Chapter 61 - Environmental Physiology Flashcards
Mountain climbers and deep sea divers know the profound effects of _____________ on human physiology and astronauts quickly learn how the physically equivalent forces of ________ and ________ affect the body.
Barometric pressure (PB)
Gravity and acceleration
________________ can modulate the many layers of our external environment
Voluntary feedback-control mechanisms
The extracellular fluid in which cells of the organism live.
milieu intérieur
The constancy of this extracellular fluid.
Fixité du milieu intérieur
Physically surrounds the whole organism affects our body functions and how we, in turn, modify our surroundings when it is necessary to improve our comfort or to extend the range of habitable environments.
milieu extérieur
The sensory input can also rise to a conscious level and if perceived as discomfort can motivate us to take ____________ that make the surroundings more comfortable.
voluntary actions
Such conscious actions are part of the __________ in a complex negative feedback system that includes sensors, afferent pathways, integration and conscious decision making in the brain, efferent pathways to our muscles and perhaps inanimate objects such as air conditioners.
effector limb
Physicians are acutely aware that factors such as medication, disease or the extremes of age can interfere with ______________.
involuntary feedback systems
____________ provides conscious clues for triggering voluntary feedback mechanisms.
Environmental temperature
The usual range of body core temperature is ___________.
36ºC to 38ºC
At an environmental temperature of 26ºC to 27ºC and a relative humidity of 50%, a naked person is in a ____________ feeling comfortable and being within the zone of vasomotor regulation of body temperature.
neutral thermal environment
The environmental temperature range of __________ is very hot and uncomfortable, and the body may fail to regulate core temperature.
39ºC to 43ºC
At ______, the heat is unbearable, and heat stroke is imminent—the body heats rapidly, and the loss of extracellular fluid to sweat may lead to circulatory collapse and death.
46ºC
At the other extreme, we regard environmental temperatures of 24ºC to 25ºC as _______ and 21ºC to 22ºC as ______________.
Cool
Slightly uncomfortable
At temperatures of __________, we feel cold, vasoconstriction occurs in the hands and feet, and muscles may be painful.
19ºC to 20ºC
________________ must be sufficient to supply enough O2 and to remove enough CO2 to keep the partial pressures of these gases within acceptable limits.
Ventilation of a room (VRoom)
In addition, it may be necessary to _________ VRoom even more, to lower relative humidity and to reduce odors.
increase
The acceptable lower limit for PO2 for work environments is ___________ in DRY AIR which is 19.5% of dry air at sea level.
148 mm Hg
The environmental atmosphere of a submarine may be kept at this _________ PO2 to minimize the chance of fires, yet retain the mental capacity of the occupants.
slightly low
An acceptable upper limit for PCO2 in working environments is _________, or 0.5% of dry air at sea level.
- 8 mm Hg
* This level of CO2 would increase total ventilation by ∼7%, a hardly noticeable rise.
Exposures to 3% CO2 in the ambient air which initially would cause more substantial _____________ could be tolerated for at least 15 MINUTES, by the end of which it would nearly double total ventilation.
respiratory acidosis
With longer exposures to 3% CO2, the metabolic compensation to respiratory acidosis would have already begun to increase plasma _________ noticeably.
[HCO−3]
Requires knowing the rate of CO2 production (VCO2) by the occupants of the room and the fraction of the room air that is CO2.
Steady-state method
*The equation is analogous to the one introduced for determining alveolar ventilation.
One monitors the washout of a gas from the room. The approach is to add a test gas (e.g., CO2) to the room and then measure the concentrations of the gas at time zero (Cinitial) and as VRoom washes out the gas over some time interval (Δt)—at some later time (Cfinal).
Exponential decay method
More insidious than hypoxia, and less noticeable, is the symptomless encroachment of ______________ gas on the oxyhemoglobin dissociation curve.
carbon monoxide (CO)
_________ which can come from incomplete combustion of fuel in furnaces, charcoal burners, or during house re-suffocates people without their being aware of its presence.
Cabon monoxide
However, the halftime for washing CO into or out of the body is ∼_________.
4 hours
Thus, if the ambient CO level were high enough to achieve a 50% saturation of Hb at equilibrium, then after a _______ exposure (i.e., one half of the half-time), the CO saturation would be 1/2 × 1/2 × 50% or 12.5%.
2-hour
*The symptoms at this point would be mild and nonspecific and would include headache, nausea, vomiting, drowsiness, and interference with night vision. Victims with limited coronary blood flow could experience angina.
After a _______ exposure (i.e., one half-time), the CO saturation would be 1/2 × 50%, or 25%.
4-hour
*The symptoms would be more severe and would include impaired mental function and perhaps unconsciousness.
________________ are reasonable environmental levels of toxic substances or physical agents (e.g., heat or noise) to which industrial workers can be exposed without causing predictable harm.
Threshold limit values (TLVs)
Rather than depending on concentrations measured in air or food, we can use _________________ to limit exposure to toxic substances by measuring the effects of these substances on animals and humans.
biological exposure indices (BEIs)
The changes detected in the body are called ______________ and correlate with the intensity and duration of exposure to toxic substances.
biomarkers of exposure
__________ must resist the G force produced by gravity and other mechanisms of acceleration
Tissues
Standing motionless on the earth’s surface at sea level, we experience a _______________ —our weight that is the product of our mass and the acceleration resulting from gravity (g = 9.8 ms−2).
gravitational force
The _________ is a dimensionless number that describes force (m · a) that we experience under a particular condition, relative to the gravitational force (m · g).
G force
An ____________, placed on a belt would show that we can jump upward with an acceleration of ∼3G.
accelerometer
*It would also show that, on landing, we would strike the ground with a force of 3G—a force that our bones and other tissues must be able to tolerate.
In one study, a 6- to 7-week period of immobilization from bed rest led to losses of ______ of calcium from bones, ______ of muscle cytoplasm, _____ in the strength of the gastrocnemius muscle, and ____ in average blood volume.
14 g
1.7 kg
21%
6%
Although the changes were reversible after these subjects resumed ambulation, it took _______ for muscle strength to return to normal during remobilization.
4 weeks
The partial pressures of gases other than water inside the body depend on ___________.
barometric pressure
