1. Unit Five: The Body Fluids and Kidneys
Chapter 27: Urine Formation By the Kidneys. II. Tubular Reabsorption and Secretion
Guyton and Hall, Textbook of Medical Physiology, 12th edition

2. Renal Tubular Reabsorption and Secretion
Tubular Reabsorption is Quantitatively Large and
Highly Selective

3. Table 27.1 Filtration, Excretion, and Reabsorption Rates of Different Substances by the Kidney
Amount Filtered
Amount Reabsorbed
Amount Excreted
% Filtered Reabsorbed
Glucose g/day
180
100
Bicarbonate
mEq/day
4320
4318 2
>99.9
Sodium
25560
25410
150
99.4
Chloride
19440
19260
99.1
Potassium
756
664 92
87.8
Urea g/day
46.8
23.4 50
Creatinine
g/day
1.8

4. Tubular Reabsorption
Fig. 27.1

5. Tubular Reabsorption (cont.)
Active Transport
Solutes transported through epithelial cells or
between cells
Primary active transport (i.e. Na+ and K+)
Secondary active transport

6. Fig. 27.2 Basic mechanism for transport of sodium through the tubular epithelial cell

7. Fig. 27.3 Mechanisms of secondary active transport

8. Tubular Reabsorption (cont.)
Secondary active secretion into the tubules (i.e.
counter-transport)
Pinocytosis-active reabsorption of proteins
Transport maximum-limit to the rate at which
a solute can be transported in secretion or
reabsorption

9. Fig. 27.4 Relations among the filtered load of glucose, the rate of glucose
reabsorption by the renal tubules, and the rate of glucose
excretion in the urine.

10. Substance Transport Maximum
Transport Maximums for Substances Actively Reabsorbed by the Tubules
Substance
Transport Maximum
Glucose
375 mg/min
Phosphate
0.10 mM/min
Sulfate
.06 mM/min
Amino Acids
1.5 mM/min
Urate
15 mg/min
Lactate
75 mg/min
Plasma protein
30 mg/min

11. Substances that are actively transported but do not
Transport Maximums for Substances Actively Secreted
Substance
Transport Maximum
Creatinine
16 mg/min
Para-aminohippuric acid
80 mg/min
Substances that are actively transported but do not
exhibit a transport maximum (i.e. Na in the proximal
tubule
h. Passive reabsorption coupled to sodium reabsorption

12. Fig. 27.5 Mechanisms by which water, chloride, and urea reabsorption
are coupled with sodium reabsorption

13. Reabsorption and Secretion Along Different Parts of the Nephron
Proximal Tubular Reabsorption - normally about 65% of
filtered load of Na and water and slightly lower percent
of chloride is reabsorbed before the loop of Henle
Have a high capacity for both active and passive
reabsorption
b. Co-transport and counter-transport occurs

14. Fig. 27.6 Cellular ultrastructure and primary transport characteristics of the proximal tubule.

15. Reabsorption and Secretion (cont.)
Concentrations of Solutes Along the Proximal Tubule
Fig. 27.7

16. Reabsorption and Secretion (cont.)
Secretion of Organic Acids and Bases
End products of metabolism
Harmful drugs and toxins
PAH (para-aminohippuric acid) clearance: used to
estimate renal plasma flow

17. Reabsorption and Secretion (cont.)
Solute and Water Transport in the Loop of Henle
Fig. 27.8

18. Reabsorption and Secretion (cont.)
Solute and Water Transport in the Loop of Henle
Fig. 27.9

19. Reabsorption and Secretion (cont.)
Distal Tubule - Macula densa of the juxtaglomerular complex
provides feedback control for GFR
Fig

20. Reabsorption and Secretion (cont.)
Late Distal Tubule and Cortical Collecting Tubule
Principal cells reabsorb sodium and secrete potassium
Fig

21. Reabsorption and Secretion (cont.)
Late Distal Tubule and Cortical Collecting Tubule (cont.)
Intercalated cells secrete hydrogen and reabsorb
bicarbonate and potassium ions
c. Permeability is controlled by concentrations of ADH

22. Reabsorption and Secretion (cont.)
Medullary Collecting Duct - absorb less than 10% of the
filtered water and sodium; final site for processing
urine
Permeability controlled by ADH
Permeable to urea
Can secrete H+ against a concentration gradient (helps
regulate acid-base balance

23. Fig

24. Summary of Concentrations of Different Solutes in the Different Tubular Segments
Fig

25. Regulation of Tubular Reabsorption
Glomerulotubular Balance- ability of the tubules to
increase reabsorption rate in response to increased
tubular load
Peritubular Capillary and Renal Interstitial Fluid
Physical Forces - hydrostatic and colloid osmotic
forces govern the rate of reabsorption across
the peritubular capillaries

26. Regulation of Tubular Reabsorption (cont.)
Fig

27. Regulation (cont.)
Regulation of Peritubular Capillary Physical Forces
Peritubular capillary hydrostatic pressure is influenced
by arterial pressure and resistance of the afferent and
efferent arterioles
Increases in these pressures tend to raise peritubular
hydrostatic pressure and decrease reabsorption rate
Increases in the resistance of the arterioles reduces the
hydrostatic pressure and increases the reabsorption rate

28. Regulation (cont.)
Regulation of Peritubular Capillary Physical Forces
Raising the colloid osmotic pressure increases peritubular
capillary reabsorption
Colloid osmotic pressure is determined by
Systemic plasma colloid osmotic pressure
Filtration fraction

29. Renal Interstitial Hydrostatic and Colloid Osmotic Pressures
Regulation (cont.)
Renal Interstitial Hydrostatic and Colloid
Osmotic Pressures
Fig

30. Regulation (cont.)
Hormonal Control of Tubular Reabsorption
Aldosterone increases Na reabsorption and stimulates
K secretion
Site of action is on the principal cells of the cortical
collecting tubule
Most important stimuli for aldosterone are increased
K and angiotensin II levels

31. Regulation (cont.)
Angiotensin II Increases Na and Water Reabsorption
Angiotensin II stimulates aldosterone secretion
Angiotensin II constricts the efferent arterioles
Angiotensin II directly stimulates Na reabsorption in
the proximal tubules, the loops of Henle, the distal
tubules, and the collecting tubules

32. Fig. 27.17 Direct effects of angiotensin II to increase proximal tubular sodium reabsorption

33. ADH Increases Water Reabsorption
Regulation (cont.)
ADH Increases Water Reabsorption
Fig

34. Regulation (cont.)
ANP Decreases Na and Water Reabsorption
PTH Increases Ca Reabsorption
Sympathetic Nervous System Activation Increases
Na Reabsorption

35. Quantifying Kidney Function
Inulin Clearance
Creatinine Clearance
PAH (para-aminohippuric acid) Clearance

36. Fig. 27.19 Measurement of the GFR from the renal clearance of inulin

37. Fig. 27.20 Effect of reducing GFR by 50% on serum creatinine concentration
and on creatinine excretion rate when the production rate of
creatinine remains constant

38. Fig. 27.21 Approximate relationship between GFR and plasma
creatinine concentration under steady-state conditions

39. Fig. 27.22 Measurement of renal plasma flow from the renal clearance
of PAG

40. Clearance Rate (ml/min)
Approximate Clearance Rates for Some of the
Substances Normally Handled by the Kidneys
Substance
Clearance Rate (ml/min)
Glucose
Sodium
0.9
Chloride
1.3
Potassium
12.0
Phosphate
25.0
Inulin
125.0
Creatinine
140.0