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Introduction and Key Concepts for the Urinary System
Figure 12-1 Overview of the Urinary System
Figure 12-2 Overview of the Kidney
Figure 12-3 Orientation of Detailed Urinary System Illustrations
Kidneys
Figure 12-4A Renal Cortex and Medulla, Kidney
Figure 12-4B Renal Cortex, Kidney
Figure 12-4C Clinical Correlation: Glomerular Disorders: Diabetic Nephropathy
Figure 12-5A Renal Corpuscle, Renal Cortex
Figure 12-5B Renal Corpuscle, Glomerulus and Bowman Capsule
Figure 12-6A Glomerulus, Renal Cortex
Figure 12-6B Glomerulus and Filtration Barrier
Figure 12-7 Glomerulus and Podocyte
Figure 12-8A Medullary Ray, Renal Cortex
Figure 12-8B The Nephron and Collecting System of the Kidney
Figure 12-9A,B Proximal Tubules
Figure 12-10A,B Distal Tubules
Figure 12-11A–C Medullary Tubules
Figure 12-11D Clinical Correlation: Renal Cell Carcinoma (Clear Cell Type)
Figure 12-12A Clinical Correlation: Renal Oncocytoma
Figure 12-12B Clinical Correlation: Hemodialysis
Synopsis 12-1 Clinical and Pathological Terms for the Urinary System
Table 12-1 Kidneys
Ureters
Figure 12-13A Ureter
Figure 12-13B Transitional Epithelium, Ureter
Figure 12-13C Clinical Correlation: Nephrolithiasis (Renal Stones)
Urinary System
CHAPTER 12 ■^ Urinary System 221
Urinary Bladder
Figure 12-14A Urinary Bladder, Bladder Wall
Figure 12-14B Urothelium, Bladder Wall
Figure 12-14C Clinical Correlation: Urothelial (Transitional) Carcinoma
Figure 12-15A,B Transitional Epithelium, Urinary Bladder
Urethra
Figure 12-16A Prostatic Urethra, Male Urethra
Figure 12-16B Penile (Spongy) Urethra, Male Urethra
Figure 12-16C Female Urethra
Introduction and Key Concepts for the
Urinary System
The urinary system is composed of two kidneys , two ureters , the bladder , and the urethra. The kidneys produce urine, the ureters transport urine to the bladder, and the bladder tempo- rarily stores and empties urine through the urethra to outside of the body. The urinary system functions to (1) filter blood and reabsorb nutrients; (2) control the water, ion, and salt balance of the body; (3) maintain the acid-base balance of the blood; (4) excrete metabolic wastes (urea and uric acid), toxins, and drug components; (5) secrete hormones, such as renin and eryth- ropoietin; and (6) produce calcitriol (an active form of vitamin D) to help the body absorb dietary calcium into the blood.
Kidneys
The kidneys are bean-shaped organs located in the posterior abdominal region on each side of the vertebral column. The kidney can be divided into the renal cortex , the renal medulla , and the hilum. The renal cortex is composed of renal corpuscles and various cortical tubules, which include the proximal con- voluted tubules, the distal convoluted tubules, and the corti- cal collecting tubules. The renal medulla is located deep to the cortex, and its tubules extend as medullary rays into the cortex region. The medulla comprises 10 to 18 renal pyramids; each pyramid contains the loops of Henle , collecting ducts , and pap- illary ducts. The apical projection of a renal pyramid is called the renal papilla. The papillary ducts empty urine at the tip of a renal papilla onto its surface, which is called the area cribrosa (perforated area). Each renal papilla is surrounded by a space, the minor calyx; several minor calices unite to form a major calyx. There are two or three major calyces for each kidney. The major calices unite to form the renal pelvis, which funnels urine into the ureter. The hilum is the region in the medial por- tion of the kidney where the renal artery, the renal vein, and the ureter enter and exit the kidney (Fig. 12-2). Functionally and structurally, the kidney can be divided into the nephron and the collecting system (Fig. 12-8B). The nephron produces urine. The collecting system adjusts the composition of urine and transports urine to the calyces.
THE NEPHRON comprises a renal corpuscle , a proximal convoluted tubule , a loop of Henele , and a distal convoluted tubule.
