Prep U: Ch 24: Structure and Function of the Kidney
A new client on hemodialysis is watching his blood being filtered through a dialyzer. He asks the nurse how much blood typically passes through the kidney every minute? The nurse responds:
1000-1300 mL/minute. explanation: In the adult, the kidneys are perfused with 1000 to 1300 mL of blood per minute, or 20% to 25% of the cardiac output.
The nurse is educating a client about renal disease. Which percentage of cardiac output perfuses the kidneys?
22% to 25% explanation: In the adult, the kidneys are perfused with 1000 to 1300 mL of blood per minute, or 22% to 25% of the cardiac output; 10% to 15% and 15% to 20% represent a decreased percentage; 27% to 30% is an increased percentage.
The nurse is caring for a critically ill client who requires measurement of hourly urine output. When assessing the urine output of the previous shift, the nurse recognizes that which volume reflects a minimum, normal urinary output?
60 mL/hour explanation: Under normal conditions, only approximately 1 mL of the 125 mL of glomerular filtrate that is formed each minute is excreted in the urine. The other 124 mL is reabsorbed in the tubules. This means that the average output of urine is approximately 60 mL/hour.
A client is scheduled for a creatinine clearance test to measure the glomerular filtration rate (GFR). The client asks the nurse what this test is used for. What is the nurse's best response?
"This test provides a gauge of renal function." explanation: The GFR provides a gauge of renal function. The GFR is the amount of filtrate that is formed each minute as blood moves through the glomeruli. The clearance rate for creatinine is the amount that is completely cleared by the kidneys in 1 minute.
A nurse is monitoring a client with renal failure. What glomerular filtration rate (GFR) would the nurse estimate if the creatinine clearance test result is 60 mL/min (1 mL/s/m2)?
60 mL/min explanation: The creatinine clearance approximates the GFR. The GFR provides a gauge of renal function. Normal creatinine clearance is 115-125 mL/min (1.92-2.09 mL/s/m2). It can be measured clinically by collecting timed samples of blood and urine. Creatinine, a product of creatine metabolism by the muscle, is filtered by the kidneys but is not reabsorbed in the renal tubule. Creatinine levels in the blood and urine can be used to measure GFR. The clearance rate for creatinine is the amount that is completely cleared by the kidneys in 1 min.
Urine is an amber, light-yellow fluid that is 5% dissolved solid. What percent of it is water?
95 explanation: Urine is 95% water and 5% dissolved solids.
When teaching a class of nursing students, the pathophysiology instructor asks, "What is the majority of energy used for by the kidney?" Which response is most accurate?
Active sodium transport mechanisms. explanation: The bulk of energy used by the kidney is for active sodium transport mechanisms that facilitate sodium reabsorption and cotransport of other electrolytes and substances such as glucose and amino acids.
A client with a traumatic amputation of the lower leg has lost >40% of blood volume and is currently not producing any urine output. The nurse bases this phenomena on which humoral substance that is responsible for causing severe vasoconstriction of the renal vessels?
Angiotensin II and antidiuretic hormone explanation: Increased sympathetic activity causes constriction of the afferent arterioles, creating a reduction in renal blood flow. Intense sympathetic stimulation can produce marked decreases in renal blood flow and glomerular filtration rate. Humoral substances, including angiotensin II, antidiuretic hormone, and endothelins produce vasoconstriction of renal blood flow. Aquaporin-2 channels, potassium ions, and albumin do not have vasoconstriction properties.
It is known that high levels of uric acid in the blood can cause gout, while high levels in the urine can cause kidney stones. What medication competes with uric acid for secretion into the tubular fluid, thereby reducing uric acid secretion?
Aspirin explanation: Small doses of aspirin compete with uric acid for secretion into the tubular fluid and reduce uric acid secretion. Large doses compete with uric acid for reabsorption and increase uric acid excretion in the urine.
Which substance released by atrial muscle cells will inhibit sodium and water reabsoption?
