Power Point Lecture Slides prepared by Janice Meeking
Power. Point® Lecture Slides prepared by Janice Meeking, Mount Royal College CHAPTER 25 The Urinary System: Part B Copyright © 2010 Pearson Education, Inc.
Tubular Reabsorption • A selective transepithelial process • All organic nutrients are reabsorbed • Water and ion reabsorption are hormonally regulated • Includes active and passive process • Two routes • Transcellular • Paracellular Copyright © 2010 Pearson Education, Inc.
Tubular Reabsorption • Transcellular route • Luminal membranes of tubule cells • Cytosol of tubule cells • Basolateral membranes of tubule cells • Endothelium of peritubular capillaries Copyright © 2010 Pearson Education, Inc.
Tubular Reabsorption • Paracellular route • Between cells • Limited to water movement and reabsorption of Ca 2+, Mg 2+, K+, and some Na+ in the PCT where tight junctions are leaky Copyright © 2010 Pearson Education, Inc.
Movement via the transcellular route involves: 1 Transport across the luminal membrane. 2 Diffusion through the cytosol. 3 Transport across the basolateral membrane. (Often involves the lateral intercellular spaces because membrane transporters transport ions into these spaces. ) 4 Movement through the interstitial fluid and into the capillary. Lateral intercellular space Tight junction Filtrate in tubule lumen The paracellular route involves: • Movement through leaky tight junctions, particularly in the PCT. Interstitial fluid Capillary endothelial cell Tubule cell Peritubular capillary Paracellular H 2 O 1 2 3 4 Transcellular Luminal membrane 1 Transcellular 3 4 2 Solutes 3 Paracellular Copyright © 2010 Pearson Education, Inc. 4 Basolateral membranes Active transport Passive transport Figure 25. 13
Sodium Reabsorption • Na+ (most abundant cation in filtrate) • Primary active transport out of the tubule cell by Na+-K+ ATPase in the basolateral membrane • Na+ passes in through the luminal membrane by secondary active transport or facilitated diffusion mechanisms Copyright © 2010 Pearson Education, Inc.
Sodium Reabsorption • Low hydrostatic pressure and high osmotic pressure in the peritubular capillaries • Promotes bulk flow of water and solutes (including Na+) Copyright © 2010 Pearson Education, Inc.
Reabsorption of Nutrients, Water, and Ions • Na+ reabsorption provides the energy and the means for reabsorbing most other substances • Organic nutrients are reabsorbed by secondary active transport • Transport maximum (Tm) reflects the number of carriers in the renal tubules available • When the carriers are saturated, excess of that substance is excreted Copyright © 2010 Pearson Education, Inc.
Reabsorption of Nutrients, Water, and Ions • Water is reabsorbed by osmosis (obligatory water reabsorption), aided by water-filled pores called aquaporins • Cations and fat-soluble substances follow by diffusion Copyright © 2010 Pearson Education, Inc.
1 At the basolateral membrane, Nucleus Filtrate in tubule lumen Na+ Tubule cell 3 Na+ 1 2 K+ 3 K+ 4 Lipid-soluble 5 substances Cl–, Ca 2+, K+ and other ions, urea 6 Tight junction Primary active transport Secondary active transport Passive transport (diffusion) Copyright © 2010 Pearson Education, Inc. Peritubular capillary 3 Reabsorption of organic 2 3 Na+ Glucose Amino acids Some ions Vitamins H 2 O Interstitial fluid Na+ is pumped into the interstitial space by the Na+-K+ ATPase. Active Na+ transport creates concentration gradients that drive: 2 “Downhill” Na + entry at the luminal membrane. Cl– Paracellular route Transport protein Ion channel or aquaporin nutrients and certain ions by cotransport at the luminal membrane. 4 Reabsorption of water by osmosis. Water reabsorption increases the concentration of the solutes that are left behind. These solutes can then be reabsorbed as they move down their concentration gradients: 5 Lipid-soluble substances diffuse by the transcellular route. 6 Cl– (and other anions), K+, and urea diffuse by the paracellular route. Figure 25. 14
Reabsorptive Capabilities of Renal Tubules and Collecting Ducts • PCT • Site of most reabsorption • 65% of Na+ and water • All nutrients • Ions • Small proteins Copyright © 2010 Pearson Education, Inc.