A renal corpuscle is composed of a glomerulus and a Bowman capsule. (1) A glomerulus consists of a spherical
knot of capillaries, which is fed by an afferent arteriole and drained by an efferent arteriole at the vascular pole. (2) A Bow- man capsule consists of a visceral layer and a parietal layer. The visceral layer is composed of podocytes, which cover the capillaries of a glomerulus. These cells have long, interdigitating cellular processes and play an important role in blood filtration. The interstitial tissues surrounding the glomerular capillaries contain cells called intraglomerular mesangial cells. The pari- etal layer of the Bowman capsule is a hollow spherical struc- ture lined by simple squamous epithelium. The space between the visceral and the parietal layers of the Bowman capsule is called the Bowman space. Blood flows through the glomerular capillaries, and its plasma passes through the glomerular filtra- tion barrier (the fused basal laminae of the endothelial cells and the podocytes); the filtrate is collected in the Bowman space (Fig. 12-6A,B). Thus, the renal corpuscle, as a whole, forms a blood-filtering unit, which allows water, metabolic wastes, ions, and small molecules to pass through the capillary wall but pre- vents circulating cells and large plasma proteins from leaving the blood.
Proximal Convoluted Tubules are long tubes that follow a serpentine course as they drain the filtrate from the renal corpuscles into the loop of Henle. Each is lined by a simple cuboidal epithelium with abundant long microvilli (brush bor- der) bordering the lumen. Each proximal convoluted tubule connects to a renal corpuscle at its urinary pole. The relatively large epithelial cells of the proximal convoluted tubule contain many mitochondria, which render their cytoplasm brightly acidophilic (pink). The lateral boundaries between the cells interdigitate, so that the boundaries between adjacent cells are unclear in light microscopy. Their long microvilli appear to fill much of the space within the lumen (Fig. 12-9A,B). The com- bined structural features of the proximal convoluted tubules contribute to their functions of actively transporting ions and reabsorbing water, glucose, amino acids, proteins, and vitamins from the fi ltrate.
The Loop of Henle is a continuation of the proximal convoluted tubule. It is a U-shaped structure that includes a descending limb and an ascending limb (Fig. 12-8B). The descending limb consists of a thick descending limb (proximal straight tubule) and a thin descending limb (descending thin segment). The ascending limb contains a thin ascending limb (ascending thin segment) and a thick ascending limb (distal straight tubule). The loop of Henle plays a crucial role in gen- erating a high sodium concentration gradient in the interstitium of the renal medulla. This permits water to move passively
CHAPTER 12 ■^ Urinary System 223
surface of the bladder is covered by adventitia , which is a layer of connective tissue without a mesothelial covering.
Urethra
The urethra is structurally different in the male and female. The proximal end of the male urethra is surrounded by an internal urethral sphincter (smooth muscle) that functions mainly to pre- vent seminal fluids from entering the bladder during ejaculation. The male urethra is about 20 cm long, and it is composed of three segments: prostatic , membranous , and penile ( spongy ) urethra. The prostatic portion is surrounded by the prostate gland and is lined by transitional epithelium. The membranous portion is a short segment surrounded by the skeletal muscle of the external sphincter (urogenital diaphragm) and is lined by pseudostratified columnar epithelium. The penile ( spongy ) urethra (also called the
cavernous urethra ) is surrounded by the corpus spongiosum of the penis, and its epithelial lining changes from pseudostratified columnar to stratified squamous. In this region, there are many small mucous glands called the glands of Littré , which secrete mucus to coat and protect the lining of the urethra. The female urethra is short, about 4 to 5 cm. It is lined chiefly by stratified squamous epithelium and, in a few places, may have patches of pseudostratified columnar epithelium. Glands of Littré are also present in the female urethra. The proximal end of female urethra is surrounded by skeletal muscle (external sphincter) where it penetrates the urogenital diaphragm. The external sphincter muscle in both male and female is innervated by the pudendal nerves; it functions to con- trol retention or release of the urine from the urinary bladder through the urethra and helps maintain urinary continence. A female does not have an internal sphincter.
224 UNIT 3 ■^ Organ Systems
Figure 12-1. Overview of the urinary system.
The urinary system plays an important role in eliminating the body’s metabolic wastes and toxins; controlling water and ion balance and regulating blood pressure; maintaining the acid-base (pH) balance of the blood; and in reabsorbing and conserving nutrients. The urinary system achieves these goals by filtering the blood and producing urine. The complex tubule system in the kidney helps to reabsorb and readjust water and ion content and to excrete urine. The urinary system consists of two kidneys , two ureters , the urinary bladder , and the urethra. The kidneys are the organs that produce urine and accomplish the essential functions listed above. After urine is produced, it passes through the ureters to the bladder for temporary storage, finally exiting the body through the urethra.
