Pressure Concepts in Physiology

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Questions and Answers

What is pressure defined as?

  • Density per unit volume
  • Force per unit area (correct)
  • Mass per unit area
  • Volume per unit time

In the equation P = ρgh, what does 'h' represent?

  • Height of the liquid column (correct)
  • Accelaration due to gravity
  • Pressure per unit area
  • Density of the column

What is the typical range for arterial blood pressure during systole?

  • 60 - 90 mmHg
  • 20 mmHg
  • 100 – 140 mmHg (correct)
  • 3 - 7 mmHg

What instrument is primarily used to measure blood pressure?

<p>Sphygmomanometer (D)</p> Signup and view all the answers

How would negative pressure in the lungs affect breathing?

<p>It allows drinking through a straw (C)</p> Signup and view all the answers

How is atmospheric pressure quantified?

<p>1 atm = 760 mmHg (A)</p> Signup and view all the answers

What is the function of the cerebral spinal fluid (CSF) in the brain?

<p>To protect the brain and maintain pressure (D)</p> Signup and view all the answers

Which of the following pressures is typically found in the middle ear?

<p>Less than 1 mmHg (C)</p> Signup and view all the answers

What happens to the volume of a gas if its absolute pressure is doubled?

<p>It is halved. (B)</p> Signup and view all the answers

What causes pressure equalization in the middle ear?

<p>Movement of air through the Eustachian tube. (A)</p> Signup and view all the answers

What can occur if the partial pressure of O2 at a depth of 30m exceeds safe levels?

<p>Oxygen poisoning. (C)</p> Signup and view all the answers

What does Henry's law state regarding the solubility of gases in liquids?

<p>Gas solubility is proportional to the partial pressure of the gas. (A)</p> Signup and view all the answers

Which condition can hyperbaric oxygen therapy help treat?

<p>Gas gangrene. (C)</p> Signup and view all the answers

What serious condition arises when cerebrospinal fluid (CSF) is trapped inside the skull due to a blocked aqueduct?

<p>Hydrocephalus (C)</p> Signup and view all the answers

What is the normal range of skull circumference values indicating healthy newborns?

<p>32 - 37 cm (A)</p> Signup and view all the answers

Which method is used for qualitatively detecting hydrocephalus based on light scattering properties of CSF?

<p>Trans illumination (A)</p> Signup and view all the answers

What is the target range for intraocular pressure (IOP) in normal eyes?

<p>12 - 23 mmHg (A)</p> Signup and view all the answers

What condition is caused by increased pressure within the eye, potentially leading to blindness?

<p>Glaucoma (D)</p> Signup and view all the answers

How does eating affect the pressure in the stomach?

<p>It increases the pressure slowly due to volume (A)</p> Signup and view all the answers

Which instrument is specifically used to measure intraocular pressure?

<p>Tonometer (D)</p> Signup and view all the answers

What happens if there is a blockage in the eye's drainage system?

<p>It affects blood supply to the retina (B)</p> Signup and view all the answers

What is the primary function of pressure in the gastrointestinal (GI) system?

<p>To maintain a unidirectional flow of food (C)</p> Signup and view all the answers

What causes an increase in gut pressure during digestion?

<p>Bacterial action generating gas (flatus) (A)</p> Signup and view all the answers

What is the function of the pylorus in the digestive system?

<p>Prevents food from flowing back into the stomach (D)</p> Signup and view all the answers

What can result from a blockage in the small or large intestine?

<p>High pressure between the blockage and the pylorus (A)</p> Signup and view all the answers

What is a primary method of treatment for intestinal blockage?

<p>Intubation with a hollow tube (B)</p> Signup and view all the answers

How does the surface area of a bone at a joint affect pressure?

<p>Distributes force and reduces pressure (D)</p> Signup and view all the answers

What is the typical maximum volume of the bladder before voiding in adults?

<p>500 ml (A)</p> Signup and view all the answers

What pressure is typically reached during the micturition reflex?

<p>150 cmH2O (C)</p> Signup and view all the answers

Which technique provides information about bladder function through direct measurement?

<p>Inserting a needle through the abdomen wall (A)</p> Signup and view all the answers

What reaction occurs in the bladder during pregnancy as the fetus exerts pressure?

<p>Increased bladder pressure (B)</p> Signup and view all the answers

What is a notable characteristic of the body in relation to pressure and gas cavities?

<p>Pressure changes have little effect on solids and liquids (C)</p> Signup and view all the answers

What pressure in cmH2O may men experience due to prostate obstruction of the urinary passage?