Reabsorptive Capabilities of Renal Tubules and Collecting Ducts • Loop of Henle • Descending limb: H 2 O • Ascending limb: Na+, K+, Cl Copyright © 2010 Pearson Education, Inc.
Reabsorptive Capabilities of Renal Tubules and Collecting Ducts • DCT and collecting duct • Reabsorption is hormonally regulated • Ca 2+ (PTH) • Water (ADH) • Na+ (aldosterone and ANP) Copyright © 2010 Pearson Education, Inc.
Reabsorptive Capabilities of Renal Tubules and Collecting Ducts • Mechanism of aldosterone • Targets collecting ducts (principal cells) and distal DCT • Promotes synthesis of luminal Na+ and K+ channels • Promotes synthesis of basolateral Na+-K+ ATPases Copyright © 2010 Pearson Education, Inc.
Tubular Secretion • Reabsorption in reverse • K+, H+, NH 4+, creatinine, and organic acids move from peritubular capillaries or tubule cells into filtrate • Disposes of substances that are bound to plasma proteins Copyright © 2010 Pearson Education, Inc.
Tubular Secretion • Eliminates undesirable substances that have been passively reabsorbed (e. g. , urea and uric acid) • Rids the body of excess K+ • Controls blood p. H by altering amounts of H+ or HCO 3– in urine Copyright © 2010 Pearson Education, Inc.
Regulation of Urine Concentration and Volume • Osmolality • Number of solute particles in 1 kg of H 2 O • Reflects ability to cause osmosis Copyright © 2010 Pearson Education, Inc.
Regulation of Urine Concentration and Volume • Osmolality of body fluids • Expressed in milliosmols (m. Osm) • The kidneys maintain osmolality of plasma at ~300 m. Osm, using countercurrent mechanisms Copyright © 2010 Pearson Education, Inc.
Countercurrent Mechanism • Occurs when fluid flows in opposite directions in two adjacent segments of the same tube • Filtrate flow in the loop of Henle (countercurrent multiplier) • Blood flow in the vasa recta (countercurrent exchanger) Copyright © 2010 Pearson Education, Inc.
Countercurrent Mechanism • Role of countercurrent mechanisms • Establish and maintain an osmotic gradient (300 m. Osm to 1200 m. Osm) from renal cortex through the medulla • Allow the kidneys to vary urine concentration Copyright © 2010 Pearson Education, Inc.
Cortex Medulla Copyright © 2010 Pearson Education, Inc. Figure 25. 15
Countercurrent Multiplier: Loop of Henle • Descending limb • Freely permeable to H 2 O, which passes out of the filtrate into the hyperosmotic medullary interstitial fluid • Filtrate osmolality increases to ~1200 m. Osm Copyright © 2010 Pearson Education, Inc.
Countercurrent Multiplier: Loop of Henle • Ascending limb • Impermeable to H 2 O • Selectively permeable to solutes • Na+ and Cl– are passively reabsorbed in the thin segment, actively reabsorbed in the thick segment • Filtrate osmolality decreases to 100 m. Osm Copyright © 2010 Pearson Education, Inc.
