Body Fluids

Question 1

In order to maintain homeostasis in terms of water what 2 factors need to be equal.

Answer 1

• Input of water
• Output of water

Question 2

What is a fluid

Answer 2

• A fluid is a substance that deforms under shear stress. Physiologically important ones are where water or fats and lipids are the solvent.

Question 3

What are some key compartments where water is found in the body

Answer 3

• Intracellular compartments
• Interstitial compartments
• Fat
• Plasma
• Transcellular fluid (separated from the extracellular fluid by a membrane)

Question 4

Describe the path water takes when ingested and how does this compare to the path water takes when excreted.

Answer 4

• Through the gut and into the plasma. Then from here into the intestinal space, intracellular compartments and transcellular compartments.
• The reverse occurs when water is being excreted

Question 5

What are some typical values for body water content

Answer 5

• 42L for a 70kg person
• Greater in men than in women
• Reduces with age
• Around 3L is in the plasma
• Around 10L is in the Interstitial fluid
• Around 28L is in the intercellular space
• Around 1L is Transcellular fluid

Question 6

What are some examples of transcellular compartments

Answer 6

• Peritoneal space - Can expand greatly
• CSF - Protected by the blood-brain barrier
• Pleural cavity
• Synovial fluid

Question 7

Describe some way of measuring body fluid compartments

Answer 7

• Destructive methods
  > Plasma volume (by exsanguination and centrifugation)
  > Total body water (weigh the body then desiccate it by heat then reweigh)
• Less Destructive methods
  > Calculating the volume of distribution

Question 8

What is the Volume of Distribution and how can it be calculated