The kidneys (Figure 28,1), which are the principal organs. natomy of the Urinary System. Anatomy of the Urinary System.

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1 Exercise 28 natomy of the Urinary System Laboratory Objectives n ompletion of the activities in this exercise, you will be able to: Describe the gross and microscopic anatomy of the urinary svstem, Trace the path of materials through the urinary system, from when they enter the kidneys to when they leave the body. Describe the functions of the various components of the urinary system, Explain the positions of the two types of nephrons, Detail the blood supply of the kidneys, Materials Compound light microscope Prepared microscope slides Human kidney Kidney, injected to demonstrate renal blood supply Ureter Urinary bladder Urethra Torso model Dissectable kidney model, coronal section Model of a nephron Model of the female pelvis Model of the male pelvis Injected sheep or pig kidney for dissection Dissection tools (scalpel, probe, forceps, dissecting pan) The kidneys (Figure 28,1), which are the principal organs of the urinary system, perform several essential regulatory functions, As they produce urine, the kidneys remove metabolic wastes and toxins from the blood and conserve glucose, water, and many essential electrolytes, These activities are critical for maintaining osmotic and ph balance in the blood plasma, The kidneys also have an endocrine function, They secrete erythropoietin, which promotes red blood cell production in the bone marrow, and renin, which plays a role in maintaining normal blood pressure, The ureters, urinary bladder, and urethra are accessory organs of the urinary system (Figure 28,1), Collectively, these structures transport, store, and excrete urine, Anatomy of the Urinary System The two retroperitoneal kidneys are located on each side of the venebral column on the posterior abdominal "vail They extend, approximately, from the T12 vertebra to the L3 vertebra, The right kidney rests 1.5 to 2 cm (0,5 to 0,7 in) lower than the left kidney due to the large area taken by the liver (Figure 28, 1a), Each kidney is approximately 12 cm (5 in) long, 6 cm (2,5 in) wide, and 3 cm 0,25 in) thick, Its lateral surface is convex and its medial surface is concave, A central region along the medial surface, called the hilus, serves as a point of entry and exit for the renal artery and vein, ureter, nerves, and lymphatic vessels (Figures 28,1 and 28,2), Each kidney is surrounded by three connective tissue coverings (Figure 28, 1b), The renal fascia is the outer fibrous connective tissue covering that anchors the kidney to the peritoneum and abdominal wall The middle adipose capsule is a fatty layer that provides shock-absorbing protection for the kidney. The inner renal capsule is a strong fibrous layer that tightly adheres to the kidney surface, It provides a protective barrier that prevents infections from spreading to renal tissue, In a coronal section of the kidney, three regions can be identified (Figure 28,2), The outer renal cortex and the middle renal medulla contain the various urine-producing tubules that comprise the nephrons. The inner region of the kidney is a cavity known as the renal sinus. It serves to collect urine that is produced in the nephrons, and to transport this fluid to the ureter. The ureters are retroperitoneal, tubular organs that are approximately 25 cm (10 in) long, They begi:n at the renal pelvis (Figure 28.2) and travel inferiorly along the posterior abdominai wall, They enter the pelvic cavity and terminate at the posterior aspect of the urinary bladder (Figure 28.1 a). The primary function of the ureters is to transport urine from the kidneys to the urinary bladder. The urinary bladder is located within the pelvic cavity, pos ~ terior to the pubic symphysis and anterior to the rectum (Figures 28.3a and b), It serves as a temporary storage sac for urine, and its shape is determined by the volume of urine it contains, An empty bladder has a pyramidal shape, with the base forming its posterior surface and the apex oriented anteroinferiorly. When the bladder is full, it becomes ovoid and the superior surface bulges into the abdominal cavity. The urethra is a muscular tube that conveys urine from the bladder to the outside of the body (Figure 28,3). At the junction with the bladder, a thick band of smooth muscle surrounds the urethra to form the internal urethral sphincter (Figure 28,3c). This sphincter is involuntary and keeps the urethra closed to prevent urine from leaking between periods of micturition (urination). A second sphincter, the external urethral sphincter, consists of skeletal muscle, In females, this voluntary sphincter is located near the external urethral orifice (Figure 28,3b); in males, it is found just below the prostate gland (Figures 28,3a and c). 491