Kidney
Urinary bladder
Abdominal aorta
Ureter
Renal artery and vein
Inferior vena cava
Urethra
General structure of the kidney: I. Renal cortex A. Renal corpuscles B. Proximal convoluted tubules C. Distal convoluted tubules D. Cortical collecting tubules II. Renal medulla (renal pyramids) A. Outer medulla B. Inner medulla C. Renal papillae III. Renal hilum A. Minor calyx B. Major calyx C. Renal pelvis
Functional and histological unit of the kidney: I. Nephron A. Renal corpuscle B. Proximal convoluted tubule C. Loop of Henle
- Descending limb a. Thick descending limb (proximal straight tubule) b. Thin descending limb (descending thin segment)
- Ascending limb a. Thin ascending limb (ascending thin segment) b. Thick ascending limb (distal straight tubule) D. Distal convoluted tubules II. Collecting system A. Cortical collecting tubule B. Collecting ducts C. Papillary ducts
Structures of the Kidney
226 UNIT 3 ■^ Organ Systems
Fig. 12-4A
Fig. 12-11A
Fig. 12-11B
Fig. 12-4B to Fig. 12-10B
Fig. 12-13A,B
Fig. 12 4A to Fig. 12-11C
Fig. 12-14A,B Fig. 12-15A,B
Fig. 12-16A,B,C
Figure 12-3. Orientation of detailed urinary system illustrations.
Structures of the Urinary System with Figure Numbers
Kidney Renal cortex and medulla Figure 12-4A Figure 12-4B Figure 12-4C
Renal corpuscles Figure 12-5A Figure 12-5B
Glomerulus and fi ltration barrier Figure 12-6A Figure 12-6B Figure 12-
Medullary ray and urinary tubules Figure 12-8A Figure 12-8B
Proximal tubules Figure 12-9A Figure 12-9B
Distal tubules Figure 12-10A Figure 12-10B
Medullary tubules Figure 12-11A Figure 12-11B Figure 12-11C Figure 12-11D Figure 12-12A
Ureter Figure 12-13A Figure 12-13B Figure 12-13C
Urinary bladder Figure 12-14A Figure 12-14B Figure 12-14C Figure 12-15A Figure 12-15B
Male and female urethrae Figure 12-16A Figure 12-16B Figure 12-16C
CHAPTER 12 ■^ Urinary System 227
CLINICAL CORRELATION
Figure 12-4C. (^) Glomerular Disorders: Diabetic Nephropathy. H&E, 216 Diabetic nephropathy , a complication of both type 1 and type 2 diabetes mellitus, may result in chronic renal failure and is the leading cause of end-stage renal disease in the United States and other Western countries. Major histologic changes in the glomeruli in diabetic nephropathy include thickening of the glomerular basement membrane , diffuse glomerulosclerosis , and nodular glomerulosclerosis , also called Kimmelstiel-Wilson disease. As the disease progresses, edema (swelling), hyperten- sion, foamy urine, fatigue, headache, and nausea and vomiting may occur. Tight control of blood glucose levels tends to delay the onset of development. Treatment includes dialysis and renal transplantation. Shown here is a renal glomerulus with nodular glomerulosclerosis, or Kimmelstiel-Wilson disease.
Kimmelstiel- Wilson nodules
C
Figure 12-4A. Renal cortex and medulla, kidney. H&E, 11
This section shows the renal cortex and the medulla. The dashed white line indicates the junction between the cortex and the medulla. The difference in appearance between the cortex and the medulla is due to the arrange- ment of the uriniferous tubules ( nephrons and collecting ducts ). The renal cortex is stained darker than the renal medulla. There are numerous renal corpuscles and various convoluted tubules in the cortex region. Both the cortex and the medulla have a rich blood supply. The arcuate vessels (arter- ies and veins) are visible at the border of the corticomedullary junction. The interlobular vessels (arteries and veins) arise from arcuate vessels and course upward (arteries) or downward (veins) in the renal cortex. The renal medulla is composed of 10 to 18 renal pyramids. Each pyramid contains numerous medullary tubules ( loops of Henle , collecting ducts , and papil- lary ducts ). Each papillary duct opens at the surface of the renal papilla (called the area cribrosa ) where it empties urine into the minor calyx. The renal medulla can be divided into inner and outer zones based on differ- ences in the types of tubules residing in the two regions (Fig. 12-11A–C).
