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Course Code
PHS 4300
Sharon Kennedy
Study Guide

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Renal System
The Filtration System:
- Renal blood flow=1200ml/minute
1. 25% cardiac output:
1-2% medulla
90% cortex (filtration occurs here)
2. 99% (180L filtered/24hrs) absorbed
- 1% (1-1.8L of urine) excreted
- Glomerulus of nephron = filtration UNIT OF KIDNEY
- Inner/outer medulla: kidney remove salt from urine; renal pelvis collect & exit thru ureter to bladder
- Kidneys require a lot of blood ti filter & constantly being profused w/ blood
Glomerular Filtration Rate
(GFR) -
- GFR: fluid volume rate filtered thru glomerular capillaries to Bowman's capsule; Units-ml/min;
- GFR: clinically measured to determine renal function;
Normal GFR range: 60+; Kidney Disease: 15-50; Kidney Failure: <15
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- Children reach adult size in 2 yrs age; Females 85-125 ml/min, Males 97-140 ml/min for 2 kidneys;
- Blacks, male, & younger age have higher GFR cuz higher avg muscle mass & creatinine generation rate
Driving Force for GFR - Glomerular capillary hydrostatic pressure
- Force going into the glomerulu = force things in a positive direction through filter
- Ultrafiltration pressure decreases along the length
of the glomerular capillaries due to high rise in colloid osmotic pressure as 20% filteration occur
- Filtration equilibrium: point on glomerular cappillaries when ultrafiltration pressure fall to 0 &
filtration stops = occur when 20% filtered cuz net forces opposing filtration = forces driving filtration
- Filtration equilibrium existence explains why increases & decreases in renal plasma flow affect GFRi.e.
- Renal plasma rate enters glomerulus affects total amount filtered even if net driving forces favor &
oppose filtration unchanged; renal plasma rate enter glomerulus affects total amount filtered
[Ex: normal adult value = 700 ml/min, GFR = 140 ml/min; RPF = 600 ml/min, filtration equilibriu occurs
when colloid osmotic pressure rises equal outwardly directed forces favoring filtration when 20%
filtered & GRF now only = 120 ml/min]]
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How To Measure GFR:
Characteristics of a Substance Used to Measure GFR:
1. Must be freely filtered
2. Must not be reabsorbed or secreted
3. Must not be synthesized or catabolized by the kidney
4. Must not alter GFR
Substances Used to Measure GFR:
1. Inulin-Gold standard
2. Creatinine-Clinical standard
3. Cystatin C
Measuring GFR Creatinine:
- CCreatinine = GFR; GFR = 
- Requires: 1. 12-24 hr urine collection
2. Mid-point blood sample
3. [Cr] in urine &plasma
a) Creatinine Clearance: Slightly Overestimates GFR
- CIn = GFR Inulin excreted at same rate that its filtered
- CCreatinine > GFR creatinine also secreted by proximal tubules
b) Plasma [Creatinine] Reflects GFR in Steady-State Conditions Due to:
1. Creatinine produced by skeletal muscle at constant rate from creatinine-phosphate;
2. Creatinine excreted mainly by filtration = Ex: GFR X plasma [Cr]
3. Renal excretion = Muscle production
4. Range of normal plasma [Cr] is 50-110 µmol/L
- If kidney function declines, creatinine builds up in plasma
c) Plasma [Creatinine] Reflects GFR in Chronic Kidney Disease (CKD):
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