THE URINARY SYSTEM

434 ✦ CHAPTER TWENTY TWO

◗ ExcretionThe urinary system is also called the excretory system be-cause one of its main functions is excretion, removal andelimination of metabolic waste products from the blood.It has many other functions as well, including regulationof the volume, acid–base balance (pH), and electrolytecomposition of body fluids.

Although the focus of this chapter is the urinary system,certain aspects of other systems are also discussed, becausebody systems work interdependently to maintain home-ostasis (internal balance). The systems active in excretionand some of the substances they eliminate are the following:

◗ The urinary system excretes water, nitrogen-contain-ing waste products, and salts. These are all constituentsof the urine.

◗ The digestive system eliminates water, some salts, andbile in addition to digestive residue, all of which arecontained in the feces. The liver is important in elimi-

nating the products of red blood cell destruction and inbreaking down certain drugs and toxins.

◗ The respiratory system eliminates carbon dioxide andwater. The latter appears as vapor, as can be demon-strated by breathing on a windowpane.

◗ The skin, or integumentary system, excretes water,salts, and very small quantities of nitrogenous wastes.These all appear in perspiration, although water alsoevaporates continuously from the skin without ourbeing conscious of it.

Figure 22-1 Male urinary system, showing blood vessels. ZOOMING IN ✦ What vessel supplies blood to the kidney? What ves-sel drains the kidney?

Diaphragm

Adrenalgland

Rightkidney

Rightureter

Urinarybladder

Prostategland

Urethra

Inferiorvena cava

Hepatic veins

Abdominalaorta

Renalvein

Renalartery

Commoniliac vein

Commoniliac artery

Internaliliac vein

Internaliliac artery

Externaliliac vein

Externaliliac artery

Checkpoint 22-1: The main function of the urinary system is toeliminate waste. What are some other systems that eliminatewaste?

◗ Organs of the Urinary SystemThe main parts of the urinary system, shown in Figure22-1, are as follows:

THE URINARY SYSTEM ✦ 435

◗ Two kidneys. These organs extract wastes from theblood, balance body fluids, and form urine.

◗ Two ureters (U-re-ters). These tubes conduct urinefrom the kidneys to the urinary bladder.

◗ A single urinary bladder. This reservoir receives andstores the urine brought to it by the two ureters.

◗ A single urethra (u-RE-thrah). This tube conductsurine from the bladder to the outside of the body forelimination.

Blood Supply to the KidneyThe kidney’s blood supply is illustrated in Figure 22-2.Blood is brought to the kidney by a short branch of theabdominal aorta called the renal artery.

After entering the kidney, the renal artery subdividesinto smaller and smaller branches, which eventuallymake contact with the functional units of the kidney, thenephrons (NEF-ronz). Blood leaves the kidney by ves-sels that finally merge to form the renal vein, which car-ries blood into the inferior vena cava for return to theheart.

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Checkpoint 22-2: What are the organs of the urinary system?

◗ The KidneysThe kidneys lie against the back muscles in the upper ab-domen at about the level of the last thoracic and firstthree lumbar vertebrae. The right kidney is slightly lowerthan the left to accommodate the liver. Each kidney isfirmly enclosed in a membranous renal capsule made offibrous connective tissue. In addition, there is a protectivelayer of fat called the adipose capsule around the organ.An outermost layer of fascia (connective tissue) anchorsthe kidney to the peritoneum and abdominal wall. Thekidneys, as well as the ureters, lie posterior to the peri-toneum. Thus, they are not in the peritoneal cavity butrather in an area known as the retroperitoneal (ret-ro-per-ih-to-NE-al) space.

Figure 22-2 Blood supply and circulation of the kidney.ZOOMING IN ✦ What vessel supplies blood to the renal artery?What vessel receives blood from the renal vein?

Checkpoint 22-3: The kidneys are located in the retroperi-toneal space. Where is this space?

Structure of the KidneyThe kidney is a somewhat flattened organ about 10 cm (4inches) long, 5 cm (2 inches) wide, and 2.5 cm (1 inch)thick (Fig. 22-3). On the medial border there is a notchcalled the hilum, where the renal artery, the renal vein,and the ureter connect with the kidney. The lateral bor-der is convex (curved outward), giving the entire organ abean-shaped appearance.

The kidney is divided into two regions: the renal cor-tex and the renal medulla (Fig. 22-3). The renal cortex isthe kidney’s outer portion. The renal medulla containsthe tubes in which urine is formed and collected. Thesetubes form a number of cone-shaped structures calledrenal pyramids. The tips of the pyramids point towardthe renal pelvis, a funnel-shaped basin that forms theupper end of the ureter. Cuplike extensions of the renalpelvis surround the tips of the pyramids and collect urine;these extensions are called calyces (KA-lih-seze; singular,calyx, KA-liks). The urine that collects in the pelvis thenpasses down the ureters to the bladder.

Checkpoint 22-4: What vessel supplies blood to the kidney andwhat vessel drains blood from the kidney?

Checkpoint 22-5: What are the outer and inner regions of thekidney called?

The Nephron As is the case with most organs, themost fascinating aspect of the kidney is too small to beseen with the naked eye. This basic unit, which actuallydoes the kidney’s work, is the nephron (Fig. 22-4). Thenephron is essentially a tiny coiled tube with a bulb at oneend. This bulb, known as the glomerular (Bowman) cap-sule, surrounds a cluster of capillaries called the glomeru-lus (glo-MER-u-lus) (pl., glomeruli [glo-MER-u-li]).Each kidney contains about 1 million nephrons; if allthese coiled tubes were separated, straightened out, andlaid end to end, they would span some 120 kilometers (75miles)! Figure 22-5 is a microscopic view of kidney tissueshowing several glomeruli, each surrounded by a


glomerular capsule. This figure also shows sectionsthrough the tubular portions of the nephrons.

A small blood vessel, the afferent arteriole, suppliesthe glomerulus with blood; another small vessel, calledthe efferent arteriole, carries blood from the glomerulus.When blood leaves the glomerulus, it does not head im-mediately back toward the heart. Instead, it flows into acapillary network that surrounds the nephron’s tubularportion. These peritubular capillaries, are named fortheir location.

The tubular portion of the nephron consists of severalparts. The coiled part leading from the glomerular cap-sule is called the proximal convoluted (KON-vo-lu-ted)tubule (PCT, or just proximal tubule). The tubule thenuncoils to form a hairpin-shaped segment called the loopof Henle. The first part of the loop, which carries fluid to-ward the medulla, is the descending limb (see Fig. 22-4).The part that continues from the loop’s turn and carriesfluid away from the medulla, is the ascending limb. Con-tinuing from the ascending limb, the tubule coils onceagain into the distal convoluted tubule (DCT, or just dis-tal tubule), so called because it is farther along the tubulefrom the glomerular capsule than is the PCT. The distalend of each tubule empties into a collecting duct, whichthen continues through the medulla toward the renalpelvis.

The glomerulus, glomerular capsule, and the proxi-mal and distal convoluted tubules of the nephron arewithin the renal cortex. The loop of Henle and collectingduct extend into the medulla (see Fig. 22-3).

