thermoregulation

Question 1

what re heat sources?

Answer 1

combustion of glucose (680Kcal.mole as heat), oxidative metabolism of glucose (420 Kcal/mole as heat, 266 Kcal/mole as ATP high energy bonds)

Question 2

what is the human heat production at rest?

Answer 2

1 Kcal/hour/Kg

Question 3

what temperature increase is potentially lethal?

Answer 3

increase of greater than 4-5 degrees C. (7-9 degrees F)

Question 4

what energy is required for evaporation of water (liquid) to gas phase?

Answer 4

584 Kcal/mole

Question 5

what are the 2 sources of insensible evaporation?

Answer 5

loss due to saturation of expired air and diffusive loss from epidermis via the stratum conium.

Question 6

what are sensible evaporation?

Answer 6

sweating due to sympathetic stimulation

Question 7

what is conduction?

Answer 7

heat can be lost or gained by contact of body with other conductive fluids, namely water or air (equation in notes).

Question 8

when is sweat not removing heat?

Answer 8

when the air temperature is less than the skin temperature and air is saturation, sweat will not evaporate and just drip off.

Question 9

equation for conduction?

Answer 9

Heat= AcKc(Tskin-Tambient)

Question 10

what are some physiological thermoregulatory compensation?

Answer 10

putting on more clothes, but generally involves changing temperature of the skin

Question 11

why is danger of hypothermia greater in water than air?

Answer 11

K value for water is 25 times greater than for air

Question 12

what is convection?

Answer 12

bulk movement of conductive fluid as a function of temperature differences within the fluid.

Question 13

what is a way to enhance conductive heat loss?

Answer 13

replacing warm air near the skin with cooler ambient temperature air (with a fan)

Question 14

why does curling up when cold help?

Answer 14

reduces Ac (surface area)

Question 15

what does the body do when exposed to radiation?

Answer 15

absorbs radiant energy, and int he case of a cold environment-> body may become source of radiant energy

Question 16

equation for radiation?

Answer 16

heat=ArKr(Tskin-Tradiator)

Question 17

what are the relative percentages of heat loss?

Answer 17

in an indoor room: 85% of heat loss is via conduction/convection and radiation, remaining 15% due to insensible evaporation.

Question 18

what is the 85% is equally divided between?

Answer 18

conduction and radiation due to nearly equal Ac and Ar, and Kc and Kr values, and equilibrium of air radiant surface temperatures.

Question 19

what is the difference physiological heat loss and evaporative heat transfer?

Answer 19

radiative and conductive/convective heat routes are bi-directional, while evaporative heat transfer always results in heat loss.

Question 20

as ambient temperature raises, what happens to the proportion of heat loss?

Answer 20

as ambient temperature raises the proportion of heat loss via evaporation increases dramatically.

Question 21

where can the body temperature be taken from?

Answer 21

oral, rectal, pulmonary artery catheter (best), and tympanic membrane.

Question 22

what is heat exchange dominated by?

Answer 22

conduction between capillary blood and the normally cooler skin surface.

Question 23

what happens during hypothermia?

Answer 23

vasoconstriction to reduce blood flow near skin, lower T skin relative to T ambient thus reducing further heat loss.

Question 24

what happens during hyperthermia?

Answer 24

vasodilation of blood vessels, body increases T skin relative to T ambient to enhance heat loss-> this decreases blood flow to core (and CNS). Especially important factor in infants where ratio of body surface area to weight is greater than in adults

Question 25

how does the skin respond to temperature changes?

Answer 25

cutaneous thermoreceptors, certain neurons distributed over the skin surface can respond to either heating (warming receptors) or cooling (cold) receptors

Question 26

how does our core respond to temperature changes?

Answer 26

neurons in pre-optic area of hypothalamus and spinal cord which respond to direct heating and cooling of these areas.

Question 27

what are the 3 major thermoregulatory states that all serve to maintain the core?

Answer 27

Vasomotor regulation, metabolic regulation, and combined sudomotor and vasomotor regulation

Question 28

which thermoregulator represents the normal resting state?

Answer 28

vasomotor regulation: mild levels of thermal stress or exercise, changes in skin blood flow are sufficient to regulate temperature

Question 29

which thermoregulator starts when maximal vasoconstriction is ineffective in preventing heat loss?