<p>Over 100 cmH2O (B)</p> Signup and view all the answers

Flashcards

Pressure

The force exerted per unit area.

Pressure of a Liquid Column

The pressure under a column of liquid is directly proportional to the density of the liquid, the acceleration due to gravity, and the height of the column. P = ρgh

Gauge Pressure

The excess pressure over atmospheric pressure.

Negative Pressure

Any pressure lower than atmospheric pressure.

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Manometer

An instrument used to measure pressure. Examples include a sphygmomanometer and a mercury manometer.

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Sphygmomanometer

A medical device used to measure blood pressure, commonly using a cuff and a gauge.

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Cerebrospinal Fluid (CSF)

The cerebrospinal fluid (CSF) is a clear fluid that circulates in the brain and spinal cord. It fills interconnected openings called ventricles.

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Intracranial Pressure

The pressure within the skull, influenced by the volume of cerebrospinal fluid (CSF), blood, and brain tissue.

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Hydrocephalus

A condition where cerebrospinal fluid (CSF) builds up in the brain, causing increased pressure and skull enlargement.

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Aqueduct

The narrow opening that connects the two ventricles in the brain.

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Crude method

A method to detect hydrocephalus by measuring the circumference of the skull just above the ears.

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Trans-illumination

A qualitative technique that uses the light-scattering properties of CSF to detect hydrocephalus.

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Glaucoma

High pressure in the eye, often caused by a blockage in the drainage system.

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Aqueous and vitreous humors

The clear fluids in the eye that transmit light to the retina.

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Retina

The sensory tissue in the back of the eye that detects light.

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By Feel

A method to measure the pressure inside the eye by pressing on the eye with fingertips.

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Boyle's Law

A law stating that for a fixed amount of gas at a constant temperature, the product of its absolute pressure and volume remains constant. This means that as pressure increases, volume decreases proportionally.

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Equalization of Middle Ear Pressure

The middle ear is an air pocket in the body that needs to maintain pressure equal to the outside environment. This happens through the Eustachian tube, which opens during swallowing, chewing, or yawning, allowing air to equalize pressure.

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Henry's Law

The amount of gas that dissolves in a liquid is directly proportional to the partial pressure of that gas.

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Hyperbaric Oxygen Therapy (HOT)

A medical treatment that involves breathing pure or enriched oxygen at an increased pressure. It helps deliver more oxygen to tissues, treating conditions like gas gangrene or carbon monoxide poisoning.

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Nitrogen Narcosis

The condition where nitrogen gas dissolves in the blood and tissues at increased depths, causing intoxication-like effects. This can lead to confusion, impaired judgment, and even unconsciousness.

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What is the pylorus?

A valve located at the junction of the stomach and small intestine, preventing food from flowing back into the stomach.

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What is a dangerous consequence of a blockage in the small or large intestine?

This occurs when a blockage prevents food from moving through the intestines, increasing pressure between the blockage and the pylorus. This can restrict blood flow to vital organs and even lead to death.

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What is intubation?

A hollow tube inserted through the nose, stomach, and pylorus to relieve pressure caused by intestinal blockage.

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Where are the highest pressures found in the body?

Bone joints, especially weight-bearing ones like the knee, experience the highest pressures in the body due to the forces exerted on them.

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How does the surface area of a joint affect pressure?

The surface area of a bone at the joint is larger than areas above or below it, allowing for force distribution, thereby reducing pressure.

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How does the bladder's pressure change as it fills?

The bladder's internal pressure is caused by its stretching as it fills with urine. As the volume increases, the pressure rises.

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What is the micturition reflex?

This reflex signals the body to empty the bladder when the pressure reaches a certain level, typically when the bladder holds about 500ml of urine, around 30 cmH2O pressure.

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How does the bladder contract to void urine?

This occurs when the bladder contracts powerfully, momentarily increasing pressure up to 150 cmH2O to expel urine.

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What is the catheter technique for measuring bladder pressure?

It's a technique of measuring bladder pressure by inserting a catheter with a pressure sensor through the urethra into the bladder.

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How can daily activities affect bladder pressure?

Activities like coughing, straining, and even pregnancy can increase bladder pressure, leading to more frequent urination.

