Presentation on theme: "Physiology 441 The Renal System, Chp. 14"— Presentation transcript:
1 Physiology 441 The Renal System, Chp. 14 Text: Human Physiology (Sherwood), 6th Ed.Julie Balch Samora, MPA, MPH, Room 3145
2 Review How is glucose transported? What is the renal threshold? Do we see this for passive transport?Do the kidneys regulate glucose/ phosphate plasma concentration?
3 Review cont… What is the vascular sequence in the nephron? What is the tubular sequence?
4 Review cont…What happens if ↓ NaCl, ↓ ECF volume, and ↓ arterial blood pressure?
5 Tubular Secretion Additional mechanism to eliminate certain substances Secretion of H+, NH3, K+, organic anions and cationsAcid and ammonia secretion imp. in acid-base balanceAmmonia is secreted during acidosis in order to buffer the secreted H+
6 H+ and NH3 secretionHydrogen and ammonia secretion aid with acid-base balanceH+ secretion provides a highly discriminating mechanism for varying the amt of H+ excreted in the urine, depending on the acidity of the body fluidsNH3 is secreted in pronounced acidosis to buffer the H+ secreted into the urine
7 K+ SecretionK+ is actively reabsorbed in the proximal tubule, but is also actively secreted in the distal tubule.Allows fine degree of control over plasma K+ concentrationSecretion of K+ is variable and subject to aldosterone controlEven slight fluctuations in ECF [K+] can alter nerve and muscle excitability
8 Organic anion and cation secretion The proximal tubule contains 2 different carriers for secreting organic ionsThese systems aid in secreting foreign organic substancesThe liver helps this process by converting many foreign substances into anionic metabolites
10 Urine excretionThe final quantity of urine formed averages about 1ml/minThis urine contains a high conc. of waste products & low or no conc. of substances needed by the bodyMinimum volume of urine to eliminate wastes is 500 ml/day
11 Plasma Clearance The amount of plasma “cleared” of a substance Plasma clearance for a substance that is FILTERED, but not REABSORBED or SECRETED == GFR == 125ml/minEXAMPLE = INULIN
12 INULIN- Filtered, NOT reabsorbed, NOT secreted Renal Processes 2
13 Plasma ClearancePlasma clearance for a substance that is FILTERED AND REABSORBED, but NOT SECRETED < GFREXAMPLE = GLUCOSE, UREAClearance rate can be anywhere from 0 up to normal clearance (125 ml/min) depending on amount reabsorbed
14 Glucose/urea- Filtered and reabsorbed, NOT secreted Renal Processes 2
15 Plasma ClearancePlasma clearance for a substance that is FILTERED AND SECRETED > GFREXAMPLE = PAH (Para-aminohippuric acid)Not only is the plasma that is filtered cleared of that substance, but additional amt cleared from plasma which was not filteredPlasma clearance rate for PAH=RENAL PLASMA FLOW
17 Plasma Clearance Questions What is the PC for a substance that is FILTERED AND REABSORBED, but NOT SECRETED?What is the PC for a substance that is FILTERED AND SECRETED?What is the PC for a substance that is FILTERED, but not REABSORBED or SECRETED?
18 OsmolarityMeasure of the concentration of individual solute particles dissolved in fluidThe higher the osmolarity, the higher the concentration of solutesWATER moves by osmosis from an area of lower osmolarity (higher water conc) to an area of higher osmolarity (lower water conc) until the concentration difference is eliminated
19 OsmolarityIsotonic- solution is the same conc. as normal body fluids (300 milliosmols/L)Hypotonic- solution is more dilute than normal body fluids (< 300 milliosmols/L)Hypertonic- solution is more concentrated than normal body fluids (> 300 milliosmols/L)
20 QuestionHow can the kidneys put out a concentrated urine when the body is dehydrated?How can the kidneys excrete a dilute urine when the body is overhydrated?
