Human Anatomy and Physiology Eleventh Edition PDF

Human Anatomy and Physiology Eleventh Edition Chapter 25 Part B The Urinary System PowerPoint® Lectures Slides prepared by Karen Dunbar Kareiva, Ivy Tech Community College...

Human Anatomy and Physiology Eleventh Edition Chapter 25 Part B The Urinary System PowerPoint® Lectures Slides prepared by Karen Dunbar Kareiva, Ivy Tech Community College Copyright © 2019, 2016, 2013 Pearson Education, Inc. All Rights Reserved 25.5 Step 2: Tubular Reabsorption (1 of 2) Tubular reabsorption quickly reclaims most of tubular contents and returns them to blood Selective transepithelial process – Almost all organic nutrients are reabsorbed – Water and ion reabsorption is hormonally regulated and adjusted Includes active and passive tubular reabsorption Substances can follow two routes: 1. Transcellular 2. Paracellular Copyright © 2019, 2016, 2013 Pearson Education, Inc. All Rights Reserved Tubular Reabsorption Tubular reabsorption Copyright © 2019, 2016, 2013 Pearson Education, Inc. All Rights Reserved 25.5 Step 2: Tubular Reabsorption (2 of 2) 1. Transcellular route  Solute enters apical membrane of tubule cells  Travels through cytosol of tubule cells  Exits basolateral membrane of tubule cells  Enters blood through endothelium of peritubular capillaries 2. Paracellular route  Between tubule cells – Limited by tight junctions, but leaky in proximal nephron Water, Ca2+, Mg2+, K+, and some Na+ in the PCT move via this route Copyright © 2019, 2016, 2013 Pearson Education, Inc. All Rights Reserved Tubular Reabsorption Occurs by Transcellular and Paracellular Routes (1 of 6) The transcellular route Filtrate Tubule cell Interstitial involves: in tubule fluid Peri- lumen 1 Transport across the apical Tight Lateral tubular intercellular membrane. junction capillary space 2 Diffusion through the cytosol. 3 Transport across the 3 4 basolateral membrane. (Often involves the lateral intercellular 1 2 3 4 spaces because membrane H2O and transporters transport ions into solutes Transcellular route these spaces.) 4 Movement through the interstitial fluid and into the Apical capillary. membrane Capillary endothelial The paracellular route involves: cell Paracellular route a Movement through leaky H2O and tight junctions, particularly in solutes the proximal convoluted tubule. a b Basolateral b Movement through the membranes interstitial fluid and into the capillary. Figure 25.15 Tubular reabsorption occurs by transcellular and paracellular routes. Copyright © 2019, 2016, 2013 Pearson Education, Inc. All Rights Reserved Tubular Reabsorption Occurs by Transcellular and Paracellular Routes (2 of 6) The transcellular route Filtrate Tubule cell Interstitial involves: in tubule fluid Peri- lumen 1 Transport across the apical Tight Lateral tubular intercellular membrane. junction capillary space H2O and 1 solutes Transcellular route Apical membrane Capillary endothelial cell Paracellular route H2O and solutes Basolateral membranes Figure 25.15 Tubular reabsorption occurs by transcellular and paracellular routes. Copyright © 2019, 2016, 2013 Pearson Education, Inc. All Rights Reserved Tubular Reabsorption Occurs by Transcellular and Paracellular Routes (3 of 6) The transcellular route Filtrate Tubule cell Interstitial involves: in tubule fluid Peri- lumen 1 Transport across the apical Tight Lateral tubular intercellular membrane. junction capillary space 2 Diffusion through the cytosol. H2O and 1 2 solutes Transcellular route Apical membrane Capillary endothelial cell Paracellular route H2O and solutes Basolateral membranes Figure 25.15 Tubular reabsorption occurs by transcellular and paracellular routes. Copyright © 2019, 2016, 2013 Pearson Education, Inc. All Rights Reserved Tubular Reabsorption Occurs by Transcellular and Paracellular Routes (4 of 6) The transcellular route Filtrate Tubule cell Interstitial involves: in tubule fluid Peri- lumen 1 Transport across the apical Tight Lateral tubular intercellular membrane. junction capillary space 2 Diffusion through the cytosol. 