Stimulating Urine Formation

Efferent

Afferent Glomerulus

Glomerular capsule

PCT

Loop of Henle

DCTCollecting Duct

Role of the Solute Gradient on Maximum Urine Concentration

• In urine formation, solutes and water move from the lumen to the interstitial spaces

• Total solute gradient will effect the movement of solute and water to these interstitial spaces

• Antidiuretic Hormone (ADH)– Increases water permeability in DCT and Collecting

Duct– Water flows from high solute conc. into the

interstitial spaces – Water is absorbed

• Procedure: Increase the Max. Total Solute Concentration of the Gradient by 300 milliosmole increments, adding ADH as well

• What happens to the Urine Concentration as Total Solute Concentration Gradient (Conc. Grad) increases?– It increases because ADH causes water

to move out of urine and the more solute there is the more concentrated the urine

Effect of Glucose Carrier Proteins on Glucose Reabsorption

• There is a limit to the amount of glucose reabsorbed because carrier proteins are needed to move them to the interstitial fluid

• If glucose carriers are being used, excess glucose is eliminated in urine

• Procedure: Increase the glucose carriers by increments of 100

• What happened to the glucose concentration in urine as the number of glucose carriers increased? – Glucose concentration in the urine decreased

because the carriers were able to get the glucose across

• If there was more glucose than could be transported by the available number of glucose carrier proteins, what would happen to the urine? – An increased glucose concentration in the

urine • Why do we expect to find glucose in the urine of

a diabetic person?– The lack of insulin causes a high glucose

concentration – The glucose can’t all be absorbed because

there are only so many glucose carriers

Effect of Hormones on Urine Formation

• Excess water = dilute urine• Dehydration = concentrated urine• Hormones control urine concentration– ADH – Produced by Hypothalamus and

Stored in Posterior Pituitary Gland• Increases water permeability• Works at DCT and Collecting Duct

– Aldosterone – Produced by Adrenal Gland• Reabsorbs sodium ions and water but loses

potassium ions • Works at the DCT

• Procedure: Compare a baseline run with one when Aldosterone is added and one when ADH is added

• How are the results different when Aldosterone is added?– Urine Volume decreases – Sodium and Water are retained – Potassium Conc. increases because it is kicked out

• How are the results different when ADH is added?– Urine Concentration increases– Urine Volume decreases

• Are the effects of Aldosterone and ADH similar or antagonistic?– Similar (Agonists) - both conserve Sodium and Water