Thermoregulation

Question 1

Heat is produced in large part by ____.

Answer 1

oxidative metabolism

Question 2

Calorie

Answer 2

energy capable of raising 1 gram of water from 0 to 1 degree celsius

Question 3

Glucose provides ____ of energy.

Answer 3

686 Kcal/mole (as heat)

or 420 Kcal/mole as heat and 266 Kcal/mole as ATP high energy bonds

Question 4

At rest, ____ are responsible for the highest percentage heat production.

Answer 4

splanchnic organs (then the brain, followed by muscle)

Question 5

Physical factors that govern temperature control

Answer 5

Evaporation (Insensible and sensible), Conduction and Convection, and Radiation

Question 6

Transition of water from liquid to gas phase requires ___ at room temperature.

Answer 6

584 cal/g

Question 7

Insensible evaporation

Answer 7

Loss due to saturation of expired air and diffusive loss from epidermis via the stratum conium. (1 Liter/day, requires 584 Kcal)
25% of caloric intake

Question 8

Sensible evaporation

Answer 8

Sweating, occurs due to cholinergic sympathetic stimulation of sweat glands, and it can exceed 2 liters/hour. Sweat is a dilute salt solution containing mainly sodium chloride, with some potassium chloride, urea, organic acid, and other trace electrolytes. Excessive sweating can lead to both serious salt and water loss. Effectiveness in cooling will depend on environmental conditions. For instance, a dry breeze will facilitate evaporation and heat transfer to the environment. If aire temperature > skin temperature and air is saturated, then sweat cannot evaporate, so sweat simply drips off without removing heat

Question 9

Conduction

Answer 9

Heat conductive = AcKc(Tskin-Tambient)
Where Ac = surface area available for conductive exchange
Kc = Conductive characteristics of the medium (still air is 6 Kcal/hr/m2/1degreeC, water is 150)
Tskin = skin surface temperature
Tambient = Temperature of conducting medium

Question 10

Convection

Answer 10

Bulk movement of conductive fluid as a function of temperature differences within the fluid (fans)

Question 11

Radiation

Answer 11

Same equation as conduction, but with radiant exchange instead of conductive exchange

Question 12

Heat exchange is dominated by ___.

Answer 12

Conduction between capillary blood and the normally cooler skin surface

Question 13

Compensatory changes in hypothermia include:

Answer 13

vasoconstriction to reduce blood flow near skin

Question 14

Core thermoreceptor locations

Answer 14

Pre-optic area of hypothalamus and in the spinal cord (which respond to direct heating or cooling of these areas)

Question 15

Vasomotor regulation

Answer 15

Changes in skin blood flow regulate temperature in normal resting state or mild levels of thermal stress or exercise

Question 16

Metabolic regulation

Answer 16

Occurs when maximal vasoconstriction is ineffective in preventing some heat loss. Responses include voluntary exercise and shivering. Shivering occurs when Tc drops below a certain threshold. It is of limited effectiveness in elevating temperature because it increases conductive and convective loss by increasing blood flow from core to muscles and by increasing movement of the body (but produces 3-fold increase in heat production)

Question 17

Sudomotor and vasomotor regulation combined

Answer 17

progressive increases in sweating and active vasodilation in response to heat accumulation

Question 18

Fever

Answer 18

Hypothalamic temperature set-point is increased to a new higher temperature, and body temperature is elevated above normal.

Question 19

Pyrogens

Answer 19

chemicals that cause a febrile response

Question 20

exogenous pyrogens

Answer 20

heat-stable, high molecular weight polysaccharides produced from gram-negative bacteria

Question 21

Endogenous pyrogens

Answer 21

Heat-labile proteins released by monocytes, macrophages and Kupffer cells in response to bacterial pyrogens.
PGE2 (prostaglandin E2) is activated by IL-1beta
Tumor necrosis factor

Question 22

Causes of hyperthermia

Answer 22

Delirium tremens, drug abuse, exertional tetanus, heatstroke (exertional), lethal catatonia, malignant hyperthermia of anesthesia, neuroleptic malignant syndrome, pheochromocytoma, salicylate intoxication, status epilepticus, thyrotoxicosis, anticholinergic drugs, autonomic dysfunction, dehydration, heatstroke (classic), neuroleptic malignant syndrome, occlusive dressings, cerebrovascular accidents, encephalitis, idiopathic hypothalamic dysfunction, neuroleptic malignant syndrome, sarcoidosis and granulomatous infections, trauma, and tumors

Question 23

Blood flow to the skin can increase to ____, or 60% of total cardiac output.

Answer 23

8 liters

Question 24

Classical Heatstroke

Answer 24

Due to excessive heat and humidity, causing increased body temperature with poor heat dissipation due to ineffectiveness of evaporative cooling. Dehydration accelerates hyperthermia. (May need electrolytes if replacing water, lowered blood pressure)

Question 25

Exertional heatstroke

Answer 25

voluntary muscle activity coupled with environmental heat stress. Drop in blood pressure rapid.

Question 26

How to manage heatstroke

Answer 26

physical cooling (sponging with cool water or fanning)

Question 27

Hypothermia

Answer 27

Core cooling to below approximately 92 degrees F

Reduces oxygen requirements and blood pressure/bleeding

Question 28

Below 90 degrees F, there is a failure of ___ and there is general ____.

Answer 28

hypothalamic-based compensatory mechanisms,

CNS depression

Question 29

With ventilatory and cardiac assists, core temperature can be maintained at ____ for many hours.

Answer 29

70-75 degrees F.