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Chapter 26: The Urinary System Copyright 2009, John Wiley & Sons, Inc. Overview of kidney functions Regulation of blood ionic composition Regulation of blood pH Regulation of blood volume Regulation of blood pressure Maintenance of blood osmolarity Production of hormones (calcitriol and erythropoietin) Regulation of blood glucose level Excretion of wastes from metabolic reactions and foreign substances (drugs or toxins) Copyright 2009, John Wiley & Sons, Inc. Anatomy and histology of the kidneys External anatomy Renal hilium – indent where ureter emerges along with blood vessels, lymphatic vessels and nerves 3 layers of tissue Renal capsule – deep layer – continuous with outer coat of ureter, barrier against trauma, maintains kidney shape Adipose capsule – mass of fatty tissue that protects kidney from trauma and holds it in place Renal fascia – superficial layer – thin layer of connective tissue that anchors kidney to surrounding structures and abdominal wall Copyright 2009, John Wiley & Sons, Inc. Organs of the urinary system in a female RIGHT KIDNEY Diaphragm Esophagus Left adrenal (suprarenal) gland Left renal vein Right renal artery LEFT KIDNEY Abdominal aorta RIGHT URETER Inferior vena cava URINARY BLADDER LEFT URETER Left ovary URETHRA Rectum Uterus Position and coverings of the kidneys Transverse plane ANTERIOR Large intestine Stomach Liver Pancreas Renal artery and vein View Layers Inferior vena cava Peritoneum Abdominal aorta Body of L2 RENAL HILUM RENAL FASCIA LEFT KIDNEY ADIPOSE CAPSULE RENAL CAPSULE Spleen Rib RIGHT KIDNEY POSTERIOR (a) Inferior view of transverse section of abdomen (L2) Quadratus lumborum muscle SUPERIOR Lung Parasagittal plane Liver Diaphragm Adrenal (suprarenal) gland Twelfth rib Peritoneum Right kidney ADIPOSE CAPSULE RENAL CAPSULE Quadratus lumborum muscle Large intestine Hip bone POSTERIOR ANTERIOR (b) Parasagittal section through right kidney Layers RENAL FASCIA Internal anatomy Renal cortex – superficial Renal medulla – inner region Outer cortical zone Inner juxtamedullary zone Renal columns – portions of cortex that extend between renal pyramids Several cone shaped renal pyramids – base faces cortex and renal papilla points toward hilium Renal lobe – renal pyramid, overlying cortex area, and ½ of each adjacent renal column Copyright 2009, John Wiley & Sons, Inc. Anatomy of the kidneys Parenchyma (functional portion) of kidney Renal cortex and renal pyramids of medulla Nephron – microscopic functional units of kidney Urine formed by nephron drains into Papillary ducts Minor and major calyces Renal pelvis Ureter Urinary bladder Copyright 2009, John Wiley & Sons, Inc. PATH OF URINE DRAINAGE: Nephron Collecting duct Renal hilum Minor calyx Renal cortex Major calyx Renal artery Renal medulla Renal pelvis Renal vein Renal column Renal pyramid in renal medulla Renal papilla Ureter Renal capsule Internal anatomy of the kidneys (a) Anterior view of dissection of right kidney Urinary bladder Blood and nerve supply of the kidneys Blood supply Although kidneys constitute less than 0.5% of total body mass, they receive 20-25% of resting cardiac output Left and right renal artery enters kidney Branches into segmental, interlobar, arcuate, interlobular arteries Each nephron receives one afferent arteriole Divides into glomerulus – capillary ball Reunite to form efferent arteriole (unique) Divide to form peritubular capillaries or some have vasa recta Peritubular venule, interlobar vein and renal vein exits kidney Renal nerves are part of the sympathetic autonomic nervous system Most are vasomotor nerves regulating blood flow Copyright 2009, John Wiley & Sons, Inc. Frontal plane Afferent arteriole Glomerulus Peritubular capillary Efferent arteriole Interlobular vein Vasa recta Blood supply of nephron Interlobular artery Renal capsule Arcuate artery Interlobar artery Segmental artery Renal cortex Renal artery Renal vein Renal pyramid in renal medulla Interlobar vein Arcuate vein Interlobular vein (a) Frontal section of right kidney Renal artery Segmental arteries Interlobar arteries Arcuate arteries Interlobular arteries Afferent arterioles