1. % of Filtered Load Reabsorbed
Reabsorption:
> large amounts are filtered
>for many substances, large amounts are reabsorbed, so little is excreted
Amount Filtered
Amount Reabsorbed
Amount Excreted
% of Filtered Load Reabsorbed
glucose
180
100
Bicarbonate (mEq/day)
4,320
4,318 2
>99.9
Sodium (mEq/day)
25,560
25,410
150
99.4
Chloride (mEq/day)
19,440
19,260
99.1
Potassium (mEq/day)
756
664 92
87.8
urea
46.8
23.4 50
Creatinine (g/day)
1.8
Urea
Table Filtration, Reabsorption, and Excretion Rates of Different Substances by the Kidneys
Glucose
Table 27-1

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

3. Brush border
Scanning EM of proximal tubule cell

4. Question: do these pressures make sense?
Pressures favoring reabsorption by bulk flow into peritubular capillaries
Figure 27-15
Question: do these pressures make sense?

5. Sodium reabsorption in the proximal tubule
Figure 27-2
Note: the Na+-K+ATPase is on the basolateral side

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

7. Passive reabsoprtion of some substances
Glomerulus
Peritubular
capillary
Bowman’s
capsule
125 ml of
filtrate
Beginning of
proximal
tubule
Na+ (active)
H2O (osmosis)
Na+ (active)
H2O (osmosis)
End of
proximal
tubule
44 ml of
filtrate
Passive diffusion
of urea down its
concentration gradient
= Urea molecules

8. Importance of transport maxima
Substance 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
Creatinine 16 mg/min
Para-aminohippuric acid 80 mg/min
Figure 27-4

9. Silverthorn Figure 19-15 - Overview

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

11. Figure 27-7

12. We’ll save loop of Henle for next time – but look at the very different appearance of the descending and ascending limbs
Figure 27-8

13. Distal tubule and collecting duct: regulated reabsorption and secretion
Figure 27-11

14. a wonderful figure; pay attention to:
Glucose and amino acids
Na+, K+, Cl-
Urea
Inulin and creatinine
PAH
Figure 27-14

15. Key hormones involved in the regulation of reabsorption
Site of Action
Effects
Aldosterone
Collecting tubule and duct
↑ NaCl, H2O reabsorption, ↑ K+ secretion
Angiotensin II
Proximal tubule, thick ascending loop of Henle/distal tubule, collecting tubule
↑ NaCl, H2O reabsorption, ↑ H+ secretion
Antidiuretic hormone
Distal tubule/collecting tubule and duct
↑ H2O reabsorption
Atrial natriuretic peptide
↓ NaCl reabsorption
Parathyroid hormone
Proximal tubule, thick ascending loop of Henle/distal tubule
↓PO4--- reabsorption, ↑ Ca++ reabsorption
Table 27-3
(we’ll focus on aldosterone and antidiuretic hormone during the next two classes)

16. For a substance that is freely filtered, but not reabsorbed or secreted:
Silverthorn Figure 19-16

17. Figure 27-19

18. Silverthorn Table 19-2

19. Clearance Rate (ml/min)or
Substance
Clearance Rate (ml/min)
Glucose    
Sodium
0.9
Chloride
1.3
Potassium
12.0
Phosphate
25.0
Inulin
125.0
Creatinine
140.0
Silverthorn Figure Overview

20. Don’t worry about memorizing these formulas, but understand what they represent and be able to define each of the terms (except we won’t distinguish between renal plasma flow and effective renal plasma flow).
Table 27-4
Term
Equation
Units
Clearance rate (Cs)
                       
ml/min
Glomerular filtration rate (GFR)
                                 
Clearance ratio
                                            
None
Effective renal plasma flow (ERPF)
                                                 
Renal plasma flow (RPF)
                                                                
Renal blood flow (RBF)
                                         
Excretion rate
Excretion rate = Us × V
mg/min, mmol/min, or mEq/min
Reabsorption rate
                                                                                              
Secretion rate
Secretion rate = Excretion rate - Filtered load
S, a substance; U, urine concentration; V, urine flow rate; P, plasma concentration; PAH, para-aminohippuric acid; PPAH, renal arterial PAH concentration; EPAH, PAH extraction ratio; VPAH, renal venous PAH concentration.