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BI6113 Renal function

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Neil Pickles

on 18 October 2013

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Transcript of BI6113 Renal function

Renal function
Dr Neil Pickles

Renal function
Urine formation
Glomerular filtration

Passive process
Glomerular filtrate - ultrafiltrate of plasma
Almost free of proteins – WHY?
Negatively charged molecules less easily filtered
Most filtered protein reabsorbed
Protein excretion < 150 mg/24h

Renal corpuscle
Depends on:
BP difference of
Glomerular capillaries
and hydrostatic pressure in

Glomerular basement membrane
Number of glomeruli

Glomerular filtration rate (GFR)
GFR figures
~120 ml/min 7200 ml/hr
172800 ml/24h
173 L/24h
Urine production is 1-2 L/24h
Ergo - most of filtrate is reabsorbed

Renal control of BP
Glomerular filtrate - plasma without proteins
PCT reabsorbs 60-70% of the filtrate
Most organic nutrients
Active and passive reabsorption of Sodium and other ions
Secretion also occurs in the PCT

Countercurrent multiplication between ascending and descending limbs of loop
Creates osmotic gradient in medulla
Facilitates reabsorption of water and solutes before the DCT
Permits passive reabsorption of water from tubular fluid

Loop of Henle
Final adjustment of urine
Active secretion or absorption
Tubular cells actively resorb Na+ and Cl- in exchange for potassium or hydrogen ions (secreted)

Water and solute loss is regulated by aldosterone and ADH
Sodium ion, bicarbonate, and urea are resorbed
pH is controlled by secretion of hydrogen or bicarbonate ions

Collecting duct
GFR declines with age
Measure urinary excretion of a substance that is completely filtered from blood
Inulin vs. Creatinine

Measuring GFR
GFR measurement
Plasma creatinine:

60-120 µmol/L
Reduction in GFR = increase in creatinine
Up to 50 % red GFR – no significant change
Beyond 50 % red, each further 50 % red = x 2 creatinine
Plasma β2-microglobulin
Completely filtered and reabsorbed
Increased in some inflammatory diseases
More suited for assessing tubular integrity
Cystatin C
Increase = reduction in GFR
Renal drugs
Depress bicarbonate reabsorption in PCT
Excretion of HCO3, Na+
and H2O is increased
Treatment of glaucoma
Reduces intraocular pressure

Carbonic anhydrase inhibitors
Other regulators of renal function
Atrial Natriuretic Peptide (ANP)
Secreted by atrial cardiac myocytes
Decreases renin release
Decreases aldosterone release
Blocks resorption salt and water
Decreases blood pressure

Alcohol - decreases ADH release
Caffeine - increases salt resorption in DCT
Full transcript