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LSS Urinary System > 3 Renal Blood Flow and Glomerular Filtration > Flashcards

3 Renal Blood Flow and Glomerular Filtration Flashcards

1
Q

Q: What is the glomerulus?

A

A: knot of capillaries surrounded by bowmans capsule

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2
Q

Q: Define glomerular filtration. An abrupt fall in glomerular filtration is? What can lead to reduced glomerular filtration?

A

A: formation of an ultrafiltrate of plasma in the glomerulus

renal failure

abnormalities in renal circulation

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3
Q

Q: Describe the energy process of glomerular filtration. What is the result of the process? Define.

A

A: fluid is ‘driven’ through the semipermeable (fenestrated) walls of the glomerular capillaries into the Bowmans capsule space by the hydrostatic pressure of heart

PASSIVE

A clear fluid (ultrafiltrate), completely free from blood and proteins, is produced containing electrolytes and small solutes = ‘primary urine’

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4
Q

Q: What is the filtration barrier in glomerular filtration? Describe its permeability. (5)

A

A: The filtration barrier (fenestrated endothelium of capillaries and semipermeable Bowman’s capsule) is highly permeable to:

  • fluids
  • small solutes (these are “freely filtered”: same concentration in filtrate and plasma)

But impermeable to:

  • cells
  • proteins
  • drugs etc carried bound to protein
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5
Q

Q: What does it mean to be freely filtered? Example. Do all substances undergo?

A

A: passes through without changing concentration (same concentration in filtrate and plasma)

small solutes in glomerular filtration

no, only those that soluble

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6
Q

Q: Draw a labelled diagram showing glomerula filtration.

A

A: REFER

renal input from renal artery-> afferent arteriole-> glomerulus

=> glomerular filtration and production of primary urine (freely filtered) -> enters tubule and undergoes reabsorption (back into blood) and secretion (enter urine tubule) => form final urine (excreted)

efferent arteriole= renal vein and ureter

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7
Q

Q: How does the concentration of a solute vary from becoming primary urine and the final excreted urine product? What determines the final concentration of a solute? (3) Equation?

A

A: solute concentration is the same in urine and in plasma (freely filtered) but concentration may be altered further down

reabsorption, secretion (blood into urine) and volume of water in urine

amount excreted= amount filtered +amount secreted -amount absorbed

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8
Q

Q: Why does reabsorption occur to primary urine?

A

A: retain valuable substances eg salts eg Na, K

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9
Q

Q: Which pressures are involved in glomerular filtration? (3) Main? What do they determine together? Equation.

A

A: Driving force:

hydrostatic pressure*** in glomerular capillaries (due to blood pressure) (Pgc)

Opposing pressures:

hydrostatic pressure of tubule (Pt)

osmotic pressure of plasma proteins in glomerular capillaries (πgc) (pi gc)

Together these determine the net ultrafiltration pressure (Puf)

Puf = Pgc - Pt - pi gc

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10
Q

Q: What’s the unit for ultrafiltration pressure? Average values?

A

A: mmHg

Ultimately there is a net ultrafiltration pressure of 10-20mmHg

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11
Q

Q: How do you calculate Glomerular Filtration Rate?

A

A: GFR = Puf x Kf

Where Kf is an ultrafiltration coefficient (membrane permeability and SA available for filtration)

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12
Q

Q: What can result in GFR imbalance? Examples (2).

A

A: changes in filtration forces or Kf

Kidney diseases may reduce number of functioning glomeruli = reduced surface area = reduces Kf

Dilation of glomerular arterioles by drugs/hormones will increase Kf

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13
Q

Q: What determines GFR aside from pressures? (2) What represents this?

A

A: membrane permeability, SA

Kf (co efficient)

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14
Q

Q: What is GFR? In terms of nephrons? Loss of nephrons results in? GFR is an index of?

A

A: Glomerular Filtration Rate

The amount of fluid filtered from the glomeruli into the Bowmans capsule per unit of time (ml/min)

Sum of filtration rate of all functioning nephrons

Loss of nephrons = loss of surface area = fall in Kf = fall in GFR

Index of kidney function

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15
Q

Q: What is the role of renal blood flow RBF? (3) What is the approx value of RBF? RPF? FF? GFR equation? Range?