The Juxtaglomerular (JG) Apparatus The firstportion of the DCT curves back toward the glomerulus topass between the afferent and efferent arterioles (Fig. 22-6). At the point where the DCT makes contact with theafferent arteriole, there are specialized cells in each thattogether make up the juxtaglomerular (juks-tah-glo-MER-u-lar) (JG) apparatus. The JG apparatus helps toregulate kidney function. When blood pressure falls toolow for the kidneys to function effectively, cells in thewall of the afferent arteriole secrete the enzyme renin(RE-nin), which raises blood pressure by a mechanismdescribed later.

Functions of the KidneyThe kidneys are involved in the following processes:

◗ Excretion of unwanted substances, such as cellularmetabolic waste, excess salts, and toxins. One productof amino acid metabolism is nitrogen-containing wastematerial, a chief form of which is urea (u-RE-ah). Aftersynthesis in the liver, urea is transported in the blood tothe kidneys for elimination. The kidneys have a spe-cialized mechanism for the elimination of urea andother nitrogenous (ni-TROJ-en-us) wastes.

Figure 22-3 Longitudinal section through the kidney showing its internal structure (left) and an enlarged diagram ofnephrons (right). Each kidney contains more than 1 million nephrons. ZOOMING IN ✦ What is the outer region of the kidney called?What is the inner region of the kidney called?

Renalpelvis

Calyx

Hilum

Ureter

Renalcortex

Nephrons

Renalmedulla

Pyramidsof medulla

Renal capsule

Checkpoint 22-6: What is the functional unit of the kidneycalled?

Checkpoint 22-7: What name is given to the coil of capillariesin the glomerular (Bowman) capsule?


◗ Maintenance of water balance. Al-though the amount of water gainedand lost in a day can vary tremen-dously, the kidneys can adapt tothese variations, so that the volumeof body water remains remarkablystable from day to day.

◗ Regulation of the acid–base balanceof body fluids. Acids are constantlybeing produced by cellular metabo-lism. Certain foods can yield acids orbases, and people may also ingestantacids, such as bicarbonate. How-ever, if the body is to function nor-mally, the pH of body fluids must re-main in the range of 7.35 to 7.45(see Chapter 21).

◗ Regulation of blood pressure. Thekidneys depend on blood pressure tofilter the blood. If blood pressurefalls too low for effective filtration,the cells of the JG apparatus releaserenin. This enzyme activates an-giotensin (an-je-o-TEN-sin), a bloodprotein that causes blood vessels toconstrict, thus raising blood pres-sure (Table 22-1). Angiotensinalso stimulates the adrenal cortexto produce the hormone aldos-terone, which promotes reten-tion of sodium and water, alsoraising blood pressure.

◗ Regulation of red blood cell produc-tion. When the kidneys do not getenough oxygen, they produce thehormone erythropoietin (eh-rith-ro-POY-eh-tin) (EPO), which stimu-lates the red cell production in thebone marrow. EPO made by geneticengineering is now available to treatsevere anemia, such as occurs in theend stage of kidney failure.

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Figure 22-4 A nephron and its blood supply. The nephron regulates the propor-tions of water, waste, and other materials according to the body’s constantly changingneeds. Materials that enter the nephron can be returned to the blood through the sur-rounding capillaries. ZOOMING IN ✦ Which of the two convoluted tubules is closer tothe glomerular capsule? Which convoluted tubule is farther away?

Afferentarteriole

Efferentarteriole

Glomerulus

To renal vein

From renal artery

Collectingduct

Proximalconvolutedtubule

Distalconvolutedtubule

Glomerular (Bowman)capsule

Peritubularcapillaries

Ascendinglimb

Descendinglimb

Loop ofHenle

Calyx

Figure 22-5 Microscopic view of the kidney. (Courtesy of Dana Morse Bittus andB. J. Cohen.)

Glomerulus

Renal tubules

Glomerular capsule

Checkpoint 22-8: What substance is pro-duced by the JG apparatus and under whatconditions is it produced?

Formation of UrineThe following explanation of urineformation describes a complexprocess, involving many back-and-forth exchanges between the blood-stream and the kidney tubules. Asfluid filtered from the blood travelsslowly through the twists and turns ofthe nephron, there is ample time forexchanges to take place. Theseprocesses together allow the kidney to“fine tune” body fluids as they adjustthe composition of the urine.


Glomerular Filtration The process of urine formationbegins with the glomerulus in the glomerular capsule.The walls of the glomerular capillaries are sievelike andpermit the free flow of water and soluble materialsthrough them. Like other capillary walls, however, theyare impermeable (im-PER-me-abl) to blood cells andlarge protein molecules, and these components remain inthe blood (Fig. 22-7).

Because the diameter of the afferent arteriole isslightly larger than that of the efferent arteriole (see Fig.22-7), blood can enter the glomerulus more easily than itcan leave. Thus, blood pressure in the glomerulus isabout three to four times higher than it is in other capil-

laries. To understand this effect, think of placing yourthumb over the end of a garden hose as water comesthrough. As you make the diameter of the openingsmaller, water is forced out under higher pressure. As aresult of increased fluid (hydrostatic) pressure in theglomerulus, materials are constantly being pushed out ofthe blood and into the nephron’s glomerular capsule. Asdescribed in Chapter 3, movement of water and dissolvedmaterials through a membrane under pressure is calledfiltration. This movement of materials under pressurefrom the blood into the capsule is therefore known asglomerular filtration.

The fluid that enters the glomerular capsule, called

Substances that Affect Renal FunctionTable 22•1

SUBSTANCE SOURCE ACTION

Renin (RE-nin)

Angiotensin (an-je-o-TEN-sin)

Aldosterone (al-DOS-ter-one)

Antidiuretic hormone (an-te-di-u-RET-ik) (ADH)

Enzyme produced by renal cellswhen blood pressure falls too lowfor effective filtration

Protein in the blood that is activatedby renin

Hormone released from the adrenalcortex under effects of angiotensin

Made in the hypothalamus andreleased from the posteriorpituitary; released when bloodbecomes too concentrated

Activates angiotensin in the blood

Causes constriction of blood vessels to raise bloodpressure; also stimulates release of aldosteronefrom the adrenal cortex

Promotes reabsorption of sodium and water in thekidney to conserve water and increase bloodpressure

Promotes reabsorption of water from the distalconvoluted tubule and collecting duct to con-centrate the urine and conserve water

Figure 22-6 Structure of the juxtaglomerular (JG) apparatus. Note how the distal convoluted tubule contacts the afferent ar-teriole (right). Cells in these two structures make up the JG apparatus. ZOOMING IN ✦ The JG apparatus is made up of cells fromwhich two structures?

Afferentarteriole

Afferentarteriole

Efferentarteriole

Efferentarteriole

GlomerulusGlomerular capsuleGlomerularcapsule




Juxtaglomerularapparatus

Juxtaglomerular (JG)apparatus

Glomerulus

Loop ofHenle


the glomerular filtrate, begins its journey along the tu-bular system of the nephron. In addition to water and thenormal soluble substances in the blood, other substances,such as vitamins and drugs, also may be filtered and be-come part of the glomerular filtrate.

is followed by a process of tubular reabsorption. As thefiltrate travels through the nephron’s tubular system,water and other needed substances leave the tubule andenter the surrounding tissue fluid, or interstitial fluid(IF). They move by several processes previously de-scribed in Chapter 3, including:

◗ Diffusion. The movement of substances from an area ofhigher concentration to an area of lower concentration(following the concentration gradient)◗ Osmosis. Diffusion of water through a semipermeablemembrane.◗ Active transport. Movement of materials through theplasma membrane against the concentration gradientusing energy and transporters

The substances that leave the nephron and enter theinterstitial fluid then enter the peritubular capillaries andreturn to the circulation. In contrast, most of the urea andother nitrogenous waste materials are kept within thetubule to be eliminated with the urine. Box 22-1 presentsadditional information on tubular reabsorption in thenephron.