3 Transport across the 3 basolateral membrane. (Often involves the lateral intercellular 1 2 3 spaces because membrane H2O and transporters transport ions into solutes Transcellular route these spaces.) Apical membrane Capillary endothelial cell Paracellular route H2O and solutes Basolateral membranes Figure 25.15 Tubular reabsorption occurs by transcellular and paracellular routes. Copyright © 2019, 2016, 2013 Pearson Education, Inc. All Rights Reserved Tubular Reabsorption Occurs by Transcellular and Paracellular Routes (5 of 6) The transcellular route Filtrate Tubule cell Interstitial involves: in tubule fluid Peri- lumen 1 Transport across the apical Tight Lateral tubular intercellular membrane. junction capillary space 2 Diffusion through the cytosol. 3 Transport across the 3 4 basolateral membrane. (Often involves the lateral intercellular 1 2 3 4 spaces because membrane H2O and transporters transport ions into solutes Transcellular route these spaces.) 4 Movement through the interstitial fluid and into the Apical capillary. membrane Capillary endothelial cell Paracellular route H2O and solutes Basolateral membranes Figure 25.15 Tubular reabsorption occurs by transcellular and paracellular routes. Copyright © 2019, 2016, 2013 Pearson Education, Inc. All Rights Reserved Tubular Reabsorption Occurs by Transcellular and Paracellular Routes (6 of 6) The transcellular route Filtrate Tubule cell Interstitial involves: in tubule fluid Peri- lumen 1 Transport across the apical Tight Lateral tubular intercellular membrane. junction capillary space 2 Diffusion through the cytosol. 3 Transport across the 3 4 basolateral membrane. (Often involves the lateral intercellular 1 2 3 4 spaces because membrane H2O and transporters transport ions into solutes Transcellular route these spaces.) 4 Movement through the interstitial fluid and into the Apical capillary. membrane Capillary endothelial The paracellular route involves: cell Paracellular route a Movement through leaky H2O and tight junctions, particularly in solutes the proximal convoluted tubule. a b Basolateral b Movement through the membranes interstitial fluid and into the capillary. Figure 25.15 Tubular reabsorption occurs by transcellular and paracellular routes. Copyright © 2019, 2016, 2013 Pearson Education, Inc. All Rights Reserved Tubular Reabsorption of Sodium (1 of 2) Sodium transport across the basolateral membrane – Na+ is most abundant cation in filtrate – Transport of Na+ across basolateral membrane of tubule cell is via primary active transport – Na+−K+ ATPase pumps Na+ into interstitial space – Na+ is then swept by bulk flow into peritubular capillaries Copyright © 2019, 2016, 2013 Pearson Education, Inc. All Rights Reserved Tubular Reabsorption of Sodium (2 of 2) Transport across apical membrane – Na+ enters tubule cell at apical surface via secondary active transport (cotransport) or via facilitated diffusion through channels  Active pumping of Na+at basolateral membrane results in strong electrochemical gradient within tubule cell – Results in low intracellular Na+levels that facilitates Na+diffusion – K+leaks out of cell into interstitial fluid, leaving a net negative charge inside cell, which also acts to pull Na+ inward Copyright © 2019, 2016, 2013 Pearson Education, Inc. All Rights Reserved Tubular Reabsorption of Nutrients, Water, and Ions (1 of 3) Na+ reabsorption by primary active transport provides energy and means for reabsorbing almost every other substance Secondary active transport – Electrochemical gradient created by pumps at basolateral surface give “push” needed for transport of other solutes – Organic nutrients reabsorbed by secondary active transport are cotransported with Na+  Glucose, amino acids, some ions, vitamins Copyright © 2019, 2016, 2013 Pearson Education, Inc. All Rights Reserved Tubular Reabsorption of Nutrients, Water, and Ions (2 of 3) Passive tubular reabsorption of water – Movement of Na+ and other solutes creates osmotic gradient for water – Water is reabsorbed by osmosis, aided by water-filled pores called aquaporins  Obligatory water reabsorption – Aquaporins are always present in PCT  Facultative water reabsorption – Aquaporins are inserted in collecting ducts only if ADH is present Copyright © 2019, 2016, 2013 Pearson Education, Inc. All Rights Reserved Tubular Reabsorption of Nutrients, Water, and Ions (3 of 3) Passive tubular reabsorption of solutes – Solute concentration in filtrate increases as water is reabsorbed  Creates concentration gradients for solutes, which drive their entry into tubule cell and peritubular capillaries – Fat-soluble substances, some ions, and urea will follow water into peritubular capillaries down their concentration gradients  For this reason, lipid-soluble drugs and environmental pollutants are reabsorbed even though it is not desirable Copyright © 2019, 2016, 2013 Pearson Education, Inc. All Rights Reserved  Tubular Reabsorption of Water and Nutrients Uses Active and PCT Passive Transport (1 of 7) 1 At the basolateral membrane, Na+ Filtrate Interstitial in tubule fluid Peri- is pumped into the interstitial space by lumen PCT cell tubular the Na+-K+ ATPase. Active Na+ capillary transport creates concentration gradients that drive: 2 “Downhill” Na+ entry at the Na+ 2 apical membrane. 