Regulation of tubular reabsorption 1-Glomerulotubular balance : If GFR^ to 150 ml/min so in proximal tubule reabsorption ^from 81 ml/min to 97.5 ml/min.(65% of GFR A-Intrinsic ability to increase reabsorption when tubular load increase ?. B-This act together with autoregulation to prevent large change in fluid flow in distal tub

2. Peritubular capillary and interstitial fluid physical forces a. Hydrostatic pr. In capillary Pc opposes -13 b. Hydrostatic pr. In interstitium Pif favors 6 c. Colloid osmotic pr. in capillary πc favors 32 d. Colloid osmotic pr. In intrst. πif opposes -15 ____ Net reab. Pr. 10 mmHg Reabsorption = Kf x Net reabsorptive pr. 12.4 x 10 = 124 ml/min

A. ^Arterial pr.^ hydrostatic decreases reabsorption Change resistance of afferent and efferent __ constrictiondecreases hydrostatic ^ reabsorption. B. ^Plasma colloid osmotic pr.^ coll. In perit.^ reabs.^Filtration fraction ^[protein] ^reabsorption

C. (A,B) if increase reabsorption^ fluids in interstitium^ hydrastatic pr. and decreases colloid pr.decreases reabsorption of fluid from renal tubules IN GENERAL FORCES INCREASE PERITUBULAR CAPILLARY REABSORPTION ALSO INCREASE REABSORPTIN FROM RENAL TUBULES AND VICE VERSA

In general forces increase peritubular cap reabsorption also increase reabsorption from renal tubules and vice versa .

3.PRESSURE NATIURESIS AND PRESSURE DIURESIS 1-GFR autoregulation 75-160 mmHg 2-Kid diseases increase BP and GFR and urine output 3-Incr BP will increase renal interstitial fluid hydrostatic P and reduce absorption of Na &water and increase urine output 4-reduce angiotensin secretion which decrease aldosterone and both decrease Na absorption & incr urine output

4. Hormonal control : A.-Aldosteron : on distal tubule and collecting duct Na Cl , H2O reabs. and K+ secretion -Addison's disease : no aldosterone  loss of Na+ , accumulation of K+ -Conn's syndrome : Na+ retention K+ depletion - Increases sodium permeability on luminal side.

B. Angiotensin II : on proximal tubule Na Cl, B. Angiotensin II : on proximal tubule Na Cl, H2O reabsorption, H+ secretion. Other effects: 1. Stimulates aldosterone secretion 2. Constricts efferent art. 3. Stimulates Na+ reabsorption on Na-K pumps ,Na-H+ exchanger & Na-bicarbonate co-transporter.

C.ADH : on distal, coll tubule and coll. duct ^H2O reabsorption. ADH+V2receptorform cyclic AMP, which activates protein Kinase which moves aquaporin-2 (AQP-2) to luminal membrane then AQP2 fuse together to form water channels.

D.Atrial natriuretic peptide ANP :Dilated atria Decrease Na+ and H2O reabsorption in distal and collecting duct Also inhibit renin secretion > decrease angiotensin formation. Important in Heart Failure E.Parathyroid hormone : Prox. , thick ascending of L.H, distal.decreases PO4- reabsorption and ^Ca++ reabsorption

5.Sympathetic N.S. : ^Na and H2O reabsorption by constricting afferent and efferent arterioles . It also increases renin and angiotensin II formation.

Renal clearance of substance Useful way of quantitating the effectiveness with which kidneys excrete various substances. Volume of plasma that is completely cleared of the substance by the kidneys per unit time . Urinary excretion rate Cs= (Us xV) GFR x Ps=Us x V Ps Cs=GFR GFR= Us x V -

For creatinine clearance & GFR GFR x Pcr=Ucr x V If GFR decrease the creatinine filtration & excretion decrease & plasma concentration increase

CLEARANCE & GFR: Inulin and Creatinine RENAL PLASMA FLOW RPF : PAH clearance 90% =UxV/P =C FILTRATION FRACTION=GFR/RPF Reabsorption=Kf x Net reabsorption force Kf : Filtration coefficient : measure of permeability and surface area of the capillaries normal=12.4 ml/min/mm Hg

Inulin clearance = GFR Amt. Filtered = Amt. Excreted - PAH clearance / 0.9 = Renal plasma flow If the substance is completely cleared from the plasma (by filtration & secretion) , the clearance of substance = to the total renal plasma flow. Amt. delivered to kidneys in blood= amt. excreted in urine.

PAH removed from the plasma by filtration & secretion (90%) called extraction ratio

TUBULAR REABSORPTION OR SECRETION If GFR x Ps > Us x V absorption If GFR x Ps < Us x V secretion