Tubular Secretion Before the filtrate leaves the bodyas urine, the kidney makes final adjustments in composi-tion by the process of tubular secretion. In this process,some substances are actively moved from the blood intothe nephron. Potassium ions are moved into the urine bythis process. Importantly, the kidneys regulate theacid–base (pH) balance of body fluids by the active secre-tion of hydrogen ions. Some drugs, such as penicillin,also are actively secreted into the nephron for elimina-tion.

Concentration of the Urine The amount of waterthat is eliminated with the urine is regulated by a com-plex mechanism within the nephron that is influenced byantidiuretic hormone (ADH), a hormone released fromthe posterior pituitary gland (see Table 22-1). Theprocess is called the countercurrent mechanism becauseit involves fluid traveling in opposite directions withinthe ascending and descending limbs of Henle’s loop. Thecountercurrent mechanism is illustrated in Figure 22-8.Its essentials are as follows:

As the filtrate passes through Henle’s loop, elec-trolytes, especially sodium, are actively pumped out bythe nephron’s cells, resulting in an increased concentra-tion of the interstitial fluid. Because the ascending limb ofHenle’s loop is not very permeable to water, the filtrate atthis point becomes increasingly dilute (see Fig. 22-8). Asthe filtrate then passes through the more permeable DCTand collecting duct, the concentrated fluids around thenephron draw water out to be returned to the blood. (Re-member, according to the laws of osmosis, water followssalt.) In this manner, the urine becomes more concen-trated as it leaves the nephron and its volume is reduced.

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Checkpoint 22-9: The first step in urine formation is glomerularfiltration. What is glomerular filtration?

Figure 22-7 Filtration process in the formation of urine.Blood pressure inside the glomerulus forces water and dissolvedsubstances into the glomerular (Bowman) capsule. Blood cellsand proteins remain behind in the blood. The smaller diameterof the efferent arteriole as compared with that of the afferent ar-teriole maintains the hydrostatic (fluid) pressure. ZOOMINGIN ✦ Which arteriole associated with the glomerulus has the widerdiameter?

Soluble molecules

Blood cells


Efferentarteriole

Bloodflow

Afferentarteriole

Glomerulus

Endothelium

Bloodflow

Proteins

Filtrate

Glomerularcapsule

Tubular Reabsorption The kidneys form about 160to 180 liters of filtrate day. However, only 1 to 1.5 litersof urine are eliminated daily. Clearly, most of the waterthat enters the nephron is not excreted with the urine,but rather, is returned to the circulation. In addition towater, many other substances the body needs, such as nu-trients and ions, pass into the nephron as part of the fil-trate, and these also must be returned. Therefore, theprocess of filtration that occurs in the glomerular capsule


The hormone ADH makes the walls of the DCT andcollecting tubule more permeable to water, so that morewater will be reabsorbed and less will be excreted withthe urine. The release of ADH from the posterior pituitary

is regulated by a feedback system. As the blood becomesmore concentrated, the hypothalamus triggers more ADHrelease from the posterior pituitary; as the blood becomesmore dilute, less ADH is released. In the disease diabetes

insipidus, there is inadequate secre-tion of ADH from the hypothalamus,which results in the elimination oflarge amounts of dilute urine accom-panied by excessive thirst.

Summary of Urine FormationThe processes involved in urine for-mation are summarized below and il-lustrated in Figure 22-9.

1. Glomerular filtration allows all dif-fusible materials to pass from theblood into the nephron.

2. Tubular reabsorption moves usefulsubstances back into the bloodwhile keeping waste products inthe nephron to be eliminated in theurine.

3. Tubular secretion moves addi-tional substances from the bloodinto the nephron for elimination.Movement of hydrogen ions is onemeans by which the pH of bodyfluids is balanced.

4. The countercurrent mechanismconcentrates the urine and reducesthe volume excreted. The pituitaryhormone ADH allows more waterto be reabsorbed from the nephron.

The kidney works efficiently to return valuable substancesto the blood after glomerular filtration. However, the car-

riers that are needed for active transport of these substancescan become overloaded, and there is also a limit to the amountof each substance that can be reabsorbed in a given time pe-riod. The limit of this rate of reabsorption is called the trans-port maximum (Tm), or tubular maximum, and it is meas-ured in milligrams (mg) per minute. For example, the Tm forglucose is approximately 375 mg/minute.

If a substance is present in excess in the blood, it may ex-

ceed its transport maximum and then, because it cannot betotally reabsorbed, some will be excreted in the urine. Thus,the transport maximum determines the renal threshold—theplasma concentration at which a substance will begin to beexcreted in the urine, which is measured in mg per deciliter(dL). For example, if the concentration of glucose in theblood exceeds its renal threshold (180 mg/dL), glucose willbegin to appear in the urine, a condition called glycosuria.The most common cause of glycosuria is uncontrolled dia-betes mellitus.

Transport Maximum

Box 22-1 Clinical Perspectives

Transport Maximum

Figure 22-8 Countercurrent mechanism for concentration of urine. Concentra-tion is regulated by means of intricate exchanges of water and electrolytes, mainlysodium, in the loop of Henle, distal convoluted tubule, and collecting duct. The in-tensity of color shows changing concentrations of the interstitial fluid and filtrate.

KIDNEY CORTEX

KIDNEY MEDULLA

Diluteinterstitial

fluid

Concentratedinterstitial

fluid

Glomerularcapsule


Descendinglimb

Ascendinglimb


Collectingduct

Loop ofHenle

Sodium (Na+) Water (H2O)

Checkpoint 22-10: What are the fourprocesses involved in the formation ofurine?


◗ The UretersEach of the two ureters is a long, slender, muscular tubethat extends from the kidney down to and through the in-ferior portion of the urinary bladder (see Fig. 22-1). Theureters, which are located posterior to the peritoneumand, at the distal portion, below the peritoneum, are en-tirely extraperitoneal. Their length naturally varies withthe size of the individual, and they may be anywhere from25 cm to 32 cm (10–13 inches) long. Nearly 2.5 cm (1inch) of the ureter’s distal portion enters the bladder bypassing obliquely (at an angle) through the inferior blad-der wall. Because of the oblique direction the ureter takesthrough the wall, a full bladder compresses the ureter andprevents the backflow of urine.

The wall of the ureter includes a lining of epithelialcells, a relatively thick layer of involuntary muscle, and fi-nally, an outer coat of fibrous connective tissue. The ep-ithelium is the transitional type, which flattens from acuboidal shape as the tube stretches. This same type ofepithelium lines the renal pelvis, the bladder, and theproximal portion of the urethra. The ureteral muscles arecapable of the same rhythmic contraction (peristalsis)that occurs in the digestive system. Urine is moved alongthe ureter from the kidneys to the bladder by gravity andby peristalsis at frequent intervals.