3Na+ 3Na+ 3 Reabsorption of organic nutrients 1 and certain ions by cotransport at the Glucose 2K+ 2K+ apical membrane. Amino acids 3 Some ions Vitamins K+ 4 Reabsorption of water by osmosis through aquaporins. Water reabsorption increases the 4 concentration of the solutes that are H2O left behind. These solutes can then be reabsorbed as they move down their gradients: 5 Lipid-soluble 5 Lipid-soluble substances substances diffuse by the transcellular route. 6 Various ions 6 Various ions (e.g., Cl−, Ca2+, K+) and urea Paracellular and urea diffuse by the paracellular Tight junction route route. Primary active transport Transport protein Secondary active transport Ion channel Passive transport (diffusion) Aquaporin Figure 25.16 Tubular reabsorption of water and nutrients uses active and passive transport. Copyright © 2019, 2016, 2013 Pearson Education, Inc. All Rights Reserved  Tubular Reabsorption of Water and Nutrients Uses Active and PCT Passive Transport (2 of 7) 1 At the basolateral membrane, Na+ Filtrate Interstitial in tubule fluid Peri- is pumped into the interstitial space by lumen PCT cell tubular the Na+-K+ ATPase. Active Na+ capillary transport creates concentration gradients that drive: Na+ 3Na+ 3Na+ 1 Glucose 2K+ 2K+ Amino acids Some ions Vitamins K+ H2O Lipid-soluble substances Various ions and urea Paracellular Tight junction route Primary active transport Transport protein Secondary active transport Ion channel Passive transport (diffusion) Aquaporin Figure 25.16 Tubular reabsorption of water and nutrients uses active and passive transport. Copyright © 2019, 2016, 2013 Pearson Education, Inc. All Rights Reserved  Tubular Reabsorption of Water and Nutrients Uses Active and PCT Passive Transport (3 of 7) 1 At the basolateral membrane, Na+ Filtrate Interstitial in tubule fluid Peri- is pumped into the interstitial space by lumen PCT cell tubular the Na+-K+ ATPase. Active Na+ capillary transport creates concentration gradients that drive: 2 “Downhill” Na+ entry at the Na+ 2 apical membrane. 3Na+ 3Na+ 1 Glucose 2K+ 2K+ Amino acids Some ions Vitamins K+ H2O Lipid-soluble substances Various ions and urea Paracellular Tight junction route Primary active transport Transport protein Secondary active transport Ion channel Passive transport (diffusion) Aquaporin Figure 25.16 Tubular reabsorption of water and nutrients uses active and passive transport. Copyright © 2019, 2016, 2013 Pearson Education, Inc. All Rights Reserved  Tubular Reabsorption of Water and Nutrients Uses Active and PCT Passive Transport (4 of 7) 1 At the basolateral membrane, Na+ Filtrate Interstitial in tubule fluid Peri- is pumped into the interstitial space by lumen PCT cell tubular the Na+-K+ ATPase. Active Na+ capillary transport creates concentration gradients that drive: 2 “Downhill” Na+ entry at the Na+ 2 apical membrane. 3Na+ 3Na+ 3 Reabsorption of organic nutrients 1 and certain ions by cotransport at the Glucose 2K+ 2K+ apical membrane. Amino acids 3 Some ions Vitamins K+ H2O Lipid-soluble substances Various ions and urea Paracellular Tight junction route Primary active transport Transport protein Secondary active transport Ion channel Passive transport (diffusion) Aquaporin Figure 25.16 Tubular reabsorption of water and nutrients uses active and passive transport. Copyright © 2019, 2016, 2013 Pearson Education, Inc. All Rights Reserved  Tubular Reabsorption of Water and Nutrients Uses Active and PCT Passive Transport (5 of 7) 1 At the basolateral membrane, Na+ Filtrate Interstitial in tubule fluid Peri- is pumped into the interstitial space by lumen PCT cell tubular the Na+-K+ ATPase. Active Na+ capillary transport creates concentration gradients that drive: 2 “Downhill” Na+ entry at the Na+ 2 apical membrane. 