2 EXERCISE TWENTY-EIGHT Inferior vena cava Right adrenal gland Right kirl,nav-~~r Rectum (cut) (a) Inferior Psoas Esophagus (cut) vena cava Aorta major Quadratus Left adrenal muscle lumborum gland I muscle Left kidney Left renal artery Left renal vein sup~ mesenteric artery Ureter Left common iliac artery artery and vein Urinary bladder Adipose capsule Hilus External artery vein (b) oblique muscle fascia capsule Kidney Spleen Ureter Parietal peritoneum Figure 28.1 Overview of the urinary system. a) Anterior view in the male illustrating anatomical relationships of the kidneys and ureters with posterior abdominal muscles, and major abdominal blood vessels; b) transverse section of the left posterior abdominal wall, showing the position of the kidney in relation to other abdominal organs. Cortex!iiIO;:;;;;;:----- capsule sinus - -4,,...;= --.: Adipose tissue ---- in renal sinus pelvis ,~- Hilum --~= i papilla -~---,>i~,-..,...,,~~. J Medulla pyramid Connection to minor calyx Minor calyx Major calyx lobe columns pyramids ~~I;t!JIL----:!!I-- sinus pelvis Major calyx --r"'":--~=-""~ Minor calyx papilla Ureter capsule...r---- lobe (a) (b) Figure Internal structure of the kidney. a) Diagram of a coronal sedion of the left kidney; b) correspondi ng cadaver dissedion. ACTIVITY 28.1 Examining Gross Anatomy of the Urinary System tions relative to the vertebrae. Also observe that the position of the liver causes the right kidney to be more inferior than the left kidney. 1. On the torso model, identify the two kidneys along the 2. Observe the lateral convex surface and medial concave posterior abdominal wall (Figure 28.1). Note their posi- surface, and identify the hilus along the center of the con-

3 ANATOMY O F TH URI NARY SYSTEM :>en oneum Urinary bladder Rectum Pubic ,-;:i-r-::: symphysis Figure 28.1 Position of the urinary bladder. Midsagittal sections of a) the male pelvic cavity, and b) the fema le pelvic cavity, illustrating the position of the urinary bladder in relation to other pelvic structures. c) Internal view of the male urinary bladder, illustrating the rugae and the trigone. External----:-..;-.;c..:;c:..,...:;-...,.,y;.;.~ urethral sphincter Penile urethra External urethral meatus (a) Male Peritoneum Uterus Rectum Urinary ~ bladder Pubic symphysis Urethra ~_~ ~ Vagina ,.*~ (b) Female Lateral umbilical ligament Rugae - --'::':--7':':'"*------""'-- Prostate gland Urogenital diaphragm Ureteral ---':-'~~-~------:-- openings --:--:-=~'"-+- Center of trigone Internal urethral sphincter External urethral sphincter (in urogenital diaphragm) (e) Urinary bladder.in male Vestibule Middle umbilical ligament 1 ~ ~~~~~~ Neck -t Prostate gland I------:;~---- Prostatic urethra H"--'--' Membranous urethra cave surface (Figures 28.Ia and 28.2). At the hilus identify the ureter, renal artery, and renal vein entering or exiting the kidney. 3. Identify the adrenal glands that rest on the superior surface of each kidney. 4. Examine a coronal sect,ion of a kidney and identify the three internal regions (Figure 28.2): renal cortex, renal medulla, and renal sinus. 5. Locate the outer renal cortex and note its appearance. 6. Locate the middle portion, the renal medulla, and identify the cone-shaped renal pyramids. They are separated by inward extensions of cortical tissue known as renal columns. Note that the base of each renal pyramid forms a border with the cortex, while the apex, known as a renal papilla, projects inwardly. 7. Identify the inner region of the kidney, which is called the renal sinus. It consists of the calyces (singular = calyx) and the renal pelvis (Figure 28.2). 8. Locate a minor calyx. Urine formed \>vithin a renal pyramid drains through the renal papilla to enter the minor calyx. 9. Follow the minor calyx inward until it joins at least one more minor calyx. The larger area marked by this junction is a major calyx. 10. Locate the renal pelvis, a funnel-shaped cavity continuous with the ureters. The renal pelvis collects urine from three to six major calyces and transmits it to the ureter. 11. On the torso model, identify the two ureters where they exit the kidneys. Observe that these tubes travel inferiorly along the posterior abdominal wall and enter the pelvic cavity (Figure 28.1a). 12. In the pelvic cavity, locate the termination of the ureters at the posterior aspect of the urinary bladder (Figures 28.3a and c). 13. On models of the female and male pelvic cavities, observe the relative position of the urinary bladder to other abdominopelvic organs. in both sexes, the urinary bladder is posterior to the pubic symphysis and anterior to the rectum (Figures 28.3a and b). In females, it is anterior to the uterus and the vagina (Figure 28.3b). In males, it is s11perior to the prostate gland (Figure 28.3a). 14. Obtain a model with an open bladder. Along the internal surface of the contracted bladder, identify the numerous rugae (Figure 28.3c), which are folds of the mucous membrane. They are present when the bladder is empty. When the bladder fills with urine, the wall stretches and the rugae disappear.

