Body Fluid Compartments

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Intracellular fluid + Extracellular fluid

What is the formula for total body water?

Plasma
Interstitial fluid
Transcellular fluids

What does extracellular fluid consist of?

Cerebrospinal
Synovial
Intraocular

Give an example of transcellular fluids. (3)

60%

In a typical man, how much of body weight is accounted for by total body water?

52%

In a typical woman, how much of body weight is accounted for by total body water?

28L (~67%)

In a typical male who has a total body water of 42L, how much intracellular fluid is there?

14L (~33%)

In a typical male who has a total body water of 42L, how much extracellular fluid is there?

11L (~26%)

In a typical male who has a total body water of 42L, how much interstitial fluid is there?

3L (7%)

In a typical male who has a total body water of 42L, how much plasma is there?

145 mmol/L

What is the average concentration of Na+ in plasma?

4 mmol/L

What is the average concentration of K+ in plasma?

2.5 mmol/L

What is the average concentration of Ca2+ in plasma?

110 mmol/L

What is the average concentration of Cl- in plasma?

26 mmol/L

What is the average concentration of HCO3- in plasma?

1 mmol/L

What is the average concentration of proteins in plasma?

20 mmol/L

What is the average concentration of Na+ in intracellular fluid?

150 mmol/L

What is the average concentration of K+ in intracellular fluid?

<<<<<<1 mmol/L

What is the average concentration of Ca2+ in intracellular fluid?

3 mmol/L

What is the average concentration of Cl- in intracellular fluid?

10 mmol/L

What is the average concentration of HCO3- in intracellular fluid?

8 mmol/L

What is the average concentration of proteins in intracellular fluid?

Proteins and Calcium
Much less in interstitial fluid
Most calcium is protein bound - if there is less protein, there is less calcium

Concentrations between plasma and interstitial fluids are similar apart from 2. What are the two solutes that differ? ...How do they differ? ...Why is this?

Dilution principles
-Known quantity of a marker substance known to be restricted to a particular compartment is injected
-Allowed to distribute
-Concentration determined

How are body fluid volumes measured?

(Amount given - Amount lost) / Concentration through body

What is the calculation for volume using dilution methods?

3^H20

What compound is used in dilution techniques to calculate total body water?

Inulin
Thiosulphate

What compounds are used in dilution techniques to calculate extracellular fluid volume? (2)

Isotopically labelled plasma proteins
Evans blue

What compounds are used in dilution techniques to calculate plasma volume?

Total body water - extracellular fluid

What is the formula for intracellular fluid volume?

Extracellular volume - plasma vollume

What is the formula for interstitial fluid volume?

Must be excluded from all cells but free to distribute throughout extracellular space

What is the requirement of a compound being used to measure extracellular fluid volume?

Must remain within the vascular system

What is the requirement of a compound being used to measure plasma volume?

Plasma volume x (1 / (1-Hct))

What is the formula for blood volume?

Water movement

What are osmolarity and osmolality units of measurement of?

1 osmol/kg

How much osmotic pressure does 1 gram of a non dissociating substance dissolved in 1 kg of water exert?

mOsmol/kg

What are the units of osmolality (usually)?

Solutions of equal osmolarity

What are isosmotic fluids?

Moles of solute particles per litre of water

What is osmolarity?

Moles of solute particles per kg of water

What is osmolality?

Osmolarity: Per litre
Osmolality: Per Kg

What is the difference between osmolarity and osmolality?

THe sum of the osmolalities due to each of the constituents in a solution

What is the total osmolality for a solution?

295-300 mOsmol/kg

What is the average osmolality of plasma?

Na+
K+
Cl-
HCO3-

What contributes to the majority of the osmolality of plasma? (4)

Na+
K+
Cl-
HCO3-

What are the principal ions of the plamsa? (4)

~10 mOsmol/kg

What osmolality does glucose contribute to the osmolality of plasma?

Causes neither swelling or shrinking

What is the effect of an isotonic solution on RBC?

Causes cells to swell

What is the effect of a hypotonic solution on RBC?

Causes cells to shrink

What is the effect of a hypertonic solution on RBC?

The influence os its osmolality on the volume of cells

What does the tonicity of a solution refer to?

Iso-osmotic and Isotonic
Because cell volume remains stable - implying two fluid have same osmolality

What are two solutions with same osmolality described as? ...Why?

Solutes can cross membranes and alter osmolalities

Why are some isotonic solutions not iso-osmotic?

(hydrostatic pressure of capillary - hydrostatic pressure of interstitum)
-
(oncotic pressure of capillary - oncotic pressure of interstitium


(hydrostatic pressure of interstitial - hydrostatic pressure of capillary)
-
(oncotic pressure of interstitial - oncotic pressure of capillary)

What is the formula for net filtration pressures from a capillary to interstitial fluid? ...How would this formula be different if net reabsorption was being calculated?

~0mmHg

What is the normal value of hydrostatic pressure of interstitium?

~25mmHg

What is the normal value of oncotic pressure of the capillary?

~2mmHg

What is the normal value of oncotic pressure of the interstitium?

~20L
~18L

On average how many litres of fluid move from capillaries into interstitial fluids a day? ...How many are reabsorbed?

-Reduced hydrostatic pressure in capillary due to blood loss causes less fluid to be filtered
-Reduced plasma increases the concentration of proteins in the plasma - causes increased oncotic pressure, which causes increased absorption

Why does haemorrhage lead to increase fluid reabsorption from interstitial fluids into plasma?

-Increased hydrostatic pressure in capillary causes more fluid to be filtered out of the kidney and less to be reabsorbed
-Causes accumulation of fluid in the tissues
-Causes oedema

How does ingestive heart failure lead to oedema?

-Reduced concentration of proteins in plasma causes decreased oncotic pressure
-So more plasma filtered out into tissues, less reabsorption
-Leads to accumulation of fluid in tissues
-Oedema

How does liver failure cause odema?

Drains into lymphatics

What happens to the excess fluid filtered into the interstitial fluid (and not reabsorbed into capillaries)?

Elephantiasis

What does blocking of lymphatics cause?

Hydrostatic pressure in the lungs is less than oncotic pressure (due to the lower pressure system)
Causes any fluid in alveoli to moves into capillary

How has the lung been adapted so that no oedema occurs (normally)?

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