Hi Phil:

> Chyme does not enter the kidneys, urine does.

Urine does not enter the kidneys - it is produced in and excreted from the 
kidneys....... Urea (which is what you mean) is taken from the blood, 
though: http://kidney.niddk.nih.gov/kudiseases/pubs/yoururinary/

"The urinary system removes a type of waste called urea from your blood. 
Urea is produced when foods containing protein, such as meat, poultry, and 
certain vegetables, are broken down in the body. Urea is carried in the 
bloodstream to the kidneys."

So you want to know what the
> pH of the urine is when it enters the kidneys, not the pH of the chyme. So
> to understand the acidification and buffering process, one would focus
> more
> on the kidneys and urine than the stomach and chyme.

No I know that chyme does not enter the kidney - it goes from the stomach
into the intestines. I am trying to follow the food trail so to speak....

I don't understand how food (or chyme which enters the blood through the
intestines) which is a certain pH (it is regulated by the stomach first and
then the pancreas [by using sodium bicarbonate]) can have a profound effect
on the blood plasma pH.

BUT you seem to say that the foods that make up the chyme, even though they
may be of one pH value, will have another pH value *effect* on the blood
plasma?

How and when during the food trail, does that happen?

I understand that blood plasma has differing levels of pH and is regulated
by the kidney in different ways including using phosphorous from the bones
if it is otherwise unavailable (where, then, is the usual site of 
availability? ...I read somewhere that the intestines
regulate the uptake of calcium depending on the pH of the blood...?)

Marilyn