Atrial natriuretic peptide (ANP) explanation: Atrial natriuretic peptide (ANP) is a hormone that is synthesized in the muscle cells of the atria of the heart and released when the atria are stretched. The primary effect of ANP is to inhibit sodium and water reabsorption, with action predominant in the collecting ducts. Angiotensin I, which has few vasoconstrictor properties, leaves the kidneys and enters the circulation. ADH and aldosterone would decrease blood flow and glomerular filtration rate.
A client with a history of previous myocardial infarction (MI) has symptomology indicating ineffective renal blood vessel dilation, resulting in increased sodium retention. Which hormone level may have been affected by the MI?
Atrial natriuretic peptide (ANP) explanation: The actions of ANP include vasodilation of the afferent and efferent arterioles, which results in an increase in renal blood flow and GFR. ANP inhibits aldosterone secretion by the adrenal gland and sodium reabsorption from the collecting tubules through its action on aldosterone and through direct action on the tubular cells. It also inhibits ADH release from the posterior pituitary gland, thereby increasing excretion of water by the kidneys. ANP also has vasodilator properties. ACTH is made in the pituitary gland in response to the release of another hormone, called corticotropin-releasing hormone (CRH), by the hypothalamus. In turn, the adrenal glands then make a hormone called cortisol, which helps your body manage stress.
When caring for a client with dehydration, the nurse anticipates the client will have an alteration in which substance in the blood?
Blood urea nitrogen explanation: During periods of dehydration, the blood volume and GFR drop, and BUN levels increase. The renal tubules are permeable to urea, which means that the longer the tubular fluid remains in the kidneys, the greater the reabsorption of urea into the blood.
A nurse is evaluating a client's morning laboratory values. Which result requires that the nurse notify the health care provider?
Creatinine: 10.6 mg/dL (937.04 µmol/L) explanation: A rise in the serum creatinine level to three times its normal value suggests that there is a 75% loss of renal function, and with creatinine values of 10 mg/dL or more, it can be assumed that approximately 90% of renal function has been lost.
A client has just been admitted to the emergency department after sustaining severe injuries and massive blood loss following a motor vehicle accident. The nurse predicts that the client's glomerular filtration rate will:
Decrease explanation: Although nearly all the blood that enters the kidney flows through the cortex, less than 10% passes into the medulla and only about 1% moves into the papillae. Under conditions of decreased perfusion or increased sympathetic nervous system stimulation, blood flow is redistributed away from the cortex toward the medulla. This redistribution of blood flow decreases glomerular filtration while maintaining the urine-concentrating ability of the kidneys, a factor that is important during conditions such as shock. With decreasing flow, the filtration rate will decrease to adapt perfusion and maintain function.
Which occurrence is most likely to cause increased urination?
Decrease in antidiuretic hormone explanation: Increased urination or polyuria is caused by low levels of ADH, which stimulates the kidneys to absorb more water. The other options do not have this physiologic effect.
The nurse collects a urine sample but forgets the sample in the client's room for several hours. What is the nurse's best action?
Discard the sample and recollect in the morning. explanation: Urine specimens that have been left standing may contain lysed red blood cells, disintegrating casts, and rapidly multiplying bacteria that could cause inaccurate results. The nurse should collect a fresh morning sample and send as soon as possible. This decision does not require input from a laboratory technician.
Urine specific gravity is normally 1.010 to 1.025 with adequate hydration. When there is loss of renal concentrating ability due to impaired renal function, low concentration levels are exhibited. When would the nurse consider the low levels of concentration to be significant?
First void in morning explanation: With diminished renal function, there is a loss of renal concentrating ability, and the urine specific gravity may fall to levels of 1.006 to 1.010 (usual range is 1.010 to 1.025 with normal fluid intake). These low levels are particularly significant if they occur during periods that follow a decrease in water intake (e.g., during the first urine specimen on arising in the morning).
When caring for the client with proteinuria, the nurse recognizes that dysfunction in which structure of the kidney allows protein to leak into the urine?
