Case Study, Porth
Chapter 30, Structure and Function of the Kidney
Rivka is an active 21-year-old who decided to take a day off from her university classes. The
weather was hot and the sun bright, so she decided to go down to the beach. When she arrived,
she found a few people playing beach volleyball, and they asked if she wanted to join in. She put
down her school bag and began to play. The others were well prepared for their day out and
stopped throughout the game to have their power drinks and soda pop. Several hours after they
began play, however, Rivka was not feeling so good. She stopped sweating and was feeling
dizzy. One player noted she hadn’t taken a washroom break at all during the day. They found a
shaded area for her, and one of the players shared his power drink with her. Rivka was thirstier
than she realized and quickly finished the drink. (Learning Objectives 2, 4, 5, 12)
1.
In pronounced dehydration, hypotension can occur. How would this affect the glomerular
filtration rate of the kidney? What actions by the juxtaglomerular apparatus would occur
to restore GFR?
2.
What is the effect aldosterone has on the distal convoluted tubule? Why would the
actions of aldosterone be useful to Rivka in her situation?
3.
What does a specific gravity test measure? If someone tested the specific gravity of
Rivka’s urine, what might it indicate? Explain your answer.
ANSWERS
1.
The glomerular filtration rate would decrease with a decline in blood pressure. The
juxtaglomerular apparatus participates in renal autoregulation and, when activated,
increases GFR. The process involves the release of renin from the juxtaglomerular cells
found in the afferent arteriole. Renin enters the bloodstream and converts inactive
angiotensinogen to angiotensin I. Angiotension-converting enzyme (from the lungs)
converts angiotension I to angiotensin II, a potent vasoconstrictor of the efferent arteriole
that in turn increases GFR. Angiotensin II also encourages sodium reabsorption by the
proximal convoluted tubule and stimulates aldosterone release by the adrenal glands.
2.
Aldosterone secretion causes sodium reabsorption and potassium secretion at the distal
convoluted tubule. Aldosterone release by the adrenal cortex is stimulated by angiotensin
II and would therefore be a component of water conservation in the dehydrated
individual; when sodium is reabsorbed, an osmotic gradient is created and allows for the
passive reabsorption of water.
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3.
The specific gravity (or osmolality) urine test determines the concentration of solutes in a
urine sample. It can therefore measure both hydration status of the patient and renal
function. Rivka’s urine would be concentrated, and her specific gravity would be high
(perhaps 1.030-1.040). This would reflect a decrease in hydration and water conservation
by the kidneys.
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Case Study, Porth
Chapter 31, Disorders of Fluid and Electrolyte Balance
Amanda is an 18-year-old with anorexia nervosa. She was recently admitted to an eating
disorders clinic with a BMI of 13.9, and although she was a voluntary patient, she was reluctant
about the treatment. She was convinced she was overweight because her clothes felt tight on her.
She complained that even her hands and feet were fat. One of her nurses explained that a protein
in her blood was low. The nurse further explained that, as difficult as it may be to believe, eating
a normal healthy diet would make the “fat hands and feet” go away. (Learning Objectives 6, 8)
1.
What protein do you suspect the nurse was referring to? How would a deficiency in this
protein contribute to edema?
2.
Compare and contrast the physiology of pitting and nonpitting edema.
3.
Because of her weakened condition, Amanda was moved around the ward in a wheelchair
when she wasn’t on bed rest. Explain how this might affect her edematous tissues.
Suggested Answers for Case Study, Porth
Chapter 31, Disorders of Fluid and Electrolyte Balance
1.
Amanda was presenting with low serum albumin. Albumin has a low molecular weight
and high concentration in the plasma, allowing it to create a strong colloidal osmotic
pressure. When albumin levels are decreased, the serum osmotic gradient declines. Fluid
therefore leaves the capillaries to the surrounding interstitial space.
2.
Pitting edema is a result of an increased level of interstitial fluid that exceeds the
absorptive capacity of the tissue gel. The edema is mobile and can shift with pressure.
Nonpitting edema involves the migration of capillary fluid and plasma proteins into the
tissue space. The protein coagulates and creates a firm edema that does not move with
pressure.
3.
Edema increases the distance between tissue cells and circulation. The diffusion of gases,
nutrients, and waste between tissue cells and capillaries is consequently decreased.
Edema can also mechanically compress tissue capillaries. Both situations leave tissues
prone to ischemic damage and, when the patient is immobile, pressure ulcers.