3Na+ 3Na+ 3 Reabsorption of organic nutrients 1 and certain ions by cotransport at the Glucose 2K+ 2K+ apical membrane. Amino acids 3 Some ions Vitamins K+ 4 Reabsorption of water by osmosis through aquaporins. Water reabsorption increases the 4 concentration of the solutes that are H2O left behind. These solutes can then be reabsorbed as they move down their gradients: 5 Lipid-soluble substances 6 Various ions and urea Paracellular Tight junction route Primary active transport Transport protein Secondary active transport Ion channel Passive transport (diffusion) Aquaporin Figure 25.16 Tubular reabsorption of water and nutrients uses active and passive transport. Copyright © 2019, 2016, 2013 Pearson Education, Inc. All Rights Reserved  Tubular Reabsorption of Water and Nutrients Uses Active and PCT Passive Transport (6 of 7) 1 At the basolateral membrane, Na+ Filtrate Interstitial in tubule fluid Peri- is pumped into the interstitial space by lumen PCT cell tubular the Na+-K+ ATPase. Active Na+ capillary transport creates concentration gradients that drive: 2 “Downhill” Na+ entry at the Na+ 2 apical membrane. 3Na+ 3Na+ 3 Reabsorption of organic nutrients 1 and certain ions by cotransport at the Glucose 2K+ 2K+ apical membrane. Amino acids 3 Some ions Vitamins K+ 4 Reabsorption of water by osmosis through aquaporins. Water reabsorption increases the 4 concentration of the solutes that are H2O left behind. These solutes can then be reabsorbed as they move down their gradients: 5 Lipid-soluble 5 Lipid-soluble substances substances diffuse by the transcellular route. 6 Various ions and urea Paracellular Tight junction route Primary active transport Transport protein Secondary active transport Ion channel Passive transport (diffusion) Aquaporin Figure 25.16 Tubular reabsorption of water and nutrients uses active and passive transport. Copyright © 2019, 2016, 2013 Pearson Education, Inc. All Rights Reserved  Tubular Reabsorption of Water and Nutrients Uses Active and PCT Passive Transport (7 of 7) 1 At the basolateral membrane, Na+ Filtrate Interstitial in tubule fluid Peri- is pumped into the interstitial space by lumen PCT cell tubular the Na+-K+ ATPase. Active Na+ capillary transport creates concentration gradients that drive: 2 “Downhill” Na+ entry at the Na+ 2 apical membrane. 3Na+ 3Na+ 3 Reabsorption of organic nutrients 1 and certain ions by cotransport at the Glucose 2K+ 2K+ apical membrane. Amino acids 3 Some ions Vitamins K+ 4 Reabsorption of water by osmosis through aquaporins. Water reabsorption increases the 4 concentration of the solutes that are H2O left behind. These solutes can then be reabsorbed as they move down their gradients: 5 Lipid-soluble 5 Lipid-soluble substances substances diffuse by the transcellular route. 6 Various ions 6 Various ions (e.g., Cl−, Ca2+, K+) and urea Paracellular and urea diffuse by the paracellular Tight junction route route. Primary active transport Transport protein Secondary active transport Ion channel Passive transport (diffusion) Aquaporin Figure 25.16 Tubular reabsorption of water and nutrients uses active and passive transport. Copyright © 2019, 2016, 2013 Pearson Education, Inc. All Rights Reserved Transport Maximum Transcellular transport systems are specific and limited – Transport maximum (Tm) exists for almost every reabsorbed substance  Reflects number of carriers in renal tubules that are available – When carriers for a solute are saturated, excess is excreted in urine  Example: hyperglycemia leads to high blood glucose levels that exceed Tm, and glucose spills over into urine Copyright © 2019, 2016, 2013 Pearson Education, Inc. All Rights Reserved Reabsorptive Capabilities of Renal Tubules and Collecting Ducts (1 of 5) Proximal convoluted tubule – Site of most reabsorption  All nutrients, such as glucose and amino acids, are reabsorbed  65% of Na+ and water reabsorbed  Many ions  Almost all uric acid  About half of urea (later secreted back into filtrate) Copyright © 2019, 2016, 2013 Pearson Education, Inc. All Rights Reserved Reabsorptive Capabilities of Renal Tubules and Collecting Ducts (2 of 5) Nephron loop – Descending limb: H2O can leave, solutes cannot – Ascending limb: H2O cannot leave, solutes can  Thin segment is passive to Na+ movement  Thick segment has Na+−K+−2Cl– symporters and Na+−H+ antiporters that transport Na+ into cell – Some Na+can pass into cell by paracellular route in this area of limb Copyright © 2019, 2016, 2013 Pearson Education, Inc. All Rights Reserved Reabsorptive Capabilities of Renal Tubules and Collecting Ducts (3 