Renal Phys 4

• the volume of plasma cleared of substance S per unit time

  the renal plasma clearance of a substance (RPC(s))
• what is U(s)?

  the urine concentration of S (mg/mL)
• what is V?

  urine volume per unit time (mL/min)
• what is P(s)?

  plasma concentration of S (mg/mL)
• renal plasma clearance

  RPC equation on bottom left

  
• the concept of renal clearance


  image:

  
• RPC measurements can be used to determine how well the _______ are functioning

  kidneys
• for substances that are freely filtered but NOT secreted nor reabsorbed,

  RPC = GFR

  ex: inulin
• RPC(inulin) = GFR ~ 125 mL/min
• for substances that are freely filtered and 100% secreted but NOT reabsorbed,

  RPC = renal plasma flow

  ex: PAH
• RPC(PAH) = RPF ~ 625 mL/min
• when RPC > GFR

  substance undergoes net secretion
• RPC < GFR

  substance undergoes net reabsorption - or is partially filtered (ex: calcium)
• renal plasma clearance of creatine


  - a more practical, less invasive way of determining GFR

  - produced by muscles at a constant rate

  freely filtered

  - not reabsorbed

  - slightly secreted (~10%)

  - RPC(Cr) = true GFR

  - P(Cr) x GFR = U(Cr) x V
• stretch-induced sensory afferent signaling to CNS

  micturition (urination)
• low parasympathetic input = relaxed detrusor muscle


  bladder filling
• high sympathetic input = contracted (closed) internal sphincter


  bladder filling
• stimulated somatic motor input = closed external sphincter


  bladder filling
• high parasympathetic input = contracted detrusor muscle


  bladder emptying
• low sympathetic input = relaxed (opened) internal sphincter


  bladder emptying
• inhibited somatic motor input = opened external sphincter


  bladder emptying
• micturition muscle vs innervation