Osmolality of interstitial fluid (m. Osm) Active transport Passive transport Water impermeable Filtrate entering the loop of Henle is isosmotic to both blood plasma and cortical interstitial fluid. H 2 O Na. CI H 2 O The descending limb: • Permeable to H 2 O • Impermeable to Na. Cl H 2 O As filtrate flows, it becomes increasingly H 2 O concentrated as H 2 O leaves the tubule by H 2 O osmosis. The filtrate osmolality increases from 300 to 1200 m. Osm. Loop of Henle (a) Countercurrent multiplier. The long loops of Henle of the juxtamedullary nephrons create the medullary osmotic gradient. Copyright © 2010 Pearson Education, Inc. Na. CI Cortex Outer medulla Na. CI Inner medulla The ascending limb: • Impermeable to H 2 O • Permeable to Na. Cl Filtrate becomes increasingly dilute as Na. Cl leaves, eventually becoming hypo-osmotic to blood at 100 m. Osm in the cortex. Na. Cl leaving the ascending limb increases the osmolality of the medullary interstitial fluid. Figure 25. 16 a
Urea Recycling • Urea moves between the collecting ducts and the loop of Henle • Secreted into filtrate by facilitated diffusion in the ascending thin segment • Reabsorbed by facilitated diffusion in the collecting ducts deep in the medulla • Contributes to the high osmolality in the medulla Copyright © 2010 Pearson Education, Inc.
Countercurrent Exchanger: Vasa Recta • The vasa recta • Maintain the osmotic gradient • Deliver blood to the medullary tissues • Protect the medullary osmotic gradient by preventing rapid removal of salt, and by removing reabsorbed H 2 O Copyright © 2010 Pearson Education, Inc.
Osmolality of interstitial fluid (m. Osm) Cortex Blood from efferent arteriole Passive transport To vein Na. CI H 2 O Na. CI H 2 O Outer medulla Inner medulla Vasa recta (b) Countercurrent exchanger. The vasa recta preserve the medullary gradient while removing reabsorbed water and solutes. Copyright © 2010 Pearson Education, Inc. The vasa recta: • Highly permeable to H 2 O and solute • Nearly isosmotic to interstitial fluid due to sluggish blood flow Blood becomes more concentrated as it descends deeper into the medulla and less concentrated as it approaches the cortex. Figure 25. 16 b
Formation of Dilute Urine • Filtrate is diluted in the ascending loop of Henle • In the absence of ADH, dilute filtrate continues into the renal pelvis as dilute urine • Na+ and other ions may be selectively removed in the DCT and collecting duct, decreasing osmolality to as low as 50 m. Osm Copyright © 2010 Pearson Education, Inc.
Active transport Passive transport Collecting duct Descending limb of loop of Henle DCT Cortex Na. CI H 2 O Outer medulla Na. CI H 2 O Urea Inner medulla (a) Absence of ADH Copyright © 2010 Pearson Education, Inc. Large volume of dilute urine Figure 25. 17 a
Formation of Concentrated Urine • Depends on the medullary osmotic gradient and ADH • ADH triggers reabsorption of H 2 O in the collecting ducts • Facultative water reabsorption occurs in the presence of ADH so that 99% of H 2 O in filtrate is reabsorbed Copyright © 2010 Pearson Education, Inc.
Active transport Passive transport Collecting duct Descending limb of loop of Henle DCT H 2 O Cortex Na. CI H 2 O Outer medulla Na. CI H 2 O Inner medulla (b) Maximal ADH Copyright © 2010 Pearson Education, Inc. H 2 O Urea H 2 O Small volume of concentrated urine Figure 25. 17 b
Diuretics • Chemicals that enhance the urinary output • Osmotic diuretics: substances not reabsorbed, (e. g. , high glucose in a diabetic patient) • ADH inhibitors such as alcohol • Substances that inhibit Na+ reabsorption and obligatory H 2 O reabsorption such as caffeine and many drugs Copyright © 2010 Pearson Education, Inc.
