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Chapter 19b The Kidneys. Reabsorption Principles governing the tubular reabsorption of solutes and water Figure 19-11 Na + is reabsorbed by active transport.

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Presentation on theme: "Chapter 19b The Kidneys. Reabsorption Principles governing the tubular reabsorption of solutes and water Figure 19-11 Na + is reabsorbed by active transport."— Presentation transcript:

1 Chapter 19b The Kidneys

2 Reabsorption Principles governing the tubular reabsorption of solutes and water Figure Na + is reabsorbed by active transport. Electrochemical gradient drives anion reabsorption. Water moves by osmosis, following solute reabsorption. Concentrations of other solutes increase as fluid volume in lumen decreases. Permeable solutes are reabsorbed by diffusion. Na + Anions H2OH2O K +, Ca 2+, urea Tubular epithelium Extracellular fluid Tubule lumen Filtrate is similar to interstitial fluid

3 Reabsorption Transepithelial transport Substances cross both apical (lumen side) and basolateral membrane Paracellular pathway Substances pass through the junction between two adjacent cells

4 Reabsorption Figure [Na + ] high [Na + ] low K+K+ Na + ATP Proximal tubule cell Interstitial fluid Tubule lumen Na + reabsorbed Na + enters cell through membrane proteins, moving down its electrochemical gradient. Na + is pumped out the basolateral side of cell by the Na + -K + -ATPase. ATP= Active transporter= Membrane protein KEY Na + Filtrate is similar to interstitial fluid Sodium reabsorption in the proximal tubule

5 Reabsorption Sodium-linked glucose reabsorption in the proximal tubule Figure = SGLT secondary active transporter = GLUT facilitated diffusion carrier [Na + ] high [glu] low Na + [Na + ] high [glu] low glu [Na + ] low [glu] high K+K+ ATP Glucose and Na + reabsorbed + Na + moving down its electrochemical gradient using the SGLT protein pulls glucose into the cell against its concentration gradient. Glucose diffuses out the basolateral side of the cell using the GLUT protein. Na + is pumped out by Na + -K + -ATPase. Proximal tubule cell Interstitial fluidTubule lumen ATP= Active transporter KEY Filtrate is similar to interstitial fluid

6 Reabsorption Urea Passive reabsorption Plasma proteins Transcytosis

7 Reabsorption Saturation of mediated transport Figure Renal threshold is plasma concentration at which saturation occurs. Transport maximum (T m ) is transport rate at saturation. Saturation occurs. Plasma [substrate] (mg/mL) Transport rate of substrate (mg/min)

8 Reabsorption Glucose handling by the nephron Figure 19-15a

9 Reabsorption Figure 19-15b

10 Reabsorption Figure 19-15c

11 Reabsorption Figure 19-15d

12 Secretion Transfer of molecules from extracellular fluid into lumen of the nephron Active process Important in homeostatic regulation K + and H + Increasing secretion enhances nephron excretion A competitive process Penicillin and probenecid

13 Excretion Excretion = filtration – reabsorption + secretion Clearance Rate at which a solute disappears from the body by excretion or by metabolism Non-invasive way to measure GFR Inulin and creatinine used to measure GFR

14 Inulin Clearance Inulin clearance is equal to GFR Figure Glomerulus Peritubular capillaries Afferent arteriole Efferent arteriole Nephron Filtration (100 mL/min) = 100 mL of plasma or filtrate Inulin concentration is 4/100 mL. GFR = 100 mL /min 100 mL plasma is reabsorbed. No inulin is reabsorbed. 100% of inulin is excreted so inulin clearance = 100 mL/min. Inulin molecules 100 mL, 0% inulin reabsorbed Inulin clearance = 100 mL/min 100% inulin excreted KEY

15 Inulin Clearance Figure 19-16, steps 1–4 Glomerulus Peritubular capillaries Afferent arteriole Efferent arteriole Nephron Filtration (100 mL/min) = 100 mL of plasma or filtrate Inulin concentration is 4/100 mL. GFR = 100 mL /min 100 mL plasma is reabsorbed. No inulin is reabsorbed. 100% of inulin is excreted so inulin clearance = 100 mL/min. Inulin molecules 100 mL, 0% inulin reabsorbed Inulin clearance = 100 mL/min 100% inulin excreted KEY

16 GFR Filtered load of X = [X] plasma  GFR Filtered load of inulin = excretion rate of inulin GFR = excretion rate of inulin/[inulin] plasma = inulin clearance GFR = inulin clearance

17 Excretion Table 19-2

18 Filtration (100 mL/min) Glucose molecules 100 mL, 100% glucose reabsorbed Glucose clearance = 0 mL/min (a) Glucose clearance No glucose excreted Plasma concentration is 4/100 mL. GFR = 100 mL /min 100 mL plasma is reabsorbed. Clearance depends on renal handling of solute. KEY = 100 mL of plasma or filtrate Excretion The relationship between clearance and excretion Figure 19-17a

19 Excretion Figure 19-17b (b) Urea clearance Plasma concentration is 4/100 mL. GFR = 100 mL /min 100 mL plasma is reabsorbed. Clearance depends on renal handling of solute. KEY Filtration (100 mL/min) Urea molecules 100 mL, 50% of urea reabsorbed 50% of urea excreted Urea clearance = 50 mL/min = 100 mL of plasma or filtrate

20 Excretion Figure 19-17c (c) Penicillin clearance Plasma concentration is 4/100 mL. GFR = 100 mL /min 100 mL plasma is reabsorbed. Clearance depends on renal handling of solute. KEY Filtration (100 mL/min) 100 mL, 0 penicillin reabsorbed Some additional penicillin secreted. Penicillin clearance = 150 mL/min More penicillin is excreted than was filtered. Penicillin molecules = 100 mL of plasma or filtrate

21 Gout Limit animal protein. Avoid or severely limit high- purine foods, including organ meats, such as liver, and herring, anchovies and mackerel. Red meat (beef, pork and lamb), fatty fish and seafood (tuna, shrimp, lobster and scallops) are associated with increased risk of gout. Because all animal protein contains purines, limit your intake. Eat more plant-based proteins. You can increase your protein by including more plant-based sources, such as beans and legumes. This switch will also help you cut down on saturated fats, which may indirectly contribute to obesity and gout. Limit or avoid alcohol. Alcohol interferes with the elimination of uric acid from your body. Drinking beer, in particular, has been linked to gout attacks

22 Micturition The storage of urine and the micturition reflex Figure 19-18a Bladder (smooth muscle) Internal sphincter (smooth muscle) passively contracted External sphincter (skeletal muscle) stays contracted (a) Bladder at rest Tonic discharge Relaxed (filling) state Higher CNS input Incontinence

23 Micturition Figure 19-18b Stretch receptors fire. Parasympathetic neurons fire. Motor neurons stop firing. Smooth muscle contracts. Internal sphincter passively pulled open. External sphincter relaxes. (b) Micturition Internal sphincter External sphincter Tonic discharge inhibited Higher CNS input may facilitate or inhibit reflex Sensory neuron Parasympathetic neuron Motor neuron Stretch receptors

24 Summary Functions of the kidneys Anatomy Kidney, nephron, cortex, and medulla Renal blood flow and fluid flow from glomerulus to renal pelvis Overview of kidney function Filtration Podocytes, filtration slits, and mesangial cells Filtration fraction, GFR, and regulation of GFR

25 Summary Reabsorption How solutes are transported Transport maximum and renal threshold Secretion Excretion Clearance, inulin, and creatinine Micturition


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