Download - Kidney Function and Regulation
SF Biology II 1
Kidney Function and RegulationKidney Function and Regulation
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Renal FiltrationRenal Filtration
• Total body water ~40 litres; • Plasma Vol. ~3 litres). • Filter ~180 litres/day • Daily urine vol. ~ l.5 litres. • Hence conclude that ~95%
is re-absorbed, i.e. conserved.
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Functional unit of the kidneyFunctional unit of the kidney
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Filtration mechanismFiltration mechanism
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Functions of the nephronFunctions of the nephron
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Osmotic gradientsOsmotic gradients
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Countercurrent multiplier (1/2)Countercurrent multiplier (1/2)
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Countercurrent multiplier (2/2)Countercurrent multiplier (2/2)
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Renal Concentration Mechanism — SummaryRenal Concentration Mechanism — Summary
• Loop of Henle as countercurrent multiplier
• Ascending limb actively extrudes Na+, K+
• Hence gradient between limbs (200 mosm)
• AND vertical gradient in medulla
– 300 mosm outside - 1200 mosm inside
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Renin-Angiotensin — SummaryRenin-Angiotensin — Summary
• Fall in NaCl, ECF, ABP …• JGA release of renin…• …catalyses angiotensinogen — AGTI• In lungs AGTI — AGTII
– …release of vasopressin — H2O reabsorption
– …arteriolar constriction — reduced renal blood flow
– …stimulates thirst — H2O intake
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Renin-Angiotensin — SummaryRenin-Angiotensin — Summary
• AGTII stimulates adrenal release of aldosterone…
– …increased reabsorption of Na+ @ renal tubules
– … hence H2O retained (osmotically) in ECF
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ADH/vasopressinADH/vasopressin
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?Possible Examination Topics?Possible Examination Topics
• Pattern/regulation of gut motility• Pancreatic secretion of bicarbonate/enzymes• Digestion/absorption of CHO (vs?) fat• Forces involved in glomerular filtration
– autoregulation
• Role of urea in hypertonicity of medulla• Basic renin-AGT-aldosterone mechanism
– effects on tubular reabsorption
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Urea Recycling — SummaryUrea Recycling — Summary
• Distal tubule and early collecting tubule • NOT permeable to urea or water*• *Vasopressin allow water to move passively• …hence urea is concentrated.• Distal collecting tubule IS permeable to urea• …hence urea diffuses into interstitium…
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Urea Recycling — SummaryUrea Recycling — Summary
• …raising osmotic pressure above tonicity
• …hence water leaves thin ascending limb (passively)
• …hence urea is concentrated in ascending limb
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Urea Recycling — AdvantagesUrea Recycling — Advantages
• Increase in medullary tonicity– allows production of hypertonic urine
• Less water per unit wt of urea excreted
• Both aid water conservation
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EquilibriumEquilibrium