Chapter 24: Structure and Function of the Kidney Porth

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Chapter 24: Structure and Function of the Kidney Porth - Essentials of Pathophysiology - 3rd edition

The ____ are paired, bean-shaped organs that lie outside the peritoneal cavity in the back of the upper abdomen.

kidneys

The ____ is the place where blood vessels and nerves enter and leave the kidney.

hilus

____ are the functional units of the kidney.

Nephrons

The ____ contains the glomeruli and convoluted tubules of the nephron and blood vessels.

cortex

The medulla consists of the _____ that extend into the medulla.

renal pyramids

Each kidney is supplied by a single renal artery that arises on either side of the ____.

aorta

The afferent arterioles that supply the _____ arise from the intralobular arteries.

glomeruli

The ____ is a unique, high-pressure capillary filtration system.

glomerulus

___ are low-pressure vessels that are adapted for reabsorption rather than filtration.

Peritubular capillaries

The _____ passes through each of these segments before reaching the pelvis of the kidney.

filtrate

The ____ is regulated by the constriction and relaxation of the afferent and efferent arterioles.

glomerular filtration rate (GFR)

Substances move from the tubular filtrate into the tubular cell along a _____ gradient but they require facilitated transport or carrier systems to move across the _____membrane into the interstitial fluid, where they are absorbed into the peritubular capillaries.

concentration, basolateral

____ uses a carrier system in which the downhill movement of one substance such as sodium is coupled to the uphill movement of another substance such as glucose or an amino acid.

Cotransport

In the ____ tubule, there is almost complete reabsorption of nutritionally important substances from the filtrate.

proximal

The plasma level at which the substance appears in the urine is called the _____.

renal threshold

The _____ established a high concentration of osmotically active particles in the interstitium surrounding the medullary collecting tubules where the antidiuretic hormone (ADH) exerts its effects.

loop of Henle

The thick portion of the loop of Henle contains a _____ cotransport system.

Na+ - K+ - 2Cl-

The ____ tubule is relatively impermeable to water, and reabsorption of sodium chloride from this segment further dilutes the tubular fluid.

distal convoluted

The ____ assists in maintenance of extracellular fluid volume by controlling the permeability of the medullary collecting tubules.

antidiuretic hormone

Increased _____ activity causes constriction of the afferent and efferent arterioles and thus a decrease in renal blood flow.

sympathetic

Renal ___ is the volume of plasma that is completely cleared each minute of any substance that finds its way into the urine.

clearance

____ functions in the regulation of sodium and potassium elimination.

Aldosterone

Atrial natriuretic peptide contributes to the regulation of ____ elimination.

sodium

The kidneys regulate body pH by conserving base ____ and eliminating ____ ions.

bicarbonate, hydrogen

____ is an end product of protein metabolism.

Urea

The synthesis of ____ is stimulated by tissue hypoxia, which may be brought by an anemia, residence at high altitudes, or impaired oxygenation of tissues due to cardiac or pulmonary disease.

erythropoietin

____ represents excessive protein excretion in the urine.

Proteinuria

Urine ____ provides a valuable index of the hydration status and functional ability of the kidneys.

specific gravity

____ levels in the blood and urine can be used to measure glomerular filtration rate (GFR).

Creatinine

_____, therefore, is related to the GFR but, unlike creatinine, also is influenced by protein intake, gastrointestinal bleeding and hydration status.

BUN

Define countertransport

The movement of one substance enables the movement of a second substance in the opposite direction.

Define Glomerular filtration rate

Milliliter of filtrate formed per minute

Define vasopressin

Stimulate expression of aquaporin-2 channels

Define cortical nephrons

Original in the superficial part of the cortex

Define vitamin D

Converted to active form in kidney

Define principal cells

Site of aldosterone action

Define juxtamedullary nephrons

Originate deeper in the cortex

Define countercurrent

Flow of fluids in opposite directions

Define transport maximum

Maximum amount of substance that can be reabsorbed per unit of time

Define Mesangial cells

Contribute to regulation of glomerular blood flow

Put the components of the renin-angiotensin-aldosterone system in order from stimulation to end hormone action:
a. Conversion of angiotensin I to angiotensin II by angiotensin converting enzyme.
b. Decreased GFR
c. Sodium and water retention
d. Angiotensin II stimulates release of ADH and aldosterone
e. Juxtaglomerular release of renin
f. Conversion of angiotensinogen to angiotensin I by renin.