Glomerular capillaries Efferent arterioles Peritubular capillaries Interlobular veins Arcuate veins Interlobar veins (b) Path of blood flow Renal vein The nephron – functional units of kidney 2 parts Renal corpuscle – filters blood plasma Glomerulus – capillary network Glomerular (Bowman’s) capsule – double-walled cup surrounding glomerulus Renal tubule – filtered fluid passes into Proximal convoluted tubule Descending and ascending loop of Henle (nephron loop) Distal convoluted tubule Copyright 2009, John Wiley & Sons, Inc. Nephrons Renal corpuscle and both convoluted tubules in cortex, loop of Henle extend into medulla Distal convoluted tubule of several nephrons empty into single collecting duct Cortical nephrons – 80-85% of nephrons Renal corpuscle in outer portion of cortex and short loops of Henle extend only into outer region of medulla Juxtamedullary nephrons – other 20-15% Renal corpuscle deep in cortex and long loops of Henle extend deep into medulla Receive blood from peritubular capillaries and vasa recta Ascending limb of LOH has thick and thin regions Enable kidney to secrete very dilute or very concentrated urine Copyright 2009, John Wiley & Sons, Inc. Renal capsule Renal corpuscle: Proximal convoluted tubule Glomerular (Bowman's) capsule Glomerulus Peritubular capillary Efferent arteriole Distal convoluted tubule Afferent arteriole Interlobular artery Interlobular vein Arcuate vein Renal cortex Renal cortex Renal medulla Renal medulla Arcuate artery Corticomedullary junction Renal papilla Loop of Henle: Minor calyx Descending limb FLOW OF FLUID THROUGH A CORTICAL NEPHRON Ascending limb Kidney Collecting duct Glomerular (Bowman's) capsule Proximal convoluted tubule Papillary duct Descending limb of the loop of Henle Renal papilla Ascending limb of the loop of Henle Distal convoluted tubule (drains into collecting duct) Minor calyx Urine (a) Cortical nephron and vascular supply Renal capsule Distal convoluted tubule Renal corpuscle: Proximal convoluted tubule Glomerular (Bowman's) capsule Glomerulus Peritubular capillary Afferent arteriole Efferent arteriole Interlobular artery Renal cortex Renal cortex Renal medulla Renal medulla Renal papilla Peritubular capillary Minor calyx Arcuate artery Corticomedullary junction Loop of Henle: Glomerular (Bowman's) capsule Descending limb of the loop of Henle Arcuate vein Collecting duct FLOW OF FLUID THROUGH A JUXTAMEDULLARY NEPHRON Proximal convoluted tubule Interlobular vein Kidney Vasa recta Descending limb Thick ascending limb Thin ascending limb Papillary duct Thin ascending limb of the loop of Henle Renal papilla Thick ascending limb of the loop of Henle Minor calyx Distal convoluted tubule (drains into collecting duct) Urine (b) Juxtamedullary nephron and vascular supply Histology of nephron and collecting duct Glomerular capsule Visceral layer has podocytes that wrap projections around single layer of endothelial cells of glomerular capillaries and form inner wall of capsule Parietal layer forms outer wall of capsule Fluid filtered from glomerular capillaries enters capsular (Bowman’s) space Copyright 2009, John Wiley & Sons, Inc. Renal corpuscle (external view) Histology of a renal corpuscle Parietal layer of glomerular (Bowman’s) capsule Afferent arteriole Mesangial cell Juxtaglomerular cell Capsular space Macula densa Ascending limb of loop of Henle Proximal convoluted tubule Mesangial cell Efferent arteriole Podocyte of visceral layer of glomerular (Bowman’s) capsule Endothelium of glomerulus (a) Renal corpuscle (internal view) Pedicel Renal tubule and collecting duct Proximal convoluted tubule cells have microvilli with brush border – increases surface area Juxtaglomerular appraratus helps regulate blood pressure in kidney Macula densa – cells in final part of ascending loop of Henle Juxtaglomerular cells – cells of afferent and efferent arterioles contain modified smooth muscle fibers Last part of distal convoluted tubule and collecting duct Principal cells – receptors for antidiuretic hormone (ADH) and aldosterone Intercalated cells – role in blood pH homeostasis Copyright 2009, John Wiley & Sons, Inc. Overview of renal physiology 1. 2. 