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Case Study, Porth
Chapter 32, Disorders of Acid-Base Balance
Shauna is a healthy, fit 28-year-old who decided to go on a 2-week tour of Mexico for young
singles. One hot afternoon in a small market community, she grabbed some fruit juice from a
street vendor. Several hours later, she developed abdominal cramping and diarrhea. The diarrhea
became so severe that she missed 3 days of the tour and stayed in her hotel room. By the end of
her illness, she felt weak and tired. Her head ached, but the mild fever had disappeared, and she
was able to join her new friends for the rest of the tour. (Learning Objectives 7, 8, 9)
1.
Predict the acid-base imbalance Shauna might have experienced and explain its etiology.
2.
Explain how the body compensates for such a condition.
3.
Describe the function and importance of the bicarbonate buffer system in the body.
Suggested Answers for Case Study, Porth
Chapter 32, Disorders of Acid-Base Balance
1.
Severe diarrhea predisposes an individual to metabolic acidosis. Intestinal secretions are
high in bicarbonate, so the loss of these fluids through prolonged or severe diarrhea
reduces pH levels. In cases of microbial infection, intestinal secretions of bicarbonate are
particularly abundant in an attempt to neutralize the metabolic acids of the pathogen. This
situation further contributes to a loss of base and development of metabolic acidosis.
2.
The immediate compensatory mechanism is an increase in the rate and depth of
respirations. The increased ventilation reduces serum PCO2 and increases pH levels in the
body. Because Shauna’s metabolic acidosis was not caused by renal disease, her kidneys
would respond by increasing H+ secretion and HCO3− reabsorption at the proximal
tubule.
3.
The bicarbonate buffer system uses carbonic acid (H2CO3) to substitute a strong acid and
a bicarbonate salt to substitute a strong base in the maintenance of serum pH levels. The
bicarbonate/carbon dioxide (HCO3−/CO2) system is particularly efficient in buffering pH
levels because of the ability to quickly form these components in the body and eliminate
them as needed.
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Case Study, Porth
Chapter 33, Disorders of Renal Function
Fred, a fit and healthy 44-year-old, was working outside one warm summer afternoon. When he
returned home by the end of the day, his lower back felt sore, and he felt nauseated. His wife
made him dinner, but he wasn’t hungry and chose to go to bed instead. Fred’s symptoms
progressed, and soon he was rolling on the bed with excruciating pain. He said his back hurt as
well as his stomach and groin area. The pain would ease off only to return a short while later,
and when it did, Fred would begin to sweat and run to the bathroom to vomit. His wife became
concerned and started the car. When his symptoms abated, she helped him into the car and
rushed him to the hospital. (Learning Objectives 4, 6, 7)
1.
At the hospital, an abdominal radiograph showed the presence of renal calculi in Fred’s
right ureter (urolithiasis). Outline the mechanism of stone formation in the kidney. What
is the role of citrate in the kidneys?
2.
Why would the administration of calcium supplements be useful for a patient with
calcium oxalate stones?
3.
Hydronephrosis can be a complication of renal calculi. Explain what this condition is.
How does back-pressure occur in a kidney, and what physiologic mechanism is
responsible for nephron damage when back-pressure is present?
Suggested Answers for Case Study, Porth
Chapter 33, Disorders of Renal Function
1.
The formation of renal calculi relies on supersaturated urine, a nidus, and a deficit in
stone inhibitors. Calculi are formed from the particular crystals that are not unbound and
highly concentrated in the urine. These components aggregate around a small nucleus of
organic or inorganic material that acts as an attracting force for stone formation. The
presence of a nidus lowers the level of supersaturation normally needed for the
development of calculi. Citrate, along with magnesium and the Tamm-Horsfall
mucoprotein, acts to inhibit stone formation. Citrate is administered clinically as a means to
prevent the formation of hypocitraturic calculi.
2.
Calcium supplementation encourages the binding of oxalate to calcium in the gut. The
oxalate fails to be absorbed into the bloodstream and is subsequently excreted.
3.
Hydronephrosis occurs when an obstruction causes urine to accumulate in and dilate the
renal pelvis and calices. Backpressure occurs in the kidney when glomerular filtration is
still occurring yet formed urine is unable to leave the kidney because of an obstruction.
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Nephrons suffer mechanical damage from the increased intrapelvic pressure and ischemic
damage from alterations in blood flow.
