Subject: Explain osmolarity, osmotic pressure, colloid osmotic pressure

I am studying to be a paramedic and the concepts of osmolarity, osmotic 
pressure, colloid osmotic pressure are very confusing for me. They are all 
important in 'Starling's Law of the Capillaries'. I underatnd the basic idea 
(amnt of pressure needed to stop osmosis, etc.) But the usage of the terms is 
hard for me to grasp. For example, if there is an increase in the number of 
sodium ions in a cell this would lead to what? The possible answers could be: 
an increase in osmotic pressure; a decrease in osmotic pressure; an increase in 
colloid pressure; a decrease in colloid pressure. I would say a decrease in 
colloid pressure because sodium ions are colloids and the pressure resisting 
osmosis would decrease (water would be pulled in, not resisted). Is this right? 

The law of the cappillaries is full of such terms: Blood colloidal osmotic 
pressure, Interstitial fluid hydrostatic pressure, etc, etc, etc. I can't 
figure out which way is which! HELP! and Thanks!!!

Re: Explain osmolarity, osmotic pressure, colloid osmotic pressure