Glomerulus explanation: Alterations in the structure and function of the glomerular basement membrane are responsible for the leakage of proteins and blood cells into the filtrate that occurs in many forms of glomerular disease.
The client with chronic kidney disease asks the nurse why he must take active vitamin D (calcitriol) as a medication. What is the most appropriate response by the nurse?
In renal disease, vitamin D is unable to be transformed to its active form. explanation: Cholecalciferol and ergocalciferol must undergo chemical transformation to become active: first to 25-hydroxycholecalciferol in the liver and then to 1,25-dihydroxycholecalciferol in the kidneys. Individuals with end-stage renal disease are unable to transform vitamin D to its active form and may require pharmacologic preparations of the active vitamin (calcitriol) for maintaining mineralization of their bones.
The nurse is reviewing the laboratory work of several medical clients. Which laboratory result is most suggestive of abnormalities in kidney function?
Increased creatinine and blood urea nitrogen (BUN) levels explanation: Increased creatinine and BUN is associated with abnormalities in renal function, as is the presence of glucose in a urine sample. Urine samples normally lack protein and have a specific gravity of 1.030 to 1.040. An elevated BUN coupled with normal creatinine is likely not attributable to impaired kidney function.
The nurse is caring for a client with profound dehydration. The nurse recognizes the body should release antidiuretic hormone (ADH) in this situation based on which type of feedback from the body?
Increased serum osmolarity explanation: ADH, which regulates the ability of the kidneys to concentrate urine, is synthesized by neurons in the hypothalamus, transported down their axons to the posterior pituitary gland, then released into the circulation. One of the main stimuli for synthesis and release of ADH is an increase in serum osmolarity.
The nurse has delegated obtaining a urine specimen for testing to the nursing assistant. What does the nurse emphasize the assistant should do to ensure accuracy of testing?
Obtain a freshly voided specimen. explanation: A freshly voided specimen is most reliable when obtaining urine for testing.
The anemia that occurs with end-stage kidney disease is often caused by the kidneys themselves. What loss of function in the kidney results in anemia of end-stage kidney disease?
Produce erythropoietin explanation: Persons with end-stage kidney disease often are anemic because of an inability of the kidneys to produce erythropoietin. This anemia usually is managed by the administration of a recombinant erythropoietin (epoetin alfa), produced through DNA technology, to stimulate erythropoiesis.
The nurse is teaching a group of nursing students about the physiologic consequences of hypotension and reduced perfusion to the kidney. Which compensatory mechanism occurs immediately after renin release from the kidney?
Production of angiotensin I explanation: The juxtaglomerular cells contain granules of inactive renin, an enzyme that functions in the conversion of angiotensinogen to angiotensin I. With release of converting enzyme, angiotensin II is released, aldosterone is secreted, and extracellular volume increases.
The nurse is caring for a client with kidney disease who has an estimated glomerular filtration rate of 75 mL/minute. The nurse interprets this data in which way?
The client has reduced glomerular filtration, reflecting damage to the kidney. explanation: Approximately 125 mL of filtrate is formed each minute. This is called the glomerular filtration rate (GFR). This rate can vary from a few milliliters per minute to as high as 200 mL/minute.
While assessing a client with urosepsis, the nurse notes the client's blood pressure is 80/54 mm Hg; heart rate is 132 beats/min; respiratory rate is 24 breaths/min; pulse oximetry 89% on 6 lpm O2. Over the last hour, the clients' urine output is 15 mL. When explaining to a new graduate nurse, the nurse will explain which physiologic principle?
The client's sympathetic nervous system has been stimulated, which has resulted in vasoconstriction of the afferent arteriole that in turn causes a decrease in renal blood flow. explanation: During periods of strong sympathetic stimulation, such as shock, constriction of the afferent arteriole causes a marked decrease in renal blood flow and thus glomerular filtration pressure. Consequently, urine output can fall almost to zero.
The nurse is caring for a client who has produced an average of 20 mL/hour for the previous day. The nurse recognizes this compares in which way to the normal urine output?
