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Flashcards in Renal Deck (50)
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1

Patients with renal artery stenosis may present with very high blood pressures due to increased renin secretion. Which of the following structures in the kidney is responsible for sensing inadequate perfusion and secreting renin?

Afferent arteriole

The juxtaglomerular (JG) cells in the afferent arteriole and the macula densa in the distal convoluted tubule together make up the JG apparatus, which is responsible for controlling renal blood fl ow via renin release. In renal artery stenosis, the blood fl ow to the kidney is low. This low pressure is detected by JG cells in the afferent arteriole that secrete renin to raise blood pressure and renal perfusion through the renin-angiotensin system.

2

A 48-year-old man is hospitalized for shock after massive blood loss in a motor vehicle accident. On the patient’s second day in the hospital, his blood urea nitrogen (BUN) and creatinine levels begin to rise and he develops pitting edema to his knees. A subsequent urinalysis shows numerous granular casts. Which of the following is the most appropriate treatment?

Fluids and dialysis

This man’s history indicates that he is suffering from acute tubular necrosis secondary to ischemia of the epithelial cells of the proximal convoluted tubule. Granular casts on urinalysis is also a signifi cant sign that this is acute tubular necrosis. These cells, given their high metabolic rate, are par-ticularly sensitive to a drop in blood pressure such as that experienced in hemorrhagic shock. In this patient, the immediate therapeutic plan is to correct the fl uid and electrolyte imbalance. The fl uid replacement should include both crystalloid (eg, normal saline, lactated Ringer’s) and blood products due to the severity of blood loss. If recovery of renal function is delayed or if the kidneys never fully recover, dialysis is indicated. The epithelium will usually regenerate in a few weeks

3

A 64-year-old man with a medical history signifi cant for hypertension, hypercholesterolemia, and coronary artery disease comes to the emergency department because of blood in his urine, nausea, and vomiting. Urinalysis reveals reddish-colored urine with no RBCs, but is positive for granular casts and protein. A basic metabolic panel shows highly elevated BUN and creatinine levels with a BUN:creatinine ratio of 10:1, as well as severe uremia. He is declared to be in acute renal failure and placed on dialysis. This patient has recently started a new drug prescribed by his family physician. Which of the following is the most likely cause of this patient’s renal failure?

A statin drug

This man is suffering from acute tubular necrosis (ATN), which is shown by the granular casts in his urine. A documented adverse effect of statin drugs is that they can cause rhabdomyolysis, or the destruction of skeletal muscle with subsequentexcretion of myoglobin by the kidneys. Myoglobin is nephrotoxic and, in signifi cant amounts, may lead to ATN (also a common complication of crush injuries). There is no hemoglobin in the urine; myoglobin is causing the urine to turn red.

4

Respiratory acidosis is a major complication in morphine overdoses. Which of the following laboratory data correspond to a pure respiratory acidosis?

pH: 7.2 Pco2: 68 HCO3-: 25 Na+: 140 Cl-: 104

Hypoventilation causes an inability on the part of the lungs to excrete the CO2 the body produces, leading to retention of CO2. This causes a drop in pH and a compensatory retention of bicarbonate. These acid-base abnormalities are consistent with respiratory acidosis. Hypoventilation (from a variety of etiologies) is a primary cause of respiratory acidosis.

5

Monitoring acid-base status is very important in individuals with kidney pathology. Which of the following diuretics causes metabolic alkalosis?

Loop diuretics and thiazides

Thiazides and furosemide lead to metabolic alkalosis. There are two components to the development of metabolic alkalosis: volume depletion and electrolyte imbalance; specifi cally hypochloremia and hypokalemia. Volume contraction leads to increased sodium reabsorption and bicarbonateretention. The diuretic-induced hypochloremia and hypokalemia lead to persistence of the alkalosis because the hypokalemia causes hydrogen to be exchanged for sodium rather than potassium at the distal convoluted tubule.

