Re: Is it true, is the compsition of tears blood, without the red blood cells?

Diane:


     Thanks for the question.  Like many broad descriptions, there is a 
kernel of truth to this, but the statement is false.  A true statement 
would be that tears contain some of the same small and macromolecular 
components as plasma (Which is what blood without red blood cells is 
called), most of the components in plasma are absolutely not present in 
tears.  

     Tears are primarily made up of three layers, consisting of the mucous 
layer, the aqueous layer and the lipid layer, each of which aids in 
lubrication and cleaning of the eye.  These components are made by 
specialzed glands in the eye and they also contain macroglobulins, sugars, 
and salts, all of which are found in plasma.  
     However, plasma consists of fluid, and a collection of several 
different cell types (White blood cells) including T cells, B cells, 
platelets etc. etc., none of which are found in tears at any appreciable 
level.  Plasms is generally considered to be one of the most complex 
biological medium on Earth consisting of thousands of small molecule 
components and tens of thousands of different proteins spanning a 
concentration range of >10^12.

A great review of tears and plasma can also be found on Wikipedia at the 
following addresses:

Tears: http://en.wikipedia.org/wiki/Tears

Blood Plasma: http://en.wikipedia.org/wiki/Blood_plasma

Thanks for your time.