Renal

Question 1

12904, 22489 – Renin secretion is controlled by
1: intrarenal baroreceptors
2: substance P
3: sodium content of the proximal and distal tubular fluid
4: glomerular filtration rate

Answer 1

TFTF
Renin is produced in the juxtaglomerular apparatus by stimuli that decrease extracellular fluid volume and blood pressure or increase sympathetic output. The control of renin secretion is achieved by an intrarenal baroreceptor mechanism which causes renin secretion to increase when the intra-arterial pressure at the juxtaglomerular cells is decreased (A true). The macula densa cells of the distal convoluted tubule form the part of the juxtaglomerular apparatus which is sensitive to the Na+ and CI- concentration of the fluid delivered to it, renin secretion being partly controlled by the rate of transport of CI- and Na+ across the macula densa cells (C true). Substance P is a neural transmitter that is liberated in the primary afferent neurons in the brain, the retina and gastrointestinal tract (B false). The glomerular filtrate is governed by the hydrostatic pressure in the afferent arteriole which, of course, affects the juxtaglomerular apparatus. However, the glomerular filtration rate does not control renin secretion (D false).

Question 2

13594 – Renin secretion is controlled by
1: intrarenal baroreceptors
2: prostaglandins
3: sodium content of the proximal and distal tubular fluid
4: glomerular filtration rate

Answer 2

TTTF
Renin is produced in the juxtaglomerular apparatus by stimuli that decrease ECF volume and blood pressure or increase sympathetic output. The control of renin secretion is achieved by an intrarenal baroreceptor mechanism which causes renin secretion to increase when the intra-arterial pressure at
the juxtaglomerular cells is decreased (A true). The macula densa cells of the distal convoluted tubule form the part of the juxtaglomerular apparatus which is sensitive to the Na+ and Cl- concentration of the fluid delivered to it, renin secretion being partly controlled by the rate of transport of Cl- and Na+ across the macula densa cells (C true). Prostaglandins stimulate renin secretion, and mediate the effects of the renal baroreceptor cells and cells of the macula densa (B true). The glomerular filtration rate is governed by the hydrostatic pressure in the afferent arteriole, which affects the juxtaglomerular apparatus. However, the glomerular filtration rate does not control renin secretion (D false).

Question 3

15498 – Renin secretion is increased by
1: cirrhosis
2: diuretics
3: upright posture
4: sodium loading

Answer 3

TTTF
Refer to Ganong, 19th Ed, Ch 24, page 433 and following

Question 4

13569 – Aldosterone increases the reabsorption of sodium from the
1: collecting duct
2: saliva
3: sweat
4: small intestine

Answer 4

TTTT
The major action of adlosterone is on the collecting duct (A true) where it promotes the reabsorption of sodium in exchange for potassium and hydrogen ions. It also has an effect in promoting sodium reabsorption in salivary and sweat glands as well as in the small bowel (B,C,D true).

Question 5

22048 – Aldosterone increases the reabsorption of sodium from the
1: distal renal tubule
2: saliva
3: sweat
4: intestine

Answer 5

TTTT
Guyton 8th ed. CHAPTER: 77 PAGE: 844-845

Question 6

13574 – Aldosterone secretion is increased by
1: high potassium intake
2: low sodium intake
3: standing
4: constriction of the inferior vena cava in the thorax

Answer 6

TTTT
Plasma K+ need only increase 1 mmol/l or less to stimulate aldosterone and such changes may occur after ingestion of a meal rich in K+ (A true). Dietary sodium restriction increases aldosterone secretion via the renin-angiotensin system. A fall in plasma Na+ also has a direct effect on the adrenal cortex (B true). In the normal individual there is an increase in plasma aldosterone concentration during that part of the day when the individual is standing. This is due to a decrease in the rate of removal of aldosterone by the liver and an increase in production due to a postural increase in renin secretion (C rtrue). Haemorrhage and constriction of the inferior vena cava in the thorax produce a decrease in the intra-arterial vascular volume, increasing renin secretion, the angiotensin II formed by the action of the renin increases the rate of secretion of aldosterone (D true).