CortexCortexCortex
InterlobularInterlobular vesselvessel
Interlobular vessel
InterlobularInterlobular vesselvessel
Interlobular vessel
MedullaMedullaMedulla ArcuateArcuate vesselvessel
Arcuate vessel
ArcuateArcuate vesselvessel
Arcuate vessel
A
RenalRenal corpusclescorpuscles
Renal corpuscles
Medullary rayMedullary rayMedullary ray
MedullaryMedullary rayray
Medullary ray
ArcuateArcuate vesselvessel
Arcuate vessel (^) Arcuate vesselArcuate vesselArcuate vessel
B Figure 12-4B.^ Renal cortex, kidney.^ H&E,^ ^32
The renal cortex is composed of the renal corpuscles , the proximal convoluted tubules , the distal convoluted tubules , and the cortical collecting tubules. The renal corpuscles look like small balls interspersed among a tangle of tubules ( cortical labyrinth ) in the cortex region. The cor- tical labyrinth (with its corpuscles) is subdivided into columns by groups of parallel tubules called medullary rays. The medullary rays belong to the renal medulla proper; however, they extend into the cortex region. The renal cortex contains various convoluted tubules and is supplied by interlobular arteries , which give rise to afferent arteries. The afferent arte- rioles supply the glomeruli of renal corpuscles; blood exits the glomeruli through efferent arterioles. The cortical tubules are supplied by a peritubu- lar capillary network, which arises from efferent arterioles that exit renal corpuscles located in the outer cortex. The renal medulla is supplied by the vasa recta , which arise from efferent arteries that exit renal corpuscles in the inner (juxtamedullary) cortex. The vasa recta follow the loop of Henle downward into the medulla and loop back toward the cortex. Both the peritubular capillaries and vasa recta converge into the interlobular vein and then drain into the arcuate vein at the corticomedullary junction.
Kidneys
CHAPTER 12 ■^ Urinary System 229
Figure 12-6A. Glomerulus, renal cortex. H&E, 310; insets 841
Each glomerulus is formed by a tuft of capillaries that is fed by the afferent arteriole and drains into the efferent arteriole. Pressure in the glomerulus due to resistance of the efferent artery provides the force for filtration into the Bowman space. The glomerular capillaries are fenestrated capillaries lined by endothelial cells with gaps ( fenestrae ) that lack the usual diaphragms (see Fig. 9-13A). These capillaries are covered by processes of podocytes. The endothelial cells, basal lamina, and podocytes combine to form a glomerular filtration bar- rier. Intraglomerular mesangial cells within the glom- erulus provide structural support as well as phagocy- tosis of debris and large molecules, thereby preventing material from accumulating on the filtration barrier. They also have a contractile capability, which may function in regulating glomerular blood fl ow.
Figure 12-6B. Glomerulus and filtration barrier. EM, 16,667; insets, lower left 29,206; upper left 41,818; upper right (color), H&E 219
The central part of a renal corpuscle is composed of a bed of capillaries, the glomerulus , and the cells and structures associated with the glomerulus. In addition to the endothelial cells of the capillaries are two other cell types, podocytes and the intraglomerular mesangial cells. The endothelial cells of the fenestrated glomerular capillaries coproduce and share a common basal lamina with the terminal podocyte processes (pedicles , foot processes) that cover them. As blood flows through the capillaries, a filtrate of plasma is formed as it passes through several layers (fenestrations of the capillary, trilayered basal lamina, and filtration slits between podocytes) to enter the Bowman space ( urinary space ). Intraglomerular mesangial cells , lodged among the podocytes and endothelial cells, serve an incompletely understood maintenance function. The upper left inset shows the basement membrane of the glomerulus, pedicles ( small podocyte processes ), and cytoplasm of the endothelial cell , which together form a filtration barrier that selectively allows water, ions, and small molecules to pass through but not large molecules and blood cells. The lower left inset shows foot processes of the podocyte resting on the basement membrane of the glomerulus. The upper right color inset indicates the afferent and efferent arterioles.
