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Lecture 5 — Body Fluids
Pathophysiology — Lymphoedema
Elephantiasis.
Inflow
• Unilateral increase in pressure/flow
Outline
– How?
Outflow
• Reduced venous drainage
• Importance of body fluids (homeostasis)
– Unilateral venous compression/block?
• Fluid compartments (volumes)
• Blockage of lymphatic drainage…
– …accumulation of fluid in tissues
• Boundaries and movement of materials
Causes
• Parasitic worms (filaria)
• Measurement of compartments.
Dr Alan Tuffery — Physiology
– [cf other sites: scarring after radiotherapy]
JS/Dip Ex Tissue Structure 2008/09 — 5
Dr Alan Tuffery — Physiology
JS/Dip Ex Tissue Structure 2008/09 — 5
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Starling’s Law of Capillaries
Lymphatic drainage
(Bulk flow — movement of water and solutes)
Arrows indicate direction of force
Sherwood 10-25
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Arteriole
37 mmHg
25 mmHg
Venule
17 mmHg
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• 3 litres per day not reabsorbed in
capillaries/venules
• Enters lymph vessels
• Pumped to lymph nodes
• Re-enters circulation near right atrium.
Dr Alan Tuffery — Physiology
Capillary BP
Capillary BP Colloid OP*
NET OUTWARD PRESSURE
~12mmHg
NET INWARD PRESSURE ~8 mmHg
Sherwood 10-23
*Colloid OP — osmotic pressure
of the plasma proteins
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Dr Alan Tuffery — Physiology
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Pathophysiology
What happens in the lungs?
• Where does fluid goes
when it leaves the
capillary?
Clue: Liver synthesises
most plasma proteins
Liver Failure
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Sherwood 10-23
Arteriole
• So why doesn’t it leave
the capillary?
Capillary BP
Colloid OP
37 mmHg
25 mmHg
Capillary BP
Venule
17 mmHg
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• Fall in plasma proteins
• Pulmonary arterial
pressure ~15 mmHg.
• Colloid OP falls
• Reduced inward flow
• Accumulation of fluid in tissues (oedema).
Dr Alan Tuffery — Physiology
JS/Dip Ex Tissue Structure 2008/09 — 5
Dr Alan Tuffery — Physiology
JS/Dip Ex Tissue Structure 2008/09 — 5
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Body fluids — importance
Maintain
• Primary transport
system between cells
 Nutrition
 Waste
 Signals
• Capillary wall is very permeable
• Bulk flow of water and solutes
Body systems
• ‘milieu intérieur’ of
Claude Bernard
Starling’s Law — Importance
Homeostasis
• Rapid Plasma and IF interchange
Is essential
for
survival
of
Make
up
• Composition critical
for cell function.
• BUT plasma is carefully regulated (kidney)
• Hence IF composition is carefully regulated
Cells
• (IF is the environment for all cells.)
Sherwood Fig. 1-5
Dr Alan Tuffery — Physiology
JS/Dip Ex Tissue Structure 2008/09 — 5
Dr Alan Tuffery — Physiology
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Abnormal Inputs and Outputs
Normal Daily Input and Output
Inputs
• Ingestion
– Fluid * (1.25 litres)
– Food (1 litre)
• Metabolism (350 ml)
•
•
•
•
Outputs
Gut (Faeces 100 ml)
Urine *(1.5 litres)
Breathing/Skin (900 ml)
Sweating (100 ml)
Outputs
Inputs
• Gut (vomiting, diarrhoea)
• Clinical
• Urine (diabetes insipidus *)
– Injection/infusion
• Breathing/Skin (burns)
• Excessive drinking
(‘polydipsia) *
• Sweating (‘hyperhydria’ *)
• Haemorrhage
• * Regulated
– [for water balance.]
Dr Alan Tuffery — Physiology
* Failure of regulation
JS/Dip Ex Tissue Structure 2008/09 — 5
Dr Alan Tuffery — Physiology
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Fluid Compartments
Body Water (70 kg healthy male)
G&S Fig. 1.5
NB 1 litre H2O weighs 1 kg
(Volumes in litres)
•
Total Body Water (TBW)
Notes
• TBW ~60% body mass
42
• ICF ~65% TBW
– Intracellular Fluid (ICF)
28
– Extracellular Fluid (EC F)
14
• Plasma (Pl)
• Interstitial Fluid (IF)
3
12
• Plasma 55% of ~5
litres blood
• Fat only ~10% water…
Dr Alan Tuffery — Physiology
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Dr Alan Tuffery — Physiology
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Estimation of Fluid Compartments
Boundaries between Compartments?
