles contract to move the body or objects
2) Internal work: All other forms of energy (two types; skeletal muscle non-movement work and everything else)
1) What is internal work a type of?
2) What is skeletal muscle non-movement work a type of?
1) Energy output
2) Internal work
What are the two types of internal work? Give examples of each
1) Skeletal muscle non-movement work: shivering, posture, etc.
2) Everything else: pumping blood, breathing, cell transport, metabolism, repair
1) Chemical energy used by the body is converted into what?
2) 50% of the energy from nutrient molecules is captured as what? What happens to the rest?
1) Thermal energy (heat)
2) ATP; lost as heat
1) What percent of total energy from nutrients is used? What percent is lost as heat?
2) When is more energy lost as heat?
3) Is heat entirely wasted?
1) About 25% is used, 75% lost as heat
2) When cells use ATP
3) No, used to maintain temperature.
1) Define metabolic rate
2) Give the formula for metabolic rate
3) What is metabolic rate normally expressed in terms of?
1) The rate at which energy is expended by external and internal work
2) Energy expenditure / time
3) Heat
1) The Basic unit of heat energy is what? Define this term.
2) What do we use for terms of human heat generation instead? Why?
3) 1 Calorie = _________ calories
1) a calorie: amount of energy required to raise temperature of 1g of H2O by 1°C
2) Too small to be useful in human heat gen; kilocalorie “Calorie”
3) 1000
What causes you to shiver or sweat?
Hypothalamus
What hormone rises at night? What rises during the day?
Melatonin rises at night, cortisol rises during the day
In the U.S. when we say “calories” we are referring to what?
Calories (kilocalories)
1) Define metabolic rate
2) What are some of the many factors it depends on?
1) rate of heat production
2) Exercise, emotional state, shivering, food intake, etc and skeletal muscle activity
What is able to raise metabolic rate to the greatest extent? What increases can affect metabolic rate?
Skeletal muscle activity ; even slight increases
Define BMR (Basal metabolic rate)
1) Metabolic activity necessary to maintain basic body functions
2) Minimal waking rate of internal energy expenditure
slide 40
1) What 3 factors does the metabolic rate need to be adjusted for?
2) Larger person has _____________ rate of heat production than a smaller person
3) _____________ hormone is the primary (but not sole) determinant of BMR
1) Size, age, sex
2) higher
3) Thyroid
1) True or false: BMR is not the body’s lowest metabolic rate, it is the baseline waking rate
2) Sleep is __________ lower likely due to ________________
1) True
2) 10-15%; muscle relaxation
1) Define neutral energy balance
2) Define positive energy balance
3) Define negative energy balance
1) Amount of energy input exactly equals energy output; energy from food intake exactly equals internal and external energy expenditure
2) Food intake energy exceeds energy expended. Body stores energy.
3) Energy expended exceeds food intake energy. Body uses stored energy.
1) Food intake is primarily regulated by what?
2) Energy is balanced through what?
1) Hypothalamus
2) Molecular signals
Energy is balanced through what 4 molecular signals?
1) How much fat is stored
2) Feeding status
3) Hunger
4) Circulating nutrients
1) What part of the hypothalamus regulates hunger?
2) Define this structure
1) Arcuate nucleus of the hypothalamus
2) Two subsets of neurons functioning in opposition
List, define, and give the functions of the two subsets of neurons (functioning in opposition) in the arcuate nucleus of the hypothalamus
1) One releases neuropeptide Y (NPY): Highly potent appetite stimulator. Promotes weight gain.
2) The other releases melanocortins: Suppress appetite in humans (allow camouflage in other animals)
Two areas of the hypothalamus are richly supplied by axons from neurons of the arcuate nucleus; what are they? What does each do?
1) Lateral hypothalamic area (LHA): Produces orexins which are potent appetite stimulators
2) Paraventricular nucleus (PVN): Release chemical messengers that decrease appetite
1) What stimulates the LHA?
2) What stimulates the PVN
1) LHA Stimulated by NPY, inhibited by melanocortins
2) Stimulated by melanocortins and inhibited by NPY
1) What is leptin essential for?
2) What does serum leptin directly correlate to?
3) What does it suppress? What does it act on?
4) What is inhibited? What is stimulated?
1) Normal body-weight regulation
2) Stored triglycerides
3) Appetite; acts on arcuate nucleus
4) Inhibits NPY, stimulates melanocortins
1) List the steps that allow decreased fat stores to increase appetite?
2) What is leptin the dominant factor of?
1) Decreased fat stores =
decreased triglycerides =
decreased leptin =
decreased inhibition of NPY and decreased stimulation of melanocortins =
increased appetite
2) Long term energy balance
1) What is insulin?
2) What does it stimulate?
3) What is an increase in insulin secretion accompanied by?
4) What does it inhibit?
1) Hormone secreted by pancreas in response to glucose and other nutrients in the blood
2) Cellular uptake, use, and storage of nutrients
3) Increased use or storage
4) NPY-secreting cells of hypothalamus
List two leptin-signaling disturbances and what causes each
1) Hypothalamic “set point” is set higher
-Receptors do not respond appropriately to high leptin levels
2) Defect in chemical messengers affecting blood-brain barrier
-Brain not responding to leptin appropriately
1) There’s an Abundance of convenient, palatable, inexpensive, energy dense foods; why?
2) Companies invest a significant amount of research into engineering what and applying what principles?
1) Combination of fats, carbs, and salt is hyperpalatable
2) “Addictive” foods and applying psychosocial principles to their marketing of these foods