Macula densaMacula densa of distal tubuleof distal tubule
Macula densa of distal tubule
FenestratedFenestrated capillary wallcapillary wall
Fenestrated capillary wall
Filtration slitFiltration slitFiltration slit
LaminaLamina rararara internainterna
Lamina rara interna
LaminaLamina rararara externaexterna
Lamina rara externa
LaminaLamina densadensa
Lamina densa
EndothelialEndothelial cellcell
Endothelial cell
BasementBasement membranemembrane
Basement membrane
PodocytePodocyte
PediclesPediclesPedicles
Podocyte
BasementBasement membranemembrane
BowmanBowman spacespace
Bowman space
Basement membrane
ErythrocyteErythrocyte
ErythrocyteErythrocyte
Erythrocyte
Erythrocyte
Luman ofLuman of GlomerularGlomerular capillarycapillary
Lumen of Glomerular capillary
BasementBasement membranemembrane
Lumen of glomerular capillary
Basement membrane
Bowman space
Podocytes
Intraglomerular mesangial cell
CapillariesCapillariesCapillaries
B ArteriolesArteriolesArterioles
Macula densaMacula densaMacula densa
ArterioleArterioleArteriole
GlomerulusGlomerulus Bowman spaceBowman space
Glomerulus Bowman space
BowmanBowman capsulecapsule
DistalDistal convoluted tubulesconvoluted tubules
Distal convoluted tubules Bowmancapsule MesangialMesangialMesangialcellcellcell
Endothelial cellEndothelial cellEndothelial cell
PodocytesPodocytesPodocytes
B
230 UNIT 3 ■^ Organ Systems
Figure 12-7. Glomerulus and podocyte. SEM, 9,
This scanning electron microscopy (SEM) image shows that the surface of the glomerulus is entirely covered by podocytes and their processes. Each podocyte is composed of a cell body (with nucleus) and several branching processes. The small terminal branches that cover the capillaries are called foot processes or pedicles. The pedicles from two podocytes interdigitate with each other. The gaps between adjacent pedicles are referred to as fi ltration slits , which are bridged by filtration slit diaphragms. The inner core of the pedicles is supported by actin filaments. The inner core of the primary processes is supported mainly by microtubules and inter- mediate filaments. The podocytes and their unique arrangement are important components in establishing the glomerular filtration barrier.
PodocytePodocytePodocyte
PediclesPediclesPedicles
Filtration slitsFiltration slitsFiltration slits
Branches ofBranches of primary processesprimary processes
Branches of primary processes
PrimaryPrimary processprocess
Primary process
PediclesPediclesPedicles
PrimaryPrimary processprocess
Primary process
PodocytePodocytePodocyte
PrimaryPrimary processprocess
Primary process
Branches ofBranches of primary processesprimary processes
Branches of primary processes
Filtration slitsFiltration slitsFiltration slits
Bowman space (filtrate into the space)
Glomerulus (filters blood)
Urinary pole
Proximal convoluted tubule
Thick descending limb (proximal straight tubule)
Thin descending limb (descending thin segment)
Ascending thin limb (ascending thin segment)
Thick ascending limb (distal straight tubule)
Distal convoluted tubule
cortical collecting tubule
Collecting duct
Papillary duct
Minor calyx
Area cribrosa
Major calyx
Renal pelvis Ureter
Urinary bladder (store)
Urethra (to outside)
Loop of Henle
Renal corpuscle
Collecting system
Production and Drainage of Urine
232 UNIT 3 ■^ Organ Systems
Figure 12-9B. Proximal tubule. EM, 4,606; inset 9,
This is a cross section of a proximal tubule. It is lined by cuboidal and low columnar cells with apical microvilli , which form a brush border , a feature that is associated with reabsorption function. The numerous mitochondria are more concentrated at the basolateral surface where they support the energy requirements of sodium pumps located in the expanded plasmalemma. The apical regions of the cells contain pinocytotic vesicles , which reflect the uptake of proteins that evaded the filtration barrier in the renal corpuscle and entered the fi ltrate. The inset shows long microvilli and pinocytotic vesicles in the apical surface of the cells.
BasementBasement membranemembrane
Basement membrane
Brush borderBrush border with glycocalyxwith glycocalyx
Brush border with glycocalyx
Nuclei of theNuclei of the cuboidal cellscuboidal cells
Nuclei of the cuboidal cells
LumenLumenLumen
A
PinocytoticPinocytotic vesclevescle
Pinocytotic vesicle
MitochondriaMitochondriaMitochondria
MicrovilliMicrovilliMicrovilli NucleusNucleusNucleus
LysosomeLysosomeLysosome
PinocytoticPinocytotic vesiclesvesicles
Pinocytotic vesicles
BasementBasement membranemembrane
Basement membrane
MicrovilliMicrovilliMicrovilli
MitochondriaLysosomeLysosome
LumenLumenLumen
B
Figure 12-9A. Proximal tubules, renal cortex. H&E, 754
Both proximal convoluted and straight tubules have a similar structure and function. They are lined by large acidophilic cuboidal cells with brush borders formed by numerous long microvilli. The brush border extends into the lumen , which, in conjunction with postmortem changes, makes the lumen appear smaller and filled with acidophilic material ( brush border and glycocalyx ). The proximal tubules have a substantial reabsorption function. About 65% of the water and sodium and more than 90% of glucose, amino acids, and bicarbonate are reabsorbed by the proximal convoluted tubules. The proximal convo- luted tubules are located in the cortical labyrinth and are connected to the renal corpuscle at the urinary pole. The proximal straight tubules are part of the loop of Henle (Fig. 12-8B).