◗ The Urinary BladderWhen it is empty, the urinary bladder (Fig. 22-10) is lo-cated below the parietal peritoneum and posterior to thepubic joint. When filled, it pushes the peritoneum up-ward and may extend well into the abdominal cavityproper. The urinary bladder is a temporary reservoir forurine, just as the gallbladder is a storage sac for bile.

The bladder wall has many layers. It is lined with mu-cous membrane containing transitional epithelium. The

bladder’s lining, like that of the stomach, is thrown intofolds called rugae when the organ is empty. Beneath themucosa is a layer of connective tissue, followed by athree-layered coat of involuntary muscle tissue that canstretch considerably. Finally, there is an incomplete coatof peritoneum that covers only the superior portion of thebladder.

When the bladder is empty, the muscular wall be-comes thick, and the entire organ feels firm. As the blad-

22

Figure 22-9 Summary of urine formation in a nephron.

Glomerularcapsule

Afferentarteriole

Urine(excreted)

ADH

Blood withreabsorbedsubstances

Efferentarteriole

Peritubularcapillaries

Filtrate

Filtration from bloodinto nephron

Reabsorptionfrom filtrateinto blood

Tubular secretionfrom blood intofiltrate

Reabsorptionof water undereffects of ADH

1

2 3 4

Figure 22-10 Interior of the male urinary bladder. Thetrigone is a triangular region in the floor of the bladder markedby the openings of the ureters and the urethra. ZOOMING IN✦ What gland does the urethra pass through in the male?

SmoothmuscleRugaeUreter

Prostate

Urethra

Externalurethral

sphincter

Internalurethral

sphincter

Openingsof ureters

Trigone


der fills, the muscular wall becomes thinner, and theorgan may increase from a length of 5 cm (2 inches) upto as much as 12.5 cm (5 inches) or even more. A mod-erately full bladder holds about 470 mL (1 pint) of urine.

The trigone (TRI-gone) is a triangular-shaped regionin the floor of the bladder. It is marked by the openingsof the two ureters and the urethra (see Fig. 22-10). As thebladder fills with urine, it expands upward, leaving thetrigone at the base stationary. This stability preventsstretching of the ureteral openings and the possible backflow of urine into the ureters.

◗ The UrethraThe urethra is the tube that extends from the bladder tothe outside (see Fig. 22-1) and is the means by which thebladder is emptied. The urethra differs in men andwomen; in the male, it is part of both the reproductivesystem and the urinary system, and it is much longer thanis the female urethra.

The male urethra is about 20 cm (8 inches) in length.Proximally, it passes through the prostate gland, where itis joined by two ducts carrying male germ cells (sperma-tozoa) from the testes and glandular secretions. Fromhere, it leads to the outside through the penis (PE-nis),the male organ of copulation. The male urethra serves thedual purpose of conveying semen with the germ cells anddraining the bladder.

The urethra in the female is a thin-walled tube about4 cm (1.5 inches) long. It is located posterior to the pubicjoint and is embedded in the muscle of the vagina’s ante-rior wall. The external opening, called the urinary mea-tus (me-A-tus), is located just anterior to the vaginalopening between the labia minora. The female urethradrains the bladder only and is entirely separate from thereproductive system.

UrinationThe process of expelling (voiding) urine from the bladderis called urination or micturition (mik-tu-RISH-un). Thisprocess is controlled both voluntarily and involuntarilywith the aid of two rings of muscle (sphincters) that sur-round the urethra (see Fig. 22-10). Near the bladder’soutlet is an involuntary internal urethral sphincterformed by a continuation of the smooth muscle of thebladder wall. Below this muscle is a voluntary externalurethral sphincter formed by the muscles of the pelvicfloor. By learning to control the voluntary sphincter, onecan gain control over emptying of the bladder.

As the bladder fills with urine, stretch receptors in itswall send impulses to a center in the lower part of thespinal cord. Motor impulses from this center stimulatecontraction of the bladder wall, forcing urine outward asboth the internal and external sphincters are made torelax. In the infant, this emptying occurs automatically as

a simple reflex. Early in life, a person learns to controlurination from higher centers in the brain until the timeis appropriate, a process known as toilet training. The im-pulse to urinate will override conscious controls if thebladder becomes too full.

The bladder can be emptied voluntarily by relaxingthe muscles of the pelvic floor and increasing the pressurein the abdomen. The resulting increased pressure in thebladder triggers the spinal reflex that leads to urination.

Checkpoint 22-11: What is the name of the tube that carriesurine from the kidney to the bladder?

Checkpoint 22-12: What is the name of the tube that carriesurine from the bladder to the outside?

◗ The UrineUrine is a yellowish liquid that is approximately 95%water and 5% dissolved solids and gases. The pH offreshly collected urine averages 6.0, with a range of 4.5 to8.0. Diet may cause considerable variation in pH.

The amount of dissolved substances in urine is indi-cated by its specific gravity. The specific gravity of purewater, used as a standard, is 1.000. Because of the dis-solved materials it contains, urine has a specific gravitythat normally varies from 1.002 (very dilute urine) to1.040 (very concentrated urine). When the kidneys arediseased, they lose the ability to concentrate urine, andthe specific gravity no longer varies as it does when thekidneys function normally.

Normal ConstituentsSome of the dissolved substances normally found in theurine are the following:

◗ Nitrogenous waste products, including urea, uric acid,and creatinine (kre-AT-ih-nin)

◗ Electrolytes, including sodium chloride (as in commontable salt) and different kinds of sulfates and phos-phates. Electrolytes are excreted in appropriateamounts to keep their blood concentration constant.

◗ Pigment, mainly yellow pigment derived from certainbile compounds. Pigments from foods and drugs alsomay appear in the urine.

Abnormal ConstituentsExamination of urine, called a urinalysis (u-rin-AL-ih-sis) (UA), is one of the most important parts of a medicalevaluation. A routine urinalysis includes observation ofcolor and turbidity (cloudiness) as well as measurementof pH and specific gravity. Laboratories also test for a va-riety of abnormal components, including:

◗ Glucose is usually an important indicator of diabetesmellitus, in which the cells do not adequately metabo-


lize blood sugar. The excess glucose, which cannot bereabsorbed, is excreted in the urine. The presence ofglucose in the urine is known as glycosuria (gli-ko-SU-re-ah) or glucosuria.

◗ Albumin. The presence of this protein, which is nor-mally retained in the blood, may indicate a kidney dis-order, such as glomerulonephritis. Albumin in theurine is known as albuminuria (al-bu-mih-NU-re-ah).

◗ Blood in the urine is usually an important indicator ofurinary system disease, including nephritis. Blood inthe urine is known as hematuria (hem-ah-TU-re-ah).

◗ Ketones (KE-tones) are produced when fats are incom-pletely oxidized; ketones in the urine are seen in dia-betes mellitus and starvation.

◗ White blood cells (pus) are evidence of infection; theycan be seen by microscopic examination of a cen-trifuged specimen. Pus in the urine is known as pyuria(pi-U-re-ah).

◗ Casts are solid materials molded within the micro-scopic kidney tubules. They consist of cells or proteinsand, when present in large number, they usually indi-cate disease of the nephrons.

More extensive tests on urine may include analysis fordrugs, enzymes, hormones, and other metabolites as wellas cultures for microorganisms. Normal values for com-mon urine tests are given in Appendix 4, Table 1.