6

A 25-year-old man comes to the emergency department with bloody sputum. A few weeks later he progresses to renal failure with signifi - cant hematuria and hypertension. A renal biopsy shows linear immunofl uorescence. Which of the following types of hypersensitivity reaction is this patient experiencing?

Type II hypersensitivity

This patient has Goodpasture’s syndrome, which is an autoimmune disease involving the formation of antibodies to the alveolar and glomerular basement membranes. This is an example of a type II hypersensitivity reaction in which antibody binds to antigen on a cell, leading to lysis by complement or phagocytosis. It is one of the several forms of rapidly progressive (or crescentic) glomerulonephritis. Patients are usually menin their 20s presenting with a history of hemoptysis and nephritic renal failure that is associated with crescent formation. Since the damage in this disease is caused by the actions of antibodies to the basement membrane, diagnosis is made by immunofl uorescence, which shows a smooth linear staining along the basement membrane.

7

A 7-year-old boy with nephrotic syndrome is brought by ambulance to the emergency department with altered mental status. His mother reports that this morning he had diffi - culty moving the right side of his body, and that she couldn’t arouse him from an afternoon nap. On physical examination the patient is obtunded and has absent right-sided movement. His prothrombin time is 12 seconds. CT of the brain is shown in the image. What is the most likely etiology of this patient’s symptoms?

Decreased antithrombin III levels

This patient is suffering from a massive left-sided stroke that occurred secondary to a hypercoagulable state. Patients with nephrotic syndrome are at increased risk for thromboembolic events due to renal losses of antithrombin III, protein C, and protein S, all of which normally function as anticoagulants. Patients with nephrotic syndrome also commonly have other factors contributing to a hypercoagulable state, including hemoconcentration, increased fi brinogen, and thrombocytosis. Mental status or neurologic changes in patients with nephritic syndrome should be taken very seriously

8

A 28-year-old woman who is 6 months pregnant presents to the emergency department with a temperature of 38.2° C (100.8° F) and complains of shaking chills and pain on her right side, which she locates by pointing to the area above her right iliac crest. During the examination she is tender to percussion at the junction of the lower ribs and the thoracic vertebrae. Urinalysis reveals WBC casts. Which of the following is the most likely diagnosis?

Pyelonephritis 

Pyelonephritis is infection of the kidneys by an ascending infection from the lower urinary tract, most often caused by Escherichia coli from the periurethral/perianal area. The classic symptoms are fever, chills, fl ank pain, and costovertebral angle tenderness, all of which are demonstrated by this patient. Casts indicate that the origin of the WBCs is the kidney, which confi rms the clinical suspicion of pyelonephritis.

9

A 64-year-old man presents to his primary care physician for a routine physical. He is in good health, smokes half a pack of cigarettes a day, and has no concomitant medical problems. However, he tells the physician that he has been diagnosed with hypertension in the past. In the course of the physical examination, the physician notes a blood pressure of 160/100 mm Hg and 1+ pitting edema to his knees. The physician also notes bilateral bruits when auscultating the abdomen. Which of the following is contraindicated in this patient’s care?

Angiotensin-converting enzyme inhibitor

This patient is most likely suffering from bilateral renal artery stenosis, which is indicated on physical exam by renal bruits. Stenosis of the renal arteries leads to a decrease in perfusion of the kidney and therefore a drop in intraglomerular pressure and glomerular fi ltration rate (GFR). The underperfused kidneys respond by the activation of the renin-angiotensin-aldosterone system. With angiotensin-converting enzyme (ACE) inhibitors, the vasoconstrictive effect of angiotensin II on the ability of the efferent arterioles to increase effective GFR will be abolished. ACE inhibitors should be avoided in patients with renal stenosis due to deterioration of renal function.

10

A 2-month-old infant is found to have a horseshoe kidney. Which structure prevents this abnormal kidney from occupying its appropriate position?

Inferior mesenteric artery

A horseshoe kidney forms when the inferior poles of two kidneys fuse during development. As the kidneys rise from the pelvis, they encounter the inferior mesenteric artery and cannot rise to the normal level in the abdomen. These patients are typically asymptomatic if they have no other abnormalities.