CHAPTER 12 ■^ Urinary System 233
Figure 12-10A. Distal tubules. H&E, 739
The distal tubules are lined by small cuboidal cells with faintly eosinophilic or clear cytoplasm. The lat- eral boundaries between cells are not as distinguishable as those of the collecting duct. The distal convoluted and straight tubules are similar in structure. The distal straight tubule exits the medullary ray and approaches the vascular pole of the renal corpuscle of the same nephron to which the distal tubule belongs. As the distal tubule passes adjacent to the afferent and efferent arteri- oles, part of its wall becomes modified as a sensory struc- ture, macula densa , which monitors ionic content and water volume of the filtrate (Fig. 12-5A,B). The macula densa is considered to mark the transition from the dis- tal straight to the distal convoluted tubule. This figure shows the distal convoluted tubules in the renal cortex. Distal tubules function mainly to remove sodium and add potassium ions to the filtrate when stimulated by aldosterone , a hormone produced by the adrenal gland.
ProximalProximal tubuletubule
Proximal tubule
ProximalProximal tubuletubule
Proximal tubule
Lumen ofLumen of distal tubuledistal tubule
Lumen of distal tubule
Lumen ofLumen of collecting ductcollecting duct
Lumen of collecting duct
A
Figure 12-10B. Distal tubule. EM, 4,441; insets 7,
A cross section of a distal tubule , which is lined by cuboidal and columnar cells, is shown. In contrast to the extravagant brush border of cells lining the proximal tubule, these cells have just a few, short microvilli. These cells have basally located nuclei and tightly interdigitated lateral walls. In distal tubules, there are many mitochondria in the cytoplasm as there are in the proximal tubules. The upper left inset shows short and irregular microvilli bulging into the lumen and many mitochondria beneath them. The lower left inset shows a nucleus and basal enfolding (basal plasma membrane enfolding) of the cell. The basal enfolding is due to corrugation of the cell membrane in the basal region of the cell. This increases the surface area of the cell and is closely associated with mitochondria, which produce adenosine triphosphate for active transport of ions.
NucleusNucleusNucleus
Blood vesselBlood vesselBlood vessel
MicrovilliMicrovilliMicrovilli
Basement membrane
Basal enfoldingBasal enfoldingBasal enfolding
LumenLumenLumen
MicrovilliMicrovilliMicrovilli
MitochondriaMitochondriaMitochondria
Basal enfoldingBasal enfoldingBasal enfolding
B
CHAPTER 12 ■^ Urinary System 235
CLINICAL CORRELATIONS
Figure 12-12A. (^) Renal Oncocytoma. H&E, 216 Renal oncocytoma is a benign and less common neoplasm of the kidney and originates from the epithelium of the proximal tubules. It is typically a solid, encapsulated mass with homogeneous enhancement in radiographic imaging. Gross examination shows a spherical mass with a mahog- any cut surface and a tan, fleshy central scar. Histologi- cally, the tumor cells are large with abundant eosinophilic cytoplasm due to the presence of numerous mitochondria. The cells are arranged in sheets or in a tubulocystic pat- tern. It is usually asymptomatic and detected as an inci- dental renal mass on imaging. Treatment options include surgical excision of the kidney ( nephrectomy ) or removal of a portion of the kidney (partial nephrectomy).
Figure 12-12B. (^) Hemodialysis. Hemodialysis is a common treatment for end-stage kidney disease. The dialyzer is a canister containing thousands of small fibers through which blood is passed. The fibers are made up of semipermeable membranes with small pores allowing wastes and extra fluids to pass from the blood into a solution. A cleansing fluid called dialysate is pumped around the fibers. Solute and extra fluids are cleared from the blood compartment by either diffusion or ultrafiltra- tion, depending on the concentration gradient and pres- sure difference between the blood and the dialysate. The cleansed blood is returned via the circuit back to the body. Hemodialysis is usually given three times a week and can be done in a dialysis center or at home. The model illus- trated here is commonly used in critical care units.