of 5) Distal convoluted tubule and collecting duct – Reabsorption is hormonally regulated in these areas – Antidiuretic hormone (ADH)  Released by posterior pituitary gland  Causes principal cells of collecting ducts to insert aquaporins in apical membranes, increasing water reabsorption – Increased ADH levels cause an increase in water reabsorption Copyright © 2019, 2016, 2013 Pearson Education, Inc. All Rights Reserved Reabsorptive Capabilities of Renal Tubules and Collecting Ducts (4 of 5) – Aldosterone  Targets collecting ducts (principal cells) and distal DCT  Promotes synthesis of apical Na+ and K+ channels, and basolateral Na+−K+ ATPases for Na+ reabsorption (water follows)  As a result, little Na+ leaves body  Without aldosterone, daily loss of filtered Na+would be 2%, which is incompatible with life  Functions: increase blood pressure and decrease K+ levels Copyright © 2019, 2016, 2013 Pearson Education, Inc. All Rights Reserved Reabsorptive Capabilities of Renal Tubules and Collecting Ducts (5 of 5) Atrial natriuretic peptide – Reduces blood Na+, resulting in decreased blood volume and blood pressure – Released by cardiac atrial cells if blood volume or pressure elevated Parathyroid hormone – Acts on DCT to increase Ca2+ reabsorption Copyright © 2019, 2016, 2013 Pearson Education, Inc. All Rights Reserved  Cortex Summary of Tubular Reabsorption 65% of filtrate volume reabsorbed H2O Regulated reabsorption Na+(by aldosterone; Cl− follows) and Secretion (1 of 2) Na+, HCO3−, and many other ions Glucose, amino acids, Ca2+ (by parathyroid hormone) and other nutrients H+ and NH4+ Regulated Some drugs secretion K+ (by aldosterone) H2O Na+, K+, Cl− Regulated Outer reabsorption medulla H2O (by ADH) Na+ (by aldosterone; Cl− follows) Urea (increased by ADH) Urea Regulated secretion K+ (by Inner aldosterone) medulla Reabsorption or secretion to maintain blood pH described in Chapter 26; involves H+, HCO3−, Figure 25.17 Summary of tubular reabsorption and and NH4+ secretion. Reabsorption Secretion Copyright © 2019, 2016, 2013 Pearson Education, Inc. All Rights Reserved Table 25.2-1 Reabsorption Capabilities of Different Segments of the Renal Tubules and Collecting Ducts (1 of 2) Table 25.2 Reabsorption Capabilities of Different Segments of the Renal Tubules and Collecting Ducts Copyright © 2019, 2016, 2013 Pearson Education, Inc. All Rights Reserved Table 25.2-2 Reabsorption Capabilities of Different Segments of the Renal Tubules and Collecting Ducts (2 of 2) Table 25.2 Reabsorption Capabilities of Different Segments of the Renal Tubules and Collecting Ducts Copyright © 2019, 2016, 2013 Pearson Education, Inc. All Rights Reserved 25.6 Step 3: Tubular Secretion (1 of 2) Tubular secretion is reabsorption in reverse Occurs almost completely in PCT Selected substances are moved from peritublar capillaries through tubule cells out into filtrate – K+, H+, NH4+, creatinine, organic acids and bases – Substances synthesized in tubule cells also are secreted (example: HCO3–) Copyright © 2019, 2016, 2013 Pearson Education, Inc. All Rights Reserved Tubular Secretion Tubular secretion Copyright © 2019, 2016, 2013 Pearson Education, Inc. All Rights Reserved 25.6 Step 3: Tubular Secretion (2 of 2) Tubular secretion is important for: – Disposing of substances, such as drugs or metabolites, that are bound to plasma proteins – Eliminating undesirable substances that were passively reabsorbed (example: urea and uric acid) – Ridding body of excess K+ (aldosterone effect) – Controlling blood pH by altering amounts of H+ or HCO3–in urine Copyright © 2019, 2016, 2013 Pearson Education, Inc. All Rights Reserved  Cortex Summary of Tubular Reabsorption 65% of filtrate volume reabsorbed Regulated reabsorption Na+(by aldosterone; and Secretion (2 of 2) H2O Na+, HCO3−, and many other ions Cl− follows) Ca2+ (by parathyroid hormone) Glucose, amino acids, and other nutrients H+ and NH4+ Regulated Some drugs secretion K+ (by aldosterone) H2O Na+, K+, Cl− Regulated Outer reabsorption medulla H2O (by ADH) Na+ (by aldosterone; Cl− follows) Urea (increased by ADH) Urea Regulated secretion K+ (by Inner aldosterone) medulla Reabsorption or secretion to maintain blood pH described in Chapter 26; involves H+, HCO3−, Figure 25.17 Summary of tubular reabsorption and and NH4+ secretion. Reabsorption Secretion Copyright © 2019, 2016, 2013 Pearson Education, Inc. All Rights Reserved 25.7 Regulation of