Chapter 14 The Urinary System

Question 1

Kidneys: Anatomy, Functions, and Basic Processes

• Each of the pair of kidneys consists of an outer renal _____ and inner renal _____.
• The kidneys form urine. They eliminate unwanted _____ constituents in the urine while conserving materials of value to the body.
• Urine from each kidney is collected in the __________, then transmitted from both kidneys through the pair of _____ to the single urinary bladder, where urine is stored until emptied through the urethra to the outside.

Answer 1

Kidneys: Anatomy, Functions, and Basic Processes

• Each of the pair of kidneys consists of an outer renal cortex and inner renal medulla.
• The kidneys form urine. They eliminate unwanted plasma constituents in the urine while conserving materials of value to the body.
• Urine from each kidney is collected in the renal pelvis, then transmitted from both kidneys through the pair of ureters to the single urinary bladder, where urine is stored until emptied through the urethra to the outside.

Question 2

Kidneys: Anatomy, Functions, and Basic Processes

• ​The urine-forming functional unit of the kidneys, the _____, is composed of interrelated vascular and tubular components.
• The vascular component consists of two capillary networks in series, the first being the _____, a tuft of capillaries that filters large volumes of protein-free plasma into the tubular component.
• The second capillary network consists of the __________, which nourish the renal tissue and participate in exchanges between the tubular fluid and _____.

Answer 2

Kidneys: Anatomy, Functions, and Basic Processes

• ​The urine-forming functional unit of the kidneys, the nephron, is composed of interrelated vascular and tubular components.
• The vascular component consists of two capillary networks in series, the first being the glomerulus, a tuft of capillaries that filters large volumes of protein-free plasma into the tubular component.
• The second capillary network consists of the peritubular capillaries, which nourish the renal tissue and participate in exchanges between the tubular fluid and plasma.

Question 3

Kidneys: Anatomy, Functions, and Basic Processes

• The tubular component begins with _________, which cups around the glomerulus to catch the filtrate, then continues a specific tortuous course to ultimately empty into the _________.
• As the filtrate passes through various regions of the tubule, cells lining the tubules modify it, returning to the plasma only those materials necessary for maintaining proper __________________.​
• What is left behind in the tubules is excreted as ________.

Answer 3

Kidneys: Anatomy, Functions, and Basic Processes

• The tubular component begins with Bowman’s capsule, which cups around the glomerulus to catch the filtrate, then continues a specific tortuous course to ultimately empty into the renal pelvis.
• As the filtrate passes through various regions of the tubule, cells lining the tubules modify it, returning to the plasma only those materials necessary for maintaining proper ECF composition and volume.
  ​
• What is left behind in the tubules is excreted as urine.

Question 4

Kidneys: Anatomy, Functions, and Basic Processes

• The kidneys perform three basic processes:
  
  1. ________________________
  2. ________________________
  3. ________________________
• Everything filtered or secreted but not reabsorbed is excreted as ____.​

Answer 4

Kidneys: Anatomy, Functions, and Basic Processes

• The kidneys perform three basic processes:
  
  1. glomerular filtration, the nondiscriminating movement of protein-free plasma from the blood into the tubules;
  2. tubular reabsorption, the selective transfer of specific constituents in the filtrate back into peritubular capillary blood; and
  3. tubular secretion, the highly specific movement of selected substances from peritubular capillary blood into the tubular fliuid.
• Everything filtered or secreted but not reabsorbed is excreted as urine.​

Question 5

Glomerular Filtration

• Glomerular filtrate is produced when part of the plasma flowing through each glomerulus is passively forced under pressure through the glomerular membrane into the underlying ______________.
• The net filtrate pressure causing filtration results from a high ____________ blood pressure that favors filtration outweighing the combined opposing forces of plasma- colloid osmotic pressure and Bowman’s capsule hydrostatic pressure.

Answer 5

Glomerular Filtration

• Glomerular filtrate is produced when part of the plasma flowing through each glomerulus is passively forced under pressure through the glomerular membrane into the underlying Bowman’s capsule.
• The net filtrate pressure causing filtration results from a high glomerular capillary blood pressure that favors filtration outweighing the combined opposing forces of plasma- colloid osmotic pressure and Bowman’s capsule hydrostatic pressure.