Answer 29

metabolic regulation->response include: voluntary exercise and shivering

Question 30

why does shivering occur?

Answer 30

when Tc drops below a certain threshold, limited effectiveness in elevating temperature because it increases conductive and convection loss by increasing blood flow from core to muscles by increasing movement of body

Question 31

which thermoregulator is in response to heat accumulation?

Answer 31

combine sudomotor and vasomotor regulation. Elevation in body temperature causes progressive increases in sweating and active metabolism

Question 32

For the natural circadian rhythm in body temperature, when is the lowest and peak of body temperatures?

Answer 32

Early evening-> highest | Pre-dawn-> lowest

Question 33

during a fever, what center is involved in the temperature increase?

Answer 33

hypothalamus temperature is set point, is increased to a new higher temperature and body temperature is elevated above normal

Question 34

what are pyrogen?

Answer 34

chemicals that cause a febrile response.

Question 35

What are two examples of pyrogens?

Answer 35

exogenous: heat-stable, high MW polysacc. product from G(-) bacteria endogenous: heat-LIABLE proteins released by monocytes, macrophages, and kupffer cells in response to bacterial pyrogens

Question 36

most important endogenous factor?

Answer 36

interleukin 1 beta

Question 37

how does interleukin 1 beta cause a fever?

Answer 37

by direct action on the hypothalamus

Question 38

what is another important cytokine/pyrogen?

Answer 38

TNF, produced by macrophages in response to G(-) bacterial endotoxin

Question 39

why might IL-1 beta work via prostoglandin E2?

Answer 39

injection of PGE2 into hypothalamus is pyrogenic and addition of aspirin inhibits PGE2 synthesis

Question 40

hyperthermia (heatstroke) is due to?

Answer 40

exogenously applied heat-load from over exertion, high ambient temperatures or both

Question 41

what sore some causes of excessive heat production?

Answer 41

delirium tremens, drug abuse, exertional hyperthermia, lethal catatonis, generalized tetanus

Question 42

what are some things that could cause diminished heat dissipation?

Answer 42

anti-cholinergic drugs, autonomic dysfunction, dehydration, heatstroke, neuroleptic malignant syndrome

Question 43

what are some disorders that can cause hypothalamic dysfunction?

Answer 43

cerebrovascular accidents, encephalitis, trauma, tumors, neuroleptic malignant syndrome

Question 44

what is the overall response to hyperthermia?

Answer 44

increase in subcutaneous blood flow to increase heat loss

Question 45

what is the normal conditions of subcutaneous blood flow?

Answer 45

300-500 ml/minute, 5-10% Cardiac output

Question 46

what can heat stress do to the normal subcutaneous blood flow?

Answer 46

increase it cardiac output can rise from 6 liters to 13 liters blow flow to skin can increase to 8 liters (60% CO)

Question 47

in hyperthermia, was is the response to apical regions? (hands, feet, etc)

Answer 47

primarily inhibit tonically expressed vasoconstriction

Question 48

in hyperthermia, was is the response to non-apical regions?

Answer 48

small increase in flow, due to removal of vasoconstriction, but the major factor increasing blood flow is active vasodilation

Question 49

what is the classical heatstroke characterized by?

Answer 49

due to excessive heat or humidity, causing increased body temperature with poor heat dissipation due to ineffectiveness of evaporative cooling.

Question 50

what are some complicating factors of hyperthermia?

Answer 50

dehydration, and drop in blood pressure due to decreased subcutaneous resistance-> replace fluid WITH electrolytes

Question 51

what is exertional hyperthermia?

Answer 51

due to voluntary muscular activity coupled with environmental heat stress (heavy exercising in hot or humid climates). Combined effect of vasodilation, demand for increased blood flow to skeletal muscle and fluid loss by sweating can cause sudden drop in blood pressure

Question 52

how is management hyperthermia treated?

Answer 52

physical cooling, anti-pyretics not useful

Question 53

why is hypothermia potentially dangerous?

Answer 53

if the core temperature drops below 90 degrees f, then hypothalamic compensatory mechanism fail

Question 54

when is clinical hypothermia use?

Answer 54

in surgical procedures to reduce O2 requirements and blood pressure/bleeding. With ventilation and cardiac assistance, core temperature ca be maintained at 70-75 degrees F for many hours.