4 EXERCIs e TWEl\TY-EIGHT 15. Identify the trigone, which is a triangular region marked by the connections of the two ureters and the urethra to the bladder wall (Figure 28.3c). This region lacks rugae and remains smooth at all times. It is noteworthy because bladder infections seem to occur most often in this area. The reason for this is not known. 16. Identify the urethra where it emerges from the inferior aspect of the urinary bladder. Notice that in females, the urethra is relatively short (approximately 3.5 cm or 1.5 in) and travels anterior to the vagina. The external urethral orifice is located anterior to the vaginal orifice and posterior to the clitoris (Figure 28.3b). Observe tha t the male urethra is relatively long (approximately 20 em or 8 in) and has the following three sections (Figures 28.3a and c). The prostatic urethra passes through the prostate gland. The membranous urethra passes through a band of muscle called the urogenital diaphragm. The penile urethra travels through the shaft of the penis. CLINICAL CORRELATION For two reasons, females are more susceptible to urinary tract infections than males. First, the female urethra is much shorter and inflammatory infections of this structure (urethritis) can easily spread to the bladder (cystitis) and possibly to the kidneys (pyelitis or pyelonephritis). Second, the external urethral orifice is very dose to the anal opening. Fecal bacteria can be transferred to the urethra particularly if an individual wipes with toilet paper in a posterior to anterior direction after defecation. ~!lfilwi'm~~ On a torso model, identify the two kidneys and lriiiii iiiili6lli...1i describe their anatomical relations to other abdominal organs. Right kidney: Tubular reabsorption, during which useful substances such as water, glucose, amino acids, and ions are returned to the blood Tubular secretion, during which unwanted substances such as excess potassium and hydrogen ions, drugs, creatinine, and metabolic acids are transported from the capillaries into the tubules Each nephron begins with Bowman's capsule, a cup-shaped structure that surrounds a tuft of capillaries called a glomerulus (plural = glomeruli). Together, the two structures comprise a renal corpuscle (Figure 28.4). In each corpuscle, fluid passes across a filtration membrane from the glomerulus to Bowman's capsule. The!1uid entering Bowman's capsule is called the filtrate. WHArS IN A WORD The term glomerulus comes from the Latin term meaning "bal\" or "globe." Indeed, the glomemlus is like a ball or tuft of capillaries. This arrangement, rather than a Single straight capillary, dramatically increases the amount of capillary surface area through which filtration can occur, allowing the kidneys to filter the blood much more rapidly. After Bowman's capsule, filtrate travels through three additional components of a nephron in the following sequence: the proximal convoluted tubule, the loop of Henle, and the distal convoluted tubule (Figure 28.4). Together, these structures form a long, twisting passageway known as the renal tubule. The convoluted tubules and the loop of Henle are capable of both reabsorption and secretion. However, there are regional specializations. For example, most reabsorption occurs in the proximal convoluted tubules, while the distal convoluted tubules have a more impoaanr role in secretion. Other tubules, the collecting ducts, are straight tubular passageways that receive urine from the nephrons and transport it to the minor calyces (Figure 28.4a). Two types of nephrons exist in the kidney. The vast majority (80% to 85%) are cortical nephrons (Figures 28.4a and b). The second type, called juxtamedullary nephrons (figures 28.4a and c), is less abundant but plays a critical role in conserving water by producing a concentrated urine. Left kidney: The Nephron The functional units of the kidney are the nephrons (Figure 28.4). They consist of various types of tubules that closely interact with capillaries during urine formation. To produce urine, the nephrons perform three basic activities. Glomerular filtration, during which water, glucose, amino acids, and nitrogen-containing wastes are passed from blood to the nephrons along a pressure gradient ACTIVITY 28.2 Examining the Nephron 1. Obtain a model or illustration of a nephron and distin guish between the following structures (Figure 28.4). corpuscle tubule Collecting duct 2. In their correct sequence, identify the specific segments of the renal tubule (Figure 28.4a). Proximal convoluted tubule Descending limb of the loop of Henle Ascending limb of the loop of Henle Distal convoluted tubule 3. Closely examine the pattern of a typical nephron and notice the following general features (Figure 28.4).

