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There are many other interesting and medically significant pressures in the body. For example, pressure caused by various muscle actions drives food and waste through the digestive system. Stomach pressure behaves much like bladder pressure and is tied to the sensation of hunger. Pressure in the relaxed esophagus is normally negative because pressure in the chest cavity is normally negative. Positive pressure in the stomach may thus force acid into the esophagus, causing “heartburn.” Pressure in the middle ear can result in significant force on the eardrum if it differs greatly from atmospheric pressure, such as while scuba diving. The decrease in external pressure is also noticeable during plane flights (due to a decrease in the weight of air above relative to that at the Earth’s surface). The Eustachian tubes connect the middle ear to the throat and allow us to equalize pressure in the middle ear to avoid an imbalance of force on the eardrum.

Many pressures in the human body are associated with the flow of fluids. Fluid flow will be discussed in detail in the Fluid Dynamics and Its Biological and Medical Applications .

Section summary

  • Measuring blood pressure is among the most common of all medical examinations.
  • The pressures in various parts of the body can be measured and often provide valuable medical indicators.
  • The shape of the eye is maintained by fluid pressure, called intraocular pressure.
  • When the circulation of fluid in the eye is blocked, it can lead to a buildup in pressure, a condition called glaucoma.
  • Some of the other pressures in the body are spinal and skull pressures, bladder pressure, pressures in the skeletal system.

Problems&Exercises

During forced exhalation, such as when blowing up a balloon, the diaphragm and chest muscles create a pressure of 60.0 mm Hg between the lungs and chest wall. What force in newtons does this pressure create on the 600 cm 2 size 12{"600"`"cm" rSup { size 8{2} } } {} surface area of the diaphragm?

479 N

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You can chew through very tough objects with your incisors because they exert a large force on the small area of a pointed tooth. What pressure in pascals can you create by exerting a force of 500 N size 12{"500"``N} {} with your tooth on an area of 1.00 mm 2 size 12{1 "." "00"`"mm" rSup { size 8{2} } } {} ?

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One way to force air into an unconscious person’s lungs is to squeeze on a balloon appropriately connected to the subject. What force must you exert on the balloon with your hands to create a gauge pressure of 4.00 cm water, assuming you squeeze on an effective area of 50 . 0 cm 2 size 12{"50" "." 0`"cm" rSup { size 8{2} } } {} ?

1.96 N

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Heroes in movies hide beneath water and breathe through a hollow reed (villains never catch on to this trick). In practice, you cannot inhale in this manner if your lungs are more than 60.0 cm below the surface. What is the maximum negative gauge pressure you can create in your lungs on dry land, assuming you can achieve 3.00 cm size 12{ - 3 "." "00"`"cm"} {} water pressure with your lungs 60.0 cm below the surface?

63.0 cm H 2 O size 12{ - "63" "." 0`"cm"`H rSub { size 8{2} } O} {}

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Gauge pressure in the fluid surrounding an infant’s brain may rise as high as 85.0 mm Hg (5 to 12 mm Hg is normal), creating an outward force large enough to make the skull grow abnormally large. (a) Calculate this outward force in newtons on each side of an infant’s skull if the effective area of each side is 70 . 0 cm 2 size 12{"70" "." 0`"cm" rSup { size 8{2} } } {} . (b) What is the net force acting on the skull?

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Source:  OpenStax, College physics. OpenStax CNX. Jul 27, 2015 Download for free at http://legacy.cnx.org/content/col11406/1.9
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