Neoplastic oncocytic cells
A
Blood from patient
Blood back to patient
Dialyzer
B
SYNOPSIS 12-1 Clinical and Pathological Terms for the Urinary System
■ Glomerulonephritis : Refers to primary glomerular disease not related to infection of the kidneys themselves. The causes of glomerulonephritis are heterogeneous, such as viral or bacterial infection; drugs; and malignancy, resulting in many distinct clinical entities including focal and segmental glomerulonephritis and membranous nephropathy. The causes are often not identifi ed (idiopathic glomerulonephritis). ■ Glomerulopathy : Refers to secondary glomerular injury as a result of systemic diseases, such as diabetes mellitus and systemic lupus erythematosus. ■ Glomerulosclerosis : Scarring or sclerosis of the renal glomeruli in diseases such as diabetic nephropathy and focal segmental glomerulosclerosis. ■ Dysuria : Pain or burning upon urination, most often caused by a urinary tract infection affecting the bladder (cystitis) or urethra (urethritis). ■ Frequency : The need to urinate more often than normal without an increase in total urine output; common causes include lower urinary tract infection and benign prostatic hyperplasia; other less common causes include tumors and extrinsic bladder compression. ■ Hematuria : The presence of blood in the urine, causes of which include trauma, infection, tumors of the urinary system, kidney stones, and hyperplasia of the prostate gland; hematuria may be microscopic or “macroscopic,” meaning visible to the unaided eye. ■ Lithotripsy : Extracorporeal shock wave lithotripsy is a procedure for treating kidney and ureteral stones using focused high-energy shock waves that pass through the body and break stones into small pieces that can then pass into the urine and be eliminated. ■ Urgency : A strong urge to urinate, most often caused by a lower urinary tract infection or other causes of bladder irritation such as interstitial cystitis, which mainly affects females.
236 UNIT 3 ■^ Organ Systems
Structure Epithelial Lining of the Tubules
Characteristics of the Tubules Main Locations
Main Functions
Nephron Renal corpuscle Simple squamous epithelium
Composed of glomerulus (blood vessels covered by podocytes) and Bowman capsule
Renal cortex Filters blood and forms urine
Proximal convoluted tubule
Simple cuboidal epithelium with long microvilli (brush border)
Long and highly convoluted tubule; relatively small lumen and acidophilic cytoplasm; abundant mitochondria; numerous basolateral plasma membrane enfoldings
Renal cortex Drains fluid from the renal corpuscle to the loop of Henle; reabsorbs 70%–80% Na+^ and Cl−^ and water; also reabsorbs glucose, amino acids, and proteins and produces calcitriol (active form vitamin D)
The Loop of Henle
Thick descending limb ( proximal straight tubule )
Simple cuboidal epithelium with long microvilli (brush border)
Similar to proximal convoluted tubule but shorter and straight; small mitochondria; no basolateral plasma membrane enfoldings
Medullary ray and outer zone of the renal medulla
Absorptive function is similar to proximal convoluted tubule but less significant
Thin descending limb ( descending thin segment )
Simple squamous epithelium
Thin, small tubule; epithelial cells may reveal basolateral enfoldings and small microvilli
Partial outer zone and most of the inner zone of the renal medulla
Highly permeable to water (loss of water from lumen to interstitium); less permeable to salt (keeps or may gain some Na+^ and Cl−^ in the lumen) Thin ascending limb ( ascending thin segment )
Simple squamous epithelium
Similar to descending thin segment; may have basolateral enfoldings and small microvilli
Inner zone of the renal medulla
Impermeable to water (retains water); highly permeable to salt (loss of Na+^ and Cl−^ from the lumen to the interstitium) Thick ascend- ing limb ( distal straight tubule )
Simple cuboidal epithelium with short microvilli
Straight tubule; numerous mitochondria; less acidophilic cytoplasm; many basolateral plasma membrane enfoldings
Medullary ray and outer zone of the renal medulla
Impermeable to water (retains water); highly permeable to salt (loss of Na+^ and Cl−^ from the lumen to the interstitium) Distal convoluted tubule
Simple cuboidal epithelium with short microvilli
Numerous mitochondria; basolateral plasma membrane enfoldings; less acidophilic cytoplasm; highly convoluted tubule
Renal cortex Reabsorbs Na+^ and secretes K+, if aldosterone stimulation is present; reabsorbs bicarbonate ions and secretes ammonium to adjust pH Collecting System Collecting tubule Simple cuboidal epithelium with few microvilli
Straight tubule; much less acidophilic cytoplasm; more than one cell type
Renal cortex Highly permeable to water; loss of water from the lumen to the interstitium when ADH is present Collecting duct Simple columnar Large straight tubule; clear cytoplasm and distinct boundaries between cells; well-developed basal enfoldings
Medullary ray and renal medulla
Highly permeable to water; loss of water from the lumen to the interstitium when ADH is present Papillary duct Simple columnar epithelium
Short duct; links collecting duct to the minor calyx
Bottom tip of the pyramid of the medulla
Conducts urine
TABLE 12-1 Kidneys
238 UNIT 3 ■^ Organ Systems
Urinary Bladder
CLINICAL CORRELATION
Figure 12-14C. (^) Urothelial (Transitional) Carcinoma. H&E, 108 Urothelial carcinoma may arise in the urinary bladder, ureters, or renal pelvis and is the most common urinary bladder carcinoma. More than 90% of bladder cancers originate from the transi- tional epithelium ( urothelium ) in the urinary system. Urothelial carcinoma is most prevalent in older men but may occur at any age. Risk factors include cigarette smoking , exposure to arylam- ines and radiation , long-term use of cyclophosphamide, and infection by the parasite Schistosoma haematobium. Infection with S. haematobium is also a risk factor for the development of squamous cell carcinoma of the urinary bladder. Symptoms include painless gross hematuria, frequency, urgency, and dysu- ria. Urothelial carcinomas typically display a papillary morphol- ogy and are subdivided into low and high grade depending on cytologic features and the amount of architectural disorder pres- ent. Treatment includes transurethral resection, chemotherapy, immunotherapy, and radical cystectomy. Tumors have a high recurrence rate after local excision.
