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Questions and Answers
What is the unit of pressure used in medicine to measure blood pressure?
How is stress defined?
How is pressure defined in a gas or liquid?
What is absolute pressure equal to?
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What is gauge pressure?
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In which situation do we experience negative pressure?
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What is the purpose of valves in the digestive tract?
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Why is intrathoracic pressure sometimes measured by the pressure in the esophagus?
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What happens to the pressure in the stomach during eating?
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What factor causes a significant increase in pressure in the stomach during eating?
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What is a common outcome of air trapped in the stomach during eating?
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In which part of the body is the pressure usually greater than atmospheric in the gastrointestinal system?
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Study Notes
Pressure and Stress
- Pressure is defined as the force per unit area in a gas or a liquid.
- Units of pressure: atm, N/m², dyne/cm², cm H₂O, mmHg, Ib/in².
Stress
- Stress is defined as the force per unit area in a solid.
Pressure in Medicine
- Pressure in medicine is measured as the height of a column of mercury (Hg).
- A peak blood pressure of 120 mmHg is equal to a column of mercury of this height.
Pressure Formula
- P = ρgh
- Where P is pressure, ρ is density of the liquid, g is acceleration due to gravity, and h is the height of the column.
Types of Pressure
- Gauge pressure: the measured pressure for a gas inside a closed system (e.g., pressure in a bicycle tire).
- Atmospheric pressure: the pressure due to the weight of the air above us.
- Absolute pressure: gauge pressure + atmospheric pressure.
- Negative pressure: the pressure in certain places in the body where the pressure is lower than atmospheric pressure (e.g., when we breathe in).
Pressure in the Body
- The body has an opening through the digestive tract, with valves designed to permit unidirectional flow of food.
- The pressure in the esophagus is coupled to the intrathoracic pressure and is usually less than atmospheric.
- In the stomach, pressure increases during eating due to the walls being stretched, but the increase is very slow.
- A more significant increase in pressure is due to air swallowed during eating, which can cause burping or belching.
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Description
Learn about pressure and stress in physics, including their definitions, units of measurement, and applications in medicine. Understand the relationship between pressure and the height of a column of mercury in medical contexts.
