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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.
SF Biology II 9
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
SF Biology II 12
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
SF Biology II 13
Renin-Angiotensin — SummaryRenin-Angiotensin — Summary
• AGTII stimulates adrenal release of aldosterone…
– …increased reabsorption of Na+ @ renal tubules
– … hence H2O retained (osmotically) in ECF
SF Biology II 15
?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
SF Biology II 16
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…
SF Biology II 17
Urea Recycling — SummaryUrea Recycling — Summary
• …raising osmotic pressure above tonicity
• …hence water leaves thin ascending limb (passively)
• …hence urea is concentrated in ascending limb
SF Biology II 18
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