Papillae in urothelial carcinoma
C
Figure 12-14A. Urinary bladder, bladder wall. H&E, 17; inset 82
The urinary bladder has three layers ( mucosa , muscularis , and adventitia / serosa ), similar to those in the ureter, but its wall is much thicker. Thick mucosa and muscularis layers make up the wall of the urinary bladder. The mucosa is composed of exten- sively folded transitional epithelium and lamina propria. This arrangement gives the bladder the distensibility needed to store urine. The muscularis consists of three smooth muscle layers: the inner longitudinal, middle circular, and outer longitudinal smooth muscle. These three smooth muscle layers are arranged in two dif- ferent orientations to help the urinary bladder contract to empty urine efficiently. The outer layer of the bladder is mainly covered by adventitia (connective tissue); its superior (free) surface is cov- ered by serosa , which is a layer of connective tissue with a lining of mesothelium.
Lamina propria
MuscularisMuscularisMuscularis
Smooth muscleSmooth muscleSmooth muscle
SubmucosaSubmucosaSubmucosa
Epithelium
A
LaminaLamina propriapropria
Lamina propria
Basal cellsBasal cellsBasal cells
Dome-shaped surface cells
B
Figure 12-14B. Urothelium, bladder wall. H&E, 278
This figure shows the urothelium (transitional epithelium) in a relaxed state. The urothelial lining of the urinary bladder is thicker than that of the ureter. The basal cells of the urothelium are cuboi- dal or columnar in shape, the cells in the middle layer of the urothe- lium are polygonal, and the surface cells are dome shaped and bulge into the lumen when the bladder is empty (relaxed state). When the bladder is full, the urothelium is stretched, the cells become fl attened, and the thickness of the urothelium is greatly reduced (see Fig. 3-17B).
CHAPTER 12 ■^ Urinary System 239
Figure 12-15A. Transitional epithelium, urinary bladder. EM, 7,
This figure shows the surface of transitional epithelium and the border between the cells of the top layer and the underlying layer. There are many flattened vesicles (membrane vesicles) in the cytoplasm of these cells. The vesicles are more numer- ous close to the apical region of the cyto- plasm. These vesicles are formed from the surface membrane when the bladder is in a relaxed state. It is important to recall that the surface of the transitional epithelium of the bladder is highly convoluted when the bladder is empty (relaxed). This may create many “pseudovesicles”; most of the vesicles disappear when the surface of the epithelium is stretched and flattened in the distended state. The boxed area indicates Figure 12-15B at higher magnification.
FlattenedFlattened vesiclesvesicles
Flattened vesicles
Border betweenBorder between two cell layerstwo cell layers
Border between two cell layers
JunctionalJunctional complexcomplex
Junctional complex
Fig. 12-14BFig. 12-14BFig. 12-14B
A
Figure 12-15B. Transitional epithelium, urinary bladder. EM, 35,
A higher power view of the surface of the top layer cells in the transitional epithelium is shown. The junction complex indicates the border of neighboring cells. Tight junctions ( zonula occludens ) and desmosomes ( macula adherens ) can be observed here. The cells are fi lled with fl attened vesicles and tonofi laments.
FlattenedFlattened vesiclesvesicles
Flattened vesicles
TonofilamentsTonofilamentsTonofilaments
Tight junctionTight junctionTight junction
DesmosomeDesmoseDesmose
MitochondrionMitochondrionMitochondrion
B