11

A 23-year-old man is beginning chemotherapy for leukemia when he develops severe intermittent left fl ank pain that soon migrates to the pelvis. Three days later, the patient’s creatinine level rises and he is diagnosed with acute renal failure. His fractional excretion of sodium is >4% with a urine osmolality of <350 mOsm/ kg. Blood and urine cultures are negative for bacteria and eosinophilia. An abdominal radiograph fails to locate any pathology. Which of the following is the most likely location of the lesion causing this patient’s renal failure?

Urethra

The history of being started on chemotherapy for leukemia is strongly suggestive of tumor lysis syndrome, which occurs when leukemic cells are lysed, releasing potentially toxic contents including potassium, phosphate, and uric acid. Uric acid stones are radiolucent, so they may not appear on x-ray fi lms. It is likely that this patient’s presentation has been caused by a kidney stonethat has passed into the left ureter and now into the urethra, causing postrenal failure. The FENa >4% is consistent with postrenal failure.

12

A 68-year-old white woman recovering from a total hip replacement following a fall at home is administered ketorolac for the management of pain. Twenty-four hours later, her urine production decreases, and her serum BUN and creatinine levels rise to 44 mg/dL and 3.1 mg/ dL, respectively. Which of the following describes the mechanism through which nonsteroidal anti-infl ammatory drugs, such as ketorolac, cause acute renal failure?

Inhibition of renal prostaglandin production and constriction of the afferent arteriole

Renal prostaglandin synthesis produces a vasodilatory effect on the afferent arterioles, while angiotensin II vasoconstricts primarily efferent arterioles. Nonsteroidal anti-infl ammatory drugs (NSAIDs) inhibit renal prostaglandin synthesis, resulting in an inability of afferent arterioles to dilate. Without adequate afferent arteriolar vasodilation, the GFR is reduced and acute renal failure ensues. The BUN:creatinine (BUN:Cr) ratio in the question stem is consistent with an intrinsic cause of renal failure, which would also be consistent with renal failure secondary to NSAIDs.

13

A 56-year-old man with a 60 pack-year smoking history and normal fl uid intake presents to his physician with 2 months of fatigue and weakness accompanied by cough and mild dyspnea. The patient’s vital signs are normal, but a lower left lobe mass is noted on x-ray of the chest. Biopsy leads to the diagnosis of small cell carcinoma. Laboratory tests show: Plasma Na+: 125 mEq/L

Plasma K+: 3.9 mEq/L

Plasma CO2: 24 mEq/L

Plasma osmolality: 253 mOsm/L

Urine Na+: 48 mEq/L

Urine osmolality: 280 mOsm/L

The hormone most likely responsible for this patient’s abnormal laboratory values has which of the following direct effects?

Activation of V2 receptors results in the insertion of aquaporins into the renal collecting duct; activation of V1 receptors leads to an increase in total peripheral resistance

In healthy people, osmoreceptors in the wall of the third ventricle sense increased body fl uid osmolarity and trigger the release of ADH from the posterior pituitary. ADH exerts its main effects on the V2 receptors located in the principal cells of the late distal tubule and collecting duct, where a Gs protein-coupled mechanism directs the insertion of aquaporin water channels into the luminal wall. These channels are permeable only to water and result in a reabsorption of water, concentration of urine, and dilution of body fl uids. Activation of the V1 receptor found in the vascular smooth muscles results in activation of Gq protein second-messenger cascade and contraction of vascular smooth muscle, leading to an increase in total peripheral resistance. In patients with the syndrome of inappropriate ADH secretion (SIADH), which can be caused by central nervous system disturbances (e.g., stroke, hemorrhage, infection), small cell lung carcinoma, intracranial neoplasms, and occasionally by pancreatic tumors, the unregulated release of ADH leads to the persistent excretion of concentrated urine high in sodium. This causes hyponatremia and decreased serum osmolality without potassium or acid-base disturbances.

