Latest / The food files / The Renal Clearance Matrix: Decoding GFR, RPF, and the Diuretic Trap

Transcript

The Renal Clearance Matrix: Decoding GFR, RPF, and the Diuretic Trap · The food files

• 0:00
  Speaker 2: Welcome back everyone.
• 0:01
  Speaker 1: We're going to restart this podcast now and we're hopefully
• 0:04
  you're excited, so we'll help you folks in the USME
• 0:09
  and we've got a different formats, so hopefully this will
• 0:11
  help your guide to the important physiological concepts needed for
• 0:15
  medical exams. Today, we're going to break down the renal
• 0:17
  clearance matrix and kidney physiology. We will cover how the
• 0:21
  glomerulist filters blood using Starlin forces, how to calculate GFR
• 0:25
  and RPF, and how the five main classes of diuretics
• 0:28
  work a different parts of the nephron. The glomular filtration
• 0:32
  is controlled by starline forces. The net pressure pushing fluid
• 0:36
  out of the glomular capillaries is about ten millivai hg.
• 0:40
  Speaker 2: This comes from glomular.
• 0:44
  Speaker 1: Capullary heterstronic pressure minus Bowman's capsule pressure and the rising
• 0:49
  on contic pressure in the capillary. The kidney uses autoregulation
• 0:53
  to keep GFR steady even when blood pressure changes. GFR
• 0:57
  is best measured using its inulin clearance. Because annuline is
• 1:01
  frequently is freely filtered out but neither reabsorbed nor secreted.
• 1:06
  The formula is GFR equals U underscore anuline times v
• 1:12
  over p underscore anuline. Creatin is used clinically as a
• 1:15
  close estimate. Renal plasma flow RPF is measured with peramino
• 1:21
  hipioic acid pH, which is almost completely removed in one
• 1:25
  pass through the kidney. Filtration fraction FF is GFR divided
• 1:29
  by RPF. Renal plasma flow normally about twenty percent.
• 1:34
  Speaker 2: Here it gives me a clinical example.
• 1:36
  Speaker 1: Patient has an annuline clearance of one hundred and twenty
• 1:38
  five millionary mn and pH clearance of six twenty five
• 1:42
  that gives GFR equals one twenty five mL, RPF equals
• 1:48
  g six P equals six two five, and constriction of
• 1:52
  the afferent artibile lowers both GFR and RPF equally FERN
• 1:57
  arterial constriction raise FF. Let's look at the different diuretics
• 2:03
  in where they act. Carbonic anhydrase inhibitors like ctlzolamide work
• 2:08
  in the proximal tubule and they're reduced by carbonate reabsorption
• 2:12
  and cause mild loss of sodium with menabolic acidosis. Number
• 2:17
  two is loop diuretics, like fluoressumide. They block the NAK
• 2:21
  two cl cooetransporter in the thick ascending limb. They cause
• 2:25
  strong sodium loss, increase calcium excretion, and activate the rendin
• 2:29
  angil Tenson system. Thioside diuretics block NaCl sodium calcium and
• 2:38
  the distal convoluted tube tubule promote sodium loss while increasing
• 2:42
  calcium reabsorption and are often used for high blood pressure.
• 2:46
  Potassium sparing diuretics like spirinal lactone or amiloride work in
• 2:51
  the collecting duct to say potassium or removing sodium, and
• 2:54
  osmodic diuretics like banitol increase osmolarity in the tubule and
• 2:59
  prevent water absorption. These drugs can cause side effects like
• 3:03
  low potassium or changes in blood volume. The effect GFR. Well,
• 3:08
  here's a couple of practice questions for you. Anuline clearance.
• 3:15
  Speaker 2: Is used to.
• 3:17
  Speaker 1: Measure glomular old fratrician filtration rate because anuline is.
• 3:24
  Speaker 2: Let's see the three options.
• 3:25
  Speaker 1: You have E freely filtered and completely reabsorbed, B freely
• 3:29
  filtered and neither reabsorbed nor secreted, or C secreted by
• 3:33
  the proximal tube. If you said B freely filtered and
• 3:37
  neither reabsorbed nor secreted, you're right. Imagine the kidney as
• 3:41
  a filter. Anuline is like a perfect test particle. It
• 3:44
  passes easily through the filter into the urine, and the
• 3:46
  kidney does not take any of it back or aunt
• 3:48
  extra to the urine. Because of this, the amount of
• 3:51
  anuline in the urine exactly shows how much fluid was filtered.
• 3:54
  That makes anuline the gold standard for measuring GFR.
• 3:59
  Speaker 2: Number two two.
• 4:00
  Speaker 1: A patient has a GFR of one twenty and an
• 4:03
  RPF of six hundred. The filtration fraction is what a
• 4:07
  zero point one five, B zero point two oh or
• 4:10
  C zero point two five.
• 4:15
  Speaker 2: If you said zero point two oh, you're right.
• 4:17
  Speaker 1: Simply divide GFR by RPF one twenty over six hundred
• 4:20
  you get twenty percent.
• 4:22
  Speaker 2: This is a normal.
• 4:22
  Speaker 1: Value, meaning one fifth of the plasma flowing through the
• 4:25
  kidneys gets filtered. And finally, which diuretic inhibits the NK
• 4:34
  NAAK two C l CO transporter The thickest sending limbit
• 4:38
  increases ubinary calcium excretion. Is it a fizide B loop
• 4:44
  diuretics or C carbon carbonic anhydrates inhibitors? If you said
• 4:52
  B loop diuretics, you are right loop. Diuretics such as
• 4:55
  frusamide block a special transport protein in the loop of
• 4:58
  Henley that normally pulls sodium, potassium, and chloride back.
• 5:02
  Speaker 2: Into the blood.
• 5:03
  Speaker 1: When blocked, a lot of sodium stays in the urine
• 5:06
  because of how the tubule works. This also makes the
• 5:08
  kidney lose more calcium in the urine, unlike thiasades thiosides,
• 5:12
  which save calcium. And finally, your exam tip on renal
• 5:17
  physiology questions, but get what the clearance formulas annual in
• 5:20
  for GFR, pH, for RPF and starling forces to determine
• 5:24
  directional changes in the GFR and FF map each diuretic
• 5:28
  to its exact nephron segment and predict ectro electrolyte and
• 5:32
  acid based consequences. Also integrate volume status effects on renting
• 5:37
  angotenson aldesterone activity. These connections frequently appear in multi step
• 5:43
  clinical vignettes linking kidney, heart and lung issues. Hopefully you
• 5:48
  enjoy our comeback here to the USMBLEE preparation exam. We're
• 5:52
  trying to make some improvements on the podcast and hopefully
• 5:55
  it worked out for you.