Na+ (65%) Glucose Amino acids H 2 O (65%) and many ions (e. g. Cl– and K+) Milliosmols Cortex (d) (a) 300 (e) Outer medulla (b) (c) 600 Some drugs – H+, HCO 3 NH 4+ Inner medulla Blood p. H regulation 1200 (a) Proximal convoluted tubule: • 65% of filtrate volume reabsorbed • Na+, glucose, amino acids, and other nutrients actively transported; H 2 O and many ions follow passively • H+ and NH 4+ secretion and HCO 3– reabsorption to maintain blood p. H (see Chapter 26) • Some drugs are secreted Copyright © 2010 Pearson Education, Inc. Active transport (primary or secondary) Passive transport Figure 25. 18 a
Milliosmols Cortex (d) (a) 300 (e) Outer medulla H 2 O (b) (c) 600 (b) Descending limb of loop of Henle • Freely permeable to H 2 O • Not permeable to Na. Cl • Filtrate becomes increasingly concentrated as H 2 O leaves by osmosis Copyright © 2010 Pearson Education, Inc. Inner medulla 1200 Active transport (primary or secondary) Passive transport Figure 25. 18 b
Milliosmols Na+ Cl– K+ Cortex (d) (a) 300 (e) Outer medulla Urea Na+ Cl– (c) Ascending limb of loop of Henle • Impermeable to H 2 O • Permeable to Na. Cl • Filtrate becomes increasingly dilute as salt is reabsorbed Copyright © 2010 Pearson Education, Inc. (b) (c) 600 Inner medulla 1200 Active transport (primary or secondary) Passive transport Figure 25. 18 c
Na+; aldosterone-regulated Ca 2+; PTH-regulated Cl–; follows Na+ Milliosmols Cortex (d) (a) 300 (e) Outer medulla (b) (c) 600 Inner medulla (d) Distal convoluted tubule • Na+ reabsorption regulated by aldosterone • Ca 2+ reabsortion regulated by parathyroid hormone (PTH) • Cl– cotransported with Na+ Copyright © 2010 Pearson Education, Inc. 1200 Active transport (primary or secondary) Passive transport Figure 25. 18 d
Milliosmols Cortex H 2 O regulated by ADH Regulated by aldosterone: Na+ K+ Blood p. H regulation H+ 300 Urea; increased by ADH (e) Outer medulla (b) (c) 600 HCO 3– NH 4+ (d) (a) Inner medulla 1200 (e) Collecting duct • H 2 O reabsorption through aquaporins regulated by ADH • Na+ reabsorption and K+ secretion regulated by aldosterone • H+ and HCO 3– reabsorption or secretion Active transport to maintain blood p. H (see Chapter 26) (primary or secondary) Passive transport • Urea reabsorption increased by ADH Copyright © 2010 Pearson Education, Inc. Figure 25. 18 e
Renal Clearance • Volume of plasma cleared of a particular substance in a given time • Renal clearance tests are used to • Determine GFR • Detect glomerular damage • Follow the progress of renal disease Copyright © 2010 Pearson Education, Inc.
Renal Clearance RC = UV/P RC = renal clearance rate (ml/min) U = concentration (mg/ml) of the substance in urine V = flow rate of urine formation (ml/min) P = concentration of the same substance in plasma Copyright © 2010 Pearson Education, Inc.
Renal Clearance • For any substance freely filtered and neither reabsorbed nor secreted by the kidneys (e. g. , insulin), RC = GFR = 125 ml/min • If RC < 125 ml/min, the substance is reabsorbed • If RC = 0, the substance is completely reabsorbed • If RC > 125 ml/min, the substance is secreted (most drug metabolites) Copyright © 2010 Pearson Education, Inc.
Physical Characteristics of Urine • Color and transparency • Clear, pale to deep yellow (due to urochrome) • Drugs, vitamin supplements, and diet can alter the color • Cloudy urine may indicate a urinary tract infection Copyright © 2010 Pearson Education, Inc.
Physical Characteristics of Urine • Odor • Slightly aromatic when fresh • Develops ammonia odor upon standing • May be altered by some drugs and vegetables Copyright © 2010 Pearson Education, Inc.
Physical Characteristics of Urine • p. H • Slightly acidic (~p. H 6, with a range of 4. 5 to 8. 0) • Diet, prolonged vomiting, or urinary tract infections may alter p. H • Specific gravity • 1. 001 to 1. 035, dependent on solute concentration Copyright © 2010 Pearson Education, Inc.