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Study Notes

Pressure in the Body

  • Pressure is defined as force per unit area
  • Pressure under a liquid column (P) is calculated using the formula: P = pgh
    • p = density of the liquid
    • g = acceleration due to gravity
    • h = height of the liquid column

Example Calculation

  • Finding the height of water that produces the same pressure as 120 mmHg

    • Given: 120 mmHg , p water = 1 g/cm³ , p Hg = 13.6 g/cm³
    • Calculated height of water = 163 cm
  • Atmospheric pressure calculation

    • 1 atm = 760 mmHg = 76 cmHg
    • Atmospheric pressure in N/m² = 1.01 x 10⁵ N/m²

Types of Pressure

  • Gauge pressure: The excess pressure over atmospheric pressure
  • Negative pressure: Any pressure lower than atmospheric pressure
    • Example: Lung pressure during inspiration

Typical Pressure in the Normal Body

Body Part Typical Pressure (mmHg)
Arterial blood pressure, max (systole) 100-140
Arterial blood pressure, min (diastole) 60-90
Venous blood pressure 3-7
Middle ear pressure Less than 1
Eye pressure 12-23
CSF (cerebrospinal fluid) inside the brain 5-12

Measurement of Pressure in the Body

  • Instrument for measuring pressure is a manometer
  • Sphygmomanometer: Common clinical instrument used for measuring pressure

Pressure Inside the Skull

  • Brain contains approximately 150 cm³ of CSF (cerebrospinal fluid)
  • CSF flows through connected openings (ventricles)

CSF Pressure Measurement Methods

  • Crude method: Measuring skull circumference above the ears
    • Normal values for newborns: 32–37 cm
  • Trans-illumination: Qualitative method using light-scattering properties of CSF

Eye Pressure

  • Normal eyes' pressure: 12–23 mmHg
  • Glaucoma: Condition due to blocked drain system; increases pressure, damaging optic nerve; symptoms include tunnel vision and blindness

Measuring Eye Pressure

  • Determining eye pressure by feeling
  • Using a tonometer to measure eye pressure

Pressure inside the Eye

  • Intraocular pressure (IOP) is measured using the formula:
  • IOP = Load/area(1 + Rlens /Rcornea )

Pressure in the Digestive System

  • Gastrointestinal (GI) system pressure is higher than atmospheric pressure
  • Affects the proper flow of food

Digestive System Pressure Factors

  • Eating increases stomach pressure due to volume increase
  • Swallowed air during eating causes belching or burping
  • Bacteria action generates gas (flatus) in the gut, increasing gut pressure

Pressure in the Gastrointestinal System

  • Pylorus: valve prevents food reflux from the small intestine
  • Blockage in the small or large intestine causes high pressure, causing organ damage or death; treatment with intubation and/or surgery
  • Belts, girdles, or swimming can affect gut pressure

Pressure in the Skeleton

  • Highest pressures in the body are in weight-bearing bones (joints)
  • Knee joint pressure can exceed 10 atm
  • Larger joint surface areas distribute force, thus lessening pressure; finger bones are flat and spread force over a greater area

Pressure in the Urinary Bladder

  • Bladder pressure varies as bladder volume increases
  • Adult bladder capacity before voiding: 500 ml
  • Micturition reflex occurs at ~30 cm H₂O

Measuring Bladder Pressure

  • Catheter with pressure sensor inserted into the bladder (urethra)
  • Needle inserted through the abdominal wall directly into the bladder

Additional Pressures

  • Coughing, straining, sitting, and fetal weight increase bladder pressure, causing frequent urination
  • Normal voiding pressure: 20-40 cm H₂O
  • Prostrate obstruction may increase pressure to over 100 cm H₂O

Diving Effects

  • The human body is composed of incompressible solids and liquids
  • Pressure changes do not significantly impact most parts of the body
  • Gas cavities are affected by sudden pressure changes

Boyle's Law:

  • Constant temperature, product of pressure and volume of a gas is constant. If pressure doubles, the volume is halved.

Middle Ear Pressure

  • Middle ear pressure should equal external pressure for comfort
  • Eustachian tube usually closed, and it's difficult to equalize pressure during swallowing, chewing, or yawning
  • Pressure difference (120 mmHg) across the ear drum can damage it (ruptures) when diving

Hyperbaric Oxygen Therapy (HOT)

  • HOT increases oxygen proportion, beneficial to tissues
  • Treats gas gangrene (bacillus cannot survive in oxygen) and carbon monoxide poisoning

Henry's Law

  • Amount of gas dissolved in a liquid is proportional to the partial pressure of that gas (in contact with the liquid)

Other Info

  • The breathing air at depth is a higher partial pressure of O₂ than at sea level; may cause oxygen poisoning
  • Breathing air at depth > 30 m is dangerous due to excess N₂ in the blood and tissue, resulting in nitrogen narcosis (intoxication)

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