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Case Study, Porth
Chapter 34, Acute Renal Failure and Chronic Kidney Disease
Will is a 68-year-old male with a history of hypertension. Eight months ago, he started regular
dialysis therapy for ESRD. Before that, his physician was closely monitoring his condition
because he had polyuria and nocturia. Soon it became difficult to manage his hypertension. He
also lost his appetite and became weak, easily fatigued, and edematous around his ankles. Will
debated with his physician about starting dialysis, but she insisted that, before the signs and
symptoms of uremia increased, the treatment was absolutely necessary. (Learning Objectives 5,
6, 7, 9)
1.
Compare and contrast azotemia and uremia.
2.
Two years ago, Will’s physician told him to decrease his protein intake. Despite what she
ordered, Will could not stop having chicken, beef, pork, or eggs at least once a day. Why
did his physician warn him about his diet?
3.
Will’s feelings of weakness and fatigue are symptoms of anemia. Why is he anemic?
4.
Knowing what you do about Will’s history, why is left ventricular dysfunction a concern
for his physician?
Suggested Answers for Case Study, Porth
Chapter 34, Acute Renal Failure and Chronic Kidney Disease
1.
Both azotemia and uremia describe the accumulation of metabolic wastes (normally
excreted as urine) in the blood. Azotemia is the presence of nitrogenous wastes (urea, uric
acid, and creatinine) in the blood and is often asymptomatic. Uremia results when all the
products of urine accumulate in the blood and cause systemic manifestations. Uremia
includes acid-base, electrolyte, and fluid imbalances. Without treatment, uremia results in
multiorgan failure, coma, and death.
2.
In renal sufficiency, the kidneys have difficulty secreting the waste products of protein
metabolism. A low protein diet during this time can slow the progression of renal failure
and decrease the symptoms of uremia.
3.
In renal failure, erythropoietin secretion declines, and red blood cell production falls
below the needs of the body. The life span of RBCs is also shortened because of
accumulation of nitrogenous waste. Finally, if Will’s anorexia was significant, a
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deficiency in dietary iron would also be a factor in the development of his anemic state.
4.
Hypertension increases workload on the left ventricle and increases oxygen demand.
Anemia contributes to left ventricular hypertrophy and ischemic events. Coupled with
extracellular fluid overload, these are all factors in Will’s history that predispose him to
left ventricular dysfunction or congestive heart failure.
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Case Study, Porth
Chapter 35, Disorders of the Bladder and Lower Urinary Tract
Alvita is a frail 89-year-old woman residing in a nursing home. She is able to move slowly around the
residence with the use of a walker, but appreciates when her daughter is there to hold her arm and walk
alongside her. When one of the health care staff changes Alvita, her daughter helps. Alvita’s
incontinence has progressed, particularly during the past 6 years since she has resided in the nursing
home. Alvita isn’t upset about her lack of bladder control, however, and says that her incontinence
really began when she was a young woman, just after the birth of her second daughter. (Learning
Objectives 8, 10)
1.
Alvita’s mobility is limited. How does this affect continence in the elderly?
2.
Shortly after the birth of her second daughter, Alvita experienced mild incontinence, particularly
after laughing or coughing. What was she experiencing? Describe the pathophysiology behind
this type of incontinence.
3.
Explain the physiologic changes in the urinary bladder that occur with age.
Suggested Answers for Case Study, Porth
Chapter 35, Disorders of the Bladder and Lower Urinary Tract
1.
Decreased mobility in the elderly has a significant effect on continence. Those who move slowly
may not make it to the bathroom in time for urination. Arthritic individuals may find it difficult
to move to the bathroom, manipulate door handles, or remove their clothes. If their vision is
failing, it becomes a challenge to navigate to a bathroom, particularly in new surroundings or at
night. Finally, stool impaction, a possibility with decreased mobility, leads to mechanical
pressure on the bladder and subsequent incontinence.
2.
Alvita began to experience stress incontinence after her second delivery. An intact pelvic floor
maintains the position of the bladder in the pelvic cavity and the posterior urethrovesical angle
between the bladder wall and urethra. When childbirth weakens the pelvic floor, the neck of the
bladder descends and “funnels” into the lower pelvis. As it descends, the bladder also tilts
posteriorly and widens the urethrovesical angle. These anatomic changes compromise
continence so that relatively mild increases in intra-abdominal pressure cause urinary leakage.
3.
In the elderly, urge incontinence becomes apparent with hyperactivity and involuntary
contraction of the detrusor muscle. The detrusor also weakens, however, so older individuals
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also tend to have higher PVR volumes. Coupled with a decrease in bladder capacity and urethral
closing pressures, incontinence becomes particularly prevalent in the aged.
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