Question 6

Glomerular Filtration

• ​Of the cardiac output, ________% is delivered to the kidneys to be acted on by renal regulatory and excretory processes.
• Of the plasma flowing through the kidneys, normally _____% is filtered through the glomeruli, for an average glomerular filtration rate (GFR) of 125 mL/min.

Answer 6

Glomerular Filtration

• ​Of the cardiac output, 20% to 25% is delivered to the kidneys to be acted on by renal regulatory and excretory processes.
• Of the plasma flowing through the kidneys, normally 20% is filtered through the glomeruli, for an average glomerular filtration rate (GFR) of 125 mL/min.

Question 7

Glomerular Filtration

• The juxtaglomerular apparatus consists of specialized _____ and _____ cells next to the _____ where the tubular and vascular components come into close proximity.
• Myogenic mechanisms and tubuloglomerular feedback, triggered by the _______________, autoregulate glomerular blood flow and the GFR despite transient changes in the driving mean arterial __________ in the range of 80 to 180 mm Hg

Answer 7

Glomerular Filtration

• The juxtaglomerular apparatus consists of specialized vascular and tubular cells next to the glomerulus where the tubular and vascular components come into close proximity.
• Myogenic mechanisms and tubuloglomerular feedback, triggered by the juxtaglomerular apparatus, autoregulate glomerular blood flow and the GFR despite transient changes in the driving mean arterial blood pressure in the range of 80 to 180 mm Hg

Question 8

Glomerular Filtration

• ​The GFR can be deliberately altered by changing the glomerular ______________ via sympathetic influence on the afferent arterioles as part of the baroreceptor reflex response that compensates for changed ____________.
• When blood pressure falls too low, ______ induced afferent arteriolar ______ lowers glomerular blood pressure and GFR.
• When blood pressure rises too high, reduced sympathetic activity causes afferent arteriolar ______, leading to a rise in ______.
• As the GFR is altered, the amount of fluid lost in urine changes correspondingly, adjusting ____________ as needed to help restore blood pressure to normal on a long-term basis.

Answer 8

Glomerular Filtration

• ​The GFR can be deliberately altered by changing the glomerular capillary blood pressure via sympathetic influence on the afferent arterioles as part of the baroreceptor reflex response that compensates for changed arterial blood pressure.
• When blood pressure falls too low, sympathetically induced afferent arteriolar vasoconstriction lowers glomerular blood pressure and GFR.
• When blood pressure rises too high, reduced sympathetic activity causes afferent arteriolar vasodilation, leading to a rise in GFR.
• As the GFR is altered, the amount of fluid lost in urine changes correspondingly, adjusting plasma volume as needed to help restore blood pressure to normal on a long-term basis.

Question 9

Tubular Reabsorption

• After the filtrate is formed, the tubules handle each filtered substance ______, so that even though the initial glomerular filtrate is ______ to plasma (with the exception of plasma proteins), the concentrations of different constituents are variously altered as the filtered fluid flows through the tubular system.

Answer 9

Tubular Reabsorption

• After the filtrate is formed, the tubules handle each filtered substance discretely, so that even though the initial glomerular filtrate is identical to plasma (with the exception of plasma proteins), the concentrations of different constituents are variously altered as the filtered fluid flows through the tubular system.

Question 10

Tubular Reabsorption

• The reabsorptive capacity of the tubular system is tremendous. More than __% of the filtered plasma is returned to the blood through reabsorption.
• ​On average, 124 mL out of the 125 mL filtered per ____ are reabsorbed.

*

Answer 10

Tubular Reabsorption

• The reabsorptive capacity of the tubular system is tremendous. More than 99% of the filtered plasma is returned to the blood through reabsorption.
• ​On average, 124 mL out of the 125 mL filtered per minute are reabsorbed.

Question 11

Tubular Reabsorption

• Tubular reabsorption involves _____________ from the tubular lumen into the _______________.
• This process may be _______ or _______.

Answer 11

Tubular Reabsorption

• Tubular reabsorption involves transepithelial transport from the tubular lumen into the peritubular capillary plasma.
• This process may be active (requiring energy) or passive (using no energy).

Question 12

Tubular Reabsorption

• The pivotal event to which most reabsorptive processes are linked is the active reabsorption of ____, driven by the energy- dependent Na⁺–K⁺ pump in the ____________ of the tubular cells.
• The transport of Na⁺ out of the cells into the lateral spaces between adjacent cells by this carrier induces the net reabsorption of Na⁺ from the ________ to the ________________.