3. Glomerular filtration Water and most solutes in blood plasma move across the wall of the glomerular capillaries into glomerular capsule and then renal tubule Tubular reabsorption As filtered fluid moves along tubule and through collecting duct, about 99% of water and many useful solutes reabsorbed – returned to blood Tubular secretion As filtered fluid moves along tubule and through collecting duct, other material secreted into fluid such as wastes, drugs, and excess ions – removes substances from blood Solutes in the fluid that drains into the renal pelvis remain in the fluid and are excreted Excretion of any solute = glomerular filtration + secretion - reabsorption Copyright 2009, John Wiley & Sons, Inc. Structures and functions of a nephron Renal tubule and collecting duct Renal corpuscle Afferent arteriole Glomerular capsule Urine (contains excreted substances) Fluid in renal tubule 1 Filtration from blood plasma into nephron 2 Tubular reabsorption from fluid into blood Efferent arteriole Peritubular capillaries Copyright 2009, John Wiley & Sons, Inc. 3 Tubular secretion from blood into fluid Blood (contains reabsorbed substances) Glomerular filtration Glomerular filtrate – fluid that enters capsular space Daily volume 150-180 liters – more than 99% returned to blood plasma via tubular reabsorption Filtration membrane – endothelial cells of glomerular capillaries and podocytes encircling capillaries Permits filtration of water and small solutes Prevents filtration of most plasma proteins, blood cells and platelets 3 barriers to cross – glomerular endothelial cells fenestrations, basal lamina between endothelium and podocytes and pedicels of podocytes create filtration slits Volume of fluid filtered is large because of large surface area, thin and porous membrane, and high glomerular capillary blood hydrostatic pressure Copyright 2009, John Wiley & Sons, Inc. The filtration membrane Podocyte of visceral layer of glomerular (Bowman’s) capsule Filtration slit Pedicel 1 Fenestration (pore) of glomerular endothelial cell: prevents filtration of blood cells but allows all components of blood plasma to pass through 2 Basal lamina of glomerulus: prevents filtration of larger proteins 3 Slit membrane between pedicels: prevents filtration of medium-sized proteins (a) Details of filtration membrane Net filtration pressure Net filtration pressure (NFP) is the total pressure that promotes filtration NFP = GBHP – CHP – BCOP Glomerular blood hydrostatic pressure is the blood pressure of the glomerular capillaries forcing water and solutes through filtration slits Capsular hydrostatic pressure is the hydrostatic pressure exerted against the filtration membrane by fluid already in the capsular space and represents “back pressure” Blood colloid osmotic pressure due to presence of proteins in blood plasma and also opposes filtration Copyright 2009, John Wiley & Sons, Inc. The pressures that drive glomerular filtration Copyright 2009, John Wiley & Sons, Inc. 1 GLOMERULAR BLOOD HYDROSTATIC PRESSURE (GBHP) = 55 mmHg 2 CAPSULAR HYDROSTATIC PRESSURE (CHP) = 15 mmHg 3 BLOOD COLLOID OSMOTIC PRESSURE (BCOP) = 30 mmHg Afferent arteriole Proximal convoluted tubule Efferent arteriole Glomerular (Bowman's) capsule Capsular space NET FILTRATION PRESSURE (NFP) = GBHP – CHP – BCOP = 55 mmHg – 15 mmHg – 30 mmHg = 10 mmHg The pressures that drive glomerular filtration Glomerular filtration Glomerular filtration rate – amount of filtrate formed in all the renal corpuscles of both kidneys each minute Homeostasis requires kidneys maintain a relatively constant GFR Too high – substances pass too quickly and are not reabsorbed Too low – nearly all reabsorbed and some waste products not adequately excreted GFR directly related to pressures that determine net filtration pressure Copyright 2009, John Wiley & Sons, Inc. 3 Mechanisms regulating GFR Renal autoregulation 1. Kidneys themselves maintain constant renal blood flow and GFR using Myogenic mechanism – occurs when stretching triggers contraction of smooth muscle cells in afferent arterioles – reduces GFR Tubuloglomerular mechanism – macula densa provides feedback to glomerulus, inhibits release of NO