5 ANATOMY OF THE URINARY SYSTEM Proximal Distal Glomerulus convoluted convoluted tubule tubule ~,.,...=----or-- Peri tubular capillaries corpuscle Peritubular --..,--:;;!./ I capillaries Collecting duct Loop of Henle Descending limb Loopof---~~~ Henle (b) Cortical nephron Ascending limb Proximal convoluted tubule Glomerulus----l~ Collecting duct i ,,..--_ Vasa recta I+---Collecting duct oj--+r---==_ Loop of Henle Minor calyx (a) Papillary ducts (c) Juxtamedullary nephron Figure 28.4 The kidney nephrons. a) Positions of cortical and Juxtamedullary nephrons in relation to the renal cortex and medulla; b) blood supply to a cortical nephron; c) blood supply to a juxtamedullary nephron. All renal corpuscles are located in the cortex. The cortex also contains the proximal and distal convoluted tubules. The loops of Henle begin and end in the cortex but descend and ascend in the medulla. The distal convoluted tubules drain urine directly into collecting ducts. 4. Identify a collecling duct and notice that it receives urine from several nephrons. Trace its path as it begins in the cortex and descends through a renal pyramid in the medulla. At the renal papilla, the collecting duct empties into a minor calyx. 5. Observe that the kidney has two types of nephrons (Figures 28.4b and c). In cortical nephrons, renal corpuscles originate in the outer two thirds of the cortex and the loops of Henle do not travel deeply into the medulla. In juxtamedullary nephrons, renal corpuscles originate in the inner one third of the cortex and the loops of Henle extend deep within the medulla.

6 EXERCISE TWENTY-EI GHT fw!hmwntj 1. Inflammation of the renal cortex is likely to affect the function of which segments of the nephrons Explain why. ' 2. Kidney stones are deposits of calcium and magnesium salts or uric acid crystals that can obstruct the urinary passageways. Which condition is likely to be more serious: a kidney stone blocking a collecling duct, or one blocking a ureter? Explain why. 7. Locate the peritubular capillaries and the vasa recta, which arise from the efferent arteriole. The peritubular capillaries are closely associated with renal tubules in the cortex and the loops of Henle of cortical nephrons. The vasa recta surround the loops of Henle of juxtameclullary nephrons (Figures 28.4b and c). Note that these capillaries empty into the venous system that drains blood from the kidney (Figure 28.5c) 8. Return to the model of the kidney and examine the venous drainage of the organ. The veins in the kidney parallel the arteries and are assigned identical names (Figure 28.5). 9. On a torso model, identify the renal vein and notice that it empties into the inferior vena cava (Figure 28.1 a). Blood Supply of the Kidney Under normal conditions, about 25% of total cardiac output travels through the kidneys at a rate of about 1.2 liters per minute. Each kidney receives its blood supply from a renal artery, which is a direct branch of the abdominal aorta (Figure 28.1a). The rena'l artery ancl its branches deliver blood to the glomeruli (Figure 28.5a), which are surrounded by Bowman's capsules in the renal cortex and are the sites of blood filtration. After passing through the glomeruli, blood enters the peritubular capillaries and vasa recta (Figures 28.4b and c). Tubular reabsorption and secretion occurs between the renal tubules and these capillary networks. The pentubular capillaries and vasa recta drain into small venules that mark the beginning of venous drainage of the kidney. ACTIVITY 28.3 Examining the Blood Supply of the Kidney 1. Obtain a model of the kidney cut in a coronal plane to examine its arterial supply (Figure 28.5). 