Question 7

20715 – S. The administration during operation of 2 litres of saline solution to a patient having an uncomplicated vagotomy for chronic duodenal ulcer results in increased sodium excretion in the urine BECAUSE R. the increase in aldosterone secretion which follows operation is completely abolished by the administration of saline solution during the procedure

Answer 7

S is true and R is false
Clinical Science for Surgeons CHAPTER: 13.5.8 PAGE: 201

Question 8

21748 – Angiotensin II
1: facilitates release of noradrenaline from sympathetic neurons
2: has less aldosterone - stimulating activity than angiotensin III
3: acts in the central nervous system to stimulate release of vasopressin
4: crosses the blood-brain barrier

Answer 8

TFTF
Ganong 20th Edition, page 441.
Angiotensin II action:
1) arteriolar constriction
2) increases aldosterone secretion
3) CNS actions - increases water intake and vasopressin secretion

Question 9

22374 – Angiotensin II produces
1: arteriolar constriction
2: a rise in diastolic blood pressure
3: increased water intake
4: inhibition of adrenocorticotrophin hormone (ACTH) secretion

Answer 9

TTTF
Ganong 19th ed. Chapter: 24 Page: 433-436
Angiotensin II action:
1) arteriolar constriction
2) increases aldosterone secretion
3) CNS actions - increases water intake and vasopressin secretion

Question 10

23709 – Angiotensin II increases water intake by acting on the
1: area postrema
2: posterior pituitary
3: pineal body
4: subfornical organ

Answer 10

FFFT
Ganong 13th ed. Chapter: 24 PAGE: 382

Question 11

10144 – In the kidney
1: potassium is largely reabsorbed in the proximal tubules
2: urea is actively reabsorbed from the tubules
3: glucose is removed from the glomerular filtrate by active transport
4: protein concentration of blood in efferent arterioles is the same as that in afferent arterioles

Answer 11

TFTF
Guyton, 9th ed, Ch 26, Ch 27, Ganong, 19th ed, Ch 39
1 - K reabsorbed in proximal tubules –> secreted in distal tubules
4 - Filtration of water, but very little protein, in the glomerulus results in an appreciable increase in protein concentration in the efferent arterioles compared to the afferent arterioles

Question 12

12884 – In the kidney
1: protein concentration of blood in efferent arterioles is the same as that in afferent arterioles
2: potassium is secreted by the distal tubules
3: glucose is removed from the glomerular filtrate by active transport
4: potassium is largely reabsorbed in the proximal tubules

Answer 12

FTTT
Approximately 65% of filtered potassium and all the filtered glucose are actively reabsorbed in the proximal tubule (D and C true). Potassium is secreted by the distal tubules (B true) and collecting ducts, in response to the negative charge resulting from sodium resorption in these segments. Filtration of water, but very little protein, in the glomerulus results in an appreciable increase in protein concentration in the efferent arterioles compared to the afferent arterioles (A false).

Question 13

12878 – With respect to the kidney
1: in the presence of hyponatraemia and hypokalaemia the renal response is to lower further the plasma K+ level
2: mean hydrostatic pressure in the peritubular capillaries is lower than that in glomerular capillaries
3: in the proximal tubule, water moves passively out of the tubule along an osmotic gradient
4: in the presence of hypokalaemia and metabolic alkalosis the renal response is to retain K+ in preference to H+

Answer 13

FTTT/TTTT
The proximal tubule is highly permeable to water which diffuses passively from the tubule (C true) and solute concentration is nearly the same on both sides of the tubular membrane. Low plasma sodium concentration leads to reduced vascular fluid volume and this stimulates aldosterone secretion, resulting in sodium resorption and potassium secretion in the collecting ducts. Thus hyponatraemia results in a lowering of plasma potassium concentration (A true). The peritubular capillaries are more distal in the vascular tree and hence at lower hydrostatic pressure (B true).

Question 14

10154 – Diuretics
1: inhibit water and solute reabsorption of tubular fluid
2: inhibit Na-K-Cl co-transport in the luminal membrane of the loop of Henle
3: inhibit H+ secretion and HCO3 reabsorption in the tubules
4: inhibit the action of aldosterone in the glomerulus

Answer 14

TTTF
Guyton 9th ed, Ch 31, Ganong, 19th ed, Ch 38

Question 15

14631 – Renal blood flow falls in
1: hypovolaemia
2: stimulation of α1 adrenergic receptors
3: stimulation of the vasomotor area in the medulla oblongata
4: exercise

Answer 15

TTTT
Refer to Ganong, 19th Ed, Ch 38, page 672

Question 16

12638 – S: A rise in the rate of renal blood flow results in increased glomerular filtration of fluid from the plasma because R: the rise in colloid osmotic pressure within the plasma of the more distal glomerular capillaries becomes less with increased plasma flow

Answer 16

S is true, R is true and a valid explanation of S
Glomerular filtration causes a rise in protein concentration and hence colloid osmotic pressure, in the distal glomerular capillaries. This increased colloid osmotic pressure opposes filtration. Renal blood flow does increase glomerular filtration because of the increase in glomerular pressure (S true). Because a small percentage of plasma is filtered, the rise in distal capillary osmotic pressure is lessened and glomerular filtration increases overall (R true and is a valid explanation of S).

