MCB 135E Discussion

MIDTERM II Review Monday the 7 th of November 2040 VLSB 6-8pm questions regarding exam well in advance

The Kidney and Urinary System Anatomy Function Hormones Circulation Development

Kidney Functions Regulates –Water –Electrolyte balance –pH Removes –Waste Secretes Hormones –Erythropoiten –Renin –Vitamin D3

Metabolic and Excretory Functions Glomerular Filtration –Selective filtration of blood Tubular Reabsorption –Takes up some solutes from filtrate and delivers them to peritubular capillaries Tubular Secretion –Adds some of its own products to the filtrate, passes filtrate on to bladder as urine

Water Metabolism Osmotic Pressure – –Force driving or pulling a solvent from lesser to greater concentration on either side of a selectively permeable membrane Regulation of solute exchange –Selective permeability of membrane –Influence of hormones and metabolites on membrane –Simple and exchange diffusion across membrane –Active secretion by the membrane

Acid Base Balance Determined By: –Hydrogen Ion Concentration (pH) Normal Max –Alkali reserve CO 2 combing power of plasma Normal 50-70% Volume –Both vary due to exercise and metabolism

Acid-Base Regulation Buffers, Ventilation, Kidney Buffers –Cellular proteins, phosphate ions, Hemeglobin (Chloride Shift) Ventilation –Rate and depth of respiration controls CO 2 release in lungs –Increased respiration in a respiratory compensation for acidosis Kidney –Excretes H + –Reabsorbs HCO 3 -

Urine Acidification Mechanisms Reabsorption of Filtered Bicarbonate –In proximal tubule: H+ exchanged for Na+ –In distal tubule and collecting duct CO2 and HCO3(-) are transported into cell and form H2CO3 by carbonic anhydrase Dissociation of H2CO3 releases H+ which is then exchanged for Na+ Secretion of Ammonia –In distal tubule NH3 + H-  NH4 (Ammonium) [formation of a titrable acid]

Mechanism for Renal Acid/Base Balance 1.Apical Na(+)/H(+) antiporter 2.Basolateral Na(+)/HCO 3 (-) symporter 3.H(+) ATPase 4.H(+)/K(+) ATPase 5.NA(+)/NH 4 (+) antiporter

Proximal Tubule Acid/Base Balance 1.H(+) is secreted into the lumen in exchange for Na(+) 2.Secreted H(+) then combines with the filtered bicarbonate to form CO 2 in the lumen 3.CO 2 diffuses into the proximal tubule cell and combines with water to form carbonic acid, this dissociates to form H(+) and HCO 3 (-) in the cytoplasm (Involves carbonic anhydrase) 4.The H(+) is secreted again by the antiport in step 1 5.The HCO 3 (-) is transported out of the cell by a NA(+)/HCO 3 (-) symporter where it can function as a buffer