1. Decreased GFR
2. Juxtaglomerular release of renin
3. Conversion of angiotensinogen to angiotensin I by renin.
4. Conversion of angiotensin I to angiotensin II by angiotensin converting enzyme.
5. Angiotensin II stimulates release of ADH and aldosterone
6. Sodium and water retention

Describe the three layers of the glomerular membrane.

The glomerular capillary membrane is composed of three layers: the capillary endothelial layer, the basement membrane, and the single-celled capsular epithelial layer. The endothelial layer contains many small perforations, called fenestrations. The epithelial layer that covers the glomerulus is continuous with the epithelium that lines Bowman's capsule. The cells of the epithelial layer have unusual octopus-like structures that possess a large number of extensions, or foot processes. These foot processes form slit pores through which the glomerular filtrate passes. The basement membrane consists of a homogeneous acellular meshwork or collagen fibers, glycoproteins, and mucopolysaccharides. The spaces between the fibers that make up the basement membrane represent the pores of a filter and determine the size-dependent permeability barrier of the glomerulus.

Describe the various methods of transport across the epithelial layer of the renal tubule.

The basic mechanisms of transport across the tubular epithelial cell membrane include active and passive transport mechanisms. Water and urea are passively absorbed along concentration gradients. Sodium, potassium, chloride, calcium, and phosphate ions, as well as urate, glucose, and amino acids, are reabsorbed using primary or secondary active transport mechanisms to move across the tubular membrane. Some substances, such as hydrogen, potassium, and urate ions, are secreted into the tubular fluids.

How does the juxtaglomerular apparatus regulate GFR?

The juxtaglomerular complex is a feedback control system that links changes in the GFR with renal blood flow. It is located at the site where the distal tubule extends back to the glomerulus and then passes between the afferent and efferent arteriole. The distal tubular site that is nearest the glomerulus is characterized by densely nucleated cells called the macula densa. In the adjacent afferent arteriole, the smooth muscle cells of the media are modified as special secretory cells called juxtaglomerular cells. These cells contain granules in inactive renin, an enzyme that functions in the conversion of angiotensinogen to angiotensin. Renin functions by means of angiotensin II to produce vasoconstriction of the efferent arteriole as a means of preventing serious decreases in the GFR. Angiotensin II also increases sodium reabsorption indirectly by stimulating aldosterone secretion from the adrenal gland and directly by increasing sodium reabsorption by the proximal tubule cells. The increase in sodium will result in an increase in water retention, which will increase blood volume and in turn increase GFR.

What are the actions of atrial natriuretic peptide (ANP)?

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.

What are the endocrine functions of the kidney?

The kidneys function as an endocrine organ in that they produce chemical mediators that travel through the blood to distant sites where they exert their actions. The kidneys participate in control of blood pressure by way of the renin-angiotensin mechanism, in calcium metabolism by activating vitamin D and in regulating red blood cell production through the synthesis of erythropoietin.

How do sodium blockers function as a diuretic?

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 within the nephron, thereby promoting the excretion of both. The increase in urine flow that a diuretic produces is related to the amount of sodium and chloride reabsorption that it blocks.

An 18-year-old girl is brought to the emergency department by her friends. Her blood pressure is 115/85; pulse is 99, respiratory rate in 35 bpm. The girl is doubled over and she is folding her abdomen saying, "I hurt so bad; I hurt so bad". Her friends deny the girl has been using recreational drugs. They tell the triage nurse that the girl started complaining that her side hurt about 3 hours prior to the trip to the emergency department. Asked if the girl's parents had been notified, the friends tell the triage nurse that they have been unable to reach the girl's parents. On examination, a suspected diagnosis of kidney impairment is arrived at. What tests would the nurse expect to be ordered to either confirm or deny the diagnosis?

Tests that the nurse would expect to be ordered to either confirm or deny the diagnosis include urine specific gravity, urinalysis with culture and sensitivity, urine osmolarity, GFR, BUN, and serum electrolytes.