Question 17

12626 – S: An increase in renal blood flow causes an increase in oxygen consumption per gram of renal tissue because R: an increase in renal blood flow increases the volume of filtrate to be reabsorbed

Answer 17

S is true, R is true and a valid explanation of S
An increase in renal blood flow results in an increase in glomerular filtration rate which in turn results in increased filtration and reabsorption of sodium. Oxygen consumption in the kidney is proportional to Na+ transport (reabsorption in the tubules) and hence to renal blood flow and the volume of filtrate reabsorbed (S and R are true and R is a valid explanation of S).

Question 18

15077 – The operation of the loop of Henle as a countercurrent multiplier depends
1: on the active transport of Na+ and Cl- out of the thick ascending limb
2: the high water permeability of its thin descending limb
3: the relative water impermeability of the thin ascending limb
4: the concentration of urea in the interstitial spaces

Answer 18

TTTT
Refer to Ganong, 19th Ed, Ch 38, page 681-685

Question 19

9973 – The protein concentration in the glomerular capillaries
1: is 20% higher at the efferent end of the glomerular capillary
2: will alter the filtration fraction
3: results in an average colloid osmotic pressure of over 30 mm Hg in the glomerular capillary
4: is lower than the protein concentration in muscle capillaries

Answer 19

TTTF
Ganong, 19th ed, Ch 38

Question 20

15458 – The glomerular filtration rate varies
1: with efferent arteriolar constriction
2: agents affecting the mesangial cells
3: with the permeability of the glomerular capillaries
4: with changes in extracellular volume

Answer 20

TTTT
Refer to Ganong, 19th Ed, Ch 38, page 673

Question 21

12512 – Which of the following normally has the highest renal clearance?
A. inulin
B. glucose
C. para-amino hippurate
D. urea
E. water

Answer 21

C
Urea is filtered at the glomerulus and partially reabsorbed in its passage along the nephron (D false). Inulin is not secreted or reabsorbed in the renal tubules and is excreted as it is filtered (A false) but para-amino hippurate is secreted in the proximal tubules so that it is nearly totally cleared from the plasma by the time the blood leaves the kidney (C true). Glucose is rapidly reabsorbed in the proximal tubule (B false) and water is reabsorbed throughout the tubules, collecting tubules and ducts (E false).

Question 22

12518 – The ascending limb of the loop of Henle
A. is impermeable to sodium ions
B. actively transports the majority of potassium ions
C. actively transports most of the filtered water into the tubule lumen
D. actively transports chloride ions out of the tubule lumen
E. actively transports sodium ions into the tubule lumen

Answer 22

D
The loop of Henle is active in the final event for increasing the osmolar concentration of urine. Sodium and chloride ions are transported into the inner medullary interstitium (by NaK2Cl channels; A and E false; D true). Similarly only 27% of filtered potassium is actively reabsorbed in the loop of Henle, 65% having previously been actively transported in the proximal tubule. D is more appropriate than B in the context of the question.

Question 23

12853 – In osmotic diuresis
1: decreased water reabsorption in the proximal tubule accounts for approximately one-quarter of the diuresis
2: significant sodium loss may occur
3: the urine becomes more acid than normal
4: the increased urine output is caused by substances which are not reabsorbed in the renal tubule system

Answer 23

FTFT
In osmotic (solute) diuresis, the increased flow is due to substances such as mannitol, which are filtered but not reabsorbed, or to substances such as glucose or urea present in amounts exceeding tubular reabsorptive capacity (D true). Decreased water reabsorption in the proximal tubules is the main cause of the diuresis (A false). As very large amounts of urine can be produced, significant losses of electrolytes, such as sodium, carried in the urine can occur (B true). No specific change in the reaction of urine occurs (C false).

