1 Drugs Acting on the Kidney Dr Alison Ingham Jan 2017 Afferent Arteriole Efferent Arteriole Glomerular Filtration • 3 layers 1) Fenestrated capillary endothelium 2) Glomerular basement membrane 3) Glomerular epithelial cells have fingerlike projections with slit-pores • 100 times more porous than normal capillary membrane • Size (<8nm) and charge important Glomerular Filtration
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• 100 times more porous than normal capillary membrane
• Size (<8nm) and charge important
Glomerular Filtration
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• GFR = 170L.day-1 (120 ml.min-1)
• Urine = 1L.day-1
• Therefore > 99% of filtrate is reabsorbed
ALMOST ALL ENERGY CONSUMED IS USED IN ACTIVE REABSORPTION
Glomerular Filtration Juxtaglomerular apparatuus
Juxtaglomerular apparatus
• Specialised segment of afferent arteriole • Contains renin secreting cells • Macula densa in the wall of the distal tubule • Renin is released in response to:-
1) sympathetic stimulation 2) decreased wall tension in afferent arteriole 3) decreased Na+ & Cl- delivery to macula densa
Renin-angiotensin system
Angiotensinogen Renin
Angiotensin I ACE vasoconstriction Angiotensin II ADH aldosterone
• DA1 receptors on luminal and basal membranes of PCT
• Inhibit Na+K+ATPase causing natiuresis • In low dose may decrease renal vascular
resistance and increase RBF • No evidence
Theophyllines
• Weak diuretic • Decreases Na+ reabsorption • Probably act by increasing cAMP in renal
tubular cells • Cause hypokalaemia
Other Bits for the Final
• Contrast induced nephropathy: – Fluids for 12 hours before – There may be some evidence for N-acetylcysteine – No evidence for sodium bicarbonate – Modern contrasts less renal toxic
• No evidence for use of dopamine, loop diuretics or mannitol for preventing AKI