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Questions and Answers
What is the typical maximum volume in the bladder before voiding?
What is the method of measuring bladder pressure by inserting a needle through the wall of the abdomen into the bladder?
What is the relationship between the increase in radius of the bladder and the increase in volume?
What is the highest pressure in the body found in?
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Why does the pressure in the knee joint increase when walking?
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How do bones adapt to reduce pressure?
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What is the relationship between the increase in radius of the bladder and the increase in pressure?
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What is the pressure in the esophagus usually compared to?
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What is the normal voiding pressure in the bladder?
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What is the method of measuring bladder pressure by passing a catheter with a pressure sensor into the bladder?
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Study Notes
Pressure
- Pressure (P) is a force per unit area:
P = F/A - Units of pressure: pascal (Pa), pounds per square inch (psi), bar (bar), atmospheric pressure (atm), millimeters of mercury (mmHg), inches of mercury (inHg), torr
Blood Pressure
- Measured using a sphygmomanometer
- Systolic pressure: maximum pressure driving blood at the peak of the pulse
- Diastolic pressure: lowest blood pressure between pulses
- Normal blood pressure: 120 mmHg systolic, 80 mmHg diastolic
Pressure in the Body
- Pressure in the circulatory system: affected by pumping action of the heart and losses associated with arterial expansion and contraction, and viscous friction
- Hydrocephalus: increased pressure in the skull due to trapped cerebrospinal fluid
- Glaucoma: increased pressure in the eye due to partial blockage of the drain system
- Pressure in the digestive system:
- Increases during eating due to air swallowed and bacterial action
- Coupled to intrathoracic pressure through the diaphragm
- External factors such as belts, girdles, flying, and swimming affect gut pressure
- Pressure in the urinary bladder:
- Increases with volume due to accumulation of urine
- Measured using indirect cystometry (passing a catheter with a pressure sensor) or direct cystometry (inserting a needle through the abdomen)
- Pressure in the skeleton:
- Highest pressures found in weight-bearing bone joints (up to 10 atm)
- Bone adaptation reduces pressure by increasing surface area (e.g., flat finger bones)
Practice Problems
- Example 1: Calculate the pressure exerted by a person on the ground
- Example 2: Calculate the force exerted by the atmosphere over an area
- Example 3: Calculate the pressure exerted by the air on the bottom surface of a rectangular box
- Example 4: Calculate the mass of a vertical column of air that exerts a pressure of 1 atm over a square surface
- Example 5: Calculate the gauge pressure and absolute pressure at the oil-water interface and at the bottom of a container
- Example 6: Calculate the difference in blood pressure between the head and feet of a person
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Description
Quiz on pressure calculations, including gauge pressure and absolute pressure, in different fluid systems.
