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Physiology II Exam 2 > Temperature Regulation > Flashcards

Flashcards in Temperature Regulation Deck (52)
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1

What factors determine heat production?

-BMR

-muscle activity

-thyroxin

-NE and epi

-increased cellular chemical activity

-extra metabolism for digestion, absorption, and food storage

2

What is malignant hyperthermia?

-heat production is far greater than heat dissipation

-due to genetic abnormalities in the ryanodine receptors in skeletal muscle which leads to excess release of Ca, leading to prolonged excitation-contraction coupling

-triggered by anesthetics

3

What are the factors that determine rate of heat loss?

-how rapidly heat can be conducted from body core to skin

-how rapidly heat can be transferred from skin to surroundings

-small amount of heat is transferred via the respiratory system

4

Explain how heat is transferred from skin to environment.

-skin and subQ act as heat insulators

-continuous venous plexus in subQ is supplied by inflow of blood from capillaries from dermis

-rate of blood flow into the plexus can be as great as 30% of total cardiac output

-8x increase in conductance between fully vasoconstricted state to fully vasodilaters state

-vasoconstriction is controlled almost entirely by sympathetic system in responses to core temperature and environmental temperature

5

What is heat conduction of the skin controlled by?

-degree of vasoconstriction of arterioles and the arteriovenous anastomosis that supply blood to the venous plexus of the skin

6

What are the three methods heat is removed from the body?

-radiation

-conduction

-convection

7

How is radiation lost?

-loss in the form of infrared heat rays

-radiated by all objects not at absolute zero

-if temp of body is greater than ambient temp, more heat is radiated from the body than to the body

8

How is conduction lost from the body?

-kinetic energy of the molecules of the skin is transferred to the air if the air is colder than the skin

9

How does convection work?

-removal of heat from the body by convection air currents

10

Low velocity has a cooling effect proportional to ______________.

The square root of the wind velocity

11

What has a greater specific heat, water or air? What does this mean?

-water

-rate of heat loss in water is usually many times greater than the rate of heart loss in the air

-for each gram of water evaporated from body, 0.58 calories of heat is lost

12

What is insensible perspiration?

-occurs at a rate of 600-700 mL/day

-causes a continual heat loss at a rate of 16-19 calories/day

13

Percentage of heat lost and method of loss

-evaporation (22%)

-radiation (60%)

-conduction to air (15%)

-conduction to objects (3%)

14

What is radiation in terms of heat transfer?

-thermal energy transferred to objects in the external environment

-amount transferred depends on temp difference and ability of object to absorb energy

15

What is conduction in terms of heat transfer?

-transfer of energy from one body to another when they are in close contact

16

What is convection in terms of heat transfer?

-heat is transferred between two objects by air or water

17

What is evaporation?

Heat is dissipated by the use of thermal energy to cause a change from fluid to gas

18

What stimulates sweating?

-stimulation of anterior hypothalamus- preoptic area in the brain electrically or by excess heat

-cholinergic sympathetic nerve fibers (muscarinic)

-circulating epi and NE

19

What is the composition of precursor secretion?

-similar to plasma without proteins

Na (142mEq/L)

Cl (104mEq/L)

20

What does strong stimulation of sweat glands do?

-large amounts of precursor secretion are formed

-ducts reabsorb only about half the NaCl

-concentrations of Na and Cl are about 50-60 mEq/L

-little water is reabsorbed

21

What are some of the differences between unacclimatized and acclimatized individuals when exposed to hot weather?

-unacclimatized person normally produces about 1 L sweat per hour

-person exposed to hot weather for 1-6 weeks may produce 2-3 L sweat/hr, increasing heat removal 10x
+due to changes in internal sweat gland cell

22

What are the principal areas of the brain that affect body temperature?

-anterior hypothalamic pre-optic area

-pre-optic area

23

What does the anterior pre-optic area contain? What do these do?

-heat sensitive neurons: increase firing rate 2-10x in response to a 10 degree C increase in body temp

-cold sensitive neurons: increase in firing rate when temp falls

24

What does heating of the pre-optic area cause?

-dilation of skin blood vessels over the entire body

-profuse sweating over the entire body

-inhibition of excess heat production

25

What are the three mechanisms to reduce body heat?

-vasodilation of skin blood vessels -> caused by inhibition of sympathetic centers in posterior hypothalamus that cause vasoconstriction

-sweating

-decrease in heat production due to inhibition of shivering and thermogenesis

26

What are the three mechanisms to increase body heat?

-skin vasoconstriction

-piloerection

-increase in thermigenesis

27

What are methods of thermogenesis?

-shivering

-metabolic pathways

-thyroxin secretion

28

Where is the primary motor area for shivering located? How does this area relate to the anterior hypothalamic preoptic area? Under what conditions is this area activated?

-dorsomedial portion of posterior hypothalamus

-normally inhibited by signals from heat center in anterior hypothalamic preoptic area

-excited by cold signals from skin and spinal cord

29

How does the dorsomedial of the posterior hypothalamus initiate shivering?

-when activated, transmits signals into lateral columns of spinal cord to anterior motor neurons -> alpha motor neurons and gamma neurons are activated

-nonrhythmical signals increase muscle tone of skeletal muscles throughout the body

-shivering begins when tone rises above a certain critical level

-may involve feedback oscillation of muscle spindle stretch reflex mechanism

30

What is chemical thermogenesis?

-increase in rate of cellular metabolism due to sympathetic stimulation or NE in blood