Question 24

12632 – S: The phosphate buffer system plays a major role in H+ buffering in the tubules because R: the phosphate buffer system has a pK suited to the pH of tubular fluid

Answer 24

S is true, R is true and a valid explanation of S
The phosphate buffers are composed of a mixture of HPO and H2PO and are poorly reabsorbed from the tubules where they become concentrated in association with water reabsorption. This makes them an important buffer source (S true). Their pK of 6.8 also makes these active buffers as the urine becomes concentrated through the tubules and the pH falls to about 6.0. That is the phosphate buffers function in their most effective range near their pK value (R is true and is a valid explanation of S).

Question 25

9910 – S: The initial decline in sodium ion excretion after haemorrhage is due to increased circulatory levels of aldosterone because R: in
haemorrhagic shock secretion of renin results in an increased aldosterone secretion

Answer 25

S is false and R is true
Ganong, 19th ed, Ch 35

Question 26

14934 – S: Even though the diameter of albumin is 7 nm, minimal amounts are found in the urine because R: albumin is a plasma protein that is negatively charge

Answer 26

S is true, R is true and a valid explanation of S
Refer to Ganong, 19th Ed, Ch 38, page 674-675

Question 27

23749 – Extra-renal losses of potassium are usually small but may be markedly increased with
1: small bowel fistulae
2: villous tumours of the rectum
3: profuse sweating
4: fulminating ulcerative colitis

Answer 27

TTFT

Question 28

12798 – Factors concerned with the onset of a diuresis in a healthy young man who drinks a litre of water in 5 minutes include
1: rise in circulating blood volume
2: rise in glomerular filtration rate
3: stimulation of volume receptors in the hypothalamus
4: suppression of ADH secretion

Answer 28

TTFT
The ingestion of 1000 ml of water, which is rapidly absorbed into the blood, will obviously increase the circulating blood volume (A true). There will be a reduction in the osmolarity of blood plasma which will cause the osmoreceptors in the hypothalamus to reduce posterior pituitary stimulation leading to a reduction in ADH secretion (D true). The rise in circulating blood volume will increase the hydrostatic pressure in the glomerular capillaries resulting in a rise in the glomerular filtration rate (GFR) (B true). There are no volume receptors in the hypothalamus (only osmoreceptor), these being located peripherally (C false).

Question 29

21228 – Factors concerned with the onset of a diuresis in a healthy young man who drinks a litre of water in 5 minutes include
1: rise in glomerular filtration rate
2: rise in circulating blood volume
3: suppression of ADH secretion
4: stimulation of volume receptors in the hypothalamus

Answer 29

TTTF
Guyton 7th Ed. Ch. 22 P. 262 Ch. 36 P. 430-431
The ingestion of 1000 ml of water, which is rapidly absorbed into the blood, will obviously increase the circulating blood volume. There will be a reduction in the osmolarity of blood plasma which will cause the osmoreceptors in the hypothalamus to reduce posterior pituitary stimulation leading to a reduction in ADH secretion. The rise in circulating blood volume will increase the hydrostatic pressure in the glomerular capillaries resulting in a rise in the glomerular filtration rate (GFR). There are no volume receptors in the hypothalamus (only osmoreceptor), these being located peripherally.

Question 30

12614 – S: During acidosis the pH of the glomerular filtrate can fall below 4.5 in the proximal tubule because R: the proximal tubule is the major site for removal of HCO from the filtrate

Answer 30

S is false and R is true
Although the bulk of H+ secretion occurs in the proximal tubule via the Na+ H+ counter-transporter, the maximum concentration gradient which can be achieved is only approximately three-fold, resulting in a proximal tubular fluid pH which is not lower than approximately 6.9 (S false). The secreted H+ combines with filtered bicarbonate to form carbonic acid which is immediately converted to H2O and CO2 by carbonic anhydrase. The CO2 diffuses back across the tubular membrane for either resynthesis of bicarbonate, or transport to the lungs for excretion.

