Body Fluid Compartments

Created by gswi5078 

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61 terms

What is the formula for total body water?

Intracellular fluid + Extracellular fluid

What does extracellular fluid consist of?

Plasma
Interstitial fluid
Transcellular fluids

Give an example of transcellular fluids. (3)

Cerebrospinal
Synovial
Intraocular

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

60%

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

52%

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

28L (~67%)

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

14L (~33%)

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

11L (~26%)

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

3L (7%)

What is the average concentration of Na+ in plasma?

145 mmol/L

What is the average concentration of K+ in plasma?

4 mmol/L

What is the average concentration of Ca2+ in plasma?

2.5 mmol/L

What is the average concentration of Cl- in plasma?

110 mmol/L

What is the average concentration of HCO3- in plasma?

26 mmol/L

What is the average concentration of proteins in plasma?

1 mmol/L

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

20 mmol/L

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

150 mmol/L

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

<<<<<<1 mmol/L

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

3 mmol/L

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

10 mmol/L

What is the average concentration of proteins in intracellular fluid?

8 mmol/L

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?

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

How are body fluid volumes measured?

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

What is the calculation for volume using dilution methods?

(Amount given - Amount lost) / Concentration through body

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

3^H20

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

Inulin
Thiosulphate

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

Isotopically labelled plasma proteins
Evans blue

What is the formula for intracellular fluid volume?

Total body water - extracellular fluid

What is the formula for interstitial fluid volume?

Extracellular volume - plasma vollume

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

Must remain within the vascular system

What is the formula for blood volume?

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

What are osmolarity and osmolality units of measurement of?

Water movement

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

1 osmol/kg

What are the units of osmolality (usually)?

mOsmol/kg

What are isosmotic fluids?

Solutions of equal osmolarity

What is osmolarity?

Moles of solute particles per litre of water

What is osmolality?

Moles of solute particles per kg of water

What is the difference between osmolarity and osmolality?

Osmolarity: Per litre
Osmolality: Per Kg

What is the total osmolality for a solution?

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

What is the average osmolality of plasma?

295-300 mOsmol/kg

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

Na+
K+
Cl-
HCO3-

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

Na+
K+
Cl-
HCO3-

What osmolality does glucose contribute to the osmolality of plasma?

~10 mOsmol/kg

What is the effect of an isotonic solution on RBC?

Causes neither swelling or shrinking

What is the effect of a hypotonic solution on RBC?

Causes cells to swell

What is the effect of a hypertonic solution on RBC?

Causes cells to shrink

What does the tonicity of a solution refer to?

The influence os its osmolality on the volume of cells

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

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

Why are some isotonic solutions not iso-osmotic?

Solutes can cross membranes and alter osmolalities

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?

(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 normal value of hydrostatic pressure of interstitium?

~0mmHg

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

~25mmHg

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

~2mmHg

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

~20L
~18L

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

-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

How does ingestive heart failure lead to oedema?

-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 liver failure cause odema?

-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

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

Drains into lymphatics

What does blocking of lymphatics cause?

Elephantiasis

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

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

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