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L7 Transport of molecules around the body (3 main body fluid compartments)
L7 Transport of molecules around the body
3 main body fluid compartments
Total body water (TBW)
60% of lean body weight
:star:Extracellular
1/3 of TBW
(20% BW)
Interstitial fluid
(interstitium)
Structure
Interstitium makes up 1/6 of the body volume
Gel-like fluid supported by:
Collagen fibre bundles
Proteoglycan filaments
Hyaluronic acid and protein
Form a mat of fine filaments
Fluid occupies minute spaces between proteoglycan filaments
Diffusion through gel is 95-99% as fast as through a fluid
Free fluid found in vesicles and rivulets
1% in normal tissues
.>50% in oedema
Plasma
¾ extracellular water =interstitial (15% BW)
¼ extracellular water = intravascular (5% BW)
Exchange of water, solutes, nutrients and gases occurs via diffusion and osmosis driven by hydrostatic and oncotic pressures
Transport around body
Force
Diffusion
uncharged solute
Movement due to a solute concentration difference
Occurs because of random motion of solute molecules (Brownian motion)
Net diffusion = flux or flow (J)
charged solute
Electrolytes will also diffuse down a concentration gradient
Presence of other similarly charged molecules will slow diffusion
Presence of oppositely charged molecules will accelerate diffusion
Creates a diffusion potential
Osmosis
( Special type of diffusion )
Definition
Flow of water across a membrane that is permeable to water but not to solutes
Water is a small polar molecule
• Passes through lipid bilayer of cell membrane
• Also passes through channels (aquaporins) in cell membrane
Water passes by diffusion from a region of higher water concentration to a region of lower water concentration (i.e. higher solute concentration)
Oncotic or colloid pressure: osmotic pressure generated by large molecules such as plasma proteins which cannot pass across the membrane
Fick's Law
Transport of water
(Net flow of water across semipermeable membranes)
Pure water
Semipermeable membrane
Constant movement of water molecules (Brownian motion), but no net diffusion or flux of water
Presence of solute produces directional water movement
Reduces water concentration
Water moves by osmosis to area of
• Lower water concentration
• Higher solute concentration
Water ‘follows salt’
Osmotic pressure
Amount of Pressure required to stop osmotic water movement
concentration expression
CF.
other concentration
(Molarity & Molality)
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osmolarity & osmolality
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Summary
Molarity = Concentration (g/L) / Molecular weight = Molar
⇒ Osmolarity = Particles/mole x Molarity = Osm/L
Molality = Concentration (g/Kg) / Molecular weight = Molal
⇒ Osmolality = Particles/mole x Molality = Osm/Kg
Tonicity
Hypertonic compartment or solution
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Hypotonic compartment or solution
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Isotonic
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homeostasis
Fluid homeostasis – maintain hydration and ion distributions
Delivery and removal of gasses, nutrients, wastes and cells
Distribution of chemical messengers
Way
Circulatory system
Functions
Exchange of substances with environment
Transport of substrates and O2 to cells
Removal of metabolites and CO2 from cells
Thermoregulation
Immune cells and mediators
Type
cardiovascular systems
Venous system
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Heart
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Arterial system
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Capillaries
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Lymphatic system
Returns proteins and fluids back to blood
component
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Function
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Movement of lymph
( Extrinsic and intrinsic pumps)
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Intracellular
2/3 of TBW
(40% BW)
Intracellular fluid
Water, solutes, nutrients and gases must cross the cell membrane
Simple diffusion and osmosis occurs for some molecules
Additional transport mechanisms are required for others
Distribution of body water
Clinical relevance
5-15% loss clinical signs dehydration
30% usually fatal if not replaced
Clinical assessment of hydration status
Composition ECF fluid & ICF