14

A 24-year-old man who is in the hospital for treatment of a severe gram-negative infection subsequently becomes oliguric. He is also having diffi culty hearing the hospital staff. Laboratory studies show elevated BUN and creatinine levels. Which of the following is the most likely cause of this patient’s symptoms?

Gentamicin

This patient is in the early stages of renal failure with symptoms of oliguria and elevated BUN and creatinine levels. Combined with the patient’s reduced hearing, these symptoms represent the ototoxicity and nephrotoxicity seen with aminoglycoside administration. Gentamicin is a type of aminoglycoside.

15

A 50-year-old man with a history of large bowel obstruction is diagnosed with colon cancer and undergoes resection of his colon. He returns to his physician for his regular checkup and complains that in the past 3 weeks he has not been feeling well and has noticed signifi cant swelling of his legs. On physical examination, the physician notes 2+ pitting edema and a blood pressure of 155/94 mm Hg. Urinalysis shows 4+ protein with no RBCs or casts. The patient has otherwise been healthy. Which of the following would most likely be present on a kidney biopsy from this patient?

A spike-and-dome pattern of deposition on electron microscopy

This vignette describes a nephrotic syndrome. Spike-and-dome deposits are only found in membranous glomerulonephritis. Membranous glomerulonephritis is an immune complex-mediated disease. Immunofl uorescence shows a granular pattern of IgG and complement along the basement membrane. Membranous glomerulonephritis is the most common cause of adult-onset nephrotic syndrome. Patients with this disease normally present with a nephrotic picture of generalized edema due to massive loss of albumin and proteins

16

A 35-year-old woman presents to the emergency department after experiencing the acute onset of right fl ank pain and fever. Laboratory results show white cell casts in the urine. Which of the following is the most prominent cell type found in the infi ltrate of the involved organ?

Polymorphonuclear leukocytes

The presence of white cell casts in the urine indicates that this is acute pyelonephritis and not just a lower urinary tract infection (UTI). Pyelonephritis is an acute infection of the renal parenchyma that most often results from an ascending progression of a UTI from the bladder. This most frequently involves Escherichia coli. Other clinical manifestations of a UTI include dysuria, urinary frequency, hematuria, bacteriuria, and pyuria. If white blood cell casts are seen, implying involvement of the kidney, the clinician can be sure that the UTI has ascended, making it a case of pyelonephritis. Acute pyelonephritis, like most acute phases of infl ammation, is characterized by a predominance of polymorphonuclear leukocytes

17

A 67-year-old woman with osteoporosis is given a diuretic to treat her hypertension. This particular diuretic has the adverse effect of limiting calcium excretion by the kidney. Referring to the image, where along the nephron does this drug act?

E.

The only diuretics that specifi cally limit calcium loss are the thiazides. They act in the early distal tubule, which is marked as region E in the image.

18

A 22-year-old college student is brought to the emergency department after he began complaining of ants crawling over his body and his friends noted increasing agitation and threatening gestures. On physical examination he is febrile, restless, and tachycardic, and his pupils are markedly dilated. Appropriate treatment would most likely include which of the following?

Acidifying urine to increase renal clearance

This patient is suffering an acute overdose of amphetamine. He should be treated with ammonium chloride to acidify his urine and increase renal clearance of the weak base. This phenomenon, called ion trapping, occurs because increasing the ratio of ionized to nonionized drug species in the renal tubule allows more of the drug to be retained in the urine and excreted. Weak bases in acidic environments have high ratios of ionized species, which are water soluble and do not cross membranes. When urine is acidifi ed, the levels of ionized amphetamine are high, and therefore more drug is trapped in the renal tubule.

