SF Biology II1 Kidney Function and Regulation. SF Biology II2 Renal Filtration Total body water ~40 litres; Plasma Vol. ~3 litres). Filter ~180 litres/day.

SF Biology II 1

Kidney Function and RegulationKidney Function and Regulation

SF Biology II 2

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