Kidney Anatomy PDF

12/7/24, 1:03 AM The Kidneys 26.1 The Kidneys Key Point The retroperitoneal kidneys lie on the posterior abdominal wall. The adrenal g...

12/7/24, 1:03 AM The Kidneys 26.1 The Kidneys Key Point The retroperitoneal kidneys lie on the posterior abdominal wall. The adrenal glands lie on their superior surface, and three layers of connective tissue stabilize each kidney. N OT DISTR O I B D The kidneys lie lateral to the vertebral column between the last thoracic and UT - third lumbar vertebrae on each side. Due to the presence of the liver on the © P E A RS O N E right side of the abdominal cavity, the right kidney sits slightly lower than the MAIL.C... left kidney (Figures 26.1 , 26.2 , and 26.3a ). G 1@ FO 90 GB R HE T A O PR EV IVAT OF E U SE https://plus.pearson.com/courses/deleon39711/products/GF9C7F0Q70I/pages/a852a5040f1436a5ef381f4b3fe8dc2e624a75b7a?locale=&redirectURL=https%3A%2… 1/23 12/7/24, 1:03 AM The Kidneys Figure 26.2 The Urinary System N OT DISTR O I B D UT - © P E A RS O N E MAIL.C... G 1@ Figure 26.3 The Urinary System in Gross Dissection FO 90 GB R HE T A O PR EV IVAT OF E U SE The anterior surface of the right kidney is covered by the liver, the right colic (hepatic) flexure, and the duodenum. The anterior surface of the left kidney is covered by the spleen, stomach, pancreas, jejunum, and left colic (splenic) https://plus.pearson.com/courses/deleon39711/products/GF9C7F0Q70I/pages/a852a5040f1436a5ef381f4b3fe8dc2e624a75b7a?locale=&redirectURL=https%3A%2… 2/23 12/7/24, 1:03 AM The Kidneys flexure. The adrenal, or suprarenal, gland sits on the superior surface of each kidney. The kidneys, adrenal glands, and ureters, which lie against the muscles of the posterior body wall, are all retroperitoneal (Figures 26.2b,c , and 26.3 ). The parietal peritoneum contacts with adjacent visceral organs, and supporting connective tissues maintain the position of the kidneys. Three concentric layers of connective tissue (Figure 26.2b,c ) protect and stabilize each kidney: 1. The fibrous capsule covers the outer surface of the entire organ. This OT DISTR layer of collagen fibers maintains the shape of the kidney and provides physical protection. O N I D B 2. A layer of adipose tissue, the perinephric fat or perirenal fat capsule UT - © P E A RS O N (peri–, around, + renes, kidneys) surrounds the fibrous capsule. E 3. Collagen fibers extend outward from the inner fibrous capsule MAIL.C... through the perinephric fat to a dense outer layer of connective tissue, the renal fascia. The renal fascia anchors the kidney to surrounding structures and attaches to the deep fascia surrounding the muscles of the posterior body wall. Another layer of adipose tissue, the pararenal G 1@ (para, near) fat body, separates the posterior and lateral portions of FO 90 the renal fascia from the body wall. Anteriorly, the renal fascia is GB R H T E attached to the peritoneum O fascia of the and to the anterior renal PR IVAT E VA opposite side. E USE OF This arrangement cushions the kidneys, preventing the day-to-day jolts of regular activity from disturbing normal kidney function. If the suspensory fibers stretch, or the amount of adipose tissue padding is reduced, the kidneys may become more vulnerable to traumatic injury. https://plus.pearson.com/courses/deleon39711/products/GF9C7F0Q70I/pages/a852a5040f1436a5ef381f4b3fe8dc2e624a75b7a?locale=&redirectURL=https%3A%2… 3/23 12/7/24, 1:03 AM The Kidneys Superficial Anatomy of the Kidney Key Point The hilum is the entry point for the renal artery and renal nerves and the exit point for the renal vein and ureter. Each brownish-red kidney has the shape of a kidney bean. A typical adult kidney is approximately 10 cm (4 in.) in length, 5.5 cm (2.2 in.) in width, and OT Dand 3 cm (1.2 in.) in thickness (Figures 26.3 N IS26.4 TR ). A single kidney IBindentation on its medial DO averages around 150 g (5.30 oz). Each kidney has an UT surface called the hilum. - © P E A RS O N E MAIL.C... G 1@ FO 90 GB R HE T A O PR EV IVAT OF E U SE