The kidneys should produce about 1.5 L of urine each day. explanation: The kidneys normally produce approximately 1.5 L or 1500 ml of urine each day.
The nurse is teaching a group of nursing students about the mechanism of action of common diuretics. What best reflects the mechanism of these drugs?
They block the reabsorption of sodium and chloride in the nephron. explanation: Most diuretics share the same mechanism of action—blockade of sodium and chloride reabsorption. By blocking the reabsorption of these solutes, diuretics create an osmotic pressure gradient within the nephron that prevents the passive reabsorption of water. Thus, diuretics cause water and sodium to be retained in the nephron, promoting the excretion of both.
A client arrives in the emergency department semi-comatose. Her breath has a "fruity" smell. Their initial blood glucose level is >600. Her mouth and mucous membranes are dry. The health care providers suspect the client may be experiencing hyperglycemic hyperosmolar syndrome. In this situation, the nurse can expect the client's lab results to reflect:
an increase in glomerular filtration rate [GFR]. explanation: The client's increase in blood glucose results in an increase in blood flow and GFR. These increases allow sodium excretion to be maintained at a near-normal level while increasing the excretion of the waste products of protein metabolism, such as urea. The same mechanism is thought to explain the large increases in renal blood flow and GFR that occur with high blood glucose levels in persons with uncontrolled diabetes mellitus.
The nurse is reviewing the results of a renal client's laboratory results. This client's urine specific gravity allows the nurse to assess the kidneys' ability to:
concentrate urine. explanation: Urine specific gravity is used to assess the kidneys' ability to concentrate urine and provides a valuable index of the hydration status and functional ability of the kidneys. Specific gravity does not evaluate electrolyte or acid-base functions of the kidneys. It is not affected by protein levels.
A client with a history of renal insufficiency is experiencing a flare-up of his arthritis and he has increased his daily dose of ibprofen (an NSAID). Knowing the effect that ibprofen has on prostaglandin synthesis, the nurse should anticipate:
decrease renal blood flow resulting in decrease in urine output. explanation: Aspirin and other nonsteroidal anti-inflamatory drugs (NSAIDs) that inhibit prostaglandin synthesis may decrease renal blood flow and GFR under certain conditions. NSAIDs can cause hematuria but rarely cause clots. Several humoral substances, including angiotensin II, ADH, and the endothelins, produce vasoconstriction of renal vessels.
In the emergency department, a client arrives following a car accident. His pulse is 122; BP 88/60; respiration is 18 bpm. Urine output is 4 mL over the first hour on arrival. When in shock, this lower urine output is primarily due to:
innervation of the sympathetic nervous system, causing constriction of the afferent arteriole. explanation: During periods of strong sympathetic stimulation, such as shock, constriction of the afferent arteriole causes a marked decrease in renal blood flow, and thus glomerular filtration pressure. Consequently, urine output can fall almost to zero. The location of the glomerulus between two arterioles allows for maintenance of a high-pressure filtration system. The glomerular filtrate has a chemical composition similar to plasma, but contains almost no proteins because large molecules do not readily pass through the openings in the glomerular capillary wall.
A nursing student studying pharmacology is learning how angiotensin converting enzyme inhibitors (ACE) work. The student is correct when stating that the mechanism of action of ACE inhibitors is to:
prevent conversion of angiotensin I to II. explanation: The juxtaglomerular cells of the kidney contain granules of inactive renin, an enzyme that functions in the conversion of angiotensinogen to angiotensin. Angiotensin I is converted to angiotensin II in the presence of converting enzyme. By blocking converting enzyme, angiotensin II, a potent vasoconstrictor, is not produced, thus lowering blood pressure
A client with end-stage kidney disease has developed anemia. The nurse teach this client that the reason anemia has developed is:
the damaged kidney is unable to produce erythropoietin. explanation: Persons with end-stage kidney disease often are anemic because of an inability of the kidneys to produce erythropoietin, the hormone that regulates the differentiation of red blood cells in the bone marrow.