19

A 19-year-old woman with a severe gastrointestinal infection presents to the emergency department with a 5-day history of vomiting and diarrhea. Serum chemistry tests show:

Na+: 138 mEq/L

K+: 3.0 mEq/L

Cl–: 88 mEq/L

HCO3 –: 21 mEq/L 

BUN: 10 mg/dL

Creatinine: 0.8 mg/dL

Glucose: 101 mg/dL

Arterial blood gas analyses shows a pH of 7.38, partial arterial carbon dioxide pressure of 37 mm Hg, partial arterial oxygen pressure of 82 mm Hg, and an oxygen saturation of 96% on room air. Which of the following statements is most accurate regarding this patient’s acid-base status?

She has a mixed metabolic alkalosis and metabolic acidosis

While this patient’s pH, bicarbonate, and carbon dioxide levels are all very close to normal, it is always important to look more closely before concluding that there is no disorder. Vomiting is a common cause of a metabolic alkalosis, while diarrhea is a common cause of non-anion-gap metabolic acidosis. The patient has had gastrointestinal symptoms that have led to acute dehydration, which indicates that these symptoms are probably quite severe. It is also important to look at the serum chemistry. One would expect a hypokalemic hypochloremic metabolic alkalosis from vomiting, but only the electrolyte defi - ciencies are present. The equalized pH suggests that the patient is losing an equal amount of acid through vomiting as she is base through diarrhea. Therefore, it is more likely that she has a mixed acid-base disorder than no electrolyte imbalances at all.

20

A 59-year-old woman with type 2 diabetes mellitus comes to her primary care physician for a routine visit. Her creatinine level has been slowly increasing over the last decade due to poor compliance with her medical regimen. If her renal disease were to progress, she would be at risk for developing which of the following conditions? 

Osteomalacia

Osteomalacia occurs in renal failure due to the kidney’s inability to maintain its normal vitamin D production. Chronic renal failure is a common complication in noncompliant diabetic patients. Chronic renal failure results in the progressive loss of renal function, eventually leading to end-stage renal disease. In chronic renal failure, the kidneys are unable to keep up their normal excretory, metabolic, and endocrine functions. The abnormalities include accumulation of toxins, underproduction of hormones (vitamin D and erythropoietin), and increased release of renin. Symptoms and clinical abnormalities associated with chronic renal failure include edema, hyperkalemia, metabolic acidosis, hyperphosphatemia, hypocalcemia, renal osteodystrophy, hypertension, pulmonary edema, congestive heart failure, uremia, anemia, nausea, vomiting, peripheral neuropathy, and pruritus. The pathogenesis of osteomalacia in patients with chronic renal disease is caused by failure of the kidney to turn 25(OH)D into the active form 1,25(OH)2D. Without active vitamin D, there is impaired mineralization of bone, leading to renal osteodystrophy

21

A 16-year-old boy comes to the physician with a 1-year history of intermittent, painless hematuria without dysuria or increased frequency of micturition. He says he has also had several respiratory infections and adds that the hematuria increased within several days of the infections. Which of the following is most likely to be found if the boy is diagnosed with IgA nephropathy (Berger’s disease)?

Mesangial deposits

IgA nephropathy (Berger’s disease) presents within several days of an infection (as opposed to poststreptococcal glomerulonephritis, which presents weeks after) with a nephritic picture due to IgA deposition in the mesangium. It is the most common global nephropathy, but it is a mild disease. It is common in children and presents as a recurrent hematuria with minimal clinical signifi - cance. On immunofl uorescence, it presents with nonlinear mesangial deposits of IgA. Treatment is with angiotensin-converting enzyme inhibitors and corticosteroids. Patients with IgA nephropathy have a risk of recurrence of the disease.

22

A 34-year-old woman comes to the hospital to deliver a full-term infant. The labor is complicated by an amniotic fl uid embolism, and subsequent blood tests show the presence of fi brin split products. The next day the patient abruptly develops anuria, gross hematuria, and fl ank pain accompanied by rapidly increasing BUN and creatinine levels and a new cardiac friction rub. The patient’s CT scan demonstrates hypodensities within the renal cortex. Which of the following is the correct treatment?