◗ Disorders of the Urinary SystemThe kidney is more prone to disorders than any otherportion of the urinary system.

Kidney DisordersKidney disorders may be acute or chronic. Acute condi-tions usually arise suddenly, most frequently as the resultof infection with inflammation of the nephrons. Thesediseases commonly run a course of a few weeks and arefollowed by complete recovery. Chronic conditions ariseslowly and are often progressive, with gradual loss of kid-ney function.

Acute glomerulonephritis (glo-mer-u-lo-nef-RI-tis),also known as acute poststreptococcal glomerulonephritis, isthe most common disease of the kidneys. This conditionusually occurs in children about 1 to 4 weeks after a strep-tococcal throat infection. Antibodies formed in response tothe streptococci attach to the glomerular membrane andcause injury. These damaged glomeruli allow protein, es-pecially albumin, to filter into the glomerular capsule andultimately to appear in the urine (albuminuria). They alsoallow red blood cells to filter into the urine (hematuria).Usually, the patient recovers without permanent kidneydamage. In adult patients, the disease is more likely to be-come chronic, with a gradual decrease in the number offunctioning nephrons, leading to chronic renal failure.

Pyelonephritis (pi-el-o-nef-RI-tis), an inflammationof the renal pelvis and the tissue of the kidney, may be ei-ther acute or chronic. In acute pyelonephritis, the inflam-mation results from a bacterial infection. Bacteria mostcommonly reach the kidney by ascending along the liningmembrane from an infection in the distal part of the uri-nary tract (see Fig. 23-15 in Chapter 23). More rarely,bacteria are carried to the kidney by the blood.

Acute pyelonephritis is often seen in people with par-tial obstruction of urine flow with stagnation (urinary sta-sis). It is most likely to occur in pregnant women and inmen with an enlarged prostate, because the prostate sur-rounds the first portion of the urethra in males. Othercauses of stasis include neurogenic bladder, which isbladder dysfunction resulting from neurologic lesions, asseen in diabetes mellitus, and structural defects in thearea where the ureters enter the bladder. Pyelonephritisusually responds to the administration of antibiotics,fluid replacement, rest, and fever control.

Chronic pyelonephritis, a more serious disease, is fre-quently seen in patients with urinary tract stasis or backflow. It may be caused by persistent or repeated bacterialinfections. Progressive damage of kidney tissue is evi-denced by high blood pressure, continual loss of proteinin the urine, and dilute urine.

Hydronephrosis (hi-dro-nef-RO-sis) is the distentionof the renal pelvis and calyces with accumulated fluid asa result of urinary tract obstruction. The most commoncauses of obstruction, in addition to pregnancy or an en-larged prostate, are a kidney stone that has formed in thepelvis and dropped into the ureter, a tumor that presseson a ureter, and scars due to inflammation. Prompt re-moval of the obstruction may result in complete recovery.If the obstruction is not removed, the kidney will be per-manently damaged.

A polycystic (pol-e-SIS-tik) kidney is one in whichmany fluid-containing sacs develop in the active tissueand gradually destroy it by pressure. This disorder mayrun in families, and treatment has not proved very satis-factory, except for the use of dialysis machines or kidneytransplantation.

Tumors of the kidneys usually grow rather slowly,but rapidly invading types are occasionally found. Bloodin the urine and dull pain in the kidney region are warn-ings that should be heeded at once. Surgical removal ofthe kidney offers the best chance of cure because mostrenal cancers do not respond to chemotherapy or radia-tion.

Kidney Stones Kidney stones, or calculi (KAL-ku-li),are made of substances, such as calcium salts or uric acid,that precipitate out of the urine instead of remaining insolution. They usually form in the renal pelvis, but mayalso form in the bladder.

The causes of stone formation include dehydration,stasis (stagnation) of the urine, and infection of the uri-

22


nary tract. The stones may vary in size from tiny grainsresembling bits of gravel up to large masses that fill therenal pelvis and extend into the calyces. The latter are de-scribed as staghorn calculi.

There is no way of dissolving these stones because sub-stances that could do so would also destroy kidney tissue.Sometimes, instruments can be used to crush small stonesand thus allow them to be expelled with the urine, but moreoften, surgical removal is required. A lithotriptor (LITH-o-trip-tor), literally a “stone-cracker,” is a device that employsexternal shock waves to shatter kidney stones. The proce-dure is called lithotripsy (LITH-o-trip-se).

Renal Failure Acute renal failure may result from amedical or surgical emergency or from toxins that dam-age the tubules. This condition is characterized by a sud-den, serious decrease in kidney function accompanied byelectrolyte and acid–base imbalances. Acute renal failureoccurs as a serious complication of other severe illnessand may be fatal.

Chronic renal failure results from a gradual loss ofnephrons. As more and more nephrons are destroyed, thekidneys gradually lose the ability to perform their normalfunctions. As the disease progresses, nitrogenous wasteproducts accumulate to high levels in the blood, causinga condition known as uremia (u-RE-me-ah). In manycases, there is a lesser decrease in renal function, knownas renal insufficiency, that produces fewer symptoms.

Two of the characteristic signs and symptoms ofchronic renal failure are the following:

◗ Dehydration (de-hi-DRA-shun). Excessive loss of bodyfluid may occur early in renal failure, when the kidneyscannot concentrate the urine and large amounts ofwater are eliminated.

◗ Edema (eh-DE-mah). Accumulation of fluid in the tis-sue spaces may occur late in chronic renal disease,when the kidneys cannot eliminate water in adequateamounts.

◗ Electrolyte imbalance, including retention of sodiumand accumulation of potassium

◗ Hypertension may occur as the result of fluid overloadand the increased production of renin (see Box 22-2).

◗ Anemia occurs when the kidneys cannot produce thehormone erythropoietin to activate red blood cell pro-duction in bone marrow.

◗ Uremia (u-RE-me-ah), an excess of nitrogenous wasteproducts in the blood. When these levels are very high,urea can be changed into ammonia in the stomach andintestine and cause ulcerations and bleeding.

In addition to forming urine, the kidneys play an integralrole in regulating blood pressure. When blood pressure

drops, cells of the juxtaglomerular apparatus secrete the en-zyme renin into the blood. Renin acts on another blood pro-tein, angiotensinogen, which is manufactured by the liver.Renin converts angiotensinogen into angiotensin I by cleav-ing off some amino acids from the end of the protein. An-giotensin I is then converted into angiotensin II by yet an-other enzyme called angiotensin-converting enzyme (ACE),which is manufactured by capillary endothelium, especially inthe lungs. Angiotensin II increases blood pressure in fourways:

1. It increases cardiac output and stimulates vasoconstriction.2. It stimulates the release of aldosterone, a hormone that

acts on the kidneys’ distal convoluted tubules to increase

sodium reabsorption, and secondarily, water reabsorp-tion.

3. It stimulates the release of antidiuretic hormone, whichacts directly on the distal convoluted tubules to increasewater reabsorption.

4. It stimulates thirst centers in the hypothalamus, resultingin increased fluid consumption.

The combined effects of angiotensin II produce a dramaticincrease in blood pressure. In fact, angiotensin II is estimatedto be four to eight times more powerful than norepinephrine,another potent stimulator of hypertension, and thus is a goodtarget for blood pressure-controlling drugs. One class of drugsused to treat hypertension is the ACE inhibitors (angiotensin-converting enzyme inhibitors), which control blood pressureby blocking the production of angiotensin II.