https://plus.pearson.com/courses/deleon39711/products/GF9C7F0Q70I/pages/a852a5040f1436a5ef381f4b3fe8dc2e624a75b7a?locale=&redirectURL=https%3A%2… 4/23 12/7/24, 1:03 AM The Kidneys Figure 26.4 Structure of the Kidney N OT DISTR O I B D UT - © P E A RS O N E MAIL.C... G 1@ FO 90 GB R HE T A O PR EV IVAT OF E U SE The fibrous capsule has inner and outer layers. The inner layer folds inward at the hilum and lines the renal sinus, an internal cavity within the kidney (Figure 26.4a ). Renal blood vessels, lymphatic vessels, nerves, and the ureter pass through the hilum and branch within the renal sinus. The thick, outer layer of the capsule extends across the hilum and stabilizes the position of these structures. https://plus.pearson.com/courses/deleon39711/products/GF9C7F0Q70I/pages/a852a5040f1436a5ef381f4b3fe8dc2e624a75b7a?locale=&redirectURL=https%3A%2… 5/23 12/7/24, 1:03 AM The Kidneys Sectional Anatomy of the Kidney Key Point The interior of each kidney contains a renal cortex, renal medulla, and renal sinus. Deep to the renal capsule lies the renal cortex (Figure 26.4a ). The renal cortex is granular and reddish-brown in color. The renal medulla is deep to OT DISTR the cortex. It consists of 6–18 distinct triangular structures, called renal N IBand the tip, the renal DO pyramids. The base of each pyramid faces the cortex, UT papilla, projects into the renal sinus. Each pyramid has a series of fine - © P E A RS O N grooves that come together at the papilla. Bands of cortical tissue, termed E renal columns, extend into the medulla of the kidney and separate the MAIL.C... adjacent renal pyramids. A kidney lobe contains a renal pyramid, the overlying area of renal cortex, and adjacent tissues of the renal columns. G Urine is produced in the kidney lobes. Ducts within each renal papilla empty 1@ FO urine into a cup-shaped drain, called a minor calyx (KĀ-liks). Four or five 90 GB R minor calyces (KĀL-i-sēz) merge to form a major calyx. The major calyces HE T chamber, the A O P combine to form a large, funnel-shaped RIV EV renal pelvis. The renal A T pelvis is connected to the ureter, which O F SE the kidney (Figure 26.4 E Udrains ). Urine production begins in the nephrons (NEF-ronz), microscopic tubular structures. Two types of nephrons are found in the kidney: cortical nephrons (in the renal cortex) and juxtamedullary nephrons (closer to the renal medulla). Each kidney has roughly 1.25 million nephrons, with a combined length of about 145 km (90 miles). https://plus.pearson.com/courses/deleon39711/products/GF9C7F0Q70I/pages/a852a5040f1436a5ef381f4b3fe8dc2e624a75b7a?locale=&redirectURL=https%3A%2… 6/23 12/7/24, 1:03 AM The Kidneys The Blood Supply to the Kidneys Key Point The kidneys receive 20 to 25 percent of the total cardiac output. Afferent arterioles supply individual nephrons and efferent arterioles drain the nephrons. Twenty to twenty-five percent of the total cardiac output, or about 1200 mL of OT DISTR blood, flows through the kidneys each minute. Each kidney receives blood N O artery branches fromIthe from a renal artery. The renal D B lateral surface of the UT abdominal aorta near the superior mesenteric artery. It enters the renal sinus - © P E A RS O N where it branches into the segmental arteries (Figure 26.5 ). Segmental E arteries divide into a series of interlobar arteries that radiate outward, MAIL.C... extending through the renal columns between the renal pyramids into the cortex. The interlobar arteries supply blood to the arcuate (AR-kū-āt) arteries, which arch along the boundary between the renal cortex and the G renal medulla. Each arcuate artery gives off a number of cortical radiate 1@ FO arteries, or interlobular arteries. These vessels supply portions of the adjacent 90 GB R kidney lobe. Numerous afferent arterioles branch from each cortical radiate HE T artery to supply individualPnephrons (Figure 26.5b,cVA ). O RIV ATE USE OF E https://plus.pearson.com/courses/deleon39711/products/GF9C7F0Q70I/pages/a852a5040f1436a5ef381f4b3fe8dc2e624a75b7a?locale=&redirectURL=https%3A%2… 