Body Fluid Compartments
• What are the body fluid compartments?
• How does fluid move between
compartments?
• What is the point?
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One compartment, two compartments
external environment
intracellular
compartment
flatworm
……………… compartment ……………. compartment
in-the-spaces
compartment
CO2
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O2
Three compartments
intracellular
- to allow efficient
cellular metabolism
interstitial
- to allow cellular
specialisation
blood
- to allow you to be
three dimensional
gas exchange
system
(gills, lungs etc)
CO2
O2
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Where is the fluid?
blood …..l
lymph
…..l
interstitial
12 l
intracellular
24 l
lymph
2.5%
extracellular
………...
………...
blood 7.5%
intracellular
………...
………...
intracellular
interstitial
…..%
….%
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Indicator dilution technique
C=M/V
V=M/C
3H
water
......................
mannitol
......................
intracellular
compartment
=
total
-
extracellular
compartment
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a barrier between
endothelium: two internal
compartments
• blood vessels
• ...........................
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Starling’s Forces
• Net force for fluid efflux at the arterial end of a capillary
• (Pc > Πc)
• Net force for fluid influx at the venous end of a capillary
• (Pc < Πc)
• Fluid circulates from the blood to the tissues and back
Starling’s Forces = [Pc - Pi] - σ[Πc – Πi]
How much fluid moves?
• ‘capillary filtration coefficient’ (Kf)
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Continuous capillaries
Permeable
to substances
< 10 nm
glucose
…… nm
• muscle
• skin
• lungs
• CNS
• Retina
• adipose tissue
• mammary glands
erythrocyte
basement
membrane
nucleus
endothelial cell
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Fenestrated capillaries
Permeable
to substances
……..…… nm
fenestration
basement
membrane
• kidneys
• pancreas
• gallbladder
• intestine
nucleus
endothelial cell
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Discontinuous capillaries
Permeable
to substances
…….…… nm
basement
membrane
• liver
• spleen
• ovaries
• some endocrine glands
nucleus
endothelial cell
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epithelium:
•
•
•
•
•
•
a barrier with the
outside world
................
lungs
................
salivary glands
................
kidney
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Salt and Water Homeostasis
at the level of the organism
• Two easily regulated determinants of
body osmolarity (concentration of body
fluids).
• Drink (....... l/d)
• Urine production (......... l/d)
•
•
•
Osmolarity: number of osmotically active particles in solution
mOsmol/l 1/1000 Osmol/l
ions dissociate in solution therefore:150mM NaCl = 300mOsmol/l
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300 mOsmol/l: Osmolarity normal
40 l
1.5 l/d
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>300 mOsmol/l: Osmolarity high
Anti diuretic
hormone
(ADH)
OsmoReceptors in
hypothalamus
<40 l
0.5 l/d
…….… feedback loop
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<300 mOsmol/l: Osmolarity low
Anti diuretic
hormone
(ADH)
>40 l
23 l/d
…….… feedback loop
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Compensation & Correction
The kidney compensates for
low salt levels
<40by
l reducing fluid volume
…. there must also be an appropriate
corrective mechansim
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