DEFINITIONS - LETTER R

REABSORPTION - a substance has left the bloodstream and is once again being absorbed into the blood; a substance could be filtered from plasma into the kidney tubules (nephrons) and reabsorbed from the same nephrons - example: glucose is filtered at the kidney but is completely reabsorbed from the renal filtrate such that glucose does not appear in urine

RED MUSCLE FIBERS - these are muscle fibers which have a high myoglobin content, are well vascularized, have plenty of mitochondria and are well set up for aerobic metabolism.  They are sometimes referred to as aerobic, slow twitch fibers.  They have great endurance and are, thus, not easily fatigued.

RENAL FILTRATE - the plasma filtrate which enters the renal tubules (nephrons) under the influence of hydrostatic pressure (blood pressure); the renal filtrate initially has about the same osmolarity as plasma and is composed of plasma minus the large circulating globular proteins which are too large to be filtered into the kidney