7/23 12/7/24, 1:03 AM The Kidneys Figure 26.5 Blood Supply to the Kidneys N OT DISTR O I B D UT - © P E A RS O N E MAIL.C... G 1@ From the nephrons, blood enters a mirror image of the arterial distribution. A FO 90 network of venules and small veins converges on the cortical radiate GB R H T O to arcuate veins (interlobular) veins. TheEcortical radiate veins deliver blood PR I E VA VAThe that empty into interlobar veins. USE OFveins merge to form the TEinterlobar renal vein; there are no segmental veins (Figure 26.5 ). Many of these blood vessels are visible in corrosion casts of the kidneys and in renal angiograms (Figures 26.6b and 26.10b ). https://plus.pearson.com/courses/deleon39711/products/GF9C7F0Q70I/pages/a852a5040f1436a5ef381f4b3fe8dc2e624a75b7a?locale=&redirectURL=https%3A%2… 8/23 12/7/24, 1:03 AM The Kidneys Figure 26.6 Renal Vessels and Blood Flow N OT DISTR O I B D UT - © P E A RS O N E MAIL.C... G 1@ FO 90 GB R HE T A O PR EV IVAT OF E U SE https://plus.pearson.com/courses/deleon39711/products/GF9C7F0Q70I/pages/a852a5040f1436a5ef381f4b3fe8dc2e624a75b7a?locale=&redirectURL=https%3A%2… 9/23 12/7/24, 1:03 AM The Kidneys Innervation of the Kidneys Key Point Both branches of the ANS innervate the kidneys. Most of the fibers are sympathetic postganglionic fibers. Urine production is regulated by altering nephron filtration rates. This is accomplished through a process termed autoregulation. Autoregulation (local OT DISTR blood flow regulation) involves reflexive changes in the diameters of the N O thereby altering Iblood arterioles supplying the nephrons, D B flow and filtration UT rates. Renal nerves innervate the kidneys and ureters. - © P E A RS O N E Both branches of the autonomic nervous system innervate the kidneys. MAIL.C... However, most of the nerve fibers are sympathetic postganglionic fibers from the celiac and inferior mesenteric ganglia. A renal nerve enters each kidney at the hilum. It then follows the branches of the renal artery to reach individual G nephrons. The sympathetic innervation (1) adjusts rates of urine formation by 1@ FO changing blood flow at the nephron and (2) influences the composition of 90 GB R urine by stimulating the release of renin. HE T A O PR EV IVAT OF E U SE https://plus.pearson.com/courses/deleon39711/products/GF9C7F0Q70I/pages/a852a5040f1436a5ef381f4b3fe8dc2e624a75b7a?locale=&redirectURL=https%3A%… 10/23 12/7/24, 1:03 AM The Kidneys Histology of the Kidney Key Point The nephron is the structural and functional unit of the kidney. The tubular segments of the nephron are named according to their location (proximal or distal), thickness (thick or thin), and shape (convoluted or straight). OT DISTR The nephron is the basic structural and functional unit of the kidney. We can N O Figure 26.7 showsIaBnephron that has been view it only with a microscope. D UT shortened and straightened out. - © P E A RS O N E MAIL.C... G 1@ FO 90 GB R HE T A O PR EV IVAT OF E U SE https://plus.pearson.com/courses/deleon39711/products/GF9C7F0Q70I/pages/a852a5040f1436a5ef381f4b3fe8dc2e624a75b7a?locale=&redirectURL=https%3A%… 11/23 12/7/24, 1:03 AM The Kidneys Figure 26.7 A Typical Nephron A diagrammatic view showing the histological structure and the major functions of each segment of the nephron (violet) and collecting system (tan). N OT DISTR O I B D UT - © P E A RS O N E MAIL.C... G 1@ FO 90 GB R HE T A O PR EV IVAT OF E U SE https://plus.pearson.com/courses/deleon39711/products/GF9C7F0Q70I/pages/a852a5040f1436a5ef381f4b3fe8dc2e624a75b7a?locale=&redirectURL=https%3A%… 12/23 12/7/24, 1:03 AM The Kidneys The Nephron and Collecting System Each nephron consists of a renal corpuscle and a renal tubule. The renal corpuscle (KOR-pus-ul), a spherical structure consisting of the glomerular capsule, a cup-shaped chamber, and a capillary network called the glomerulus (glō-MER-ū-lus; plural, glomeruli). The renal tubule, a long tubular passageway, begins at the renal corpuscle. Each renal tubule empties into the collecting system, a series of tubes