Urine Concentration and Volume (1 of 4) One main function of kidneys is to make any adjustment needed to maintain body fluid osmotic concentration at around 300 mOsm – Osmolality: number of solute particles in 1 kg of H2O  1 osmol = 1 mole of particle per kg H2O  Body fluids have much smaller amounts, so expressed in milliosmols (mOsm) = 0.001 osmol Copyright © 2019, 2016, 2013 Pearson Education, Inc. All Rights Reserved 25.7 Regulation of Urine Concentration and Volume (2 of 4) Kidneys produce only small amounts of urine if the body is dehydrated, or dilute urine if overhydrated Accomplish this by using countercurrent mechanism – Fluid flows in opposite directions in two adjacent segments of same tube with hairpin turn Copyright © 2019, 2016, 2013 Pearson Education, Inc. All Rights Reserved 25.7 Regulation of Urine Concentration and Volume (3 of 4) – Two types of countercurrent mechanisms  Countercurrent multiplier: interaction of filtrate flow in ascending/descending limbs of nephron loops of juxtamedullary nephrons  Countercurrent exchanger: blood flow in ascending/descending limbs of vasa recta Copyright © 2019, 2016, 2013 Pearson Education, Inc. All Rights Reserved 25.7 Regulation of Urine Concentration and Volume (4 of 4) – These two countercurrent mechanisms work together to:  Establish and maintain medullary osmotic gradient from renal cortex through medulla – Gradient runs from 300 mOsm in cortex to 1200 mOsm at bottom of medulla – Countercurrent multiplier creates gradient – Countercurrent exchanger preserves gradient – Collecting ducts can then use gradient to vary urine concentration Copyright © 2019, 2016, 2013 Pearson Education, Inc. All Rights Reserved Osmotic Gradient in the Renal Medulla This greatly enlarged nephron and collecting duct show you the arrangement of structures that pass through the osmotic gradient in the renal medulla. If you keep this anatomy in mind, it will help you understand the process of making either very dilute or very concentrated urine. The osmolality of the interstitial fluid in the 300 renal cortex is isotonic 300 at 300 mOsm. 400 600 900 1200 The osmolality of the interstitial fluid of the renal medulla increases progressively from 300 mOsm at the 1200 900 cortex-medulla 600 400 300 300 junction to 1200 mOsm at the medulla-pelvis junction. 120 900 0 00 12 0 600 90 0 400 60 0 300 40 0 300 30 0 30 Figure 25.18 Osmotic gradient in the renal medulla. Copyright © 2019, 2016, 2013 Pearson Education, Inc. All Rights Reserved Juxtamedullary Nephrons The big picture: Three key players Create an Osmotic interact with the medullary Gradient within the Renal 300 Osmotic gradient. Medulla that Allows the 300 Kidney to Produce Urine The osmotic gradient: 400 of Varying Concentration The osmolality (solute concentration) of the 600 The long nephron loops of juxtamedullary nephrons create (1 of 7) medullary interstitial fluid Progressively increases 900 the gradient. They act as countercurrent multipliers. from the 300 mOsm of 1200 normal body fluid to 1200 mOsm at the deepest part of the medulla. 300 Lower 300 concentration of solutes 400 600 The vasa recta preserve the gradient. They act as 900 countercurrent exchangers (see Figure 25.19). Higher 1200 concentration of solutes 300 300 400 The collecting ducts of all nephrons use the gradient 600 to adjust urine osmolality (see Figure 25.20). FOCUS FIGURE 25.1 900 Medullary Osmotic Gradient 1200 Copyright © 2019, 2016, 2013 Pearson Education, Inc. All Rights Reserved Countercurrent Multiplier (1 of 4) Countercurrent multiplier involves the nephron loop and depends on: – Filtrate flow in opposite directions (descending/ascending) – Difference in permeabilities between descending nephron loop and ascending loop – Active transport of solutes out of ascending limb Limbs of nephron loop are not in direct contact but are close enough to influence each other’s exchanges with surrounding interstitial fluid Copyright © 2019, 2016, 2013 Pearson Education, Inc. All Rights Reserved Countercurrent Multiplier (2 of 4) Ascending limb of nephron loop is impermeable to H2O and selectively permeable to solutes – Na+and Cl–are actively reabsorbed in thick segment (some passively reabsorbed in thin segment) Descending limb of nephron loop is freely permeable to H2O, impermeable to solutes – H2O passes out of filtrate into hyperosmotic medullary interstitial fluid – Causes remaining filtrate