The Renin-Angiotensin Pathway: The Kidneys’ Route to BloodPressure Control

Box 22-2 A Closer Look

The Renin-Angiotensin Pathway: The Kidneys’ Route to BloodPressure Control

Checkpoint 22-13: What is the difference between acute andchronic kidney disorders?

Renal Dialysis and Kidney TransplantationDialysis (di-AL-ih-sis) means “the separation of dissolvedmolecules based on their ability to pass through a semi-permeable membrane” (Fig. 22-11 A). Molecules that canpass through the membrane move from an area of greaterconcentration to one of lesser concentration. In patientswho have defective kidney function, the accumulation ofurea and other nitrogenous waste products can be re-duced by passage of the patient’s blood through a dialysismachine. The principle of “molecules leaving the area ofgreater concentration” thus operates to remove wastesfrom the blood. The fluid in the dialysis machine, thedialysate, can be adjusted to regulate the flow of sub-stances out of the blood.

There are two methods of dialysis in use: hemodialy-sis (blood dialysis) and peritoneal dialysis (dialysis in the


abdominal cavity). In hemodialysis, the dialysis mem-brane is made of cellophane or other synthetic material.In peritoneal dialysis, the surface area of the peritoneumacts as the membrane (see Fig. 22-11 B). Dialysis fluid isintroduced into the peritoneal cavity and then periodi-cally removed along with waste products. This proceduremay be done at intervals through the day or during thenight.

A 1973 amendment to the Social Security Act pro-vides federal financial assistance for people who havechronic renal disease and require dialysis. Most he-modialysis is performed in freestanding clinics. Treat-ment time has been reduced; a typical schedule involves2 to 3 hours, three times a week. Access to the blood-stream has been made safer and easier through surgicalestablishment of a permanent exchange site (shunt). Peri-toneal dialysis also has been improved and simplified, en-abling patients to manage treatment at home. (Box 22-3gives an overview of what to expect in a career as a he-modialysis technician.)

The final option for treatment of renal failure is kid-ney transplantation. Surgeons have successfully per-formed many of these procedures. Kidneys have so muchextra functioning tissue that the loss of one kidney nor-mally poses no problem to the donor. Records show thattransplantation success is greatest when surgeons use akidney from a living donor who is closely related to thepatient. Organs from deceased donors have also proved

satisfactory in many cases. The problem of tissue rejec-tion (the rejection syndrome) is discussed in Chapter 17.

Disorders of the UretersAbnormalities in structure of the ureter include subdivi-sion at the renal pelvis and constricted or abnormally nar-row parts, called strictures (STRICK-tures). Abnormalpressure from tumors or other outside masses may causeureteral narrowing.. Obstruction also may be caused bystones from the kidneys, or kinking of the tube becauseof a dropping of the kidney, a condition known as renalptosis (TO-sis). In cases of ureterocele (u-RE-ter-o-sele),the end of the ureter bulges into the bladder (Fig. 22-12).The result is urinary obstruction that leads to distentionof the ureter (hydroureter) and renal pelvis (hy-dronephrosis). The usual cause of ureterocele is a con-genital (present at birth) narrowing of the ureteral open-ing.

Ureteral Stones The passage of a small stone along theureter causes excruciating pain, called renal colic. Relief ofthis pain usually requires morphine or an equally powerfuldrug. The first “barber surgeons,” operating without bene-fit of anesthesia, were permitted by their patients to cutthrough the skin and the muscles of the back to removestones from the ureters. “Cutting for stone” in this way wasrelatively successful, despite the lack of sterile technique,

22

Figure 22-11 A hemodialysis system and a peritoneal dialysis system. (A) In hemodialysis, a cellophane membrane separatesthe blood compartment and dialysis fluid compartment. This membrane is porous enough to allow all of the constituents except theplasma proteins (PRO) and blood cells (WBC, RBC) to diffuse between the two compartments. (B) In peritoneal dialysis, a semiper-meable membrane richly supplied with blood vessels lines the peritoneal cavity. With dialysate dwelling in the peritoneal cavity, wasteproducts diffuse from the network of blood vessels into the dialysate. (A, Reprinted with permission from Porth CM. Pathophysiol-ogy. 7th ed. Philadelphia: Lippincott Williams & Wilkins, 2004; B, reprinted with permission from Cohen BJ. Medical Terminology.4th ed. Philadelphia: Lippincott Williams & Wilkins, 2004.)

RBC

H2O

H2O

H2O

PRO

WBC

A B

Dialysis fluid

From artery

To veinBlood

From dialysisfluid supply

Bicarbonate

PotassiumTo waste

Newsolution

Catheter Oldsolution

Peritonealcavity


Figure 22-12 Ureterocele. The ureter bulges into the blad-der. The resulting obstruction causes urine to back up into theureter and renal pelvis. (Reprinted with permission from CohenBJ. Medical Terminology. 4th ed. Philadelphia: LippincottWilliams & Wilkins, 2004.)

Ureterocele

Ahemodialysis technician, also called a renal technician ora nephrology technician, specializes in the safe and effec-

tive delivery of renal dialysis therapy to patients sufferingfrom kidney failure. Before treatment begins, the technicianprepares the dialysis solutions and ensures that the dialysismachine is clean, sterile, and in proper working order. Thetechnician measures and records the patient’s weight, temper-ature, and vital signs, inserts a catheter into the patient’s arm,and connects the dialysis machine to it. During dialysis, thetechnician monitors the patient for adverse reactions andguards against any equipment malfunction. After the treat-ment is completed, the technician again measures and records

the patient’s weight, temperature, and vital signs. To performthese duties, hemodialysis technicians need a thorough un-derstanding of anatomy and physiology. Most technicians inthe United States receive their training from a college or tech-nical school, and many states require that the technician becertified.

Hemodialysis technicians work in a variety of settings suchas hospitals, clinics, and patients’ homes. As populations age,the incidence of kidney disease is expected to rise, as will theneed for hemodialysis. For more information about this ca-reer, contact the National Association of Nephrology Techni-cians.

Hemodialysis Technician

Box 22-3 • Health Professions

Hemodialysis Technician

because the approach through the back avoided the peri-toneal cavity and the serious risk of peritonitis.

Modern surgery employs a variety of instruments forremoval of stones from the ureter, including endoscopessimilar to those described in Chapter 19. Thetransurethral route through the urethra and urinary blad-der and then into the ureter, as well as entrance throughthe skin and muscles of the back, may be used to removecalculi from the kidney pelvis or from the ureter.

sitating immediate surgical repair. Blood in the urine is arather common symptom of infection or tumors, whichmay involve the bladder.

Cystitis Inflammation of the bladder, called cystitis(sis-TI-tis), is 10 times as common in women as in men.This may be due, at least in part, to the very short urethraof the female compared with that of the male. The usualpath of infection is that bacteria ascend from the outsidethrough the urethra into the bladder (see Fig. 23-15 inChapter 23). The common contaminants are colon bacte-ria, such as E. coli, carried to the urethra from the anus.Urinary stasis and catheterization to remove urine fromthe bladder are other possible sources of infection. Pain,urgency to urinate, and urinary frequency are commonsymptoms of cystitis.