2. Identify the renal artery entering the kidney at the hilus. Notice that the first branches of the renal artery are the segmental arteries. 3. The segmental arteries give rise LO a number of interlobar arteries that travel toward the cortex through the renal columns. 4. At the junction between the cortex and medulla, observe how interlobar arteries branch to form the arcuate arteries. The arcuate arteries provide a good landmark for identifying the corticomedullary boundary. 5. The arcuate arteries give off several interlobular arteries, which can be seen ascending into the cortex. 6. Obtain a model or illustration of a nephron. Identify the afferent arteriole leading to a glomerulus, and Lhe efferent arteriole which exits the glomerulus (Figure 28.4). f'jlwntl Explain why it is important for the kidneys to re.... _._ ceive a large daily volume of blood. Microscopic Anatomy of the Urinary System The histology of the kidney is centered on the structure of the nephrons. As described earlier, each renal corpuscle consists of a Bowman's capsule and a glomerulus. These structures have a distinctive appearance and are easy to identify throughout the renal cortex. The renal tubules and collecling ducts, which are found in both the cortex and medulla, are lined mostly by a simple cuboidal epithelium, although squamous and columnar epithelia are found in some regions. You will also observe arteries and arterioles that supply blood to the kidney and capillary networks that surround the renal tubules. The capillaries are crit,ical for normal renal function because of their active role in reabsorption and secretion during the produclion of urine. The accessory urinary organs are uni.que because they possess a mucous membrane with a transitional epithelium. This epithelium is noteworthy for its ability to undergo dramatic structural transformations to adjust for the changing physical conditions of the organs where it is located. ACTIVITY 28.4 Examining the Microscopic Anatomy of the Urinary System The Kidney 1. Obtain a slide of the kidney. 2. Scan the slide under low magnification until your field of view is.vithin the renal cortex. The cortex can be easily identified because it contains numerous renal corpuscles, each consisting of a glomerulus surrounded by Bowman's capsule (Figure 28.6a). Each glomerulus will appear as a

7 ANATOMY OF THE URINARY SYSTEM Interlobular arteries Interlobular veins Interlobular vein Interlobular artery Arcuate artery Arcuate vein -t~~s:~~~~::",. Interlobar arteries.rf Af----lnterlobar vein :~#---- Interlobar artery Segmental artery Suprarenal artery (b) artery vein Interlobar """"I--++!---=-~l-----:..r."', veins (a) vein artery 1 Segmental arteries! Interlobar veins Interlobar arteries f Arcuate veins t Interlobular veins t Venules Arcuate arteries Interlobular arteries Afferent arterioles NEPHRONS Peritubular Glomerulus capillaries L. Efferent arteriole (e) Figure 28.5 Blood supply to the kidney. a) Coronal section of the kidney, ill ustrating the major arteries and veins; b) a closer view of the blood supply to a renal pyramid and the adjacent cortex; c) summary chart of the blood flow through the kidney.

