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Narrow range of atmospheric pressure

Pressure is a force exerted by a substance that is in contact with another substance. Atmospheric pressure is pressure exerted by the mixture of gases (primarily nitrogen and oxygen) in the Earth’s atmosphere. Although you may not perceive it, atmospheric pressure is constantly pressing down on your body. This pressure keeps gases within your body, such as the gaseous nitrogen in body fluids, dissolved. If you were suddenly ejected from a space ship above Earth’s atmosphere, you would go from a situation of normal pressure to one of very low pressure. The pressure of the nitrogen gas in your blood would be much higher than the pressure of nitrogen in the space surrounding your body. As a result, the nitrogen gas in your blood would expand, forming bubbles that could block blood vessels and even cause cells to break apart.

Atmospheric pressure does more than just keep blood gases dissolved. Your ability to breathe—that is, to take in oxygen and release carbon dioxide—also depends upon a precise atmospheric pressure. Altitude sickness occurs in part because the atmosphere at high altitudes exerts less pressure, reducing the exchange of these gases, and causing shortness of breath, confusion, headache, lethargy, and nausea. Mountain climbers carry oxygen to reduce the effects of both low oxygen levels and low barometric pressure at higher altitudes ( [link] ).

Harsh conditions

This photo shows Mount Everest as seen from a distance. It is a large, pyramid-shaped, craggy peak with many smaller snow-covered peaks in the foreground. The peak of Mount Everest is partially occluded by clouds.
Climbers on Mount Everest must accommodate extreme cold, low oxygen levels, and low barometric pressure in an environment hostile to human life. (credit: Melanie Ko/flickr)

Homeostatic imbalances

Decompression sickness

Decompression sickness (DCS) is a condition in which gases dissolved in the blood or in other body tissues are no longer dissolved following a reduction in pressure on the body. This condition affects underwater divers who surface from a deep dive too quickly, and it can affect pilots flying at high altitudes in planes with unpressurized cabins. Divers often call this condition “the bends,” a reference to joint pain that is a symptom of DCS.

In all cases, DCS is brought about by a reduction in barometric pressure. At high altitude, barometric pressure is much less than on Earth’s surface because pressure is produced by the weight of the column of air above the body pressing down on the body. The very great pressures on divers in deep water are likewise from the weight of a column of water pressing down on the body. For divers, DCS occurs at normal barometric pressure (at sea level), but it is brought on by the relatively rapid decrease of pressure as divers rise from the high pressure conditions of deep water to the now low, by comparison, pressure at sea level. Not surprisingly, diving in deep mountain lakes, where barometric pressure at the surface of the lake is less than that at sea level is more likely to result in DCS than diving in water at sea level.

In DCS, gases dissolved in the blood (primarily nitrogen) come rapidly out of solution, forming bubbles in the blood and in other body tissues. This occurs because when pressure of a gas over a liquid is decreased, the amount of gas that can remain dissolved in the liquid also is decreased. It is air pressure that keeps your normal blood gases dissolved in the blood. When pressure is reduced, less gas remains dissolved. You have seen this in effect when you open a carbonated drink. Removing the seal of the bottle reduces the pressure of the gas over the liquid. This in turn causes bubbles as dissolved gases (in this case, carbon dioxide) come out of solution in the liquid.

The most common symptoms of DCS are pain in the joints, with headache and disturbances of vision occurring in 10 percent to 15 percent of cases. Left untreated, very severe DCS can result in death. Immediate treatment is with pure oxygen. The affected person is then moved into a hyperbaric chamber. A hyperbaric chamber is a reinforced, closed chamber that is pressurized to greater than atmospheric pressure. It treats DCS by repressurizing the body so that pressure can then be removed much more gradually. Because the hyperbaric chamber introduces oxygen to the body at high pressure, it increases the concentration of oxygen in the blood. This has the effect of replacing some of the nitrogen in the blood with oxygen, which is easier to tolerate out of solution.

The dynamic pressure of body fluids is also important to human survival. For example, blood pressure, which is the pressure exerted by blood as it flows within blood vessels, must be great enough to enable blood to reach all body tissues, and yet low enough to ensure that the delicate blood vessels can withstand the friction and force of the pulsating flow of pressurized blood.