Another type of cystitis, called interstitial cystitis,may cause pelvic pain with discomfort before and afterurination. The tissues below the mucosa are involved.The disease can be diagnosed only with the use of a cys-toscope, a type of endoscope used to examine the bladder(Fig. 22-13). Because no bacteria are involved, antibioticsare not effective treatment and may even be harmful.

Obstruction by an enlarged prostate gland in a maleor from pregnancy may lead to urinary stasis and cystitis.Reduction of a person’s general resistance to infection, asin diabetes, may also lead to cystitis. The danger of cysti-tis is that the infection may ascend to other parts of theurinary tract.

Tumors Tumors of the bladder, which are most preva-lent in men older than 50 years of age, include benign pa-pillomas and various kinds of cancer. About 90% of blad-der tumors arise from the epithelial lining. Possiblecauses include toxins (particularly certain aniline dyes),chronic infestations (schistosomiasis), heavy cigarettesmoking, and the presence of urinary stones, which maydevelop and increase in size within the bladder.

Checkpoint 22-14: What is the scientific name for stones, asmay occur in the urinary tract?

Disorders Of the BladderA full (distended) bladder lies in an unprotected positionin the lower abdomen, and a blow may rupture it, neces-


Blood in the urine (hematuria) and frequent urina-tion, in the absence of pain or fever, are early signs of abladder tumor. A cystoscopic examination (see Fig. 22-13) and biopsy should be performed as soon as thesesigns are detected. Treatment includes removal of thetumor, which may be done cystoscopically, and localizedchemotherapy. More serious cases may require irradia-tion. Removal before the tumor invades the muscle wallgives the best prognosis.

pressure in the abdomen. These activities includecoughing, sneezing, laughing, lifting or exercising.

◗ Urge incontinence, also called overactive bladder, re-sults from an inability to control bladder contractionsonce the sensation of bladder fullness is perceived.

◗ Overflow incontinence is due to neurologic damage orurinary obstruction that causes the bladder to overfill.Excess pressure in the bladder results in involuntaryloss of urine.

◗ Enuresis (en-u-RE-sis) is involun-tary urination, usually during thenight (bed-wetting)

Some treatment approaches to in-continence include muscle exercises,dietary changes, biofeedback, medica-tion, surgery or, in serious cases, self-catheterization.

22

Figure 22-13 Cystoscopy. A lighted cystoscope is introduced through the urethrainto the bladder of a male subject. Sterile fluid is used to inflate the bladder. The cys-toscope is used to examine the bladder, remove specimens for biopsy, and remove tu-mors. (Reprinted with permission from Cohen BJ. Medical Terminology. 4th ed.Philadelphia: Lippincott Williams & Wilkins, 2004.)

Urinary bladder

Light cord

Tube for fluid

Prostate

Scrotum

Figure 22-14 Ileal conduit. The ureters are vented through a segment of the ileumto open at the body surface through an ileostomy. (Reprinted with permission fromCohen BJ. Medical Terminology. 4th ed. Philadelphia: Lippincott Williams & Wilkins,2004.)

Divertedureters

Segment ofileum

Ileostomy

If it is necessary to remove thebladder in a cystectomy (sis-TEK-to-me), the ureters must be vented else-where. They may be diverted to thebody surface through a segment ofthe ileum, a procedure known as anileal conduit (Fig. 22-14), or divertedto some other portion of the intestine.Alternatively, surgeons may create abladder out of a section of the colon.

Urinary Incontinence Urinary in-continence (in-KON-tin-ens) refers toan involuntary loss of urine. The con-dition may originate with a neurologicdisorder, trauma to the spinal cord,weakness of the pelvic muscles, im-paired bladder function or medica-tions. Different forms of urinary in-continence have specific names:

◗ Stress incontinence is due to ure-thral incompetence that allowssmall amounts of urine to be re-leased when an activity increases

Checkpoint 22-15: What is the term forinflammation of the bladder?

Disorders of theUrethraCongenital anomalies may involve theurethra as well as other parts of theurinary tract. The opening of the ure-thra to the outside may be too small,or the urethra itself may be narrowed.Occasionally, an abnormal valve-likestructure is found at the point where


the urethra enters the bladder. If it is not removed surgi-cally, it can cause back pressure of the urine, with seriousconsequences. There is also a condition in the male inwhich the urethra opens on the undersurface of the penisinstead of at the end. This is called hypospadias (hi-po-SPA-de-as) (Fig. 22-15).

Urethritis, which is characterized by inflammation ofthe mucous membrane and the glands of the urethra, ismuch more common in men than in women. It is oftencaused by infection with gonococci or chlamydias, al-though many other bacteria may be involved.

“Straddle” injuries to the urethra are common in men.This type of injury occurs when, for example, a man walk-ing along a raised beam slips and lands with the beam be-tween his legs. Such an accident may catch the urethra be-tween the hard surfaces of the beam and the pubic arch andrupture the urethra. In accidents in which the bones of thepelvis are fractured, rupture of the urethra is fairly common.

◗ The Effects of AgingEven without kidney disease, aging causes the kidneys tolose some of their ability to concentrate urine. With aging,progressively more water is needed to excrete the sameamount of waste. Older people find it necessary to drinkmore water than young people, and they eliminate largeramounts of urine (polyuria), even at night (nocturia).

Beginning at about 40 years of age, there is a decreasein the number and size of the nephrons. Often, more thanhalf of them are lost before the age of 80 years. There maybe an increase in blood urea nitrogen (BUN) without se-rious symptoms. Elderly people are more susceptible thanyoung people to urinary system infections. Childbearingmay cause damage to the musculature of the pelvic floor,resulting in urinary tract problems in later years.

Enlargement of the prostate, common in older men,may cause obstruction and back pressure in the uretersand kidneys. If this condition is untreated, it will causepermanent damage to the kidneys. Changes with age, in-cluding decreased bladder capacity and decreased muscletone in the bladder and urinary sphincters, may predis-pose to incontinence. However, most elderly people (60%in nursing homes, and up to 85% living independently)have no incontinence.

Figure 22-15 Hypospadias. A ventral view of the penis isshown here. (Reprinted with permission from Cohen BJ. Med-ical Terminology. 4th ed. Philadelphia: Lippincott Williams &Wilkins, 2004.)

Glans

Scrotum

Urethral opening

Word Anatomy

Medical terms are built from standardized word parts (prefixes, roots, and suffixes). Learning the meanings of these parts can help youremember words and interpret unfamiliar terms.

WORD PART MEANING EXAMPLE

The Kidneysretro- backward, behind The retroperitoneal space is posterior to the peritoneal cavity.ren/o kidney The renal artery carries blood to the kidney.nephr/o kidney The nephron is the functional unit of the kidney.juxta- next to The juxtaglomerular apparatus is next to the glomerulus.

The Uretersextra- beyond, outside of The ureters are extraperitoneal.

Disorders of the Urinary Systempyel/o renal pelvis Pyelonephritis is inflammation of the nephrons and renal pelvis.cyst/o sac, bladder A polycystic kidney develops many fluid-containing sacs.dia- through Dialysis is the separation (-lysis) of molecules based on their ability to pass through

a semipermeable membrane.-cele swelling, enlarged space A uterocele is formed as the end of the ureter bulges into the bladder.trans- across, through A transurethral route is through the urethra.

The Effects of Agingnoct/i night Nocturia is excessive urination at night.


