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CHAPTER 20
URINARY SYSTEM
LEARNING OBJECTIVE 1: Name the organs of the urinary system and list their
general functions.
Lecture Suggestions and Guidelines
1. Introduce the location, structure, and function of the kidneys.
2. Describe the location, structure, and function of the ureters.
3. Describe the location, structure, and function of the urinary bladder.
4. Introduce the location, structure, and function of the urethra.
Application Question(s)
1. What diagnostic tests are performed during a routine urinalysis?
Answer: Appearance, color, specific gravity, pH, and the presence of protein,
glucose, ketones, bile products, and hemoglobin are routinely examined
macroscopically. A microscopic examination would include screening for the
presence of white blood cells, red blood cells, epithelial cells, casts, crystals,
bacteria, yeast, mucin, and parasites.
Critical Thinking Issue(s)
1. Discuss the principle of a urine pregnancy slide test based on direct latex particle
agglutination.
Answer: Commercially designed latex particles are coated with anti-HCG serum.
These particles are incubated with the patient’s urine. The test is positive if the
particles agglutinate, i.e., HCG is present in the patient’s urine. If no agglutination
is observed, HCG is absent, and the test is interpreted as negative.
LEARNING OBJECTIVE 2: Describe the locations of the kidneys and the structure of
a kidney.
and
LEARNING OBJECTIVE 3: List the functions of the kidneys.
Lecture Suggestions and Guidelines
1. Reiterate the location of the kidneys.
2. Describe the renal sinus, renal pelvis, major and minor calyces, renal papillae,
medulla, and cortex.
3. Discuss the functions of the kidneys, including the removal and excretion of
metabolic wastes, regulation of red blood cell production, blood pressure, and
calcium ion absorption.
4. Discuss the kidneys’ roles in regulating the volume, composition, and pH of the
blood.
Application Question(s)
1. Dissect a porcine kidney and ask students to locate and give the functions of the
major kidney structures.
Answer: Responses should include a discussion of the renal pyramid, major and
minor calyces, renal capsule, renal pelvis, renal column, renal papilla, renal
medulla, and renal cortex.
Critical Thinking Issue(s)
1. A 42-year old male on a high calcium diet has complained of dull persistent pain
in the lower back and flank regions for several days. He exercises daily but fails
to replenish water lost through urination and perspiration on a regular basis. This
morning he awakened with intense pain in the abdomen. A routine urinalysis
reveals a significant level of hematuria. What may be a likely diagnosis?
Answer: The patient was experiencing the movement and subsequent lodging of
a urinary calculus (kidney stone). Urinary calculi are solid masses often formed
by the precipitation of calcium oxalate, calcium phosphate, or uric acid. Small
kidney stones may be passed, but many are not, leading to obstruction, pain, and
infection.
LEARNING OBJECTIVE 4: Trace the pathway of blood through the major vessels
within a kidney.
Lecture Suggestions and Guidelines
1. Lecture on the pathway of arterial blood through the renal blood vessels. The
pathway includes the renal artery, interlobar arteries, arciform arteries,
interlobular arteries, afferent arterioles, glomerular capillaries, efferent arterioles,
and peritubular capillaries.
2. Discuss the flow of venous blood, which corresponds generally to the arterial
pathways.
3. Describe the renal vein as it joins the inferior Venn cava.
Application Question(s)
1. Ask students to develop a flowchart depicting the pathway of blood through the
kidney and nephron, beginning with the renal artery and ending with the renal
vein.
Answer: The flowchart should include the renal artery, interlobar artery, arciform
artery, interlobular artery, afferent arteriole, glomerular capillary, efferent
arteriole, vasa recta and peritubular capillary, interlobular vein, arciform vein,
interlobar vein, and renal vein.
Critical Thinking Issue(s)
1. Following a streptococcal infection, a child has demonstrated the following signs
and symptoms: hematuria, azotemia, fluid retention, oliguria, and minimal
proteinuria. These manifestations appear to be the result of glomerular damage,
which has led to a reduction in glomerular filtration. What condition should be
further investigated?
Answer: A discussion of nephritic syndrome should provide insight into this
issue.
LEARNING OBJECTIVE 5: Describe a nephron and explain the functions of its major
parts.
Lecture Suggestions and Guidelines
1. Describe the nephron as the functional unit of the kidney.
2. Describe the structure of the renal corpuscle and renal tubule.
3. Discuss the structure and function of the juxtaglomerular apparatus.
4. Compare the cortical and juxtamedullary nephrons.
5. Reiterate the blood supply mechanism of a nephron.
Application Question(s)
1. Provide students with a diagram of a nephron and ask them to correctly label it.
Answer: The diagram should include the glomerulus, glomerular capsule,
proximal convoluted tubule, efferent and afferent arteriole, distal convoluted
tubule, interlobular vein and artery, peritubular capillary, nephron loop and
collecting duct.
