Flashcards in Biochemistry Renal Function Deck (31)
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• Glomerular function tests
o Urea
o Creatinine
o eGFR
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Functions of the kidney
Excretion of metabolic waste products
Water and solute homeostasis
Synthetic activity
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Synthetic activity of the kidney
• Renin
• 1,25 (OH)2 vit D
• Erythropoietin
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Inulin
gold standard renal function test
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Glomerular filtration Rate (GFR) Definition
The quantity of glomerular filtrate formed each minute in all nephrons of both kidneys
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GFR depends
• Number of functioning nephrons
• Glomerular function (acute)
• Intra-capillary pressure (shock)
• Tubular luminal pressure (BPH – outflow block)
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Proximal Tubule:
• Bulk reclamation of solutes
o 70% Na, K, Ca, Cl
o 100% HCO3-, Glucose, Urate, Amino Acids
• Isosmotic reabsorption of water (70%)
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High glycosuria: 2 causes
1. Renal glomerular disease - High glucose blood levels
2. Renal tubular disease - Defect in renal
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Counter-current multiplication →
• Active
• Loop of Henle
• Dilutes urine
• Generates hypertonic medulla
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Counter-current exchange →
• Passive
• Distal tubule and collecting duct
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Distal Tubule
• Homeostatic solute adjustment
→ Sodium – hydrogen exchange
→ Sodium – potassium exchange
• Isosmotic water reabsorption
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Renin-aldosterone system: Triggers
Low arterial pressure (via carotid sinus detection)
Low sodium intake
Low renal blood flow
High potassium –promotes sodium potassium exchange (potassium excretion)
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Renin-aldosterone system: Detection of stimuli at
Kidney – juxtaglomerular apparatus
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Renin-aldosterone system: Triggers release of
Renin
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Renin-aldosterone system: Renin pathway
Renin substrate stimulates Angiotensin I (inactive)
Angiotensin I stimulates Angiotensin II release
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Renin-aldosterone system: Angiotensin II action
Stimulates thirst
Causes Vasoconstriction
Aldosterone secretion
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Renin-aldosterone system: Vaso-constriction causes
Increased perfusion pressures
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Renin-aldosterone system:Aldosterone action
Renal sodium and water retention
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Renin-aldosterone system: Aldosterone secretion
High potassium
Angiotensin I
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Renin-aldosterone system: Inhibition of R-A-A
Increased perfusion pressure
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Antidiuretic Hormone: Stimulants
• Drugs e.g. opiates, chlorpropamide
• Stress e.g. pain and nausea
• Decreased blood volume (stretch receptors and baroreceptors)
• Increased plasma osmolality
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Antidiuretic Hormone: Stimulants act on the
• Hypothalamus – Supra-optic and Para-ventricular nuclei
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Antidiuretic Hormone: Stimulant of hypothalamus
ADH release
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Antidiuretic Hormone: ADH action on the kidney
Increased water permeability
Causing increased water reabsorption and decreased plasma osmolality (negative feedback)
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Antidiuretic Hormone: Relying on ADH solely?
Reabsorb water and cause hyponatraemia – decreases osmolaity
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Urea – breakdown of proteins increases
o Poor nutrition = urea is low (conserve proteins)
o Gastrointestinal bleed – urea increases as globulin presence and so urea increases
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Glomerular Function Tests →
Serum creatinine concentration proportional to 1/GFR
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Direct estimates of GFR:
Measured Creatinine Clearance
CCL = Urine [creatinine] x (Urine volume/collection time)
Serum [creatinine]
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Indirect estimates of GFR:
eGFR
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eGFR
Creatinine production rate is related to muscle mass, which can be estimated from age and sex
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