I. Excretion- removal and elimination ofmetabolic waste

A. Systems that eliminate waste1. Urinary- removes waste from blood

a. Other functions- regulates blood volume, pH, andelectrolytes

2. Digestive system—eliminates water, salts, bile with di-gestive residue

3. Respiratory system—eliminates carbon dioxide, water4. Skin—eliminates water, salts, nitrogen waste

II. Organs of the urinary systema. Kidneys (2)b. Ureters (2)c. Urinary bladder (1)d. Urethra (1)

III. Kidneys1. In upper abdomen against the back2. In retroperitoneal space (posterior to the peritoneum)

A. Blood supplya. Renal artery—carries blood to kidney from aortab. Renal vein—carries blood from kidney to inferior

vena cavaB. Structure of the kidney

1. Cortex—outer portion2. Medulla—inner portion3. Pelvis

a. Upper end of ureterb. Calyces—cuplike extensions that receive urine

4. Nephrona. Functional unit of kidneyb. Parts

(1) Glomerular (Bowman) capsule—aroundglomerulus

(2) Proximal convoluted tubule (PCT)(3) Loop of Henle- descending and ascending limbs(4) Distal convoluted tubule (DCT)

c. Blood supply to nephron(1) Afferent arteriole—enters glomerular capsule(2) Glomerulus—coil of capillaries in glomerular

capsule(3) Efferent arteriole—leaves glomerular capsule(4) Peritubular capillaries—surround nephron(5) Juxtaglomerular apparatus

a. Consists of cells in afferent arteriole and distal con-voluted tubule

b. Releases renin to regulate blood pressure via an-giotensin

C. Functions of the kidney1. Excretion of waste, excess salts, toxins2. Water balance3. Acid–base balance (pH)4. Regulation of blood pressure5. Releases hormone erythropoietin (EPO)- stimulates red

blood cell production

D. Formation of urine1. Glomerular filtration—driven by blood pressure in

glomerulusa. Water and soluble substances forced out of blood

and into glomerular capsuleb. Blood cells and proteins remain in bloodc. Glomerular filtrate—material that leaves blood and

enters the nephron2. Tubular reabsorption

a. Most of filtrate leaves nephron by diffusion, osmosisand active transport

b. Returns to blood through peritubular capillaries3. Tubular secretion—materials moved from blood into

nephron for excretion4. Concentration of urine

a. Countercurrent mechanism—method for concentrat-ing urine based on movement of ions and permeabil-ity of tubule(1) ADH

(a) Hormone from posterior pituitary(b) Promotes reabsorption of water

IV. The ureters—carry urine from thekidneys to the bladder

V. Urinary bladdera. Stores urine until it is eliminatedb. Trigone—triangular region in base of bladder; re-

mains stable as bladder fills

VI. Urethra—carries urine out of body1. Male urethra—20 cm long; carries both urine and semen2. Female urethra—4 cm long; opening anterior to vagina

A. Urination (micturition)1. Both voluntary and involuntary2. Sphincters

a. Internal urethral sphincter—involuntary (smoothmuscle)

b. External urethral sphincter—voluntary (skeletalmuscle)

3. Stretch receptors in bladder wall signal reflex emptying4. Can be controlled through higher brain centers

VII. Urine1. pH averages 6.02. Specific gravity—measures dissolved substances

A. Normal constituents—water, nitrogenous waste, elec-trolytes, pigments

B. Abnormal constituents—glucose, albumin, blood, ketones,white blood cells, casts

VIII. Disorders of the urinary systemA. Kidney disorders

1. Examplesa. Acute glomerulonephritis—damages glomerulib. Pyelonephritis—inflammation of kidney and renal

pelvis

22

Summary

MatchingMatch each numbered item with the most closely related lettered item.___ 6. Produced by the kidney in response to low blood pressure___ 7. Stimulates vasoconstriction___ 8. Produced by the kidney in response to hypoxia___ 9. Stimulates kidneys to produce concentrated urine___ 10. Produced by the liver during protein catabolism


c. Hydronephrosis—distention with obstructed fluidsd. Polycystic kidney—fluid-containing sacs develope. Tumors

2. Kidney stones- calculi3. Renal failure

a. Types1) Acute—results from medical emergency or toxins2) Chronic—signs include dehydration, electrolyte

imbalance, edema, hypertension, anemia, uremia4. Renal dialysis and kidney transplantation

a. Renal dialysis—removes unwanted substances fromblood when kidneys fail

B. Disorders of the ureters1. Stricture (narrowing)2. Stones (calculi)

C. Disorders involving the bladder1. Cystitis—inflammation; most common in females2. Tumors3. Urinary incontinence

D. Disorders of the urethra1. Hypospadias—urethra opens on underside of penis2. Urethritis—inflammation

IX. Effects of aging1. Polyuria—increased elimination of urine2. Nocturia—urination at night3. Incontinence4. Increased blood urea nitrogen (BUN)5. Prostate enlargement

Questions for Study and Review

Building UnderstandingFill in the blanks1. Each kidney is located outside the abdominal cavity ina ______ space.2. The renal artery, renal vein, and ureter connect to thekidney at the ______.3. The part of the bladder marked by the openings of theureters and urethra is called the ______.

4. The amount of dissolved substances in urine is indi-cated by its ______.5. The presence of glucose in the urine is known as______.

a. ureab. erythropoietinc. antidiuretic hormoned. renine. angiotensin

Multiple choice___ 11. The functional unit of the renal system is the

a. renal capsuleb. kidneyc. nephrond. juxtaglomerular apparatus

___ 12. The loop of Henle is located in the renala. cortexb. medullac. pelvisd. calyx

___ 13. Fluid moves out of the glomerulus bya. filtrationb. diffusionc. osmosisd. active transport

___ 14. One’s ability to delay urination is due tovoluntary control of thea. trigoneb. internal urethral sphincterc. external urethral sphincterd. urinary meatus

___ 15. Pus in the urine is termeda. pyuriab. uremiac. anemiad. enuresis

Understanding Concepts16. List four organ systems active in excretion. What arethe products eliminated by each?17. Compare and contrast the following terms:

a. glomerular capsule and glomerulusb. afferent and efferent arteriolec. proximal and distal convoluted tubuled. ureter and urethra

18. Trace the pathway of a urea molecule from the affer-ent arteriole to the urinary meatus.19. Describe the four processes involved in the formationof urine.20. Compare the male urethra and female urethra instructure and function. Why is cystitis more common inwomen than in men?


22

21. List some of the dissolved substances normally foundin the urine.22. Differentiate between the following disorders:

a. albuminuria and hematuriab. glomerulonephritis and pyelonephritisc. hydronephrosis and polycystic kidneyd. renal ptosis and ureterocele

23. What is meant by the word dialysis and how is thisprinciple used for patients with kidney failure? Whatkinds of membranes are used for hemodialysis? for peri-toneal dialysis?

Conceptual Thinking24. Christie is fourteen years old and suffers from anorexianervosa. Her parents take her to the hospital after she reportssharp pain in the lumbar region of her back. While there, sheis diagnosed with hydronephrosis. What is the relationshipbetween her eating disorder and her renal disorder?25. A class of antihypertensive drugs called loop diuret-ics prevents sodium reabsorption in the loop of Henle.How could a drug like this lower blood pressure?

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THE URINARY SYSTEM