•
Intracellular/Interstitial
– cell membrane
• Interstitial Fluid/Plasma
• Dilution expt
– capillary wall
• selectively permeable
• ion pumps
• permeable (to small mols.)
– Stable marker
– Enters compartment quickly
– Stays in that compartment
– Na+/K+/ATPase
•
•
•
•
Intracellular (ICF)
• Na+ low (pump)
• Cl- low
• K+ high (pump)
Extracellular
Na+ high (pump)
Cl- high
K+ low (pump)
• TBW — D2O, 3H2O
– Measure in Plasma!
• Principal Anions
– PO4 3-, Proteins (Pr-).
Dr Alan Tuffery — Physiology
JS/Dip Ex Tissue Structure 2008/09 — 5
Dr Alan Tuffery — Physiology
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Estimation of ECF
Estimation of Plasma Volume
• Choices
• Properties of
Marker?
•
– *Na+
– Leaves plasma
– Does not enter cells
• Measure in Plasma
• Some enters cells…
• Overestimates ECF
• Evans Blue (?!)
– Inulin [ sic] , mannitol
• not metabolised
• do not reach all
ECF…
• underestimates ECF
Dr Alan Tuffery — Physiology
131I-albumin
•
51Cr-labelled
rbc
– measures blood volume
– correct by haematocrit
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Dr Alan Tuffery — Physiology
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Estimation of ICF and IF
Osmosis
See also G&S Fig. 4.18 and Toolbox, p 122
• Water moves…
• No suitable markers
– From lower to higher
solute concentration
• ICF = TBW - ECF
• Cell membrane is
permeable to water
but not solute —
semipermeable
– Clinically 65% TBW
• IF = ECF - Plasma
Dr Alan Tuffery — Physiology
• Movement is passive
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Dr Alan Tuffery — Physiology
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Osmolarity vs Osmolality
Osmolality
Osmolarity
•
Concentration of solute
particles
– Glucose 0.1 mole/litre = 0.1
Osmole (Osm)
– NaCl 0.1 mole/litre
= 0.2 Osm
(dissociation: Na+ , C l-)
•
•
Tonicity
ICF/ECF ~300 mOsm
Water moves to the higher
concentration
•
Effect of solute concentration on cell volume
Concentration/kg soln
– (moles/kg)
•
•
•
In dilute (physiological)
solution approx. same as
osmolarity
Clinical use because TBW
determined by body weight.
•
Solute cannot cross
membrane (impermeant)
Hence H2 O moves
(a) hypotonic solution
– Cell gains water —
swells
(b) hypertonic solution
G&S Fig. 4.20
– Cells loses water —
shrinks.
Dr Alan Tuffery — Physiology
JS/Dip Ex Tissue Structure 2008/09 — 5
Dr Alan Tuffery — Physiology
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Fluid replacement
Body Fluid — Summary
• Haemorrhage
• Key importance — homeostasis
• Fluid balance (outline)
– Replace blood with
isotonic saline (NaCl)
– No change in cell
volume
– Inputs/outputs
• Compartments
–
–
–
–
• Sports drinks
– Replace water and
ions
Volumes
Exchanges (Starling’s Law)
Pathophysiology (oedema)
Estimation.
END/
Dr Alan Tuffery — Physiology
JS/Dip Ex Tissue Structure 2008/09 — 5
Dr Alan Tuffery — Physiology
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Movement of water by osmosis
Learning Outcomes 1
To be able to:
• Semipermeable
membrane
1. describe the composition of the three principal fluid
compartments in the body
– Permits water
movement
– Stops solute
movement
Intracellular (ICF) — high [K+], low [Na+ ]; PrInterstitial (IF) — high [Na+ ], low [K+ ]
Plasma — as IF, plus Proteins
• Hence water moves
along concentration
gradient
Dr Alan Tuffery — Physiology
2. explain their respective compositions in term of the
nature of the compartments’ boundaries
ICF/IF — cell membrane: semipermeable, Na+/K+ pump
Plasma/IF — capillary wall: bulk flow (not proteins).
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Learning Outcomes 2
To be able to:
3. explain the importance of the movement of material
between compartments
Plasma/IF —plasma closely regulated (kidney) hence IF (milieu
intérieur) regulated
ICF/IF — cell membrane regulates ICF
4. explain the effects of tonicity on cell volume
Osmotic effect on cell volume of solutions of different
concentrations of non-penetrating solute: hypertonic—
cell loses water…
Review osmosis, tonicity.
Dr Alan Tuffery — Physiology
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