that carry tubular fluid away from the nephron. Blood arrives at the glomerulus through the afferent arteriole and leaves by the efferent arteriole (Figure 26.7 ). Filtration across the walls of the N OT DISTR glomerulus produces a protein-free solution known as the glomerular filtrate, O I B D or simply filtrate. From the renal corpuscle, the filtrate enters a long tubular UT - passageway that has three major subdivisions: (1) the proximal convoluted © P E A RS O N E tubule, (2) the nephron loop , or loop of Henle (HEN-lē), and (3) the distal MAIL.C... convoluted tubule. Each nephron empties into the collecting system. A connecting tubule carries the filtrate from the distal convoluted tubule toward a nearby G 1@ collecting duct. The collecting duct leaves the cortex and descends into the FO 90 medulla. It carries filtrate toward a papillary duct that drains into the renal GB R pelvis. HE T A O PR EV IVAT OF E U SE Nephrons from different locations within the kidney differ slightly in structure. Roughly 85 percent of all nephrons are cortical nephrons. These nephrons are located almost entirely within the superficial cortex of the kidney. In a cortical nephron, the nephron loop is relatively short, and the efferent arteriole delivers blood to a network of peritubular capillaries, which surround the entire renal tubule (Figure 26.8a,e ). These capillaries drain into small venules that carry blood to the interlobular veins (Figure 26.5c ). https://plus.pearson.com/courses/deleon39711/products/GF9C7F0Q70I/pages/a852a5040f1436a5ef381f4b3fe8dc2e624a75b7a?locale=&redirectURL=https%3A%… 13/23 12/7/24, 1:03 AM The Kidneys Figure 26.8 Histology of the Nephron N OT DISTR O I B D UT - © P E A RS O N E MAIL.C... G 1@ FO 90 GB R HE T A O PR EV IVAT OF E U SE The remaining 15 percent of nephrons are juxtamedullary (juks-ta-MED-ū- lar-ē; juxta, near) nephrons. These nephrons are located closer to the medulla, and they have longer nephron loops that extend deep into the renal pyramids (Figure 26.8a,f ). Because they are more numerous than juxtamedullary nephrons, cortical nephrons perform most of the reabsorptive and secretory functions of the kidneys. However, the juxtamedullary nephrons create the conditions necessary for producing concentrated urine. https://plus.pearson.com/courses/deleon39711/products/GF9C7F0Q70I/pages/a852a5040f1436a5ef381f4b3fe8dc2e624a75b7a?locale=&redirectURL=https%3A%… 14/23 12/7/24, 1:03 AM The Kidneys The urine arriving at the renal pelvis is very different from the filtrate produced at the renal corpuscle. The passive process of filtration allows movement across a barrier based solely on the size of the solute. A filter with pores large enough to permit the passage of large metabolic wastes is unable to prevent the passage of water, ions, and other smaller metabolic molecules, such as glucose, fatty acids, or amino acids. The distal segments of the nephron are therefore responsible for: reabsorbing all the useful metabolic substrates from the filtrate, reabsorbing more than 80 percent of the water in the filtrate, and secreting into the filtrate waste products that were missed by the filtration OT DISTR process. O N I D B We will now examine each of the segments of a juxtamedullary nephron in UT - © P E A RS O N greater detail. E MAIL.C... G 1@ FO 90 GB R HE T A O PR EV IVAT OF E U SE https://plus.pearson.com/courses/deleon39711/products/GF9C7F0Q70I/pages/a852a5040f1436a5ef381f4b3fe8dc2e624a75b7a?locale=&redirectURL=https%3A%… 15/23 12/7/24, 1:03 AM The Kidneys The Renal Corpuscle The renal corpuscle averages 150–250 μm in diameter. It includes the capillaries of the glomerulus and the glomerular capsule (Bowman’s capsule). The glomerulus projects into the glomerular capsule in the same way that the heart projects into the pericardial cavity. The outer wall of the capsule is made up of a simple squamous epithelium and is called the capsular outer layer (parietal layer). This layer ends at the visceral layer, which covers the glomerular capillaries. The visceral