Chapter 61 - Environmental Physiology

Question 1

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.

Answer 1

Barometric pressure (PB)

Gravity and acceleration

Question 2

________________ can modulate the many layers of our external environment

Answer 2

Voluntary feedback-control mechanisms

Question 3

The extracellular fluid in which cells of the organism live.

Answer 3

milieu intérieur

Question 4

The constancy of this extracellular fluid.

Answer 4

Fixité du milieu intérieur

Question 5

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.

Answer 5

milieu extérieur

Question 6

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.

Answer 6

voluntary actions

Question 7

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.

Answer 7

effector limb

Question 8

Physicians are acutely aware that factors such as medication, disease or the extremes of age can interfere with ______________.

Answer 8

involuntary feedback systems

Question 9

____________ provides conscious clues for triggering voluntary feedback mechanisms.

Answer 9

Environmental temperature

Question 10

The usual range of body core temperature is ___________.

Answer 10

36ºC to 38ºC

Question 11

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.

Answer 11

neutral thermal environment

Question 12

The environmental temperature range of __________ is very hot and uncomfortable, and the body may fail to regulate core temperature.

Answer 12

39ºC to 43ºC

Question 13

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.

Answer 13

46ºC

Question 14

At the other extreme, we regard environmental temperatures of 24ºC to 25ºC as _______ and 21ºC to 22ºC as ______________.

Answer 14

Cool

Slightly uncomfortable

Question 15

At temperatures of __________, we feel cold, vasoconstriction occurs in the hands and feet, and muscles may be painful.

Answer 15

19ºC to 20ºC

Question 16

________________ must be sufficient to supply enough O2 and to remove enough CO2 to keep the partial pressures of these gases within acceptable limits.

Answer 16

Ventilation of a room (VRoom)

Question 17

In addition, it may be necessary to _________ VRoom even more, to lower relative humidity and to reduce odors.

Answer 17

increase

Question 18

The acceptable lower limit for PO2 for work environments is ___________ in DRY AIR which is 19.5% of dry air at sea level.

Answer 18

148 mm Hg

Question 19

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.

Answer 19

slightly low

Question 20

An acceptable upper limit for PCO2 in working environments is _________, or 0.5% of dry air at sea level.

Answer 20

3. 8 mm Hg

* This level of CO2 would increase total ventilation by ∼7%, a hardly noticeable rise.

Question 21

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.

Answer 21

respiratory acidosis

Question 22

With longer exposures to 3% CO2, the metabolic compensation to respiratory acidosis would have already begun to increase plasma _________ noticeably.

Answer 22

[HCO−3]

Question 23

Requires knowing the rate of CO2 production (VCO2) by the occupants of the room and the fraction of the room air that is CO2.

Answer 23

Steady-state method

*The equation is analogous to the one introduced for determining alveolar ventilation.

Question 24

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).

Answer 24

Exponential decay method

Question 25

More insidious than hypoxia, and less noticeable, is the symptomless encroachment of ______________ gas on the oxyhemoglobin dissociation curve.

Answer 25

carbon monoxide (CO)

Question 26

_________ 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.

Answer 26

Cabon monoxide

Question 27

However, the halftime for washing CO into or out of the body is ∼_________.

Answer 27

4 hours

Question 28

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%.

Answer 28

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.

Question 29

After a _______ exposure (i.e., one half-time), the CO saturation would be 1/2 × 50%, or 25%.

Answer 29

4-hour

*The symptoms would be more severe and would include impaired mental function and perhaps unconsciousness.

Question 30

________________ 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.

Answer 30

Threshold limit values (TLVs)

Question 31

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.

Answer 31

biological exposure indices (BEIs)

Question 32

The changes detected in the body are called ______________ and correlate with the intensity and duration of exposure to toxic substances.

Answer 32

biomarkers of exposure

Question 33

__________ must resist the G force produced by gravity and other mechanisms of acceleration

Answer 33

Tissues

Question 34

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).

Answer 34

gravitational force

Question 35

The _________ is a dimensionless number that describes force (m · a) that we experience under a particular condition, relative to the gravitational force (m · g).

Answer 35

G force

Question 36

An ____________, placed on a belt would show that we can jump upward with an acceleration of ∼3G.

Answer 36

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.

Question 37

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.

Answer 37

14 g
1.7 kg
21%
6%

Question 38

Although the changes were reversible after these subjects resumed ambulation, it took _______ for muscle strength to return to normal during remobilization.

Answer 38

4 weeks

Question 39

The partial pressures of gases other than water inside the body depend on ___________.

Answer 39

barometric pressure