Dialysis

This patient has diffuse cortical necrosis: generalized infarctions of the cortices of both kidneys, which is a common complication of disseminated intravascular coagulation (DIC). DIC commonly occurs after a complication of pregnancy such as amniotic fl uid embolus and placental abruption, and affected patients develop the abrupt onset of the triad of anuria, gross hematuria, and fl ank pain. The diagnosis can usually be established by ultrasonography, which will demonstrate hypodense areas in the renal cortex. Although many patients can be sustained on dialysis, only 20%–40% have partial recovery of kidney function. Indications for acute dialysis in DIC include (1) acidosis refractory to bicarbonate, (2) severe electrolyte abnormalities refractory to medical intervention (especially high potassium levels), (3) intoxication with some drugs, (4) volume overload refractory to diuretics, and (5) uremic symptoms (e.g., cardiac friction run, altered mental status). The fact that this patient has a new-onset pericardial friction rub indicates uremia and makes dialysis imperative.

23

A 40-year-old man presents to his physician with sharp, sudden, sporadic pain in his lower back and hematuria. His blood pressure is normal and his physical examination is signifi cant for fl ank pain. A plain fi lm of the pelvis doesnot show any renal calculi. Which of the following is the most likely cause of this man’s symptoms?

Hyperuricemia

Normally hyperuricemia leads to kidney stones that are radiolucent and therefore not seen on x-ray. These stones are often seen in the setting of diseases with increased cell proliferation and turnover, such as leukemia and myeloproliferative disorders. Remember that uric acid is a metabolite of nucleic acid turnover, which is heightened in the setting of cell destruction

24

Angiotensin II (AT II) stimulates the Na+-H+ exchanger in the proximal tubule. How does this affect the handling of HCO3 – and H+ in the proximal tubule?

D. Net HCO3- resorption increases and no efffect for H+ resorption

Angiotensin II (AT II) increases the activity of the Na+-H+ exchanger in the proximal tubule to facilitate salt and water resorption. As a result, increased H+ is pumped into the tubular lumen. Luminal H+ is then returned to the tubular cell in the process of HCO3 – resorption as H+ and HCO3 – join and form water and carbon dioxide after catalysis by brush border carbonic anhydrase. Water and carbon dioxide diffuse back into the tubular cell and again liberate H+ and HCO3 – after carbonic anhydrase catalysis. Here, the HCO3 – is transported into the bloodstream while the H+ is free to participate in another round of HCO3 – resorption via the Na+-H+ exchanger. Thus, the net result of increased Na+- H+ exchange is an increase in HCO3 – resorption and no net change in H+ secretion. Increased HCO3 – reabsorption after AT II stimulation accounts for the contraction alkalosis that occurs as a result of volume depletion

25

A patient is recovering at the hospital from a suspected bacterial pneumonia. Over the course of a few days he develops fever, rash, dysuria, and urinary urgency. Urinalysis shows a specifi c gravity of 1.001 with hematuria and mild proteinuria. Renal biopsy shows partial effacement of the tubulointerstitial structures with pronounced edema and infi ltration of the interstitium with polymorphonuclear leukocytes, eosinophils, and lymphocytes with papil-lary necrosis. What is most likely to have caused this condition?

Antibiotics 

Given the patient’s fever, rash, loss of urine concentrating ability (low specifi c gravity of urine), and biopsy fi ndings, this patient most likely has acute interstitial nephritis. Acute interstitial nephritis has a variety of causes, but by far the most common is drugs, which include antibiotics such as β-lactams, sulfonamides, quinolones, and rifampin; anticonvulsant drugs; infection with certain strains of bacteria (Streptococcus, Staphylococcus, Legionella); and viruses (Epstein-Barr virus, cytomegalovirus, HIV).

26

A 56-year-old woman who has been taking cefoxitin for treatment of Klebsiella pneumonia is found to still have Klebsiella organisms in her blood 1 week after beginning treatment. Another drug is added to the patient’s regimen. Two days later, laboratory tests show:

Na+: 141 mEq/L

K+: 4.3 mEq/L

Cl–: 102 mEq/L

HCO3 –: 24 mEq/L

BUN: 65 mg/dL

Creatinine: 4.4 mEq/L

Which of the following medications was most likely added to this patient’s regimen?