Critical Thinking Issue(s)
1. Describe acute glomerulonephritis.
Answer: The glomeruli become very permeable which may lead to hematuria,
albuminuria, and casts. Oliguria may occur. The patient often experiences chills
and fever, weakness, and edema. The cause of acute glomerulonephritis is
commonly a previous streptococcal infection. This condition may also lead to
uremia and eventual kidney failure. The prognosis is generally good.
LEARNING OBJECTIVE 6: Explain how glomerular filtrate is produced and describe
its composition.
and
LEARNING OBJECTIVE 7: Explain how various factors affect the rate of glomerular
filtration and how this rate is regulated.
Lecture Suggestions and Guidelines
1. Give an overview of the process of glomerular filtration.
2. Describe the hydrostatic pressure and osmotic pressure, which affect filtration.
3. Comment on the composition of filtrate.
4. Discuss variations in filtration rate as they relate to pressure, arteriole diameter,
and capillary surface area.
5. Describe the effects of sympathetic nerve activity on glomerular filtration rate.
6. Define autoregulation.
Application Question(s)
1. Compare the normal concentrations of various plasma, glomerular filtrate, and
urine components.
Answer: Responses should include a discussion of sodium, potassium, calcium,
magnesium, chloride, bicarbonate, sulfate, phosphate, glucose, urea, uric acid, and
creatinine.
Critical Thinking Issue(s)
1. Describe the effects of angiotensinogen on the regulation of the rate of glomerular
filtration.
Answer: Angiotensinogen reacts to form angiotensin I which is subsequently
converted to angiotensin II. Angiotensin II is a vasoconstrictor, increases
aldosterone secretion, increases ADH secretion, and increases thirst.
LEARNING OBJECTIVE 8: Discuss the role of tubular reabsorption in urine
formation.
and
LEARNING OBJECTIVE 9: Explain why the osmotic concentration of the glomerular
filtrate changes as it passes through a renal tubule.
Lecture Suggestions and Guidelines
1. Discuss the selective reabsorption process.
2. Explain why the peritubular capillary is adapted for reabsorption.
3. Describe how various substances, for example, glucose, water, and proteins,
utilize different modes of transport during reabsorption.
4. Discuss events, which occur when the concentration of a substance in the filtrate
exceeds its renal plasma threshold.
5. Describe the reabsorption of sodium ions.
Application Question(s)
1. What is the effect of diabetes mellitus on renal plasma threshold?
Answer: The limited transport capacity is overloaded due to an excess number of
glucose molecules. More glucose molecules remain in the filtrate, having driven
the renal plasma threshold to a critical level. The excess glucose molecules “spill
over” into the urine and are excreted.
Critical Thinking Issue(s)
1. Ask students to explain the process of water reabsorption by osmosis.
Answer: This process can be condensed into four major steps: 1) the reabsorption
of sodium and potassium ions; 2) the passive transport of ions due to the attractive
forces of positively and negatively charged particles; 3) increased osmotic
pressure as a result of an increased concentration of solute in the plasma; and 4)
the movement of water via osmosis from the renal tubule to the capillaries.
LEARNING OBJECTIVE 10: Describe a countercurrent mechanism and explain how
it helps concentrate urine.
Lecture Suggestions and Guidelines
1. Discuss how the vasa recta countercurrent mechanism helps maintain sodium
chloride concentration.
2. Discuss the effects of ADH on permeability.
3. Define urea and uric acid. Explain their reabsorption mechanisms.
Application Question(s)
1. Compare and contrast the functional differences of the ascending and descending
limbs of the nephron loop.
Answer: The ascending limb is relatively thick, impermeable to water, and
absorbs sodium, chloride, and potassium ions. The descending limb is relatively
thin, permeable to water, and impermeable to solutes.
Critical Thinking Issue(s)
1. Discuss the role of ADH in regulating urine concentration and volume.
Answer: Ask the students to develop a set of six index cards, each of which
summarizes a sequential step in the regulation of urine concentration and volume
by ADH. Shuffle the cards and allow students to place them in the correct
sequence.
LEARNING OBJECTIVE 11: Define tubular secretion and explain its role in urine
formation.
Lecture Suggestions and Guidelines
1. Define tubular secretion and describe its function.
2. Discuss mechanisms by which various substances are secreted. Examples include
organic compounds, hydrogen ions, and potassium ions.
3. Review the process of active and passive transport.
Application Question(s)
1. What are white blood cell casts and what conditions might they indicate?
Answer: Generally, urinary casts are protein coagulum formed in renal tubules,
which are subsequently visible in urine. One type of cast appears densely packed
with white blood cells and is often indicative of acute or chronic
glomerulonephritis.
Critical Thinking Issue(s)
1. Discuss the role of renal tubular secretion in the regulation of the pH of body
fluids.
Answer: The renal tubules will increase their secretion of hydrogen ions into the
urine as the concentration of hydrogen ions in body fluids increases. This concept
is discussed in detail in Chapter 21.
LEARNING OBJECTIVE 12: Describe the structure of the ureters, urinary bladder,
and urethra.
Lecture Suggestions and Guidelines
1. Review the location, structure, and function of the ureters.
2. Describe the length and diameter of the ureters. Describe the walls of smooth
muscle, the rate of contraction, and the prevention of backflow.