layer is composed of large cells with complex processes that wrap around the glomerular capillaries. These specialized cells are called podocytes (PŌD-ō-sīts; podos, foot, + cyte, cell). The capsular space separates the parietal and visceral epithelia (Spotlight Figure 26.9 ). N OT DISTR O I B D UT - © P E A RS O N E MAIL.C... G 1@ FO 90 GB R HE T A O PR EV IVAT OF E U SE https://plus.pearson.com/courses/deleon39711/products/GF9C7F0Q70I/pages/a852a5040f1436a5ef381f4b3fe8dc2e624a75b7a?locale=&redirectURL=https%3A%… 16/23 12/7/24, 1:03 AM The Kidneys Spotlight Figure 26.9 The Renal Corpuscle N OT DISTR O I B D UT - © P E A RS O N E MAIL.C... G 1@ FO 90 GB R HE T A O PR EV IVAT OF E U SE The parietal and visceral epithelia are connected at the vascular pole of the renal corpuscle. At the vascular pole, the glomerular capillaries are connected to the afferent and efferent arterioles. Blood arrives at these capillaries through the afferent arteriole and exits in the smaller-diameter efferent arteriole (Spotlight Figure 26.9 ). Filtration occurs as blood pressure forces fluid and dissolved solutes out of the glomerular capillaries and into the capsular space. The resulting filtrate is https://plus.pearson.com/courses/deleon39711/products/GF9C7F0Q70I/pages/a852a5040f1436a5ef381f4b3fe8dc2e624a75b7a?locale=&redirectURL=https%3A%… 17/23 12/7/24, 1:03 AM The Kidneys very similar to plasma with the blood proteins removed. The filtration process at the renal corpuscle involves five filtration barriers (Spotlight Figure 26.9 ): 1. The endothelial surface layer: The luminal surface (surface facing the lumen) of the endothelial cells of the glomerular capillaries has a thick, carbohydrate-rich meshwork. This glycocalyx limits filtration of large plasma proteins out of the glomerular capillaries. 2. The capillary endothelium: The glomerular capillaries are fenestrated capillaries with pores 60–100 nm (0.06–0.1 μm) in diameter. pp. 571– 572 These openings are small enough to prevent the passage of blood cells, but they are too large to prevent the diffusion of solutes, even OT DISTR those the size of smaller plasma proteins. O N I 3. The basement membrane: The basement membrane surrounding the D B glomerular capillary endothelium is several times thicker than a UT - © P E A RS O N typical capillary basement membrane. This prevents the passage of E larger plasma proteins, but permits the movement of small plasma MAIL.C... proteins, amino acids, glucose, and ions. Unlike basement membranes elsewhere in the cardiovascular system, the basement membrane of the glomerular capillaries encircles two or more capillaries. Mesangial cells are located between the endothelial cells G 1@ of adjacent capillaries. Mesangial cells provide physical support for FO 90 the capillaries and play a role in regulating glomerular blood flow and GB R H T filtration. They do O E this by engulfing organic materials and regulating PR I E VA VATE capillaries. USE OF the diameters of the glomerular 4. The glomerular epithelium: The podocytes have long cellular processes that wrap around the outer surfaces of the basement membrane of the glomerular capillaries. These delicate secondary processes, or “feet,” are separated by narrow gaps called filtration slits. Because the filtration slits are very narrow, the filtrate entering the capsular space consists of water with dissolved ions, small molecules, and few if any plasma proteins. 