Energy Balance and Temperature Regulation Flashcards
What is the difference between external and internal work performed by the body?
1.) internal work: skeletal muscle contraction not used for external work (posture, shivering), and life sustaining activities (heart beating, breathing, active transport across membrane)
2.) contraction of skeletal muscles in order to move body or move object
Where does the energy used in internal work eventually go?
ultimately ends up as thermal energy
What is metabolic rate? Is it constant?
metabolic rate: rate at which energy is expended by the body
varies greatly depending on activity
Does muscular tone produce body heat? Or only active movement of skeletal muscles?
much heat generated by skeletal muscle contraction (even muscular tone)
What is basal metabolic rate (BMR)? What largely determines the BMR?
BMR: minimal metabolic rate necessary to power life sustaining activities while awake (measured under conditions minimizing skeletal muscle contractions as much as possible)
What is the difference between a positive, negative or neutral energy balance?
positive: input energy > energy expended (increase in stored energy, weight gain)
neutral: input energy = energy expended (no change in stored energy)
negative: input energy < energy expended (decrease in stored energy, weight loss)
Where is the arcuate nucleus and why is it important?
located in the hypothalamus
plays a central role in long term control of body weight and short term control of food intake
What are the general functions of neuropeptide Y and melanocortins?
neuropeptide Y: released by subset of arcuate neurons; potent appetite stimulator
melanocortins: released by subset of arcuate neurons; suppress appetite
Does insulin suppress or increase appetite? How about leptin?
insulin: inhibits cells in arcuate that release neuropep. Y -> suppresses appetite
leptin: Inhibits neuropeptide Y-secreting neurons and excites melanocortin-producing neurons in arcuate -> suppresses appetite
What are adipokines?
hormones released by adipocytes (fat cells)
some adipokines cause inflammation in obese fat stores, others affect energy balance
Why do we stop eating before the nutrients in a meal actually enter the bloodstream?
How does our body know to stop?
peptide YY: hormone released by small and large intestines, increasing as a meal progresses…. signalling satiety
CCK: hormone released by duodenum when fat and protein-rich chyme enters small intestine
- Excites neurons in the satiety center of the brainstem (nucleus tractus solitarius (NTS))
- Causes individual to feel “full” and finish their meal even though nutrients haven’t been absorbed yet
Stretch receptors stimulated by stomach distension also excite NTS
What is the body’s core temperature maintained at? Why is it important to maintain core
temperature?
core temp maintained at 100 degrees F
-increase in core temp speeds speeds up chem reaction, decrease slows them down
- core temp at 110 is upper limit of life (convulsions begin at 106)
What are the various processes by which heat is exchanged between the body and
environment?
1.) radiation: emission or absorption of heat energy as electromag. waves (half of body heat loss via radiation)
2.) conduction: transfer of heat energy by direct contact
3.) convection: transfer of heat energy by moving currents
4.) evaporation: heat energy used as the water in sweat undergoes state of change from liquid to gas
What are sources of heat input to the body?
sweating, vasoconstriction or dilation of skin arterioles, nonshivering thermogenesis
What detects changes in core temperature? How about changes in skin temperature?
Where in the brain is this information sent?
change in core temp: central thermoreceptors in hypothalamus, abdominal organs, and elsewheres
change in skin temp: peripheral thermoreceptors in skin
information sent to hypothalamic centers for thermoregulation (body’s thermostat)
Could you describe what compensations the body might produce for an increase in core
temperature? How about for a decrease in core temperature?
-increase:
-sweating (active evaporative heat loss),
-vasodilation
-decrease:
-shivering,
-nonshivering thermogenesis (sympathetic nervous activation of brown adipose fat during chronic cold exposure)
-vasoconstriction
What does the thermoneutral zone mean?
environmental temperatures between upper 60s and mid 80s where body temperature can be mediated solely by vasomotor activity
What is hypothermia?
fall in body temp. when heat-producing and heat-conserving mechanisms cannot match heat loss
- high cerebral function impaired first, loss of judgement, apathy, disorientation, and tiredness
-depression of respiratory center, decreasing ventilation
- heart rate slows and cardiac output decreases
-cardiac rhythm disturbed-> ventricular fibrillation and death
What is hyperthermia?
rise in body temperature
What is heat exhaustion? How does it differ from heat stroke?
state of collapse (fainting) brought on by drop in blood pressure
1.) extensive sweating decreases plasma volume
2.) pronounced vasodilation decrease total peripheral resistance (lowering bp)
-fainting usually leads to cessation of activity leading to hyperthermia
what is heat stroke? how is it different from heat exhaustion?
chronically increased core temp shuts down hypothalamic thermoregulatory center
-sweating increases-> core temp rises with no control