8 EXERCIS TWENTY-EIGHT spherical mass of pink- to red-staining tissue surrounded by a clear space. This space, the capsular space, is the cavil)' within Bowman's capsule that receives the filtrate (Figure 28.6b). 3. Much of the field of v,iew consists of cross-sectional and longitudinal profiles of renal tubules typically lined by a simple cuboidal epithelium (Figure 28.6). Locate these tubules. Most of these are either proximal convoluted tubules or distal convoluted tubules, but collecting ducts are also present. Kidney tubules with simple cuboidal epithelium (a) Glomerulus corpuscles tubules Glomerular capsular space 4. Switch to high power and examine a glomerulus and Bowman's capsule more carefully (Figure 28.6b). Like all blood vessels, the walls of the glomerular capillaries are lined by simple squamous epithelium (the endothelium). You cannot clearly see the arrangement of this epithelium with this preparation; however, many of the nuclei in the glomerulus belong to the endothelial cells. 5. Examine a Bowman's capsule, The epithelium lining it is also a simple squamous type, Look carefully across the capsular space from the glomerulus and identify the single layer of squamous cells that line the outer wall of the capsule (Figure 28,6b), 6. The afferent and efferent arterioles may be identified on some glomeruli; however, you will be unable to distin guish one vessel from the other (Figure 28.6b), 7. Switch back to low power ami move the slide to a region where glomeruli are absent. This is the renal medulla (Figure 28.7). The field of view is filled with cross sectional and longitudinal profiles of the loops of Henle and collecting ducts. 8. The collecting ducts are relatively easy to identify because the cuboiual epithelium that lines these tubules stains lighter than the other cells on the slide (Figure 2ft?). 9. Obtain a slide labeled, "kidney, injected." This slide has been specially prepared so that renal blood vessels can be easily identified. 10. Scan the slide under low power. blood vessels appear as bright red channels traveling throughout the field of view. Kidney tubules are barely visible, because they stain very faintly (Figure 28.8). Do not be concerned about identifying the tubules on this slide. Focus your attention on the blood vessels. Loops of Henle Position of afferent/efferent Simple squamous Beginning arterioles epithelium of of a proximal Bowman's capsule convoluted tubule (b) Figure 28.6 The renal cortex. a) low-power light micrograph of the renal cortex. corpuscles are distributed throughout the field of view (lm x 100). b) High-power light micrograph of a renal corpuscle, which includes a glomerulus enclosed by a Bowman's capsule, Kidney tubules surround the corpuscle (lm x 300), Collecting ducts Figure 28.7 The renal medulla. light micrograph of renal tubules in the medulla of the kidney, Notice the lack of renal corpuscles in this region of the kidney (lm x 300).

9 ANATOMY OF THE URINARY SYSTEM C"tIIUS!:- bular artery Peritubular +=~l:===== :apillaries 11. Locate the cortex by looking for glomeruli, which will no\\ appear as bright red spherical structures (Figure 28.8). 12. Identify the afferent and efferent arterioles. Depending on the plane of section, you may see both vessels, only one vessel, or no vessels at all. In most cases, it is not possible to distinguish these vessels from each other, but if you scan the slide carefully, you may see the afferent arteriole branching off an interlobular artery and traveling to a glomerulus (Figure 28.8a). 13. Other blood vessels in the cortex are the interlobular arteries and peri tubular capillaries. These blood vessels can be seen throughout a typical field of view of the cortex. The interlobular arteries have a larger diameter and are easily distinguishable from the narrower and more abundant peritubular capillaries (Figure 28.8a). 14. Move [he slide to a region where the glomeruli abruptly stop occurring. This is the border between the cortex and medulla. Scan the slide and attempt to find blood vessels traveling along this border. These are the arcuate arteries (Figure 28.8b). These vessels mayor may not be visible, depending on the plane of section of the tissue you are viewing. 15. Move the slide deeper into the medulla. The blood vessels that you see here are the vasa recta, which are intimately associated with the loops of Henle (Figure 28.8b). The Ureters (a) Afferent arteriole Cortex Arcuate artery Glomeruli 1. Obtain a slide of the ureter and examine it under low power. Identify the three tissue layers in the wall of the ureter (Figure 28.9a): the mucosa (mucous membrane), the muscularis (smooth muscle layer), and the adventitia (connective tissue layer). 2. Switch to high power and confirm the following (Figure 28.9a). The inner mucous membrane contains a transitional epithelium and an underlying lamina propria. The middle muscle layer has an inner longitudinal and an outer circular layer of smooth muscle. The outer adventitia is composed of fibrous connective tissue. The Urinary Bladder Corticomedullary boundary Vasa recta (b) Medulla Figure 28.8 blood vessels. a) light micrograph of the blood vessels in the renal cortex (lm x 60); b) light micrograph of blood vessels at the border between the renal cortex and renal medulla (lm x 10). 1. Obtain a slide of the bladder. This slide has two sections of tissue. Both are longitudinal sections of the urinary bladder wall. View both sections under low power and notice that one is much thicker than the other. The thicker section illustrates the contracted wall of an empty bladder (Figure 28.9b); the thinner section is the distended wall of a full bladder. 2. Examine the section of the contracted bladder wall. Identify the mucous membrane, which consists of transitional epithelium and a layer of connective tissue called the lamina propria. Observe that the epithelium is relatively thick, with several layers of cuboidal cells. Also notice that the mucous membrane is arranged into a number of tissue folds known as rugae (Figure 28.9b).

