body fluid compartments

examples of where fluid can exist in the body

• intracellular (inside the cells)

• extracellular

  • plasma

  • interstitial

  • transcellular (fluid trapped in spaces surrounded by epithelial cells)

examples of trenscellular fluid

Fluids trapped within spaces are surrounded completely by epithelial cells: 

• Synovial fluid 

• Cerebrospinal fluid 

• Aqueous humour  

• Pericardial fluid 

• Pleural fluid 

how can you measure a compartments volume

• requirements for the tracer

Measurement of compartment volume: 

• Inject knows volume of a tracer substance at a known concentration into the compartment  

• Allow it to equilibrate through the compartment and then measure the concentration in that compartment  

The tracer needs to be: 

• Non-toxic and easy to assay 

• Doesn’t alter normal fluid distribution 

• Doesn’t get metabolised/ taken up by cells 

• Rapidly/ evenly distributed through compartment  

• Not significantly excreted during equilibrium period

fluid compartment calculation equation

Tracer vol. X tracer conc. = compartment vol. X final conc. 

Compartment vol = (tracer vol. X tracer conc.)/ final conc. 

if you want plasma volume, what should the tracer be able to bind to

• Use tracers that bind to albumin in the blood (evans blue) 

• what are starling forces

P,O

• explains the physical pressures that determine how fluid moves between the bloodstream and surrounding tissues

  • hydrostatic pressure (pusher)

  • osmotic pressure (puller)

• what determines osmotic pressure in plasma

• what does Kf represent in filtration equation

• what is the reflection coefficient and what symbol is it represented by

• albumin protein

• filtration coefficient - permeability of the capillary to water

• reflection coefficient - how impermeable the capillary is to proteins (σ)

what feature of capillaries affects the capillary Kf

• name the 3 types

• more of these affects the Kf how

Endothelial structure affects capillary Kf (fenestrations/permeability)

Continuous  

• Most capillary beds 

Fenestrated  

• Kidneys 

Sinusoidal/discontinuous

• Liver/ spleen 

More fenestrations------> higher Kf 

inflammation

• how does it affect Kf

• how does it affect σ

  • what happens during inflammation

  • endothelium

  • BF

  • what exits the blood stream

  • what plasma protein leaks

Inflammation: 

Inflammatory mediators trigger increased Kf and decreased 𝜎 , via activation of endothelial cells  

During inflammation  

1. WBCs cause the activation of endothelial cells causing: 

• Activation of smooth muscle cells = vasodilation 

• Breakdown of tight junctions  

• Inflammatory mediator production/secretion  

2. Increased blood flow  

3. Leukocytes leave the blood stream  

• Neutrophils, NK cells  

4. Leakage of plasma proteins  

• Complement 

lymphatic system

• where does filtrate travel to

• venous plasma

osmotic pressure

• what channel protein allows water to travel through cells

• what is one unit of osmotic concentration

• what is normal plasma osmolarity

• what is the process of managing osmosis called

• Water shifts between intracellular and extracellular compartments along an osmotic pressure gradient, using aquaporins. 

• Osmole= unit of osmotic concentration 

• Normal plasma osmolarity is 290 mOsmoles/L

• osmoregulation

what are the 3 states of osmosis

HYPERTONIC: 

• Cells loose water by osmosis 

• Interferes with cellular function 

ISOTONIC: 

• There is an equal amount of water leaving and entering the cell 

HYPOTONIC: 

• Cells take up water by osmosis and expand 

• Could cause lysis  

rehydration

• 2 routes

Orally (enters through the GIT) 

IV fluid resuscitation (intravenously) 

• Crystalloid (solutions containing Nacl) 

• Colloid (albumin, starches, gelatin solutions) 

• water