osmolality to increase to ~1200 mOsm Copyright © 2019, 2016, 2013 Pearson Education, Inc. All Rights Reserved Countercurrent Multiplier (3 of 4) Countercurrent mechanism: – The more NaCl the ascending limb actively transports out into interstitial fluid, the more water diffuses out of the descending limb – The more water that diffuses out of the descending limb, the saltier the filtrate becomes – Ascending limb then uses salty filtrate to further raise osmolality of medullary interstitial fluid Copyright © 2019, 2016, 2013 Pearson Education, Inc. All Rights Reserved Countercurrent Multiplier (4 of 4) Constant difference of 200 mOsm always exists between two limbs of nephron loop and between ascending limb and interstitial fluid Difference is “multiplied” along length of loop (from 300 to 1200 mOsm = difference of 900 mOsm) Copyright © 2019, 2016, 2013 Pearson Education, Inc. All Rights Reserved Juxtamedullary Nephrons Long nephron loops of juxtamedullary nephrons create the gradient. The countercurrent multiplier depends on three properties These properties establish a positive feedback cycle Create an Osmotic Gradient of the nephron loop to establish the osmotic gradient. that uses the flow of fluid to multiply the power of the salt pumps. Filtrate flows in the within the Renal Medulla that opposite direction (countercurrent) through two Allows the Kidney to Produce adjacent parallel Water leaves the Interstitial fluid sections of a descending limb osmolality nephron loop. Urine of Varying H2O NaCI H2O NaCI Concentration (2 of 7) The descending limb is permeable The ascending limb is Osmolality of filtrate Salt is pumped out Start here impermeable to to water, but not water, and pumps in descending limb of the ascending limb to salt. out salt. Active transport Passive transport Water impermeable Osmolality of filtrate entering the ascending limb As water and solutes are reabsorbed, the loop first concentrates the filtrate, then dilutes it. 300 300 100 Cortex 100 300 300 1 Filtrate entering the 5 Filtrate is at its most dilute nephron loop is isosmotic H2O NaCI as it leaves the nephron loop. to both blood plasma and At 100 mOsm, it is hypo- cortical interstitial fluid. osmotic to the interstitial fluid. Osmolality of interstitial fluid (mOsm) H2O NaCI 400 400 200 H2O NaCI 4 Na+ and Cl– are pumped out Outer of the filtrate. This increases the medulla H2O NaCI interstitial fluid osmolality. 600 600 400 2 Water moves out of the H2O filtrate in the descending limb down its osmotic gradient. NaCI This concentrates the filtrate. H2O 900 900 700 H2O 3 Filtrate reaches its highest concentration at the bend of the Inner loop. medulla FOCUS FIGURE 25.1 Medullary Nephron loop 1200 1200 Osmotic Gradient Copyright © 2019, 2016, 2013 Pearson Education, Inc. All Rights Reserved Juxtamedullary Nephrons Long nephron loops of juxtamedullary nephrons create the gradient. The countercurrent multiplier depends on three properties These properties establish a positive feedback cycle that Create an Osmotic Gradient of the nephron loop to establish the osmotic gradient. uses the flow of fluid to multiply the power of the salt pumps. within the Renal Medulla that Filtrate flows in the opposite direction (countercurrent) through two Allows the Kidney to Produce adjacent parallel sections of a nephron loop. Water leaves the descending limb Interstitial fluid osmolality Urine of Varying H2O Concentration (3 of 7) NaCI H2O NaCI Start The ascending limb here The descending is impermeable to Osmolality of filtrate limb is permeable Salt is pumped out water, and pumps in descending limb to water, but not of the ascending limb out salt. to salt. Active transport Passive transport Water impermeable Osmolality of filtrate entering the ascending limb As water and solutes are reabsorbed, the loop first concentrates the filtrate, then dilutes it. 300 300 100 Cortex 100 300 300 1 Filtrate entering the nephron loop is isosmotic H2O NaCI to both blood plasma and Osmolality of interstitial fluid (mOsm) cortical interstitial fluid. H2O NaCI 400 400 200 H2O NaCI Outer medulla H2O NaCI 600 600 400 H2O NaCI H2O 900 900 700 H2O Inner FOCUS FIGURE 25.1 Medullary medulla Nephron loop 1200 1200 Osmotic Gradient Copyright © 2019, 2016, 2013 Pearson Education, Inc. All Rights Reserved Juxtamedullary Nephrons Long nephron loops of juxtamedullary nephrons create the gradient. The countercurrent multiplier