10 EXERCISE TWENTY-EIGHT (a) Ureter \--=----'-"'-'---+Smooth muscle Rugae --~ Erectile tissue of penis Transitional ~~~~~~~~~ epithelium, Lamina Mucosa """~~f- Smooth propria muscle ~~~~~~~l~~~~~~~~j- Mucosa Outer connective tissue layer Lumen of urinary bladder ~=::L- Submucosa :~~'"'-2'+- Blood vessels (e) Urethra (b) Urinary bladder...""'-'f-- Visceral peritoneum Figure 28.9 Histology of the accessory organs of the urinary system. a) The ureter; b) the urinary blad der in the contracted state; c) the urethra. 3. Just below the mucous membrane, identify a second layer. of connective tissue, called the submucosa, and a region of smooth muscle, known as the muscularis. The muscularis consists of three layers of intersecting smooth muscle rtbers, collectively rderred to as the detrusor muscle (Figure 28.9b). 4. Identify the serosa (visceral peritoneum) that covers the outer wall of the bladder (Figure 28.9b). This is a very thin serous membrane, which may not be present on your slide. S. Examine the section or the distended bladder. Notice that the bladder wall here lacks rugae. 6. Examine the epithelium on this section. It is strikingly different on this section, consisting of only two or three layers of squamous cells. The transitional epithelium that you are viewing on this slide and in the previous slide of the ureter is unique to the urinary tract. 7. Identify the other layers in the bladder wall described previously. WHAT'S IN It. WORD The term transitional implies some kind of change. The cells in transitional epithelium alter their shapes with changing physical conditions. When the bladder is empty and its wall is relaxed, the epithelium is relatively thick with se\' erallayers of cuboidal cells. As the bladder fills,"vith urine, these same cells become squamous and the epithelium is reduced to two to three layers to allow for bladder expansion. The Urethra 1. Obtain a slide of the urethra and examine it under low power. Identify the epithelium and lamina propria in the mucous membrane and circular layers of smooth muscle (Figure 28.9c). 2. Switch to high power and examine the mucous membrane more closely. The epithelium lining the mucous membrane will vary depending on the region of the urethra that you are viewing. Near the junction with the urinary bladder, the epithelium is transiti onal.

11 ANATOMY OF THE URINARY SY STEM There is a gradual change to pseudostratified columnar toward the middle section of the urethra. This is the primary epithelial type. Near the urethra orifice, the epithelium changes to stratified squamous. Based on the epithelial type, what region of the urethra are you viewing7 Interlobar artery Segmental artery Minor and vein artery and vein calyx Cortex 1. When examining a microscopic structure of the kidney, the presence or absence of renal corpuscles is a reliable criterion for determining whether you are Yie'wing the renal cortex or the renal medulla. Explain why. 2. Based on your microscopic observations in the previous activity, identify structural similariti.es and differences in the structure of the ureters, urinary bladder, and urethra. Focus your attention on the organization of the mucous membrane and muscle layers. Similarities: Differences: Ureter pelvis papilla pyramid column Figure Dissection of the sheep kidney. The kidney has been cut along a frontal plane to expose internal structures. The arteries have been injected with red latex and th e veins with blue latex. Kidney Dissection In the following activity, you will dissect an intact sheep or pig kidney. Pig kidneys are much larger and flatter than sheep kidneys. However, both types are quite similar, anatomically, to the human kidney and are excellent models for studying renal structure. As you dissect, have models, illustrations, or photographs of the human kidney readily available so that you can make structural comparisons. ACTIVITY 18.5 Dissecting a Kidney 1. Obtain a preserved kidney from the laboratory instructor. The kidneys may be double-injected specimens, meaning the blood vessels have been injected with colored latex for easier identification (red = arteries; blue = veins). 2. Before making any incisions, observe the external structures of the kidney. Similar to the human kidney, the sheep (or pig) kidney has a lateral convex surface and a medial concave surface. The hilus is located along the medial sur- face. Identify the ureter, renal artery, and renal vein at the hilus (Figure 28.10). From superior to inferior, these structures are positioned in the following order. artery vein Ureter 3. Of the three connective tissue capsules that cover the kidney, only the innermost renal capsule is intact. It appears as a thin, shiny membrane that adheres tightly to the surface of the kidney. To observe this capsule more closely, lift a portion of the membrane from the surface with a forceps. The other two coverings, the renal fascia and adipose capsule, have been removed, but remnants may remain near the hilus. 4. With a scalpel, make an incision that will divide the kidney into anterior and posterior halves. Begin at the superior margin and cut along the lateral convex surface, toward the medial concave surface. Try to cut as close to the midline as possible. You can cut completely throug!1

