Urine Acidification

URINE ACIDIFICATION BUFFERS Source of acids Carbonic acids Non carbonic acids Source of H+ • Diet • CO2 produced as end of metabolism • Secretion of H by renal tubules DEFENCE MECHANSIMS FOR REMOVAL OF ACID BLOODHaemoglobin Carbonic acid bicarbonate system HPO2. H2CO3. TIPS TO REMEMBER 1. Whole blood is very good buffer 2. Majority is attributed to H hemoglobin 3. Buffering action of haemoglobin is due to histidine Majority of urine acidification occurs in DCT AND CT All of of H is secreted in, nothing is filtrate Limiting pH of urine 4.4 Three main buffers remove free H+ 1. Bicarbonate system 2. Phosphate system 3. Ammonia system

BUFFER SYSTEMS IN KIDNEY BICARBONATE SYSTEM Secreted H in PCT reacts with HCO3 to form H2CO3 and help in HCO3 reabsorption NO NET H SECRETION OCCURS 2. THEREFORE pH remains unchanged 3. H secreted in excess is buffered by two other systems Diphasic phosphate systems SITE PCT NOTE H secreted is buffered with HPO4 H is secreted in exchange for Na and N

1 70%-75% of filtered HPO4 is reabsorbed 2. 25% available for bufferinga2 HPO4 INTO Na H2PO4 5. Na H2PO4 EXCRETD IN URINE

AMMONIA SYSTEM SITE

DCT and CT

Secreted and synthesized not by filtrate Formation of ammonia Mainly form glutamine NH3 diffuses form tubular cells into lumen where it combines with H to form NH4 NH4 is lipid insoluble, therefore remains in lumen

Excretion NH4 is excreted in urine

TIPS TO REMEMBER • H secreted that reacts with HCO3 is not excreted • H recast with NH4 is excreted TITRABLE ACID major site PCT