5. The subpodocyte space: The subpodocyte space occupies approximately 60 percent of the filtration space of the glomerulus. This narrow space lies between the secondary processes of the https://plus.pearson.com/courses/deleon39711/products/GF9C7F0Q70I/pages/a852a5040f1436a5ef381f4b3fe8dc2e624a75b7a?locale=&redirectURL=https%3A%… 18/23 12/7/24, 1:03 AM The Kidneys podocytes and the soma of the podocytes. It assists the filtration slits of the glomerular epithelium in the filtration process. In addition to metabolic wastes, the filtrate contains other organic compounds such as glucose, free fatty acids, amino acids, and vitamins. The proximal convoluted tubule reabsorbs these potentially useful materials. The Proximal Convoluted Tubule The proximal convoluted tubule (PCT) is the first part of the renal tubule. The PCT begins at the tubular pole of the renal corpuscle, opposite the vascular pole (Spotlight Figure 26.9 ). The tubule is lined by a simple N OT DISTR cuboidal epithelium with microvilli on the apical surface. These microvilli O I B D increase the surface area for reabsorption (Figures 26.7 and 26.8a,b ). UT - © P E A RS O N E The primary function of the proximal convoluted tubule is reabsorption. Its MAIL.C... cells actively reabsorb organic nutrients, ions, and plasma proteins (if any) from the filtrate. In addition, as the tubular fluid passes through the tubule, the epithelial cells reabsorb 60 percent of the sodium ions, chloride ions, and water. The tubule also actively reabsorbs potassium, calcium, magnesium, G 1@ bicarbonate, phosphate, and sulfate ions. As these solutes are reabsorbed, FO 90 osmotic forces pull water across the wall of the PCT and into the surrounding GB R H fluid. peritubular (interstitial) T EP A O RIV V ATE USE OF E https://plus.pearson.com/courses/deleon39711/products/GF9C7F0Q70I/pages/a852a5040f1436a5ef381f4b3fe8dc2e624a75b7a?locale=&redirectURL=https%3A%… 19/23 12/7/24, 1:03 AM The Kidneys The Nephron Loop The proximal straight tubule ends as the renal tubule enters the medulla. This bend marks the start of the nephron loop (Figure 26.8a,d ). The nephron loop is divided into a descending limb and an ascending limb. Fluid in the ascending limb flows toward the renal cortex. The descending and ascending limbs of the nephron loop are lined with a simple squamous epithelium and are found within the deeper medulla. The ascending limb contains active transport mechanisms that pump sodium and chloride ions out of the tubular fluid. As a result, the medullary interstitial fluid contains an unusually high concentration of solutes. The limbs contain thin and thick segments. The terms thick and thin refer to the height of the epithelium, not the diameter of the lumen (Figures 26.7 N OT DISTR and 26.8a,d ). O I B D UT - Solute concentration is usually expressed in terms of milliosmoles (mOsm). © P E A RS O N E Near the base of the loop, in the deepest part of the medulla, the solute MAIL.C... concentration of the interstitial fluid is four times that of plasma (1200 mOsm versus 300 mOsm). The descending thin and ascending thick limbs are freely permeable to water, but are impermeable to ions and other solutes. The high osmotic concentration surrounding the nephron loop results in an osmotic G 1@ flow of water out of the nephron. The vasa recta, a group of slender FO 90 capillaries, absorb the water and return it to the general circulation (Figure GB R 26.8f ). HE T A O PR EV IVAT OF E U SE The net effect is that the nephron loop reabsorbs an additional 25 percent of the water from the tubular fluid and an even higher percentage of the sodium and chloride ions. Reabsorption in the PCT and nephron loop reclaims all of the organic nutrients, 85 percent of the water, and more than 90 percent of the sodium and chloride ions. The remaining water, ions, and all the organic wastes filtered at the glomerulus remain in the nephron loop and enter the distal convoluted tubule. https://plus.pearson.com/courses/deleon39711/products/GF9C7F0Q70I/pages/a852a5040f1436a5ef381f4b3fe8dc2e624a75b7a?locale=&redirectURL=https%3A%… 20/23 12/7/24, 1:03 AM The Kidneys The Distal Convoluted Tubule The distal convoluted tubule (DCT) ascends out of the medulla of the kidney and enters the cortex. The distal convoluted tubule passes between the afferent and efferent arterioles at the vascular pole (Spotlight Figure 26.9 ). In sectional view (Figures 26.7 and 26.8b,c ), the DCT differs from the PCT in three ways: (1) the DCT has a smaller diameter; (2) its epithelial cells lack microvilli; and (3) the boundaries between the epithelial cells in the DCT are easily