depends on three properties These properties establish a positive feedback cycle that Create an Osmotic Gradient of the nephron loop to establish the osmotic gradient. uses the flow of fluid to multiply the power of the salt pumps. Filtrate flows in the within the Renal Medulla that opposite direction (countercurrent) through two Allows the Kidney to Produce adjacent parallel Water leaves the Interstitial fluid sections of a descending limb osmolality nephron loop. Urine of Varying H2O NaCI H2O NaCI Concentration (4 of 7) The descending limb is permeable The ascending limb is impermeable to Osmolality of filtrate Start here Salt is pumped out water, and pumps in descending limb to water, but not of the ascending limb out salt. to salt. Active transport Passive transport Water impermeable Osmolality of filtrate entering the ascending limb As water and solutes are reabsorbed, the loop first concentrates the filtrate, then dilutes it. 300 300 100 Cortex 100 300 300 1 Filtrate entering the nephron loop is isosmotic H2O NaCI to both blood plasma and Osmolality of interstitial fluid (mOsm) cortical interstitial fluid. H2O NaCI 400 400 200 H2O NaCI Outer medulla H2O NaCI 600 600 400 2 Water moves out of the H2O filtrate in the descending limb down its osmotic gradient. NaCI This concentrates the filtrate. H2O 900 900 700 H2O Inner medulla Nephron loop FOCUS FIGURE 25.1 Medullary 1200 1200 Osmotic Gradient Copyright © 2019, 2016, 2013 Pearson Education, Inc. All Rights Reserved Juxtamedullary Nephrons Long nephron loops of juxtamedullary nephrons create the gradient. The countercurrent multiplier depends on three properties These properties establish a positive feedback cycle that Create an Osmotic Gradient of the nephron loop to establish the osmotic gradient. uses the flow of fluid to multiply the power of the salt pumps. within the Renal Medulla that Filtrate flows in the opposite direction (countercurrent) through two Allows the Kidney to Produce adjacent parallel Water leaves the Interstitial fluid sections of a descending limb osmolality nephron loop. Urine of Varying H2O H2O Concentration (5 of 7) NaCI NaCI Start The ascending limb here The descending limb is permeable is impermeable to Osmolality of filtrate water, and pumps Salt is pumped out to water, but not in descending limb of the ascending limb to salt. out salt. Active transport Passive transport Water impermeable Osmolality of filtrate entering the ascending limb As water and solutes are reabsorbed, the loop first concentrates the filtrate, then dilutes it. 300 300 100 Cortex 100 300 300 1 Filtrate entering the nephron loop is isosmotic H2O NaCI to both blood plasma and Osmolality of interstitial fluid (mOsm) cortical interstitial fluid. H2O NaCI 400 400 200 H2O NaCI Outer medulla H2O NaCI 600 600 400 2 Water moves out of the H2O filtrate in the descending limb down its osmotic gradient. NaCI This concentrates the filtrate. H2O 900 900 700 H2O 3 Filtrate reaches its highest concentration at the bend of the Inner loop. FOCUS FIGURE 25.1 Medullary medulla Nephron loop 1200 1200 Osmotic Gradient Copyright © 2019, 2016, 2013 Pearson Education, Inc. All Rights Reserved Juxtamedullary Nephrons Long nephron loops of juxtamedullary nephrons create the gradient. The countercurrent multiplier depends on three properties These properties establish a positive feedback cycle that Create an Osmotic Gradient of the nephron loop to establish the osmotic gradient. uses the flow of fluid to multiply the power of the salt pumps. Filtrate flows in the within the Renal Medulla that opposite direction (countercurrent) through two Allows the Kidney to Produce adjacent parallel Water leaves the Interstitial fluid sections of a descending limb osmolality nephron loop. Urine of Varying H2O NaCI H2O NaCI Concentration (6 of 7) The descending limb is permeable The ascending limb is impermeable to Osmolality of filtrate Start here Salt is pumped out water, and pumps in descending limb to water, but not of the ascending limb out salt. to salt. Active transport Passive transport Water impermeable Osmolality of filtrate entering the ascending limb As water and solutes are reabsorbed, the loop first concentrates the filtrate, then dilutes it. 300 300 100 Cortex 100 300 300 1 Filtrate entering the nephron loop is isosmotic H2O NaCI to both blood plasma and Osmolality of interstitial fluid (mOsm) cortical interstitial fluid. H2O