1 Table Filtration, Reabsorption, and Excretion Rates of Different Substances by the Kidneys GlucoseUrea Amount FilteredAmount ReabsorbedAmount Excreted% of Filtered Load Reabsorbed glucose Bicarbonate (mEq/day)4,3204,3182>99.9 Sodium (mEq/day)25,56025, Chloride (mEq/day)19,44019, Potassium (mEq/day) urea Creatinine (g/day) Table 27-1 Reabsorption: > large amounts are filtered >for many substances, large amounts are reabsorbed, so little is excreted

2 Reabsorption across tubular epithelial cells Brush border Figure 27-1 PC=proximal convoluted DC=distal convoluted BB=brush border

Brush border Scanning EM of proximal tubule cell 3

4 Figure Pressures favoring reabsorption by bulk flow into peritubular capillaries

5 Figure 27-2 Sodium reabsorption in the proximal tubule

6 Figure 27-3 Version from the Silverthorn text Secondary active transport

7 Glomerulus Bowman’s capsule Beginning of proximal tubule Peritubular capillary Na + (active) H 2 O (osmosis) Na + (active) H 2 O (osmosis) Passive diffusion of urea down its concentration gradient 44 ml of filtrate 125 ml of filtrate End of proximal tubule = Urea molecules Figure Page 534 Passive reabsoprtion of some substances

8 Figure 27-4 Importance of transport maximaSubstance Transport Maximum Glucose 375 mg/min Phosphate 0.10 mM/min Sulfate 0.06 mM/min Amino acids 1.5 mM/min Urate 15 mg/min Lactate 75 mg/min Plasma protein 30 mg/min Transport Maximums for Substances That Are Actively Secreted. Substances that are actively secreted Substance Transport Maximum Creatinine 16 mg/min Para-aminohippuric acid 80 mg/min

9 Silverthorn Figure Overview

10 Figure 27-6 Different segments are specialized for different things: Proximal Tubule: REABSORBTION, secretion

11 Figure 27-7

12 Figure 27-8 We’ll save loop of Henle for next time

13 Figure Distal tubule and collecting duct: regulated reabsorption and secretion

14 Figure (a wonderful figure; pay attention to: Glucose and amino acids Na+, K+, Cl- Urea Inulin and creatinine PAH

15 HormoneSite of ActionEffects AldosteroneCollecting tubule and duct↑ NaCl, H 2 O reabsorption, ↑ K + secretion Angiotensin IIProximal tubule, thick ascending loop of Henle/distal tubule, collecting tubule ↑ NaCl, H 2 O reabsorption, ↑ H + secretion Antidiuretic hormone Distal tubule/collecting tubule and duct↑ H 2 O reabsorption Atrial natriuretic peptide Distal tubule/collecting tubule and duct↓ NaCl reabsorption Parathyroid hormone Proximal tubule, thick ascending loop of Henle/distal tubule↓PO reabsorption, ↑ Ca ++ reabsorption Table 27-3 Key hormones involved in the regulation of reabsorption (we’ll focus on aldosterone and antidiuretic hormone during the next two classes)

16 Silverthorn Figure For a substance that is freely filtered, but not reabsorbed or secreted:

17 Figure 27-19

18 Silverthorn Table 19-2

19 Silverthorn Figure Overview Clearance: or SubstanceClearance Rate (ml/min) Glucose 0 Sodium0.9 Chloride1.3 Potassium12.0 Phosphate25.0 Inulin125.0 Creatinine140.0

20 TermEquationUnits Clearance rate (C s ) ml/min Glomerular filtration rate (GFR) Clearance ratio None Effective renal plasma flow (ERPF) ml/min Renal plasma flow (RPF) ml/min Renal blood flow (RBF) ml/min Excretion rateExcretion rate = U s × Vmg/min, mmol/min, or mEq/min Reabsorption rate mg/min, mmol/min, or mEq/min Secretion rateSecretion rate = Excretion rate - Filtered loadmg/min, mmol/min, or mEq/min S, a substance; U, urine concentration; V, urine flow rate; P, plasma concentration; PAH, para-aminohippuric acid; P PAH, renal arterial PAH concentration; E PAH, PAH extraction ratio; V PAH, renal venous PAH concentration. Table 27-4 Don’t worry about memorizing these formulas, but understand what they represent