*

Answer 12

Tubular Reabsorption

• The pivotal event to which most reabsorptive processes are linked is the active reabsorption of Na⁺, driven by the energy- dependent Na⁺–K⁺ pump in the basolateral membrane of the tubular cells.
• The transport of Na⁺ out of the cells into the lateral spaces between adjacent cells by this carrier induces the net reabsorption of Na⁺ from the tubular lumen to the peritubular capillary plasma.

Question 13

Tubular Reabsorption

• Most Na⁺ reabsorption takes place early in the _____ in constant unregulated fashion, but in the distal and collecting tubules, the reabsorption of a small percentage of the filtered Na⁺ is variable and controlled, mostly by the _________.

Answer 13

Tubular Reabsorption

• Most Na⁺ reabsorption takes place early in the nephron in constant unregulated fashion, but in the distal and collecting tubules, the reabsorption of a small percentage of the filtered Na⁺ is variable and controlled, mostly by the renin–angiotensin– aldosterone system (RAAS).

Question 14

Tubular Reabsorption

• Because Na⁺ and its attendant anion, Cl^{​ –}, are the major osmotically active ions in the ECF, the ECF volume is determined by the _______ in the body.
• In turn, the _______, which reflects the total ECF volume, is important in the long-term determination of arterial blood pressure.
• Whenever the Na⁺ load, ECF volume, plasma volume, and arterial blood pressure are below normal, the ______________ secretes renin, an enzymatic hormone that triggers _____, ultimately leading to increased aldosterone secretion by the adrenal cortex.
• Aldosterone increases Na⁺ reabsorption from the ______________ of the tubule, thus correcting for the original reduction in Na⁺, ECF volume, and blood pressure.

Answer 14

Tubular Reabsorption

• Because Na⁺ and its attendant anion, Cl^{​ –}, are the major osmotically active ions in the ECF, the ECF volume is determined by the Na⁺ load (total amount of Na⁺) in the body.
• In turn, the plasma volume, which reflects the total ECF volume, is important in the long-term determination of arterial blood pressure.
• Whenever the Na⁺ load, ECF volume, plasma volume, and arterial blood pressure are below normal, the juxtaglomerular apparatus secretes renin, an enzymatic hormone that triggers RAAS, ultimately leading to increased aldosterone secretion by the adrenal cortex.
• Aldosterone increases Na⁺ reabsorption from the distal portions of the tubule, thus correcting for the original reduction in Na⁺, ECF volume, and blood pressure.

Question 15

Tubular Reabsorption

• By contrast, Na⁺ reabsorption is inhibited by the __________, ANP and BNP, hormones released from the cardiac _____ and _____, respectively, in response to expansion of the ECF volume and a subsequent increase in _____.

Answer 15

Tubular Reabsorption

• By contrast, Na⁺ reabsorption is inhibited by the natriuretic peptides, ANP and BNP, hormones released from the cardiac atria and ventricles, respectively, in response to expansion of the ECF volume and a subsequent increase in blood pressure.

Question 16

Tubular Reabsorption

• In addition to driving the reabsorption of Na⁺, the energy used by the Na⁺–K⁺ pump is ultimately responsible for the reabsorption of organic nutrients (_____ or _____) from the _____ tubule by _____ active transport.

Answer 16

Tubular Reabsorption

• In addition to driving the reabsorption of Na⁺, the energy used by the Na⁺–K⁺ pump is ultimately responsible for the reabsorption of organic nutrients (glucose or amino acids) from the proximal tubule by secondary active transport.

Question 17

Tubular Reabsorption

• Other electrolytes actively reabsorbed by the tubules, such as PO4^-3 and Ca⁺², have ______ functioning carrier systems within the ___________.

Answer 17

Tubular Reabsorption

• Other electrolytes actively reabsorbed by the tubules, such as PO4^-3 and Ca⁺², have independently functioning carrier systems within the proximal tubule.

Question 18

Tubular Reabsorption

• Because the electrolyte and nutrient carriers can become ____, each exhibits a maximal carrier-limited transport capacity (T_m).
• Once the filtered load of an actively reabsorbed substance exceeds the T_m, reabsorption proceeds at a ____ maximal rate, and any additional filtered quantity of the substance is ____.