Tobramycin

On its own, tobramycin, an aminoglycoside, can cause nephrotoxicity. However, when combined with a cephalosporin (such as cefoxitin), the nephrotoxic effects are greatly increased. Renal failure is refl ected by the elevated creatinine level.

27

A -year-old boy is brought to the emergency department with complaints of fever, chills, and fl ank pain. His immunizations are up to date and his mother states that this is the second time he has been seen because of these symptoms. His temperature is 39.1° C (102.2° F) and physical examination is unremarkable except for costovertebral angle tenderness on the right. A complete blood cell count shows leukocytosis, and urinalysis demonstrates the presence of WBCs and RBCs in the urine. What is the most likely mechanism of this patient’s recurrent complaints?

Vesicoureteral reflux

This patient presents with pyelonephritis, which is characterized by costovertebral angle tenderness, fever, and chills. Symptoms of lower UTI may also be present, such as dysuria, increased frequency of urination, and urgency. The onset of symptoms of pyelonephritis often occurs approximately 1 week after the onset of a lower UTI. In children, recurrent UTIs suggest an anatomic abnormality and warrant further investigation. Lower UTIs may ascend to the kidneys through incompetent ureterovesical sphincters, leading to pyelonephritis, dilatation of the ureters, and renal pelves, potentially causing renal scarring. Thus urologic repair is often recommended to prevent renal damage in children with vesicoureteral refl ux.

28

ADH exerts its effects on the collecting ducts of the kidney. Which of the following best characterizes ADH activity, as depicted in the image?

Binds at F and activates Gs -mediated cyclic adenosine monophosphate cascade

ADH binds V2 receptors on the basolateral side of the principal cell and activates a Gs -mediated cyclic adenosine monophosphate cascade. The fi nal result is that aquaporin transmembrane channels, previously sequestered within intracellular vesicles, are mobilized to the luminal surface of the cells. Net water movement may now occur from the collecting duct lumen to the hyperosmolar interstitium, decreasing urine output and conserving volume.

29

A 40-year-old woman presents to the emergency department after a 5-day course of profuse vomiting. She has a history of rheumatoid arthritis, which is treated with celecoxib. She complains of joint pain at present. Which of the reasons below describes why celecoxib would be contraindicated in this patient at presentation?

Because of its effects on the arterioles of the kidney

When the amount of fl uids in the body contracts, the body attempts to compensate by releasing angiotensin II, a potent vasoconstrictor. In order to protect the kidney from losing its perfusion due to this vasoconstriction, the kidney simultaneously releases prostaglandins at both the afferent and efferent arterioles, where they act as vasodilators. By inhibiting cyclooxygenase (COX)-1 and/or (COX)-2 enzymes, the pathway that produces the prostaglandins that keep the kidneys perfused becomes blocked, leading to decreased blood fl ow to the kidneys and resulting in a prerenal cause of renal failure. Celecoxib is a selective COX-2 inhibitor that affects the arterioles of the kidney and can cause renal failure in dehydrated patients.

30

A medical student is doing research to measure the effects of newly bioengineered molecules on the function of the glomerulus. Which of the following mechanisms is likely to result in an overall increase in renal blood fl ow?

Stimulation of renal dopamine and bradykinin receptors

Renal blood fl ow is determined by the equation: fl ow = change in pressure/resistance. In the kidney, resistance is provided by the glomerular afferent and efferent arterioles. These arterioles can be modifi ed by a number of endogenous substances and physiologic actions. Dopamine has a selective action such that low levels dilate cerebral, cardiac, splanchnic, and renal arterioles. Similarly, bradykinin induces the vasodilation of arterioles. The combined actions of these substances act to reduce resistance and thus increase renal blood fl ow