What does ‘Homeothermic’ mean?
Homeothermic: capable of maintaining body temperature
within very narrow limits
Describe what it means to be homeothermic wrt humans
-Relative constant high core body temperature (~37oC)
-Frees Biochemical reaction
-Precise regulatory mechanism
-Highly elevated temperature leads to nerve malfunction, protein denaturation etc.
-Upper limit ~43oC
What is used as an estimate of core temperature?
(core = internal organs)
the temperature of the body that reflects most accurately that of the cores is where?
the esophagus (at the cardia)
Normal Body Temperature (Core) can vary due to: (2) name and describe
-EXOGENOUS FACTORS: Internal temperature can vary few degrees depending on activity patterns and external temperature
-ENDOGENOUS FACTORS: (e.g., progesterone) can increase body temperature
WRT exogenous agents, what are some of the variations that can take place?
What are some normal core endogenous temperatures?
age and body size
2. How is heat lost or gained?
Total energy expenditure equals what?
Internal heat produced +External work performed +Energy stored
What are channels of heat transfer?
Heat transmitted via emitted electromagnetic waves (infrared heat rays). All objects emits radiation.
Heat transfer by conduction occurs within a solid or between two or more solids in close contact.
wrt clothing (dry or wet) which increases heat loss
wet clothing increases conduction of heat -increase heat loss
Heat transfer by convection occurs in a fluid or between a fluid (gas) and a solid, providing a temperature gradient exist
describe the difference between conduction and convection
Differs from conduction in that the fluid or gas can be moving and therefore heat is not only transferred but displaced.
Describe how Convection currents work. What influences them?
carries away saturated air layer near skin
(influenced by the thickness of the thermal boundary).
Heat transfer occurs by means of a change in state, from a liquid to a gas.
Describe how evaporation takes place wrt energy
The transformation of water into water vapor requires energy
The amount of energy vaporise 1g of water is 0.685 kcal or 2.86 kJ.
(Latent heat of vaporization).
constant evaporation insensible heat loss (50ml/hr)
During severe exercise 1600 ml/hr heat loss by vaporization varies from 30 - 900 kcal/hr
What are the Factors affecting evaporation?
Humidity: dry air increases evaporation;
Humid air decreases evaporation
Describe “Zone of Thermal Neutrality”
The range of ambient temperature in which the body maintains its heat balance without increasing either heat production or heat loss above their minimum level
Describe how surface area and volume affect heat loss
Higher the ratio (SA/V),
Higher the heat loss
The lower temperature of the extremities (e.g., Finger, ear etc) in a windless environment reflects what? what happens wrt heat?
large SA/V ratio (of the limb) relative to the trunk
very high heat loss
3. Regulation and control of core body temperature
skin temperature regulation begins with peripheral thermoreceptors
Core temperature regulations begins with central thermoreceptors
Describe the shivering and non-shivering roles wrt heat
Hypothalamus involves an involuntary motor responses to cause shivering skeletal muscles
hypothalamus involves sympathetic nerves to cause non-shivering via the adrenal medulla, sweat gland and skin arterioles
What is the hypothalamus?
serves as the primary overall integrator of reflexes
It is the brain's inner thermostat
Thermoreceptors come in two forms- name and describe
Warm fibers: located in Ruffini's corpuscles => responds to high temperatures
Cold Fibers: located in End-bulb of Krause. => activated in lower temperatures
A secondary consequence of activation of SNS is what?
the stimulation of a1 receptors in the vascular smooth muscle (Vasoconstriction) leading to reduced heat loss.
If a neonate is lacking brown fat such as in prematurity, what could be a result?
Describe how thyroid hormones effect heat
In Hyperthyrodism (Graves & Thyroid Tumor): Metabolic rate increased Heat Production increase
In Hypothyroidism (Thyroiditis, surgical removal of the thyroid, iodine deficiency) decreases metabolic rate and decreased heat production
Describe the difference in voluntary and involuntary response
involuntary=> hypothalamus stimulation, thyroid hormones, sweat glands, heat transfer by circulation
voluntary=> skeletal contractions
What are behavioral changes wrt voluntary heat production?
Change is surface area
Change in clothing
Change in surroundings
describe temperature acclimatization
A person in a hot new environment has poor ability to perform work initially as core temperature increases and weakness may occur.
After several days there is a great improvement in work tolerance and much less increased core temperature
4. Hypothermia and Hyperthermia
hyperthermia: elevated body temperature due to failed thermoregulation that occurs when a body produces or absorbs more heat than it dissipates.
Hypothermia: a condition in which core temperature drops below the required temperature for normal metabolism and body functions which is defined as 35.0 °C (95.0 °F)
Define and describe Heat Exhaustion:
Bodies Response to increased temperature includes vasodilatation and sweating.
Excessive sweating, decreases ECF volume, decreased blood volume, decreased arterial pressure leading to Fainting.
Define and describe Heat Stroke:
Body temperature increases to a point of tissue damage. Usually the normal response to elevated Temperature is impaired (i.e., sweating) core temperature increases to dangerous limits.
Define and describe Malignant Hyperthermia:
During activities where it is hot and humid, How should a person combat this to avoid heat stroke?
increase intake of NaCl and fluid
What is Fever?
regulated rise in body temperature that is independent of ambient temperature
associated with increased thermopreferendum
What are the physiological differences between fever and hyperthermia?
- regulated rise in body temperature
- independent of ambient temperature
- associated with increased thermopreferendum
- impairment of thermoregulatory mechanisms
- dependent on ambient temperature
- decreased thermopreferendum
What are Some common pathogenic stimuli that induce fever?
Kupffer cell activation
Complement cascade activation
Vagus nerve stimulation
microbial and non-microbial agents can cause fever
What happens during an acute phase reaction?
Increases in temperature, slow wave sleep, acute phase proteins, neutrophils, pancreatic insulin, glucagon, SNS
Decreases in feeding
Pituitary hormones and behavior is altered
What are some benefits of fever?
enhace neutrol migration, phagocytosis
increase IFN production, antiviral/antitumor activities of IFN
Increase radical production, T cell proliferation, increase survival rate
reduced growth rate and viability of iron-dependent microbes
What is a routine anti-febrile therapy?