Answer 18

Tubular Reabsorption

• Because the electrolyte and nutrient carriers can become saturated, each exhibits a maximal carrier-limited transport capacity (T_m).
• Once the filtered load of an actively reabsorbed substance exceeds the T_m, reabsorption proceeds at a constant maximal rate, and any additional filtered quantity of the substance is excreted in the urine.

Question 19

Tubular Reabsorption

• Active Na⁺ reabsorption also drives the passive reabsorption of Cl ^– (via an ______), H₂O (by ______), and urea (down a _______________ created as a result of extensive osmotic-driven H₂O reabsorption).
• ___% of the filtered H₂O is reabsorbed from the proximal tubule in unreg- ulated fashion, driven by active Na⁺ reabsorption.
• Reabsorption of H₂O increases the concentration of other substances remaining in the tubular fluid, most of which are filtered _________.
• The small urea molecules are the only waste products that can passively permeate the _________, so urea is the only waste product partially (50%) reabsorbed as a result of being concentrated.

*

Answer 19

Tubular Reabsorption

• Active Na⁺ reabsorption also drives the passive reabsorption of Cl ^– (via an electrical gradient), H₂O (by osmosis), and urea (down a urea concentration gradient created as a result of extensive osmotic-driven H₂O reabsorption).
• 65% of the filtered H₂O is reabsorbed from the proximal tubule in unreg- ulated fashion, driven by active Na⁺ reabsorption.
• Reabsorption of H₂O increases the concentration of other substances remaining in the tubular fluid, most of which are filtered waste products.
• The small urea molecules are the only waste products that can passively permeate the tubular membranes, so urea is the only waste product partially (50%) reabsorbed as a result of being concentrated.

Question 20

Tubular Reabsorption

• The other waste products besides urea, which are not reabsorbed, remain in the ____ in highly concentrated form.

Answer 20

Tubular Reabsorption

• The other waste products besides urea, which are not reabsorbed, remain in the urine in highly concentrated form.

Question 21

Tubular Secretion

• Tubular secretion involves transepithelial transport from the __________________ into the ____________. ​
• By tubular secretion, the kidney tubules can selectively ______ some substances to the quantity already filtered.
• Secretion of substances hastens their ______ in the ______.

Answer 21

Tubular Secretion

• Tubular secretion involves transepithelial transport from the peritubular capillary plasma into the tubular lumen.
  ​
• By tubular secretion, the kidney tubules can selectively add some substances to the quantity already filtered.
• Secretion of substances hastens their excretion in the urine.

Question 22

Tubular Secretion

• The most important secretory systems are for
  
  1. H⁺ (helps regulate acid–base balance);
  2. (2) K⁺ (keeps the plasma K⁺ con- centration at the level needed to maintain normal membrane excitability in the heart, other muscles, and nerves); and
  3. (3) organic ions (accomplishes more ef cient elimination of foreign organic compounds from the body).

Answer 22

Tubular Secretion

• The most important secretory systems are for
  
  1. H⁺ (helps regulate acid–base balance);
  2. K⁺ (keeps the plasma K⁺ concentration at the level needed to maintain normal membrane excitability in the heart, other muscles, and nerves); and
  3. organic ions (accomplishes more efficient elimination of foreign organic compounds from the body).

Question 23

Tubular Secretion

• H⁺ is secreted in the _____, _____, and _____ tubules.
• K⁺ is secreted only in the _____ and _____ tubules under control of _____.
• Organic ions are secreted only in the _____ tubule.

Answer 23

Tubular Secretion

• H⁺ is secreted in the proximal, distal, and collecting tubules.
• K⁺ is secreted only in the distal and collecting tubules under control of aldosterone.
• Organic ions are secreted only in the proximal tubule.

Question 24

Urine Excretion and Plasma Clearance

• Of the 125 mL/min of glomerular filtrate formed, normally only 1 mL/min remains in the ____ to be excreted as urine.
• Only ____ and ________ not wanted by the body are left behind, dissolved in a given volume of H₂O to be eliminated in the urine.

Answer 24

Urine Excretion and Plasma Clearance

• Of the 125 mL/min of glomerular filtrate formed, normally only 1 mL/min remains in the tubules to be excreted as urine.
• Only wastes and excess electrolytes not wanted by the body are left behind, dissolved in a given volume of H₂O to be eliminated in the urine.

Question 25

Urine Excretion and Plasma Clearance

• Because the excreted material is removed or “cleared” from the plasma, the term plasma clearance refers to the ______ of plasma cleared of a particular substance each minute by ____________.