Chemical Composition of Urine • 95% water and 5% solutes • Nitrogenous wastes: urea, uric acid, and creatinine • Other normal solutes • Na+, K+, PO 43–, and SO 42–, • Ca 2+, Mg 2+ and HCO 3– • Abnormally high concentrations of any constituent may indicate pathology Copyright © 2010 Pearson Education, Inc.
Ureters • Convey urine from kidneys to bladder • Retroperitoneal • Enter the base of the bladder through the posterior wall • As bladder pressure increases, distal ends of the ureters close, preventing backflow of urine Copyright © 2010 Pearson Education, Inc.
Ureters • Three layers of wall of ureter 1. Lining of transitional epithelium 2. Smooth muscle muscularis • Contracts in response to stretch 3. Outer adventitia of fibrous connective tissue Copyright © 2010 Pearson Education, Inc.
Lumen Adventitia Circular layer Longitudinal layer Transitional epithelium Lamina propria Copyright © 2010 Pearson Education, Inc. Figure 25. 20
Renal Calculi • Kidney stones form in renal pelvis • Crystallized calcium, magnesium, or uric acid salts • Larger stones block ureter, cause pressure and pain in kidneys • May be due to chronic bacterial infection, urine retention, Ca 2+ in blood, p. H of urine Copyright © 2010 Pearson Education, Inc.
Urinary Bladder • Muscular sac for temporary storage of urine • Retroperitoneal, on pelvic floor posterior to pubic symphysis • Males—prostate gland surrounds the neck inferiorly • Females—anterior to the vagina and uterus Copyright © 2010 Pearson Education, Inc.
Urinary Bladder • Trigone • Smooth triangular area outlined by the openings for the ureters and the urethra • Infections tend to persist in this region Copyright © 2010 Pearson Education, Inc.
Urinary Bladder • Layers of the bladder wall 1. Transitional epithelial mucosa 2. Thick detrusor muscle (three layers of smooth muscle) 3. Fibrous adventitia (peritoneum on superior surface only) Copyright © 2010 Pearson Education, Inc.
Urinary Bladder • Collapses when empty; rugae appear • Expands and rises superiorly during filling without significant rise in internal pressure Copyright © 2010 Pearson Education, Inc.
Peritoneum Ureter Rugae Detrusor muscle Ureteric orifices Bladder neck Internal urethral sphincter External urethral sphincter Urogenital diaphragm (b) Female. Copyright © 2010 Pearson Education, Inc. Trigone Urethra External urethral orifice Figure 25. 21 b
Urethra • Muscular tube • Lining epithelium • Mostly pseudostratified columnar epithelium, except • Transitional epithelium near bladder • Stratified squamous epithelium near external urethral orifice Copyright © 2010 Pearson Education, Inc.
Urethra • Sphincters • Internal urethral sphincter • Involuntary (smooth muscle) at bladderurethra junction • Contracts to open • External urethral sphincter • Voluntary (skeletal) muscle surrounding the urethra as it passes through the pelvic floor Copyright © 2010 Pearson Education, Inc.
Urethra • Female urethra (3– 4 cm): • Tightly bound to the anterior vaginal wall • External urethral orifice is anterior to the vaginal opening, posterior to the clitoris Copyright © 2010 Pearson Education, Inc.
Peritoneum Ureter Rugae Detrusor muscle Ureteric orifices Bladder neck Internal urethral sphincter External urethral sphincter Urogenital diaphragm (b) Female. Copyright © 2010 Pearson Education, Inc. Trigone Urethra External urethral orifice Figure 25. 21 b
Urethra • Male urethra • Carries semen and urine • Three named regions 1. Prostatic urethra (2. 5 cm)—within prostate gland 2. Membranous urethra (2 cm)—passes through the urogenital diaphragm 3. Spongy urethra (15 cm)—passes through the penis and opens via the external urethral orifice Copyright © 2010 Pearson Education, Inc.