3. Review the location, structure, and function of the urinary bladder.
4. Describe three openings, which form the trigone. Describe the three layers, which
form the bladder wall and the bladder’s ability to expand.
5. Review the location, structure, and function of the urethra.
6. Describe the internal and external urethral sphincters.
7. Compare the structure of the female and male urethra.
Application Question(s)
1. What conditions might a cystoscopy reveal?
Answer: A cytoscope is an instrument used by a physician to directly visualize
the urinary tract via the urethra. A cystoscopy may reveal the presence of urinary
calculi, polyps, tumors, etc.
Critical Thinking Issue(s)
1. Discuss the manifestations of pyelonephritis.
Answer: Pyelonephritis, (PN), is a suppurative inflammation of the kidney, renal
pelvis, and ureter. It is usually due to an infectious agent transported through the
blood, lymph, or lower urinary tract. PN predisposes the patient to urinary tract
infections caused by urinary stagnation. Kidney tissues may be damaged.
Symptoms include chills, fever, back pain, dysuria, pyuria, and hematuria.
LEARNING OBJECTIVE 13: Discuss the process of micturition and explain how it is
controlled.
Lecture Suggestions and Guidelines
1. Describe the roles of the internal and external urethral sphincters.
2. Describe the activation of stretch receptors caused by bladder distension.
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3. Discuss the role of nerve impulses from the sacral region in facilitating bladder
reflex contractions.
4. Describe incontinence and urinary retention.
Application Question(s)
1. a. Ask students to make eight labels, each of which is a summary of one major
event of micturition. Paste the labels randomly on a sheet of paper and have
students draw arrows labeled with numbers, which reflect the correct sequence of
events.
Answer: The eight major events include distension of the urinary bladder,
stimulation of the micturition center, nerve impulses which stimulate the detrusor
muscle, urethral sphincter contraction, impulse generation from the pons and
hypothalamus, detrusor muscle contraction, muscle relaxation and reflex center
fatigue.
Critical Thinking Issue(s)
1. Discuss possible causes of incontinence.
Answer: Causes include: loss of external sphincter control, undeveloped control
of the external sphincter, stress or emotional trauma, pregnancy due to physical
pressure, stroke, deep sleep, or injury to the spinal cord.
LEARNING OBJECTIVE 14: Describe how the components of the urinary system
change with age.
Lecture Suggestions and Guidelines
1. Describe the kidney’s structural changes that occur both externally and internally.
2. Discuss the reasons for kidney shrinkage.
3. Identify the circulatory changes that accompany age.
Application Question(s)
1. Ask students to prepare a report that addresses the physiological and
psychological effects of incontinence. Interview some elderly adults in order to
collect relevant information.
Answer: Responses will vary, but should ensure patient confidentiality.
Critical Thinking Issue(s)
1. Ask students to develop a community education plan that would be of value in
educating the elderly population about life-changes that occur with growing older.
Include information about changes in the urinary system.
Answer: Recommendations will vary.
RELATED DISEASES OF HOMEOSTATIC INSTABILITY
1. Acute Glomerulonephritis—A degenerative inflammation of the glomeruli caused
by an antigen-antibody reaction. The glomeruli become very permeable, resulting
in hematuria, albuminuria, and protein/blood casts. The cause appears to be
related to a previous streptococcus infection.
2. Pyelonephritis—Suppurative inflammation of the kidney and renal pelvis, and the
expanded upper end of the ureter. It is usually due to an infectious agent, such as
E. coli, streptococcus, or staphylococcus infection. Kidney tissue may be
damaged or atrophy.
3. Renal Calculus—Commonly referred to as a “kidney stone,” it is a solid mass
formed by precipitation of salts. These salts are often composed of calcium
oxalate or calcium phosphate. Smaller stones can be passed; larger stones may
require medication, lithotripsy, or surgery.
SUGGESTIONS FOR ADDITIONAL READING
Culliton, Barbara J. May 5, 1994. Hubert Humphrey’s bladder cancer. Nature, vol. 369.
The former vice president died of bladder cancer in 1978. Genetic techniques applied
in 1994 reveal that his cancer was present years before he was diagnosed.
Flieger, Ken. March 1990. Kidney disease: When those fabulous filters are foiled. FDA
Consumer. Drugs, devices, and transplants can restore vital kidney function.
Lewis, Ricki. June 1990. Wilm’s tumor: The genetic plot thickens. Journal of NIH
Research. Unraveling a childhood kidney cancer reveals how this complex organ
develops.
Lewis, Ricki. April 1994. IL-2 and kidney cancer. FDA Consumer. IL-2 offers hope to
kidney cancer patients.
Luke, R. G. August 11, 1994. New issues in therapy after renal transplantation. New
England Journal of Medicine, vol. 331. Drug therapy must follow a kidney transplant,
to prevent rejection.
Seppa, Nathan. January 11, 2003. Determined at birth? Kidney makeup may set
hypertension risk. Science News, vol. 163, no. 2, pg. 19.