Fluid Compartments Flashcards
What proportion of our body is water?
Males: 60%
Females:50% (have more fat)
Which 3 fluid compartments is water spread over?
Fluid in cells - Intracellular fluid (ICF)
Blood plasma - Extracellular fluid (ECF)
Interstitial fluid- Extracellular fluid (ECF)
What is transcellular fluid?
The fluid that is trapped within spaces completely surrounded by epithelial cells e.g cerebrospinal fluid or pericardial fluid
What is the equation to measure concentration?
Amount divided by volume
How would you measure the concentration of fluid compartments?
Add a marker to the compartment and then measure its concentration after equilibrium
What are the properties of a good marker for fluid compartments?
Confined to the compartment Even distribution Non toxic and easy to measure Not metabolised or excreted (e.g add a marker to protein that sits in the fluid compartment)
What is diffusion?
The net movement of anything from a region of high concentration to a region of lower concentration
What is brownian motion?
The random dispersion of molecules form high to low concentration
What is the barrier between plasma and interstitial fluid ?
Capillary wall
What are the properties of the capillary barrier and what can pass through it?
- One layer of cells
- Have pores (fenestrations) and junctions between cells allow exchange between blood and cells
- water-freely permeable
- small molecules-permeable
- large molecules-impermeable
What is the barrier between the interstitial fluid and the intracellular fluid?
Cell membrane
What are the properties of the cell membrane barrier and what can pass through it?
- Lipid bilayer
- Has channels and carriers
- water-freely permeable
- ions-relatively impermeable
- larger molecules-relatively impermeable
What is osmosis?
The passive movement of water across a semipermeable membrane driven by a difference in water concentration across the membrane
During osmosis, what osmotic pressure does water flow from?
Flows from low osmotic pressure (high water conc) to high osmotic pressure (low water conc)
-flows from a weak solution to a strong one
Is osmotic pressure determined by particle size?
No
-osmotic pressure is determined by solute particle number and not size
What is the formula to calculate moles?
Mass (g) divided by molecular weight (Mr)
What is avogradro’s constant and what does it refer to?
6.022 x10^23
Refers to the number of particles in one mole of any substance
What is an osmole?
One osmole= 6x 10^23 particles in a solution
If a solution dissociates into ions this must be taken into account
-e.g 1 mole of sodium chloride =2 osmoles
What is osmolarity and how is it calculated?
Osmolarity is how strong a solution is
(think like diluting squash)
- Osmolarity = molar concentration x number of osmoles
-e.g osmolarity of 1 mole of sodium chloride = 1x2=2
What are starling forces?
A force that drives the fluid movement across capillary wall
What are the starling forces driving movement out of the capillary?
Capillary Hydrostatic Pressure (Pcap)
Capillary Oncotic Pressure ( ∏cap)
What are the starling forces driving movement into the capillary?
Interstitial Fluid Hydrostatic Pressure (Pi)
Interstitial Fluid Oncotic Pressure (∏i)
What is the equation for the net driving pressure for filtration in the capillaries?
Net driving pressure = [ (Pcap - Pi) - (∏cap - ∏i) ]
What are the 2 coefficients that must be applied when calculating starling forces?
The Reflection coefficient (sigma) -not all capillaries are 100% impermeable to proteins
The Filtration coefficient (Kf)-how leaky the capillary is
What is starlings equation?
Q= Kf (Pcap - Pi) - sigma(∏cap - ∏i)
What are the 3 types of capillaries?
Continuous
Fenestrated
Sinusoid
What are sinusoids?
Sinusoids are a type of capillary that have a wide diameter and have large gaps between endothelial cells
How do different capillaries have different filtration coefficients?
- Continuous capillaries have the lowest Kf as they have no gaps- therefore not leaky
- Fenestrated capillaries have a higher Kf as they have pores/fenestrations -therefore slightly leaky
- Sinusoid capillaries have the highest Kf as they have gaps between endothelial cells and incomplete basement membrane- therefore very leaky
