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Learning objectives

By the end of this section, you will be able to:

  • Explain the concept of pressure in the human body.
  • Explain systolic and diastolic blood pressures.
  • Describe pressures in the eye, lungs, spinal column, bladder, and skeletal system.

Pressure in the body

Next to taking a person's temperature and weight, measuring blood pressure is the most common of all medical examinations. Control of high blood pressure is largely responsible for the significant decreases in heart attack and stroke fatalities achieved in the last three decades. The pressures in various parts of the body can be measured and often provide valuable medical indicators. In this section, we consider a few examples together with some of the physics that accompanies them.

[link] lists some of the measured pressures in mm Hg, the units most commonly quoted.

Typical pressures in humans
Body system Gauge pressure in mm Hg
Blood pressures in large arteries (resting)
Maximum (systolic) 100–140
Minimum (diastolic) 60–90
Blood pressure in large veins 4–15
Eye 12–24
Brain and spinal fluid (lying down) 5–12
While filling 0–25
When full 100–150
Chest cavity between lungs and ribs −8 to −4
Inside lungs −2 to +3
Digestive tract
Esophagus −2
Stomach 0–20
Intestines 10–20
Middle ear <1

Blood pressure

Common arterial blood pressure measurements typically produce values of 120 mm Hg and 80 mm Hg, respectively, for systolic and diastolic pressures. Both pressures have health implications. When systolic pressure is chronically high, the risk of stroke and heart attack is increased. If, however, it is too low, fainting is a problem. Systolic pressure increases dramatically during exercise to increase blood flow and returns to normal afterward. This change produces no ill effects and, in fact, may be beneficial to the tone of the circulatory system. Diastolic pressure can be an indicator of fluid balance. When low, it may indicate that a person is hemorrhaging internally and needs a transfusion. Conversely, high diastolic pressure indicates a ballooning of the blood vessels, which may be due to the transfusion of too much fluid into the circulatory system. High diastolic pressure is also an indication that blood vessels are not dilating properly to pass blood through. This can seriously strain the heart in its attempt to pump blood.

Blood leaves the heart at about 120 mm Hg but its pressure continues to decrease (to almost 0) as it goes from the aorta to smaller arteries to small veins (see [link] ). The pressure differences in the circulation system are caused by blood flow through the system as well as the position of the person. For a person standing up, the pressure in the feet will be larger than at the heart due to the weight of the blood ( P = hρg ) size 12{ \( P=hρg \) } {} . If we assume that the distance between the heart and the feet of a person in an upright position is 1.4 m, then the increase in pressure in the feet relative to that in the heart (for a static column of blood) is given by

Δ P = Δ hρg = 1.4 m 1050 kg /m 3 9.80 m /s 2 = 1 . 4 × 10 4 Pa = 108 mm Hg . size 12{ΔP=ρ ital "gh"= left ("1050"`"kgm" rSup { size 8{ - 3} } right ) left (9 "." "80"`"m/s" rSup { size 8{2} } right ) left (1 "." 4`m right )=1 "." 4 times "10" rSup { size 8{4} } `"Pa"="108"`"mm"`"Hg"} {}

Increase in pressure in the feet of a person

Δ P = Δ hρg = 1.4 m 1050 kg /m 3 9.80 m /s 2 = 1 . 4 × 10 4 Pa = 108 mm Hg . size 12{ΔP=ρ ital "gh"= left ("1050"`"kgm" rSup { size 8{ - 3} } right ) left (9 "." "80"`"m/s" rSup { size 8{2} } right ) left (1 "." 4`m right )=1 "." 4 times "10" rSup { size 8{4} } `"Pa"="108"`"mm"`"Hg"} {}

Questions & Answers

how can I read physics...am finding it difficult to understand...pls help
rerry Reply
try to read several books on phy don't just rely one. some authors explain better than other.
And don't forget to check out YouTube videos on the subject. Videos offer a different visual way to learn easier.
hope that helps
I have a exam on 12 february
David Reply
what is velocity
the speed of something in a given direction.
what is a magnitude in physics
Jiti Reply
Propose a force standard different from the example of a stretched spring discussed in the text. Your standard must be capable of producing the same force repeatedly.
Giovani Reply
What is meant by dielectric charge?
It's Reply
what happens to the size of charge if the dielectric is changed?
Brhanu Reply
omega= omega not +alpha t derivation
Provakar Reply
u have to derivate it respected to time ...and as w is the angular velocity uu will relace it with "thita × time""
do to be peaceful with any body
Brhanu Reply
the angle subtended at the center of sphere of radius r in steradian is equal to 4 pi how?
Saeed Reply
if for diatonic gas Cv =5R/2 then gamma is equal to 7/5 how?
define variable velocity
Ali Reply
displacement in easy way.
Mubashir Reply
binding energy per nucleon
Poonam Reply
why God created humanity
Manuel Reply
Because HE needs someone to dominate the earth (Gen. 1:26)
why god made humenity
and he to multiply
stuff happens
God plays dice
Is the object in a conductor or an insulator? Justify your answer. whats the answer to this question? pls need help figure is given above
Jun Reply
ok we can say body is electrically neutral ...conductor this quality is given to most metalls who have free electron in orbital d ...but human doesn't have ...so we re made from insulator or dielectric material ... furthermore, the menirals in our body like k, Fe , cu , zn
when we face electric shock these elements work as a conductor that's why we got this shock
how do i calculate the pressure on the base of a deposit if the deposit is moving with a linear aceleration
ximena Reply
Practice Key Terms 5

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