causing afferent arterioles to constrict and decreasing GFR Copyright 2009, John Wiley & Sons, Inc. Some stimulus disrupts homeostasis by Increasing Glomerular filtration rate (GFR) Tuboglomerular feedback Receptors Macula densa cells of JGA detect increased delivery of Na+, Cl –, and water Input Control center Juxtaglomerular apparatus Return to homeostasis when response brings GFR back to normal Decreased secretion of nitric oxide Effectors Output Afferent arteriole constricts, which decreases blood flow through glomerulus Decrease in GFR Mechanisms regulating GFR Neural regulation 2. Kidney blood vessels supplied by sympathetic ANS fibers that release norepinephrine causing vasoconstriction Moderate stimulation – both afferent and efferent arterioles constrict to same degree and GFR decreases Greater stimulation constricts afferent arterioles more and GFR drops Hormonal regulation 3. Angiotensin II reduces GFR – potent vasoconstrictor of both afferent and efferent arterioles Atrial natriuretic peptide increases GFR – stretching of atria causes release, increases capillary surface area for filtration Copyright 2009, John Wiley & Sons, Inc. Tubular reabsorption and tubular secretion Reabsorption – return of most of the filtered water and many solutes to the bloodstream About 99% of filtered water reabsorbed Proximal convoluted tubule cells make largest contribution Both active and passive processes Secretion – transfer of material from blood into tubular fluid Helps control blood pH Helps eliminate substances from the body Copyright 2009, John Wiley & Sons, Inc. Reabsorption routes and transport mechanisms Reabsorption routes Paracellular reabsorption Between adjacent tubule cells Tight junction do not completely seal off interstitial fluid from tubule fluid Passive Transcellular reabsorption – through an individual cell Transport mechanisms Reabsorption of Na+ especially important Primary active transport Secondary active transport Symporters, antiporters Transport maximum (Tm) Sodium-potassium pumps in basolateral membrane only Upper limit to how fast it can work Obligatory (following solute) vs. facultative (adapting to need) water reabsorption Copyright 2009, John Wiley & Sons, Inc. Tubule cell Fluid in tubule lumen Na+ Peritubular capillary Na+ Na+ Paracellular reabsorption Reabsorption routes: paracellular reabsorption and transcellular reabsorption ATP Na+ Na+ ADP Na+ Na+ Key: Transcellular reabsorption Diffusion Basolateral membrane Apical membrane Tight junction Interstitial fluid Active transport Sodium–potassium pump (Na+/K+ ATPase) Reabsorption and secretion in proximal convoluted tubule (PCT) Largest amount of solute and water reabsorption Secretes variable amounts of H+, NH4+ and urea Most solute reabsorption involves Na+ Solute reabsorption promotes osmosis – creates osmotic gradient Symporters for glucose, amino acids, lactic acid, water-soluble vitamins, phosphate and sulfate Na+ / H+ antiporter causes Na+ to be reabsorbed and H+ to be secreted As water leaves tubular fluid, solute concentration increases Urea and ammonia in blood are filtered at glomerulus and secreted by proximal convoluted tubule cells Copyright 2009, John Wiley & Sons, Inc. Reabsorption and secretion in the proximal convoluted tubule Fluid in tubule lumen Proximal convoluted tubule cell ATP 2 Na+ Na+ Peritubular capillary Na+ Na+ ADP Key: Na+–glucose symporter Glucose Glucose Glucose Glucose facilitated diffusion transporter Diffusion Tight junction Brush border (microvilli) Interstitial fluid Sodium–potassium pump Fluid in tubule lumen Proximal convoluted tubule cell Peritubular capillary Reabsorption and secretion in the proximal convoluted tubule Na+ Na+ HCO3– HCO3– HCO3– H+ H+ ATP Na+ Na+ H2CO3 Metabolic reactions Key: ADP Na+/H+ antiporter CA Na+ CO2 H2O CO2 CO2 HCO3– facilitated diffusion transporter Diffusion Interstitial fluid (a) Na+ reabsorption and H+ secretion Sodium–potassium pump Fluid in tubule lumen Peritubular capillary Na+ HCO3– Na+ ATP Reabsorption and secretion in the proximal convoluted tubule Na+ Key: ADP H+ H+ CA H2CO3 H2CO3 CO2 H2O HCO3– H2O CO2 HCO3– Na+/H+ antiporter HCO3– facilitated diffusion