urine formation.pptx

dilute and concentrated urine formation

1. URINE FORMATION BY: Ms.Keerthi Asst.professor Vijay marie con

2. FORMATION OF DILUTE URINE Glomerular filtrate has the ratio of water and solute particles as blood. Its osmolarity is about 300mosm/lit. Fluid leaving PCT still is isotonic to plasma when dilute urine is being formed. The osmolarity of fluid in tubular lumen increases as it flows down the descending limb of LOH and then decreases as it flows up the ascending limb and still decreases as it flows through rest of nephron and collecting duct.

3. FORMATION OF DILUTE URINE These changes in the osmolarity results from the following conditions along the path of the tubular fluid: Because osmolarity of interstitial fluid of renal medulla becomes progressively greater. More and more water is reabsorbed by osmosis as tubular fluid flows along descending limb towards tip of loop. As a result the fluid remaining in the lumen becomes progressively more concentrated

4. FORMATION OF DILUTE URINE 2.Cells lining ascending limb of LOH have symporters that actively absorbs Na+,K + and Cl- from tubular fluid. The ions pass from tubular fluid into thick ascending limb cells then into interstitial fluid and finally some diffuse into blood inside vasa recta.

5. FORMATION OF DILUTE URINE 3. Although solutes are being reabsorbed in thick A/L . The water permeability of this portion of the nephron is always quiet low, so water cannot follow by osmosis. As solutes but not water molecules are leaving the tubular fluid , its osmolarity drops to about 150mosm/lit. The fluid entering DCT is thus more dilute than plasma.

6. FORMATION OF DILUTE URINE 4. While the fluid continues flowing along DCT, additional solutes but only a few water molecules are reabsorbed. DCT cells are not very permeable to water and are not regulated by ADH. Finally the principal cells of collecting ducts are impermeable to water when ADH is very low

7. FORMATION OF DILUTE URINE Thus tubular fluid becomes progressively more dilute as it flows onward. By the time tubular fluid drains into renal pelvis, its concentration can be as low as 65-70mosm/lit. This is 4 times more dilute than blood plasma or glomerular filtrate.

8. FORMATION OF CONCENTRATED URINE When water intake is low or water loss is high kidneys must conserve water still eliminating wastes and excess ions. Under the influence of ADH , kidneys produce a small volume of highly concentrated urine. Urine can be 4 times more concentrated upto 1200mosm/lit than blood plasma or glomerular filtrate (300mosm/lit). The ability of ADH to cause excretion of concentrated urine depends on presence of osmotic gradient of solutes in interstitial fluid of renal medulla.

9. FORMATION OF CONCENTRATED URINE The solute concentration of interstitial fluid in kidney increases from about 300mosm/lit in renal cortex to about 1200mosm/lit deep in renal medulla. The 3 major solutes that contribute to high osmolarity are Na+,CL - and urea. 2 main functions that contribute to building and maintaining this osmotic gradient: Differences in solute and water permeability and reabsorption in different sections of long LOH and collecting duct. The countercurrent flow of fluid in neighboring A/L and D/L of LOH.

10. FORMATION OF CONCENTRATED URINE IN LONG LOOP NEPHRONS , SYMPORTERS IN THICK A/L CELLS OF LOH ESTABLISH OSMOTIC GRADIENT IN RENAL MEDULLA:

11. FORMATION OF CONCENTRATED URINE

12. FORMATION OF CONCENTRATED URINE

13. FORMATION OF CONCENTRATED URINE