21 Other nephrons emptying into the same collecting duct DistaltubuleDistaltubuleGlomerulusProximaltubuleBowman’scapsuleProximaltubuleCortexMedullaDescendinglimb ofloop ofHenleCollectingductLoop of HenleOther nephrons emptying intothe same collecting ductVasa rectaAscendinglimb ofloop ofHenleTo renalpelvisFig. 14-5, p. 505
22 Countercurrent System There is a vertical osmotic gradient in the interstitial fluid of the medullaThis gradient, with the help of ADH (vasopressin) allows the kidney to vary the concentration of the urine depending on the body’s needsCountercurrent multiplication- loops of Henle and Juxtamedullary nephronsCountercurrent exchange- vasa recta of the juxtamedullary nephrons
23 Countercurrent System At the end of the proximal tubule and beginning the loop of Henle, the filtrate is isotonic (300 mosm/L)Na+ is actively reabsorbed against its concentration gradient in the proximal tubule, creating an osmotic gradient, pulling water across to maintain osmotic equilibrium
24 Countercurrent Multiplication The loops of Henle of the juxtamedullary nephrons are responsible for establishing the concentration gradient in the renal medullaDesc. limb is freely permeable to H2O, but NOT NaCl – so H2O goes into IFThe ascending limb actively transports out NaClAsc. Limb IMPERMEABLE to water
26 Medullary vertical osmotic gradient There is a countercurrent flow produced by the close proximity of the two limbsThe ascending limb produces an interstitial fluid that becomes hypertonic to the ascending limb.This interstitial fluid faces against the flow of fluid (countercurrent) in the descending limb, attracting the water by osmosis for reabsorption
27 Countercurrent Multiplication The fluid in the descending limb becomes progressively more concentratedAt the bottom, its concentration is 1200 mosm/L!!As the asc. Limb is impermeable to water, when NaCl is pumped out, water remains, causing the remaining liquid in the loop to become hypotonic (100 mosm/L)
28 Countercurrent Multiplication Therefore, a vertical osmotic gradient varying from 300 to 1200 mosm/L exists in the medullaThe filtrate as it leaves the loop of Henle to enter the distal tubule is HYPOTONICGets its name due to the flow in opposing directions through the two limbs and the stepwise multiplication of concentration due to transport and permeabilities
32 Countercurrent exchange The vasa recta are responsible for preserving the concentration gradient in the medulla that has been established by the loop of HenleThe blood in the vasa recta follows the same course as the loops of Henle of the juxtamedullary nephrons.The vasa recta are exposed to the same gradient in the IF-blood concentration is similar
33 Countercurrent exchange This process is a passive, osmotic exchange b/t the IF and two closely opposed vessels with fluid flowing in opposite directions
35 Importance of the Vertical Gradient The collecting ducts are normally impermeable to waterHowever, if the body needs to conserve H2O, ADH (vasopressin) is secretedADH increases the permeability of the distal tubules and collecting tubules to H2O
36 ADH- Saving WaterDue to the vertical osmotic gradient, the tubular fluid loses more water into the IF, which eventually enters the plasmaAt the end of the collecting tubule, it is possible to have urine concentrated to 1200 mosm/L (very small volume excreted)
37 Role of ADHADH is produced in the hypothalamus and stored in the posterior pituitary. The release of this substance signals the distal tubule and collecting duct, facilitating the reabsorption of water.ADH works on tubule cells through a cyclic AMP mechanism.During a water deficit, the secretion of ADH increases. This increases water reabsorption.During an excess of water, the secretion of ADH decreases. Less water is reabsorbed. More is eliminated.
40 Elimination of excess H2O If overhydrated, no ADH released, therefore distal tubules and collecting ducts remain impermeable to H2OEven though water wants to leave (due to osmotic forces), it cannotTherefore, a large volume of dilute urine is excreted
43 SummaryThe medullary vertical osmotic gradient and ADH allow the kidney to excrete urine of varying concentrationsWithout this osmotic gradient, we could not produce a concentrated urine, and would be unable to conserve waterWe would likewise be unable to rid the body of excess water w/o this system