12 EXERCISE TWENTY-EIGHT the organ or, if you prefer, keep the two halves connected at the hilus. The resulting incision will give you a coronal section of the kidney (Figure 28.10). 5. Identify the following internal structures (Figure 28.10). The outer layer is the renal cortex, which has a granular texture and light color. The middle layer is the renal medulla. Observe the alternating renal pyramids and renal columns. The pyramids have a darker color than the cortex and have a striped appearance due to the longitudinal arrangement of kidney tubules. The apex of each pyramid (renal papilla) projects inward and the base borders the cortex. The renal columns, located between the pyramids, are extensions of and have the same appearance as the cortex. The inner region is the renal sinus, into which urine drains before!1owing into the ureter. The sinus consists of minor calyces, major calyces, and the renal pelvis. Identify several minor calyces, located adjacent to the renal papillae. Locate the major calyces as they are formed by the convergence of several minor calyces. The renal sinus is formed by the merging of the major calyces. Locate this funnel-shaped structure as it joins the ureter. 6. Attempt to identify some of the blood vessels that serve the kidney (Figure 28.10). Carefully dissect within a renal column and locate an interlobar artery and vein. Along the corticomedullary border, identify examples of the arcuate blood vessels. Finally, try to identify the fragile interlobular arteries and veins as they travel through the cortex. Compare the anatomy of the human kidney with the sheep or pig kidney and identify structural similarities and differences. Similarities: Differences:

13 Exercise 28 Review Sheet Anatomy of the Urinary System Name Lab Section Date ----~ Questions 1-9: Match the structure in column A with the appropriate description in column B. A B 1. artery 2. Bowman's capsule 3. pyramid 4. Afferent arteriole 5. Minor calyx 6. column 7. Distal convoluted tubule 8. Arcuate artery 9. cortex a. This structure is a branch of an interlobular artery and delivers blood to a glomerulus. b. An interlobar artery travels in this region of the kidney. c. This structure is the first portion of a nephron. It receives the blood filtrate. d. This blood vessel travels along the border between the renal medulla and cortex. e. This portion of the renal sinus receives urine directly from collecting ducts at a renal papilla. r. This blood vessel is a direct branch of the aorta, and delivers blood to the kidney. 10. Briefly describe the three functions that occur in the nephron during the process of urine production. g. This cone-shaped structure, located in the renal medulla, contains loops of Henle and collecting ducts. h. corpuscles are found in this region of the kidney. i. This portion of a nephron drains urine directly into a collecting ducl. 11. Compare the two types of nephrons that are found in the kidney: cortical nephrons and juxtamedullar nephrons. 12. Describe the pathway of blood through the kidney. 13. Why is transitional epithelium unique to other epithelial types? Why is it important that this type of epithelium be located in the wall of the urinary bladder? l

14 EXERCISE TWENTY-EIGHT 14. Compare the anatomical relationships of the urinary bladder in the male and female. 15. Explain why females are more vulnerable to urinary tract infections than males. Questions 16-23: identify the Labeled structures Ln the following diagram l Questions 24-33: In the following diagram, identify the structures by labeling with the color that is indicated. 24. Descending limb of the loop of Henle = green 25. Distal convoluted tubule = blue 26. Glomerulus = red 27. Efferent arteriole = orange 28. Proximal convoluted tubule = brown 29. Ascending limb of the loop of Henle = purple 30. Afferent arteriole = black 3L Bowman's capsule = pink 32. interlobular artery = tan 33. Collecting duct = yellow [