TUBULAR REABSORPTION

DR.NILESH KATE. M.D.

ASSOCIATE PROFESSOR,DEPARTMENT OF

PHYSIOLOGY,

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

------- SMITH.

OBJECTIVES

General principles of renal tubular transport.

Transport across different segments of renal tubule.

Renal handling of common solutes & water.

Renal threshold,

Tubular maximum.

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.

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.

Renal tubular Transport. Across cell membrane.

Passive transport. Diffusion. Facilitated

diffusion. Active transport.

Carrier mediated. Endocytosis.

TRANSEPITHELIAL TRANSPORT.

Transcellular Apical membrane Basolateral

membrane. Paracellular.

Tubular mechanism. Tubular reabsorption

Active transport – Solutes. Passive movements -- water.

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

reabsorption.

PATTERN OF RENAL HANDLING

Glomerular filtration & tubular secretion.

Glomerular filtration & partial reabsorption &

secretion.

No Glomerular filtration , no absorption

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

Proximal tubule reabsorption.

Characteristics of PCT VILLI

Key element Na- K-ATPase in Basolateral membrane.

Sodium reabsorption. Early Proximal

tubule. ISOOSMOTIC. Basolateral

membrane Apical membrane

Na-H antiporter. Na-Glu symporter.

LATE PROXIMAL TUBULE.

WATER REABSORPTION. 2/3rd

Transcellular 1/3rd

Paracellular.

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)

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.

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+

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

Water reabsorption.

1

Proximal convoluted tubule. (PASSIVE)

Loop of Henle (IMPERMEABLE)

Distal convoluted tubule.(IMPERMEABLE)

Collecting duct.REABSORBED

(ADH)

Glomerular capsule.

Water reabsorption. Obligatory. (85%)

Transtubular osmotic

gradient

67% (PCT)

15-18% (DTS)

Facultative. From collecting tubule.

Under control of ADH.

MECHANISM OF ACTION OF DIURETICS.

Bicarbonate Reabsorption

BICARBONATE REABSORPTION IN PCT

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

Bicarbonate Reabsorption

5% Primary Active

Secretion of Hydrogen Ions

Intercalated Cells of Late Distal and Collecting Tubules

RENAL HANDLING OF GLUCOSE. Glomerular filtration Tubular reabsorption

Carrier mediated Na-glu cotransport.

Facilitated diffusion.

Glucose titration curve.

Filtered load Renal threshold. (180

mg%) Transport maximum.

(350 mg %) Splay.

Causes. Heterogeneity Variability in TmG of the

Nephron.

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.

Thank You