transporter Diffusion Sodium–potassium pump (b) HCO3– reabsorption Fluid in tubule lumen Cl– K+ Ca2+ Mg2+ Urea H2O Proximal convoluted tubule cell Diffusion Osmosis Peritubular capillary Cl– K+ Ca2+ Mg2+ Urea H2O Reabsorption in the loop of Henle Chemical composition of tubular fluid quite different from filtrate Glucose, amino acids and other nutrients reabsorbed Osmolarity still close to that of blood Reabsorption of water and solutes balanced For the first time reabsorption of water is NOT automatically coupled to reabsorption of solutes (A-LOH somewhat impermeable to water) Independent regulation of both volume and osmolarity of body fluids Na+-K+-2Cl- symporters function in Na+ and Cl- reabsorption – promotes reabsorption of cations Little or no water is reabsorbed in ascending limb – osmolarity decreases Copyright 2009, John Wiley & Sons, Inc. Fluid in tubule lumen Vasa recta Thick ascending limb cell Na+ ATP Na+–K+-2Clsymporter in the thick ascending limb of the loop of Henle Na+ ADP Na+ 2Cl– K+ Cations: Na+ K+ Ca2+ Mg2+ Na+ Na+ 2Cl– 2Cl– 2Cl– K+ Cations Key: Na+–K+–2Cl– symporter Apical membrane (impermeable to water) Interstitial fluid is more negative than fluid in tubule lumen Leakage channels Sodium–potassium pump Diffusion Reabsorption and secretion in the late distale convoluted tubule and collecting duct Reabsorption on the early distal convoluted tubule Na+-Cl- symporters reabsorb Na+ and ClMajor site where parathyroid hormone stimulates reabsorption of Ca+ depending on body’s needs Reabsorption and secretion in the late distal convoluted tubule and collecting duct 90-95% of filtered solutes and fluid have been returned by now Principal cells reabsorb Na+ and secrete K+ Intercalated cells reabsorb K+ and HCO3- and secrete H+ Amount of water reabsorption and solute reabsorption and secretion depends on body’s needs Copyright 2009, John Wiley & Sons, Inc. Fluid in tubule lumen Principal cell K+ K+ ATP Na+ Peritubular capillary Na+ Na+ ADP K+ Na+ Key: Diffusion Interstitial fluid Leakage channels Sodium–potassium pump Hormonal regulation of tubular reabsorption and secretion Angiotensin II - when blood volume and blood pressure decrease Aldosterone - when blood volume and blood pressure decrease Decreases GFR, enhances reabsorption of Na+, Cl- and water in PCT Stimulates principal cells in collecting duct to reabsorb more Na+ and Cl- and secrete more K+ Parathyroid hormone Stimulates cells in DCT to reabsorb more Ca2+ Copyright 2009, John Wiley & Sons, Inc. Regulation of facultative water reabsorption by ADH Antidiuretic hormone (ADH or vasopressin) Increases water permeability of cells by inserting aquaporin-2 in last part of DCT and collecting duct Atrial natriuretic peptide (ANP) Large increase in blood volume promotes release of ANP Decreases blood volume and pressure by inhibiting reabsorption of Na+ and water in PCT and collecting duct, suppress secretion of ADH and aldosterone Some stimulus disrupts homeostasis by Increasing Osmolarity of plasma and interstitial fluid Receptors Osmoreceptors in hypothalamus Input Nerve impulses Control center Hypothalamus and posterior pituitary ADH Return to homeostasis when response brings plasma osmolarity back to normal Increased release of ADH Effectors Output HO Principal cells 2 become more permeable to water, which increases facultative water reabsorption Decrease in plasma osmolarity Production of dilute and concentrated urine Even though your fluid intake can be highly variable, total fluid volume in your body remains stable Depends in large part on the kidneys to regulate the rate of water loss in urine ADH controls whether dilute or concentrated urine is formed Absent or low ADH = dilute urine (alcohol) Higher levels = more concentrated urine through increased water reabsorption Copyright 2009, John Wiley & Sons, Inc. Formation of dilute urine Glomerular filtrate has same osmolarity as blood 300 mOsm/liter Fluid leaving PCT is isotonic to plasma When dilute urine is being formed, the osmolarity of fluid increases as it goes down the descending loop of Henle, decreases as it goes up the ascending limb, and decreases still more as it flows through the rest