Why is XXXX made in the kidney? The kidney functions as a 'critmeter' to regulate the hematocrit.

@entity417 @entity2178 @entity26 @entity1372 @entity1307 @entity177
The normal hematocrit is not a random number, but one that maximizes @entity26 delivery. While the feedback loop wherein tissue @entity26 pressure determines the production of @entity1307 , which further drives the production of red blood cells in the bone marrow, explains how the hematocrit is generated, it does not speak to how the hematocrit is regulated. The regulation of the hematocrit requires the coordination of the plasma volume and the red cell mass. By controlling red cell mass via @entity1307 and plasma volume through excretion of salt and water, the kidney is able to generate the hematocrit. It is hypothesized that the kidney functions as a critmeter by sensing the relative volumes of each component of the blood through the common signal of tissue @entity26 tension. The kidney's unique ability to sense ECF volume through tissue @entity26 signal allows it to coordinate these two volumes to produce the normal hematocrit. Hence, it may be the kidneys ability to report a measure of ECF volume as a tissue @entity26 signal and thus to regulate the hematocrit that establishes it as the logical site of @entity1307 production. The critmeter is proposed to be a functional unit located at the tip of the cortical labyrinth at the juxta-medullary region of the kidney where @entity1307 is made physiologically. Renal vasculature and nephron segment heterogeneity in @entity1372 reabsorption likely provides the anatomical construct to generate the marginal tissue @entity26 pressure required to trigger the production of @entity1307 . The balance of @entity26 consumption for @entity1372 reabsorption and @entity26 delivery is reflected by the tissue @entity26 pressure. This balance hence determines RBC mass adjusted to plasma volume. Factors that affect blood supply and @entity1372 reabsorption in a discordant manner may modulate the critmeter, e.g. @entity2178 . The objective of this work is to describe the hypothesis of the kidney's function as a critmeter, including the anatomical and physiological components, and the role of the renin-angiotensin system in modulating @entity1307 . Clinical examples of the dysregulation of the critmeter may be found in the @entity417 of @entity177 and in @entity417 .