Answer 25

Urine Excretion and Plasma Clearance

• Because the excreted material is removed or “cleared” from the plasma, the term plasma clearance refers to the volume of plasma cleared of a particular substance each minute by renal activity.

Question 26

Urine Excretion and Plasma Clearance

• The kidneys can excrete urine of varying volumes and concentrations to either ______ or ______ H₂O, depending on whether the body has a H₂O deficit or excess, respectively.
• The kidneys can produce urine ranging from 0.3 mL/min at 1200 mOsm/L to 25 mL/min at 100 mOsm/L by reabsorbing variable amounts of H₂O from the ______ portions of the nephron.

Answer 26

Urine Excretion and Plasma Clearance

• The kidneys can excrete urine of varying volumes and concentrations to either conserve or eliminate H₂O, depending on whether the body has a H₂O deficit or excess, respectively.
• The kidneys can produce urine ranging from 0.3 mL/min at 1200 mOsm/L to 25 mL/min at 100 mOsm/L by reabsorbing variable amounts of H₂O from the distal portions of the nephron.

Question 27

Urine Excretion and Plasma Clearance

• This variable reabsorption of water is made possible by a vertical _________ in the _____ interstitial fluid, established by the long loops of Henle of the juxtamedullary nephrons via countercurrent multiplication and preserved by the _______ of these nephrons via countercurrent exchange.
• This vertical osmotic gradient, to which the hypotonic (100 mOsm/L) tubular fluid is exposed as it passes through the distal portions of the nephron, establishes a __________for progressive reabsorption of H₂O from the tubular fluid, but the actual extent of H₂O reabsorption depends on the amount of _______________ secreted.

Answer 27

Urine Excretion and Plasma Clearance

• This variable reabsorption of water is made possible by a vertical osmotic gradient in the medullary interstitial fluid, established by the long loops of Henle of the juxtamedullary nephrons via countercurrent multiplication and preserved by the vasa recta of these nephrons via countercurrent exchange.
• This vertical osmotic gradient, to which the hypotonic (100 mOsm/L) tubular fluid is exposed as it passes through the distal portions of the nephron, establishes a passive driving force for progressive reabsorption of H₂O from the tubular fluid, but the actual extent of H₂O reabsorption depends on the amount of vasopressin (antidiuretic hormone) secreted.

Question 28

Urine Excretion and Plasma Clearance

• Vasopressin increases the _____ of the distal and collecting tubules to H₂O; they are _____ to H₂O in its absence.
• Vasopressin secretion increases in response to a H₂O _____, increasing H₂O reabsorption.
• Its secretion is inhibited in response to a H₂O _____, reducing H₂O reab- sorption.
• Thus vasopressin-controlled H₂O reabsorption helps correct any _________.

Answer 28

Urine Excretion and Plasma Clearance

• Vasopressin increases the permeability of the distal and collecting tubules to H₂O; they are impermeable to H₂O in its absence.
• Vasopressin secretion increases in response to a H₂O deficit, increasing H₂O reabsorption.
• Its secretion is inhibited in response to a H₂O excess, reducing H₂O reab- sorption.
• Thus vasopressin-controlled H₂O reabsorption helps correct any fluid imbalances.

Question 29

Urine Excretion and Plasma Clearance

• Once formed, urine is propelled by _____ contractions through the _____ from the kidneys to the urinary bladder for temporary storage.

Answer 29

Urine Excretion and Plasma Clearance

• Once formed, urine is propelled by peristaltic contractions through the ureters from the kidneys to the urinary bladder for temporary storage.

Question 30

Urine Excretion and Plasma Clearance

• The bladder can accommodate up to 250 to 400 mL of urine before _______ within its wall initiate the ____ reflex.
• This reflex causes involuntary emptying of the bladder by simultaneous bladder contraction and opening of both the internal and the external ____________.
• Micturition can transiently be voluntarily prevented by deliberately tightening the ____ sphincter and ________.

Answer 30

Urine Excretion and Plasma Clearance

• The bladder can accommodate up to 250 to 400 mL of urine before stretch receptors within its wall initiate the micturition reflex.
• This reflex causes involuntary emptying of the bladder by simultaneous bladder contraction and opening of both the internal and the external urethral sphincters.
• Micturition can transiently be voluntarily prevented by deliberately tightening the external sphincter and pelvic diaphragm.