Chapter review

Humans cannot survive for more than a few minutes without oxygen, for more than several days without water, and for more than several weeks without carbohydrates, lipids, proteins, vitamins, and minerals. Although the body can respond to high temperatures by sweating and to low temperatures by shivering and increased fuel consumption, long-term exposure to extreme heat and cold is not compatible with survival. The body requires a precise atmospheric pressure to maintain its gases in solution and to facilitate respiration—the intake of oxygen and the release of carbon dioxide. Humans also require blood pressure high enough to ensure that blood reaches all body tissues but low enough to avoid damage to blood vessels.

Questions & Answers

if a person is visiting Denver CO why may they need to increase the rate of ventilation until they adapt?
Amy Reply
pressure changes between the atmosphere and thoracic cavity will change creating more ventilation. Also there is less pressure of Oxygen and hemoglobin already has less affinity for it than CO2 so there is less to bind than your body might be used to, increasing CO2 build up.
Kevin
To compensate for the CO2 build up we breathe faster to make our blood less acidic. Eventually EPO will kick in build more RBC to compensate for the lower O2 concentration.
Kevin
what is the fuction of tostiriol glands
abdifitah Reply
It's tonsilar?
Dr.
or tostiriol
Dr.
what are some examples of muscles predominantly composed of Fast glycolytic fibers?
Rey Reply
what is cardinal signs, and pathophysiology of those cardinal signs. can anyone explain..
Richard Reply
cardinal signs of inflammation!
Madhuri
then they are rubor,tumor,calor,dolar,functio laesa
Madhuri
rubor is redness due to vasodilatation
Madhuri
tumor is swelling due exudation of plasma
Madhuri
calor is rise in temperature
Madhuri
dolar is pain due to stimulation of nerve ending
Madhuri
functio laesa is loss of function
Madhuri
correct The Question
Abdi Reply
why are tha bp
Dharm Reply
Your question is wrong
Nisha
Kya puchna chahate ho
Yamini
wrong question
Asif
blood pressure
SAJJAD
means
Dr.
means diastolic 85 up
Mohamed
whats is the cell cycle
Dharm Reply
The cell cycle is the series of events that take place in a cell leading to its division and duplication of its DNA to produce two daughter cells
Nisha
where are the rest of the chapters
Donna Reply
formation of bone in calcium
Dharm
which is the largest or smallest muscle of human body?
pankaj Reply
largest muscle is sartoreus
Asif
smallest is pyramedalis muscle
Asif
largest is Gluteus maximus
Rianicole
smallest muscle stapedius
Rianicole
smallest muscle of our body
pankaj
Stapedius muscle
PL
stapedius muscle
Dr.
describe the formation of bone
RITA Reply
in female the outer urethral opening is immediately............... to the vaginal opening
perpetual Reply
above
Madhuri
opens above
Dr.
above opening
shakra
Explain in detail anatomy of kidney with diagram
Chinna Reply
which of the main digestive organ has not got any digestive function
Awelama Reply
appendix
Rodney
appendix is a lymph node which kills bacteria
Nejat
it is also believed Appendix stores good bacteria that help us with digestion, but its function is unknown
Nejat
so the answer is appendix
Nejat
appendix
Onavwie
right answer is appendix
Asif
appendix
Himani
what is the functional units of kidney?
Subathra Reply
nephrons
Phuong
Yep Nephron,
Nejat
filter the blood
Yamini
oops sorry
Yamini
filter and refresh the blood
Sunny
nephrons
Hashini
nephrons
Himani
nephrones
Dr.
Nephrons is correct answer
Subathra
right answer is nephrons
Asif
nephrons
Himani
nephros means kidney it is tha function urin fitration and excriction
Dharm
nephrons
Hilal
Nephron
Frank
nephron
Onavwie
nephrons which collectively forms kidney
Madhuri
how many bones has the sacrum?
Kabwe Reply
5 bone in sacrum
Asif
S1 to S5
Dharm
good
Asif
very good
Kabwe

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Source:  OpenStax, Anatomy & Physiology. OpenStax CNX. Feb 04, 2016 Download for free at http://legacy.cnx.org/content/col11496/1.8
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