This document provides an overview of tubular reabsorption in the kidney. It discusses the general principles of renal tubular transport, including transport across cell membranes and between epithelial cells. It describes transport across the different segments of the renal tubule, including the proximal tubule, Loop of Henle, distal tubule, and collecting duct. Key solutes discussed are sodium, chloride, potassium, bicarbonate, glucose and water. The mechanisms of action of diuretics and the renal handling of these solutes are also summarized.

1. TUBULAR
REABSORPTION
DR.NILESH KATE.
M.D.
ASSOCIATE PROFESSOR,
DEPARTMENT OF
PHYSIOLOGY,

2.  The composition of the blood ( internal
environment ) is determined not by what
the mouth ingest but by what the kidney
keep.
------- SMITH.

3. OBJECTIVES
 General principles of renal tubular transport.
 Transport across different segments of renal tubule.
 Renal handling of common solutes & water.
 Renal threshold,
 Tubular maximum.

4. TUBULAR FUNCTION
 Reabsorption: Removal of a
substance from the filtrate
Filtered load
--excretion.
 180 lit filtered – 178.5 lit
reabsorbed only 1.5 lit excreted.
 Determine composition &
volume of urine.
 Consequently control volume,
osmolality, composition & pH of
ICF & ECF.

5. GENERAL PRINCIPLES.
 Renal tubular Transport.
 Transport across cell membrane.
 Transepithelial transport.
 Parameters of active transport.
 Transport across different segments.
 Proximal tubule.
 Henle’s loop.
 Distal tubule
 Collecting duct.
 Tubular transport of common solute & water.
 Tubular transport of Na, Cl, K, Glucose & water.

6. Renal tubular Transport.
 Across cell membrane.
 Passive transport.
 Diffusion.
 Facilitated
diffusion.
 Active transport.
 Carrier mediated.
 Endocytosis.

7. TRANSEPITHELIAL TRANSPORT.
 Transcellular
 Apical membrane
 Basolateral
membrane.
 Paracellular.

8. Tubular mechanism.
 Tubular reabsorption
 Active transport – Solutes.
 Passive movements -- water.

9. PATTERN OF RENAL HANDLING
 Glomerular filtration only
 Glomerular filtration & partial reabsorption.
 Glomerular filtration & complete tubular
reabsorption.

10. PATTERN OF RENAL HANDLING
 Glomerular filtration & tubular secretion.
 Glomerular filtration & partial reabsorption &
secretion.
 No Glomerular filtration , no absorption

11. Transport across different
segments of renal tubule.
 Across proximal
tubule.– absorbs
 67% of filtered water,
Na, Cl, K
 All glucose & amino
acids.
 Do not reabsorbs
 Inulin, creatinine,
sucrose, mannitol

12. Proximal tubule reabsorption.
 Characteristics of PCT
 VILLI
 Key element
 Na- K-ATPase in Basolateral membrane.

13. Sodium reabsorption.
 Early Proximal
tubule.
 ISOOSMOTIC.
 Basolateral
membrane
 Apical membrane
 Na-H antiporter.
 Na-Glu symporter.

14. LATE PROXIMAL TUBULE.

15. WATER REABSORPTION.
 2/3rd
Transcellular
 1/3rd
Paracellular.

16. TRANSPORT ACROSS LOOP OF
HENLE
 Thin descending limb
of loop of Henle.
 Thin Ascending limb
of loop of Henle.
 Thick ascending limb
of loop of Henle.
( Loop diuretics)

17. Transport across distal tubule & collecting
duct.
 Early distal tubule
 Na-Cl symporter
 Cortical diluting segment.
 Thiazide diuretics.
 Late distal tubule &
collecting duct.
 Principal cells
 Intercalated cells.

18. TRANSPORT ACROSS DISTAL TUBULE
& COLLECTING DUCT.
 Principal cells
 Na reabsorption.
 Cl reabsorption.
 ADH – AQUAPRINS
 Water channels.
 Role of aldosterone on Principal cells.
 Increases Na reabsorption.
 Intercalated cells
 Reabsorb K+
& secrete H+

19. RENAL HANDLING OF SODIUM
& WATER.
 Site & mechanism of
reabsorption of Na.
 Proximal tubule – 67% (active)
 LH – 20%
 DTS – PASSIVE
 ATS – PASSIVE
 TAL – ACTIVE.
 Distal tubule – 7% -- ACTIVE
 Collecting duct. – 5% -- ACTIVE
 Sodium recycling

20. Water reabsorption.
11
Proximal convoluted tubule.
(PASSIVE)
Loop of Henle
(IMPERMEABLE)
Distal convoluted tubule.
(IMPERMEABLE)
Collecting duct.
REABSORBED
(ADH)
Glomerular capsule.

21. Water reabsorption.
 Obligatory. (85%)
 Transtubular osmotic
gradient
 67% (PCT)
 15-18% (DTS)
 Facultative.
 From collecting tubule.
 Under control of ADH.

22. MECHANISM OF ACTION OF
DIURETICS.

23. Bicarbonate Reabsorption

24. BICARBONATE REABSORPTION IN
PCT

25. Bicarbonate Reabsorption
 95%
 The epithelial cells of the
proximal tubule, the thick
segment of the ascending
loop of Henle, and the early
distal tubule
 All secrete H+
into the
tubular fluid by sodium-
hydrogen counter-transport

26. Bicarbonate Reabsorption
 5%
 Primary Active
Secretion of
Hydrogen Ions
 Intercalated Cells of
Late Distal and
Collecting Tubules

27. RENAL HANDLING OF GLUCOSE.
 Glomerular filtration
 Tubular reabsorption
 Carrier mediated Na-glu
cotransport.
 Facilitated diffusion.

28. Glucose titration curve.
 Filtered load
 Renal threshold. (180
mg%)
 Transport maximum.
(350 mg %)
 Splay.
 Causes.
 Heterogeneity
 Variability in TmG of the
Nephron.

29. APPLIED
 Mechanism of actions of Diuretics.
 Renal handling of clearance.
 Importance of ADH.
 Basis of counter current mechanism.
 Glycosuria in Diabetes mellitus.
 Acidification of urine.

30. Thank
You