of the nephron and collecting duct Copyright 2009, John Wiley & Sons, Inc. Formation of dilute urine Osmolarity of interstitial fluid of renal medulla becomes greater, more water is reabsorbed from tubular fluid so fluid become more concentrated Water cannot leave in thick portion of ascending limb but solutes leave making fluid more dilute than blood plasma Additional solutes but not much water leaves in DCT Low ADH makes late DCT and collecting duct have low water permeability Afferent arteriole Glomerular (Bowman's) capsule Glomerulus Distal convoluted tubule Efferent arteriole 100 300 Proximal convoluted tubule 90 300 300 350 350 150 Interstitial fluid in renal cortex 350 Collecting duct 550 550 750 750 350 550 80 Interstitial fluid in renal medulla 550 750 70 900 Loop of Henle 65 65 Papillary duct Dilute urine Formation of concentrated urine Urine can be up to 4 times more concentrated than blood plasma Ability of ADH depends on presence of osmotic gradient in interstitial fluid of renal medulla 3 major solutes contribute – Na+, Cl-, and urea 2 main factors build and maintain gradient Differences in solute and water permeability in different sections of loop of Henle and collecting ducts Countercurrent flow of fluid though descending and ascending loop of Henle and blood through ascending and descending limbs of vasa recta Copyright 2009, John Wiley & Sons, Inc. Countercurrent multiplication Process by which a progressively increasing osmotic gradient is formed as a result of countercurrent flow Long loops of Henle of juxtamedullary nephrons function as countercurrent multiplier Symporters in thick ascending limb of loop of Henle cause buildup of Na+ and Cl- in renal medulla, cells impermeable to water Countercurrent flow establishes gradient as reabsorbed Na+ and Cl- become increasingly concentrated Cells in collecting duct reabsorb more water and urea Urea recycling causes a buildup of urea in the renal medulla Long loop of Henle establishes gradient by countercurrent multiplication Copyright 2009, John Wiley & Sons, Inc. Countercurrent exchange Process by which solutes and water are passively exchanged between blood of the vasa recta and interstitial fluid of the renal medulla as a result of countercurrent flow Vasa recta is a countercurrent exchanger Osmolarity of blood leaving vasa recta is only slightly higher than blood entering Provides oxygen and nutrients to medulla without washing out or diminishing gradient Vasa recta maintains gradient by countercurrent exchange Copyright 2009, John Wiley & Sons, Inc. Vasa recta Mechanism of urine concentration in long-loop juxtamedullary nephrons Loop of Henle Juxtamedullary nephron and its blood supply together Afferent arteriole Efferent arteriole 300 400 600 Osmotic gradient 800 Proximal convoluted tubule Interstitial fluid in renal medulla 1 Symporters in thick ascending limb cause buildup of Na+ and Cl– in renal medulla Glomerular (Bowman’s) capsule Distal convoluted tubule 200 HO H2O 2 300 H2O Interstitial fluid in renal cortex Flow of tubular fluid 320 300 Collecting duct 300 H2O 100 Na+Cl– 380 H2O 580 200 300 320 H2O 400 H2O 3 Principal cells in collecting duct reabsorb more water when ADH 500 is present Na+Cl– 400 600 H2O 400 H2O Na+Cl– 600 H2O 780 H2O 600 Urea 800 1000 800 980 2 H2O Countercurrent 1200 1200 flow through loop 1200 of Henle Loop of Henle establishes 1200 osmotic gradient (a) Reabsorption of Na+, Cl–, and water in long-loop juxtamedullary nephron 1000 H2O Na+Cl– Blood flow Presence of Na+–K+–2Cl– symporters Glomerulus 700 4 Urea recycling 800 causes buildup of urea in renal medulla H2O 900 H2O Na+Cl– 1000 Na+Cl– 1100 Papillary duct 1200 Concentrated urine (b) Recycling of salts and urea in vasa recta RENAL CORPUSCLE PROXIMAL CONVOLUTED TUBULE Glomerular filtration rate: 105–125 mL/min of fluid that is isotonic to blood Reabsorption (into blood) of filtered: Water 65% (osmosis) Na+ 65% (sodium–potassium pumps, symporters, antiporters) K+ 65% (diffusion) Glucose 100% (symporters and facilitated diffusion) Amino acids 100% (symporters and facilitated diffusion) Cl– 50% (diffusion) HCO3– 80–90% (facilitated diffusion) Urea 50% (diffusion) Na+ 