Energy Balance and Temperature Regulation

Question 1

What is the difference between external and internal work performed by the body?

Answer 1

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

Question 2

Where does the energy used in internal work eventually go?

Answer 2

ultimately ends up as thermal energy

Question 3

What is metabolic rate? Is it constant?

Answer 3

metabolic rate: rate at which energy is expended by the body
varies greatly depending on activity

Question 4

Does muscular tone produce body heat? Or only active movement of skeletal muscles?

Answer 4

much heat generated by skeletal muscle contraction (even muscular tone)

Question 5

What is basal metabolic rate (BMR)? What largely determines the BMR?

Answer 5

BMR: minimal metabolic rate necessary to power life sustaining activities while awake (measured under conditions minimizing skeletal muscle contractions as much as possible)

Question 6

What is the difference between a positive, negative or neutral energy balance?

Answer 6

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)

Question 7

Where is the arcuate nucleus and why is it important?

Answer 7

located in the hypothalamus
plays a central role in long term control of body weight and short term control of food intake

Question 8

What are the general functions of neuropeptide Y and melanocortins?

Answer 8

neuropeptide Y: released by subset of arcuate neurons; potent appetite stimulator

melanocortins: released by subset of arcuate neurons; suppress appetite

Question 9

Does insulin suppress or increase appetite? How about leptin?

Answer 9

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

Question 10

What are adipokines?

Answer 10

hormones released by adipocytes (fat cells)
some adipokines cause inflammation in obese fat stores, others affect energy balance

Question 11

Why do we stop eating before the nutrients in a meal actually enter the bloodstream?
How does our body know to stop?

Answer 11

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

Question 12

What is the body’s core temperature maintained at? Why is it important to maintain core
temperature?

Answer 12

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)

Question 13

What are the various processes by which heat is exchanged between the body and
environment?

Answer 13

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

Question 14

What are sources of heat input to the body?

Answer 14

sweating, vasoconstriction or dilation of skin arterioles, nonshivering thermogenesis

Question 15

What detects changes in core temperature? How about changes in skin temperature?
Where in the brain is this information sent?

Answer 15

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)

Question 16

Could you describe what compensations the body might produce for an increase in core
temperature? How about for a decrease in core temperature?

Answer 16

-increase:
-sweating (active evaporative heat loss),
-vasodilation

-decrease:
-shivering,
-nonshivering thermogenesis (sympathetic nervous activation of brown adipose fat during chronic cold exposure)
-vasoconstriction

Question 17

What does the thermoneutral zone mean?

Answer 17

environmental temperatures between upper 60s and mid 80s where body temperature can be mediated solely by vasomotor activity

Question 18

What is hypothermia?

Answer 18

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

Question 19

What is hyperthermia?

Answer 19

rise in body temperature

Question 20

What is heat exhaustion? How does it differ from heat stroke?

Answer 20

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

Question 21

what is heat stroke? how is it different from heat exhaustion?

Answer 21

chronically increased core temp shuts down hypothalamic thermoregulatory center
-sweating increases-> core temp rises with no control