Protonephridia

Metanephredia of Earthworm

Kidney approximatly fist sized, 160 g, outside peritoneum against the back.

A NEPHRON may be cortical of juxtamedullary, the longer the loop of Henle, the greater the ability to concentrate the urine and save water.

Roles of the Kidney Filtration -- 180 liters/day of water, all NaCl, sugar, amino acids Absorption -- 178.5 liters reabsorbed with 95-99% of NaCl, all glucose, amino acids Secretion -- acids and bases, toxins, antibiotics Concentration

Blood flow in the vas recta is counter-current to the flow of fluid in the loop of Henle

The Glomerular Filtration Rate is a measure of the health of the glomerulus. The GFR is measured by following the concentration of substance that is not secreted and not reabsorbed by the kidney, so only the amount that is filtered is present in the urine. Concentration blood x GFR = Concentration urine x urine formation rate. A polymer of fructose, inulin is used to measure GFR. Example: The urine concentration of inulin is 30 mg/ml and the plasma concentration is 0.5 mg/ml. If the rate of urine formation is 2 mls/ minute, then the GFR is 120 mls/minute.

Urea Clearance If urine formation rate is 2 mls/minute and the urine concentration of urea is 7.5 mg/ml, a realistic estimate of urea concentration in the plasma is .2 mg/ml and the urea clearance rate would be 75 mls/minute. This is less than the GFR because some urea is reabsorbed.

Plasma Clearance Not all the fluid going to the glomerulus passes into the kidney tubule, so not all of a substance is cleared from the plasma in a single pass -- unless it is also secreted into the tubule from the efferent arteriole -- then all of the substance can be “cleared” in a single pass. The plasma clearance also tells us how much plasma is going to a nephron in a single pass. PAH (paraamino hippuric acid) is used. From PAH measurements 625 mls plasma are cleared/ minute or 1.1 liters of blood (45% cells, 55% plasma).

Creatine Creatine also used to measure kidney health Waste product of muscle creatine Filtered and little secreted and usually matches GFR If GFR decreases, then plasma creatine will increase to signal a kidney problem

Glomerulonephritis This is an autoimmune discease induced by a strep infection. The basement membrane of the glomerulus is destroyed and proteins enter the filtrate or primary urine. The plasma osmotic pressure also falls.

Reabsorption 65% water and 100% glucose and amino acids are reabsorbed in the proximal tubule. Na/K ATPase at the basolateral surface powers Na linked glucose and amino acid movment across the apical surface These carriers can saturate, the transport max of glucose is 375 mg/min, if there is more glucose in the primary urine it will not be completely reabsorbed. As fluid leaves the proximal tubule its volume is 65% of the primary urine and it is isoosmotic to the plasma