A

A: Delivers oxygen, nutrients and substances for excretion

Renal blood flow (RBF) = approx 1L/min (1/5 of cardiac output)

Renal plasma flow (RPF) = approx 0.6L/min (60% of blood)

Filtration fraction (FF) = 0.2 (ratio between RPF and amount of filtrate filtered by glomerulus, which is normally 20%- rate that blood plasma enters kidneys)

Glomerular filtration rate (GFR) = RPF x FF and is approx (volume of filtrate formed in 1 minute) – is kept within a narrow range

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16
Q

Q: What is the normal value for GFR? Someone with kidney dysfunction? What is it subject to? by? (2) Result?

A

A: 120mL/min

30-40

physiological regulation

achieved by neural or hormonal input to the afferent/efferent arteriole

resulting in changes in Puf

17
Q

Q: List 5 factors affecting GFR.

A

A: Glomerular capillary pressure (Pgc)

Plasma oncotic pressure (pi gc)

Tubular pressure (Pt)

Glomerular capillary surface area (part of Kf)

membrane permeability (part of Kf)

18
Q

Q: Give an example for when autoregulation would be needed for GFR? What’s the mechanism? Result?

A

A: when exercising and heart rate and pressure go up-> would naturally dilate blood vessels inc afferent arteriole to nephron-> MYOGENIC MECHANISM kicks in to counteract the dilation and constrict the blood vessel (increases resistance)

GFR remains constant even when blood pressure and therefore hydrostatic pressure is raised

19
Q

Q: How would these factors affect GFR?

Severe haemorrhage

Obstruction in nephron tubule

Reduced plasma protein concentration

Small increase in blood pressure

A

A: decrease

decrease

increase (decreased oncotic pressure)

same

20
Q

Q: What is measured to determine someone’s renal function? What is this? Quantitatively?

A

A: renal clearance

As substances in the blood pass through the kidney they are filtered to different degrees. The extent to which they are removed from the blood is called clearance.

Clearance is the number of litres of plasma that are completely cleared of the substance per unit time.

21
Q

Q: What’s the equation for renal clearance? Unit?

A

A: C = U x V
…………———
……………..P

mL/min

U = concentration of substance in urine
P = concentration of substance in plasma
V = rate of urine production
22
Q

Q: How can GFR be estimated using clearance? Molecule? Properties? (4) Gives clearance value of? Practically?

A

A: If a molecule is freely filtered and neither reabsorbed nor secreted in the nephron then the amount filtered equals amount excreted. Thus GFR can be measured by measuring clearance of this molecule

Inulin:

  • a plant polysaccharide
  • freely filtered and neither reabsorbed nor secreted
  • not toxic
  • measureable in urine and plasma

120mL/min which is GFR for average adult

But not found in mammals so needs to be transfused etc = difficult therefore use an endogenous molecule with a similar clearance

23
Q

Q: How is GFR practically measured? Properties? (5) 2 ways of interpretting?

A

A: GFR in humans is normally estimated from creatinine clearance.

Creatinine:

  • a waste product from creatine in muscle metabolism
  • amount of creatinine released is fairly constant
  • if renal function stable, amount creatinine in urine is stable
  • freely filtered
  • not excreted or absorbed
  • low values of creatinine clearance may indicate renal failure
  • high plasma creatinine may indicate renal failure (more simple method)
24
Q

Q: Why would someone be sent for creatinine clearance measuring? (3)

A

A: -suspected renal problems

  • when prescribing certain drugs when drug dose depends on glomerular filtration
  • > particularly problematic for drugs that are dependant on clearance through kidney rather than liver metabolism or one with a narrow therapeutic window
25
Q

Q: What does having a narrow therapeutic window mean?

A

A: can very easily over dose

26
Q

Q: Sodium has renal clearance value of 1.0mL/min. What can you interpret from this?

A

A: despite being freely filtered-> lots of it is reabsorbed from urine back into plasma

27
Q

Q: How is renal plasma flow RPF measured? Normal value? Explain.

A

A: by PAH (Para aminohippurate) clearance = 625ml/min

Freely filtered as normal and remaining 80% that wasn’t filtered is excreted into the urine (all the PAH is removed from the plasma) IN ONE PASS OF THE KIDNEY, thus its clearance equals the renal plasma flow

28
Q

Q: What is a fall in GFR indicative of? What happens if GFR falls? What can be fatal? When does this need to be taken into account?

A

A: A fall in GFR is the cardinal feature of renal disease

If GFR falls, excretory products will build up in the plasma.

Excretion of many other substances will also be impaired in renal failure - including some drugs. This needs to be taken into account when calculating drug doses - PHARMACOKINETICS.

29
Q

Q: Who has a naturally higher creatinine concentration? (2)

A

A: muscular people

if you had a protein drink

LSS Urinary System (7 decks)

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