Peritoneum Ureter Rugae Detrusor muscle Adventitia Ureteric orifices Trigone of bladder Bladder neck Internal urethral sphincter Prostate Prostatic urethra Urogenital diaphragm External urethral sphincter Membranous urethra Spongy urethra Erectile tissue of penis External urethral orifice (a) Male. The long male urethra has three regions: prostatic, membranous and spongy. Copyright © 2010 Pearson Education, Inc. Figure 25. 21 a
Micturition • Urination or voiding • Three simultaneous events 1. Contraction of detrusor muscle by ANS 2. Opening of internal urethral sphincter by ANS 3. Opening of external urethral sphincter by somatic nervous system Copyright © 2010 Pearson Education, Inc.
Micturition • Reflexive urination (urination in infants) • Distension of bladder activates stretch receptors • Excitation of parasympathetic neurons in reflex center in sacral region of spinal cord • Contraction of the detrusor muscle • Contraction (opening) of internal sphincter • Inhibition of somatic pathways to external sphincter, allowing its relaxation (opening) Copyright © 2010 Pearson Education, Inc.
Micturition • Pontine control centers mature between ages 2 and 3 1. Pontine storage center inhibits micturition: • Inhibits parasympathetic pathways • Excites sympathetic and somatic efferent pathways 2. Pontine micturition center promotes micturition: • Excites parasympathetic pathways • Inhibits sympathetic and somatic efferent pathways Copyright © 2010 Pearson Education, Inc.
Brain Urinary bladder filling stretches bladder wall Allow or inhibit micturition as appropriate Pontine micturition center Afferent impulses from stretch receptors Simple spinal reflex Higher brain centers Promotes micturition by acting on all three spinal efferents Pontine storage center Inhibits micturition by acting on all three spinal efferents Spinal cord Parasympathetic activity Sympathetic activity Detrusor muscle contracts; internal urethral sphincter opens Parasympathetic activity Somatic motor nerve activity External urethral sphincter opens Micturition Copyright © 2010 Pearson Education, Inc. Somatic motor nerve activity Inhibits Figure 25. 22
Developmental Aspects • Three sets of embryonic kidneys forming succession 1. Pronephros degenerates but pronephric duct persists 2. Mesonephros claims this duct and it becomes the mesonephric duct 3. Metanephros develops by the fifth week, develops into adult kidneys and ascends Copyright © 2010 Pearson Education, Inc.
Degenerating pronephros Urogenital ridge Developing digestive tract Duct to yolk sac Mesonephros Allantois Mesonephric duct (initially, pronephric duct) Hindgut Cloaca Ureteric bud (a) Week 5 Copyright © 2010 Pearson Education, Inc. Figure 25. 23 a
Degenerating pronephros Duct to yolk sac Allantois Body stalk Mesonephros Mesonephric duct (b) Week 6 Copyright © 2010 Pearson Education, Inc. Urogenital sinus Rectum Ureteric bud Metanephros Figure 25. 23 b
Developmental Aspects • Metanephros develops as ureteric buds that induce mesoderm of urogenital ridge to form nephrons • Distal ends of ureteric buds form renal pelves, calyces, and collecting ducts • Proximal ends become ureters • Kidneys excrete urine into amniotic fluid by the third month • Cloaca subdivides into rectum, anal canal, and urogenital sinus Copyright © 2010 Pearson Education, Inc.
Gonad Urogenital sinus (developing urinary bladder) Rectum Metanephros (kidney) (c) Week 7 Copyright © 2010 Pearson Education, Inc. Figure 25. 23 c
Urinary bladder Gonad Urethra Kidney Anus Ureter Rectum (d) Week 8 Copyright © 2010 Pearson Education, Inc. Figure 25. 23 d
Developmental Aspects • Frequent micturition in infants due to small bladders and less-concentrated urine • Incontinence is normal in infants: control of the voluntary urethral sphincter develops with the nervous system • E. coli bacteria account for 80% of all urinary tract infections • Streptococcal infections may cause long-term renal damage • Sexually transmitted diseases can also inflame the urinary tract Copyright © 2010 Pearson Education, Inc.
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