Body fluid compartments - Unit 2 Flashcards
Out of the average 42L of water that is within the body, how much of it is intracellular and extracellular?
What is the interstitial and transcellular fluid?
-Extracellular compartment which is in direct contact with the actively respiring cells of a skeletal muscle or organ
-Fluid found trapped within spaces completely surrounded by epithelial cells e.g. cerebrospinal fluid, pleural fluid
What is the haematocrit?
-The fraction of volume of blood that is actually made up of cells → 40% as 60% is plasma
In order to measure the volume of a body fluid compartment, what is injected into it?
-A known volume of tracer of a known concentration, which then equilibrates through the compartment and then measure concentration in that compartment
What are some requirements of this tracer?
- Non-toxic and easy to assay
- Doesn’t alter normal fluid distribution
- Not significantly excreted during equilibration period
- Not metabolised or taken up by cellls
- Rapidly and evenly distributed through compartment
Equations to find compartment volume?
A subject is injected with 4 mL of a 3 mg/mL solution of Evan’s Blue. 1 hour later a blood sample was taken and the subject was found to have a plasma concentration of Evan’s Blue of 2 μg/mL. What was their plasma volume?
- 4 x 3 = 12mg of Evans blue
- 12mg / 0.002mg/ml
= 6000ml
How do we move fluid from plasma into the interstitial space, to regulate respiratory gases and nutrients?
- Occurs in capillary beds
-Metabolites are pumped rapidly around the body by bulk flow of blood to the capillaries. > This is uses the high arterial pressure created by the heart
1. Plasma can be filtered across epithelial lining into interstitial space > capillary lining isn’t impermeable to water movement .. gaps between cells
What are the driving forces to move fluid from plasma to interstitial space? Why is this known as net filtration?
- Hydrostatic pressure - brings fluid out
- Colloid osmotic pressure - brings fluid in
What is the filtration co-efficient dependent on?
- Endothelial structure
How is the filtration rate affected by inflammation?
- Enhanced filtration rate
> Activation of inflammatory mediators trigger release of cytokines which ACTIVATE ENDOTHELIAL CELLS :
Increased Kf greater gaps between endothelial cells and decreased o protein less impermeant as it was before
We get net filtration via starlings forces. However if this continues plasma vol would decrease and interstitial fluid would increase. Why does this not happen?
- Excess fluid filtered in from the plasma to the interstitial fluid is recycled back into the plasma via lymphatic system.
Why is the lymphatic system important?
-If lymphatics are blocked e.g. parasite
-Excess build up of fluid in interstitial space
How do we exchange between intracellular and extracellular fluid?
-Across cell membrane
-Water shifts between intracellular and extracellular compartments along an osmotic pressure gradient
What drives do we need to move water internally and externally?
- Osmotic pressure gradient - solutes differentially distributed
- Permeability pathway - aqua porins
There is a difference in the composition of the intracellular and extracellular fluids but this does not matter because…?
- Bulk electroneutrality
- Similar osmolarity
- What is the normal plasma osmolarity?
- How does the osmolarity of urine range?
- 290 mOsmoles/L
- 30-1200 mOsmoles/L
What happens when we Eaten too much salt
Drunk too little water and vice versa?
What also happens to our cells?
What happens in these scenarios?