5% (symporters) variable (diffusion) CI– 5% (symporters) Ca2+ variable (stimulated by parathyroid hormone) Ca2+, Mg2+ Filtered substances: water and all solutes present in blood (except proteins) including ions, glucose, amino acids, creatinine, uric acid EARLY DISTAL CONVOLUTED TUBULE Reabsorption (into blood) of: Water 10–15% (osmosis) Secretion (into urine) of: H+ variable (antiporters) NH4+ variable, increases in acidosis (antiporters) Urea variable (diffusion) Creatinine small amount LATE DISTAL CONVOLUTED TUBULE AND COLLECTING DUCT Reabsorption (into blood) of: At end of PCT, tubular fluid is still isotonic to blood (300 mOsm/liter). LOOP OF HENLE Water 5–9% (insertion of water channels stimulated by ADH) Na+ 1–4% (sodium–potassium pumps and sodium channels stimulated by aldosterone) HCO3– variable amount, depends on H+ secretion (antiporters) Urea variable (recycling to loop of Henle) Reabsorption (into blood) of: Water 15% (osmosis in descending limb) Na+ 20–30% (symporters in ascending limb) K+ 20–30% (symporters in ascending limb) CI– 35% (symporters in ascending limb) HCO3– 10–20% (facilitated diffusion) Ca2+, Mg2+ variable (diffusion) Secretion (into urine) of: Urea variable (recycling from collecting duct) At end of loop of Henle, tubular fluid is hypotonic (100–150 mOsm/liter). Urine Secretion (into urine) of: K+ variable amount to adjust for dietary intake (leakage channels) H+ variable amounts to maintain acid– base homeostasis (H+ pumps) Tubular fluid leaving the collecting duct is dilute when ADH level is low and concentrated when ADH level is high. Evaluation of kidney function Urinalysis (See Table 26.5, 26.6) Analysis of the volume and physical, chemical and microscopic properties of urine Water accounts for 95% of total urine volume If disease alters metabolism or kidney function, traces if substances normally not present or normal constituents in abnormal amounts may appear Copyright 2009, John Wiley & Sons, Inc. Evaluation of kidney function Blood tests… Blood urea nitrogen (BUN) – measures blood nitrogen that is part of the urea resulting from catabolism and deamination of amino acids Plasma creatinine results from catabolism of creatine phosphate in skeletal muscle – measure of renal function Renal plasma clearance More useful in diagnosis of kidney problems than above Volume of blood cleared of a substance per unit time High renal plasma clearance indicates efficient excretion of a substance into urine Copyright 2009, John Wiley & Sons, Inc. Urine transportation, storage, and elimination Ureters Each of 2 ureters transports urine from renal pelvis of one kidney to the bladder Peristaltic waves, hydrostatic pressure and gravity move urine No anatomical valve at the opening of the ureter into bladder – when bladder fills it compresses the opening and prevents backflow Copyright 2009, John Wiley & Sons, Inc. Ureters, urinary bladder, and urethra in a female Ureters Ureteral openings Frontal plane Rugae of mucosa Peritoneum Detrusor muscle Trigone Internal urethral orifice Internal urethral sphincter (involuntary) Urethra External urethral sphincter in deep muscles of perineum (voluntary) Hip bone (pubis) External urethral orifice Anterior view of frontal section Urinary bladder and urethra Urinary bladder Hollow, distensible muscular organ Capacity averages 700-800mL Micturition – discharge of urine from bladder Combination of voluntary and involuntary muscle contractions When volume increases stretch receptors send signals to micturition center in spinal cord triggering spinal reflex – micturition reflex In early childhood we learn to initiate and stop it voluntarily Urethra Small tube leading from internal urethral orifice in floor of bladder to exterior of the body In males discharges semen as well as urine Copyright 2009, John Wiley & Sons, Inc. Sagittal plane Uterus Urinary bladder Pubic symphysis Rectum Urethra Vagina External urethral orifice (a) Sagittal section, female Sagittal plane Urinary bladder Rectum Pubic symphysis Prostatic urethra Prostate Deep muscles of perineum Membranous urethra Penis Spongy urethra Testis Scrotum (b) Sagittal section, male External urethral orifice
