Renal Functions: Renal Functions: Renal Function: Produce Urine

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1 Renal Functions: Excrete metabolic waste products Reabsorb vital nutrients Regulate osmolarity: Maintain ion balance Regulate extracellular fluid volume (and thus blood pressure) Renal Functions: Regulate blood ph Reabsorb essential nutrients Excrete excess water, ions and foreign substances Produce hormones: Erythropoietin Calcitriol (activated vitamin D; essential for Ca++ absorption) Renin Renal Function: Produce Urine More solutes = darker urine Measured in specific gravity or osmolarity Measuring solutes: PURE water: Dilute urine: Concentrated urine: 1.035

2 Urine Characteristics Urine may become dilute due to: Excess drinking, diuretics, renal failure Urine may become concentrated due to: Inadequate fluid intake, fever, pyelonephritis Abnormal solutes signal problems: Glucose due to excess sugar intake or diabetes Proteins due to physical exertion, pregnancy, glomerulonephritis, hypertension Pus urinary tract infection Blood bleeding in the urinary tract Bile pigments liver disease (hepatitis)

3 Anatomy Review Retroperitoneal, below diaphragm and liver Each one: 160 g; 12 cm x 6 cm (size of a fist) 25% of blood flow from heart goes to renal arteries

4 The Nephron: Vascular Elements Vascular elements: Renal artery! Afferent arteriole! Glomerulus! efferent arteriole! peritubular capillaries! venules! veins! renal vein Notice something strange here? The Nephron: Tubular Elements Renal corpuscle Glomerulus + Bowman's capsule Proximal tubule Loop of Henle Distal tubule Collecting duct Nephron Processes

5 Filtration (F) Movement of fluid from blood to nephron lumen Once in the lumen, what is it? Where is it? Specific or non-specific? Filtration What drives filtration?

6 Filtration These are fenestrated capillaries (L: fenestra = window) Filtration is driven by hydraulic pressure (about 10 mm Hg) But is it selective? Rate of Filtration Glomerular Filtration Rate (GFR) = volume of fluid filtering into Bowman's capsule per unit time = 115 ml/ min in women and 125 ml/ min in men Why does fluid leave the capillary and enter the capsule? (Here we go again )

7 Exchange is now from one tube to another!

8 Filtration SO, if filtration is driven by hydraulic pressure, does the rate of filtration by the glomerulus change as hydraulic pressure changes? Regulation of GFR Extrinsic regulation: ANS Intrinsic regulation: Autoregulation Intrinsic regulation: Tubuloglomeruler feedback

9 Autoregulation Autoregulation

10 Tubuloglomerular Feedback Reabsorption (R) Returning fluid from the lumen to the blood 180L of plasma is filtered, but 99% of that (178.2L) is reabsorbed WHY? Why do it the Hard Way?

11 Reabsorption may be: Active: Primary, secondary active transport! Passive: diffusion, leak channels, facilitated diffusion carriers And how do you know what kind of transport it is? Here we go again... Saturation, specificity, competition

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13 Transport Maxima Ex: Glucose transport saturation Normal: Gluc 100 mg/dl blood Gluc 0 mg/dl urine! Diabetes mellitus: Gluc > 300 mg/dl blood Tm 300 mg/dl reabsorption

14 Secretion (S) Transporting substances from the blood to lumen! Depends mostly on membrane transport systems Excretion (E) Urine is very different from the filtrate entering the nephron What is enriched? What is removed?

15 Excretion (E) Urine is formed 24/7, but (thankfully) stored Urinary Bladder Is hollow Exhibits plasticity Holds about 500 ml comfortably Excretion (E) Urethra Internal sphincter: tonic contraction of smooth muscle External sphincter: skeletal muscle under control of somatic motor neurons; tonic stimulation from CNS except during urination Gender differences... urethral challenges...

16 Seriously... How much excretion? Obligatory water loss = 400 ml / day Maximum? What do you think? How is this regulated? Journey Through the Tubules and TWO BIG QUESTIONS: How can the kidneys produce urine that is hypertonic to the blood being filtered?! and! How is urine volume / osmolarity regulated as hydration levels change?

17 Proximal Tubule Filtrate is isoosmotic w/ plasma (300 mosm) Na+/K+ pumps Cl- ions follow Na+ and water follows all!! So... is peritubular blood isoosmotic? Regulation here? Loop of Henle Reabsorption of 20% of salts and water, regardless of hydration state Regulation here? Ascending limb: Na+ is actively extruded from the filtrate, Cl- follows passively. What about water? Loop of Henle Walls of the ascending limb are not permeable to water.

18 Descending Limb Impermeable to salt Permeable to water; water moves by osmosis out of the descending limb in response to the hypertonic tissue fluid Descending Limb Countercurrent Multiplication Effect Effects of Urea Contributes to the hypertonicity of tissue fluid in the medulla.

19 Show Me the Regulation! Where s the control?

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21 Other Hormonal Effects