An 18-year-old girl is brought to the emergency department by her friends. Her blood pressure is 115/85; pulse is 99, respiratory rate in 35 bpm. The girl is doubled over and she is folding her abdomen saying, "I hurt so bad; I hurt so bad". Her friends deny the girl has been using recreational drugs. They tell the triage nurse that the girl started complaining that her side hurt about 3 hours prior to the trip to the emergency department. Asked if the girl's parents had been notified, the friends tell the triage nurse that they have been unable to reach the girl's parents. On examination, a suspected diagnosis of kidney impairment is arrived at. The girl says, "My father just had a kidney stone removed. Is that what I have?" What noninvasive test would the nurse expect to be ordered to rule out a kidney stone?

A simple flat-plat radiograph will show the kidneys, ureters, and any radio-opaque stones that may be in the kidney pelvis or ureters.

Many substances are both filtered out of the blood and reabsorbed into the blood in the kidneys. What is the plasma level at which a specific substance can be found in the urine?

The plasma level at which the substance appears in the urine is called the renal threshold.

You are admitting to the floor a 45-year-old woman with a presumptive diagnosis of diabetes mellitus. While taking her history, she mentions that she has been eating a lot of sweets lately. How would you expect this diet to impact her renal system?

Increase renal blood flow. With ingestion of a high-protein diet, renal blood flow increases 20% to 30% within 1 to 2 hours. Although the exact mechanism for this increase is uncertain, it is thought to be related to the fact that amino acids and sodium are absorbed together in the proximal tubule (secondary active transport). 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 renal clearance of a substance is measured independently. What are the factors that determine renal clearance of a substance?

The ability of the substance to be filtered in the glomeruli and the capacity of the renal tubules to reabsorb or secrete the substance. With insulin, after intravenous injection, the amount that appears in the urine is equal to the amount that is filtered in the glomeruli (i.e. the clearance rate is equal to the GFR). Because of these properties, insulin can be used as a laboratory measure of the GFR.

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 in to the tubular fluid, thereby reducing uric acid secretion?

Aspirin. Small doses of aspirin compete with uric acid for secretion into the tubular fluid and reduce uric acid secretion, and large doses compete with uric acid for reabsorption and increase uric acid excretion in the urine.

Many drugs are eliminated in the urine. These drugs cannot be bound to plasma proteins in the glomerulus is going to filter them out of he blood. In what situation would it be necessary to create either an alkaline or acid diuresis in a client?

In the case of a drug overdose. Alkaline or acid diuresis may be used to increase elimination of drugs in the urine, particularly in situations of drug overdose.

The anemia that occurs with end-stage kidney disease is often caused by the kidneys themselves. What inability of the kidney disease causes anemia in end-stage kidney disease?

Produce erythropoietin. 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 eryhtropoiesis.

Diuretics can either block the reabsorption of components of the urine, or they can block the reabsorption of water back into the body. What does the increase in urine flow from the body depend on with a patient taking diuretics?

The amount of sodium and chloride reabsorption that it blocks. The increase in urine flow that a diuretic produces is related to the amount of sodium and chloride reabsorption that it blocks.

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 the morning. With diminished renal function, there is a loss of renal concentrating ability, and 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).

An elderly man is brought into the clinic by his daughter who states, "My father hasn't been himself lately. Now I think he looks a little yellow." What test would the nurse expect to have ordered to check this man's creatinine level?

Serum creatinine. Creatinine is freely filtered in the glomeruli, is not reabsorbed from the tubules into the blood, and is only minimally secreted into the tubules from the blood; therefore, its blood values depend closely on the GFR. A normal serum creatinine level usually indicates normal renal function. In addition to its use in calculating the GFR, the serum creatinine level is used in estimating the functional capacity of the kidneys. If the value doubles, the GFR - and renal function - probably has fallen to half of its normal state. A rise in serum creatinine level to three times its normal value suggests that there is a 75% loss of renal function. A BUN, 24-hour urine test, and urine test to first void in the morning do not tell you about serum creatinine levels.

A patient suffering from a previous myocardial infarction is displaying an inability to dilate the blood vessels and increased sodium retention. Which hormone level may have been affected by the MI?

ANP. 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.

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