seen. These anatomical characteristics reflect the major functional differences: The PCT is involved in reabsorption, while the DCT is involved in secretion. N OT DISTR O I B D UT - The DCT is an important site for (1) active secretion of ions, acids, and other © P E A RS O N E materials, (2) reabsorption of sodium and calcium ions from the tubular fluid, MAIL.C... and (3) reabsorption of water, which helps concentrate the tubular fluid. The sodium transport activities of the distal tubule are controlled by circulating levels of aldosterone secreted by the adrenal cortex. G 1@ FO 90 GB R HE T A O PR EV IVAT OF E U SE https://plus.pearson.com/courses/deleon39711/products/GF9C7F0Q70I/pages/a852a5040f1436a5ef381f4b3fe8dc2e624a75b7a?locale=&redirectURL=https%3A%… 21/23 12/7/24, 1:03 AM The Kidneys The Juxtaglomerular Complex The juxtaglomerular complex is a structure that helps regulate blood pressure and filtrate formation. Renin and erythropoietin elevate blood volume, hemoglobin levels, and blood pressure and restore normal rates of filtrate production. It is composed of three specialized cells (Spotlight Figure 26.9 ): 1. Macula densa: The macula densa is a group of tall, closely packed epithelial cells in the distal convoluted tubule epithelium, immediately adjacent to the afferent arteriole, at the vascular pole of the glomerulus. They are thought to monitor the Na + concentration in OT DISTR the tubular fluid and regulate both the glomerular filtration rate and N O I the release of renin from the juxtaglomerular cells. B D UT 2. Juxtaglomerular cells: The juxtaglomerular cells are modified - © P E A RS O N E smooth muscle cells in the wall of the afferent arteriole that secrete renin. MAIL.C... 3. Extraglomerular mesangial cells: Extraglomerular mesangial cells are located in the triangular space between the afferent and efferent glomerular arterioles. These cells provide feedback control between G 1@ the macula densa and the juxtaglomerular cells. FO 90 GB R HE T A O PR EV IVAT OF E U SE https://plus.pearson.com/courses/deleon39711/products/GF9C7F0Q70I/pages/a852a5040f1436a5ef381f4b3fe8dc2e624a75b7a?locale=&redirectURL=https%3A%… 22/23 12/7/24, 1:03 AM The Kidneys The Collecting System The distal convoluted tubule is the last segment of the nephron. It opens into the collecting system, which consists of connecting tubules, collecting ducts, and papillary ducts (Figure 26.8a,d ). Every nephron is connected to a connecting tubule, and several connecting tubules are connected to a collecting duct (Figure 26.8a,e,f ). Several collecting ducts converge and empty into the larger papillary duct that empties into a minor calyx in the renal pelvis. The epithelium lining the collecting system begins as simple cuboidal cells in the connecting tubules and changes to a columnar epithelium in the collecting and papillary ducts (Figure 26.7 ). N OT DISTR The collecting system transports tubular fluid from the nephron to the renal O I B D pelvis and makes final adjustments to its osmotic concentration and volume. UT - Antidiuretic hormone (ADH) controls the permeability of the collecting © P E A RS O N E system. This permeability change is significant because the collecting ducts MAIL.C... pass through the medulla, where the nephron loop has established very high solute concentrations in the interstitial fluids. If collecting duct permeability is low, most of the tubular fluid reaching the collecting duct will flow into the renal pelvis and the urine will be dilute. However, if collecting duct G 1@ permeability is high, this promotes the osmotic flow of water out of the duct FO 90 into the medulla. This results in a small amount of highly concentrated urine. GB R H circulating ADH, the greater the amount of water The higher the levels of T EP A O RIV the urine. V ATE USE OF E reabsorbed, and the more concentrated Concept Check 26.1 Interactive https://plus.pearson.com/courses/deleon39711/products/GF9C7F0Q70I/pages/a852a5040f1436a5ef381f4b3fe8dc2e624a75b7a?locale=&redirectURL=https%3A%… 23/23