L31: Glomerular function Flashcards by Danelle Rens

what determines glomerular filtration

filtration barrier
renal blood flow
driving forces

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what is filtration

movement of plasma from the glomerular capillaries (blood) into the glomerular capsule (nephron)

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what is freely filtered

small molecules

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what is not filtered

large molecules

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what % of the cardiac output it detected to the kidneys

renal blood flow is 20% of cardiac output per minute

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why does the kidneys have a high flow right

high flow right for filtration rather than metabolism

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what does a decrease in flow rate cause

a decrease in filtration

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what is the 2 driving forces of glomerular filtration

hydrostatic pressure
colloid osmotic pressure

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what is hydrostatic pressure

pressure due to the volume of fluid/water
where more fluid = more pressure
pushes fluid away

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what is colloid osmotic pressure

osmotic pressure due to large proteins
proteins acts like water magnets
pulls fluid towards the protein

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what is a positive pressure

favors filtration = driving movement of fluid from the glomerular capillaries into the capsular space

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what is a negative pressure

opposes filtration = driving movement of fluid from the capsular space into the glomerular capillaries

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what is glomerular hydrostatic pressure (GHP)

pushing pressure from water (plasma) in the capillaries
+50 mmHg

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what is blood colloid osmotic pressure (BCOP)

pulling pressure from plasma proteins (albumin)
-25 mmHg

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what is capsular hydrostatic pressure (CsHP)

pushing pressure from fluid (filtrate) in the capsular space
-15 mmHg

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what is capsular colloid osmotic pressure (CsCOP)

pulling pressure from protein in capsular space
proteins however aren’t normally found in the space unless your kidneys aren’t functioning properly
+ 0mmHg

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what determines the net filtration pressures

the 4 pressures
- GHP
- BCOP
- CsHP
- CsCOP

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what is the net filtration pressure

10 mmHg

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what is filtration fraction

20% of the plasma which enters the kidneys (renal plasma flow) is filtered though the glomeruli into the nephrons

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what % of plasma is filtered

20% of the RPF is filtered into the
from glomerular capsule to nephron

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what % of plasma is not filtered

80% of plasma remains in the glomerular capillaries (blood)
from the efferent arteriole to peritubular capillaries

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what is the glomerular filtration rate

the amount of plasma filtered per minute or day by the kidneys

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what is the GFR determined by

renal plasma flow x filtration fraction

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what is the average range of GFR

125 - 180 mL/min

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how much urine do you produce per day

1.5L of urine per day

how much control is there over GFR

tightly regulated

when does the GFR decline

declines slowly from age 30

how is RDF and GFR measured

RDF and GFR cannot be measured directly so the renal clearance of substance with particular characteristics is used to estimate them

what is the renal filtered load

the amount of a particular substance (solute) in the plasma is filtered per unit of time (per min/hour/day)

how much blood and plasma do the kidneys receive

renal blood flow = 20% renal plasma flow = 625mL/min

what proportion of the plasma which enters the kidneys (renal plasma flow) is filtered

filtration fraction = 20% of renal plasma flow

how much plasma is filtered per min

glomerular filtration rate = 125 mL/min

how much of a substance in the plasma is filtered per min

renal filtered load

what is renal clearance

clearance is the volume of plasma that is cleared of a substance by the kidneys per unit time

what can clearance be used for

- understand and quantify how a substance is handled by the kidneys - estimate glomerular filtration rate = creatinine or inulin - estimate renal plasma flow = PAH

what is the clearance of creatinine and inulin

- freely filtered - not reabsorbed - not secreted - all filtered is excreted in the urine

what is the clearance of medications and toxins

- freely filtered - entirely secreted - not reabsorbed - all in blood is excreted in urine

what is the clearance of PAH an indication of

all plasma flowing through the kidneys per min

what is the clearance of glucose

- freely filtered - not secreted - fully absorbed in the PCT - none excreted in urine

what is the clearance of sodium

- freely filtered - not secreted - almost fully reabsorbed in most parts of nephron - small amount excreted in urine

what does a substance's clearance have to be in order to be used to measure GFR

1. be freely filtered 2. not be reabsorbed from the tubule 3. not be secreted into the tubule

what does GFR mean in a clearance context

this means that all the plasma that is filtered each min will be cleared from the substance

what 2 substances meet the requirements to measure GFR

1. inulin 2. creatinine

what is inulin and where can it be found

- polysaccharide that is not metabolized by the body - not found in the body = must be injected

what is creatinine and where can it be found

- waste product produced by muscles - already in the body

what is ideal for clinically estimating GFR

measuring the clearance of creatinine

what does a substance's clearance have to be in order to be used to measure RPF

1. all be filtered and/or secreted into the tubule 2. not be reabsorbed from tubule

what does RPF mean in a clearance context

this means that all of the plasma that passes through the kidneys each min will be cleared of the substance

what substance meets the requirements to measure RPF

PAH

what is PAH and where can it be found

- small molecule - not found in the body - freely filtered and fully secreted from the plasma of the peritubular capillaries into the PCT

what is ideal for clinically measuring RPF

the clearance of PAH

what can clearance measure

clearance can be measured for all substances that can be detected in the plasma and urine

what can clearance be used for to understand

understand and quantify a substance that is handled by the kidneys

what does it mean when a substance has low clearance

shows substance is mostly/fully reabsorbed back into the plasma because the body needs it

what does it mean when a substance has a high clearance

shows substance is not reabsorbed and may also be secreted from plasma because the body does not need it

what can plasma creatinine concentration be an indicator of

kidney function

what is the concentration of creatinine when both kidneys are working

low

what is the concentration of creatinine when if only one kidney is working

still relatively low

what happens when GFR is less than 25 mL/min

plasma creatinine concentration increases as the kidneys ability to clear products from blood has been reduced

what happens when you have kidney failure

GFR <15 mL/min as the ability to clear creatinine has been greatly reduced

L31: Glomerular function Flashcards

(60 cards)