Buffers

-prevent a change in pH when H+ ions are added to or removed from a solution.

- are most effective within 1.0 pH unit of the pK of the buffer (i.e., in the linear portion of the titration curve).

Table 5-7. Summary of Hormones that Act on the Kidney

Hormone

Stimulus for Secretion

Time Course

Mechanism of Action

Actions on Kidneys

PTH

1 plasma [Ca2+]

Fast

Basolateral receptor Adenylate cyclase cAMP -> urine

I phosphate reabsorption (proximal tubule) T Ca2+ reabsorption (distal tubule) Stimulates la-hydroxylase (proximal tubule)

ADH

T plasma osmolarity I blood volume

Adenylate cyclase cAMP

(Note: Vi receptors are on blood vessels; mechanism is Ca2+-IP3)

T H20 permeability (late distal tubule and collecting duct principal cells)

Aldosterone

I blood volume (via renin-angiotensin II) T plasma [K+]

Slow

New protein synthesis

T Na+ reabsorption (distal tubule principal cells) t K+ secretion (distal tubule principal cells)

T H+ secretion (distal tubule a-intercalated cells)

ANF

T atrial pressure

Fast

I Na+ reabsorption

Angiotensin II

1 blood volume (via renin)

Fast

T Na+-H+ exchange and HC03-reabsorption (proximal tubule)

ADH = antidiuretic hormone; ANF = atrial natriuretic factor; cAMP = cyclic adenosine monophosphate; cGMP = cyclic guanosine monophosphate; GFR = glomerular filtration rate; PTH = parathyroid hormone.

ADH = antidiuretic hormone; ANF = atrial natriuretic factor; cAMP = cyclic adenosine monophosphate; cGMP = cyclic guanosine monophosphate; GFR = glomerular filtration rate; PTH = parathyroid hormone.

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