Question 31

10149 – The ability of the kidneys to conserve urinary chloride depends on the
1: efficiency of Na+ reabsorption in the distal tubules
2: active Cl- reabsorption in the ascending limb of the loop of Henle
3: efficiency of Na+ reabsorption in the proximal tubules
4: varying permeability to chloride of the distal convoluted tubules and collecting ducts

Answer 31

TTTF
Ganong, 19th ed, Ch 38

Question 32

14098 – S: Hydrogen ion that reacts with bicarbonate contributes to urinary titratable acidity because R: the titratable acidity is the amount of alkali that is added to urine to return the pH to 7.4, the pH of the glomerular filtrate

Answer 32

S is false and R is true
Ganong, 19th Ed, Ch 38, page 687
Coz those H+ will either react with bicarb/ hydrogen phosphate/ ammonia in urine

Question 33

24344 – Beer in moderate quantity causes diuresis because the
1: water in beer significantly increases the glomerular filtration rate
2: alcohol in beer inhibits anti-diuretic hormone release
3: alcohol in beer inhibits tubular sodium reabsorption
4: water in beer inhibits anti-diuretic hormone release

Answer 33

FTFT
Guyton 7th ed. CHAPTER: 75 PAGE: 893-894 Ganong, 19th Ed, Ch 38, p691

Question 34

15072 – The production of urine with a high osmolarity is associated with
1: a decrease in membrane permeability of the distal tubule and collecting duct to water
2: a decrease in medullary blood flow
3: an increase in secretion of aldosterone
4: an increase in secretion of antidiuretic hormone

Answer 34

FTFT
Refer to Guyton, 9th Ed, Ch 28, page 356; Ganong, 19th Ed, Ch 38, page 681 and following
2: slower medullary blood flow - more Na accumulated at medulla –> less reabsorption of Na from LoH

Question 35

19210 – Elevated serum bicarbonate is commonly associated with each of the following EXCEPT
A. chronic emphysema
B. duodenal ulcer with obstruction
C. total parenteral nutrition
D. milk-alkali syndrome
E. hyperaldosteronism

Answer 35

C
Burkett - C. S. S. CHAPTER: 13.8.1 Ganong, 19th Ed, Ch 39, p703-704, 359
A - resp acidosis
B - met alkalosis
C - TPN - met acidosis
D - met alkalosis
E - reabsorption of Na in exchange of H+ - met alkalosis

Question 36

14912 – S: The bicarbonate buffer system is the most important in the body because R: its pK is close to the pH of the extra-cellular fluid

Answer 36

S is true and R is false
Refer to Ganong, 19th Ed, Ch 39, page 698-699

Question 37

21978 – Hydrogen ions
1: directly stimulate the respiratory centre
2: are excreted in the urine predominantly by combining with urinary buffers
3: can be secreted against a concentration gradient until a urine pH of approximately 4.5 is reached
4: can be secreted against a large concentration gradient in the collecting ducts

Answer 37

TTTT

Question 38

15453 – H+ ions are
1: secreted into the proximal tubule
2: secreted into the distal tubule in increased amounts in the presence of aldosterone
3: buffered by HCO3 in the proximal tubule
4: exchanged for K+ in the distal tubule

Answer 38

TTTF
Refer to Guyton, 9th Ed, Ch 27, page 337; Ganong, 19th Ed, Ch 38, page 676 and following.
Aldosterone: reabsorption of Na+ in exchange of H+.
Hydrogen ions are actively secreted in the proximal and distal tubules and the collecting ducts. Although aldosterone mainly causes potassium to be secreted into the tubules in exchange for sodium it also causes tubular secretion of hydrogen ions in exchange for sodium. The secreted hydrogen ions are buffered by bicarbonate, varying with the extracellular concentration of carbon dioxide. Hydrogen ions are exchanged for sodium but not for potassium ions (4 false).

Question 39

12894 – H+ ions are
1: exchanged for potassium in the early distal tubule
2: secreted into the distal tubule in increased amounts in the presence of aldosterone
3: buffered by HCO3- in the proximal tubule
4: secreted into the proximal tubule

Answer 39

FTTT
Hydrogen ions are actively secreted in the proximal (D true) and distal tubules and the collecting ducts. Although aldosterone mainly causes potassium to be secreted into the tubules in exchange for sodium it also causes tubular secretion of hydrogen ions in exchange for sodium (B true). The secreted hydrogen ions are buffered by bicarbonate (C true), varying with the extracellular concentration of carbon dioxide. Hydrogen ions are exchanged for sodium but not for potassium ions (A false).

Question 40

22399 – Blood urea concentration may be influenced by
1: glomerular filtration rate
2: dietary protein intake
3: hepatic function
4: body hydration state

Answer 40

TTTT
Guyton 8th ed. Page: 324

Question 41

21678 – Urinary potassium excretion rate usually
1: increases in pyloric stenosis
2: decreases in the first 24 hours after injury
3: is not influenced by ADH (vasopressin)
4: remains the same during osmotic diuresis

Answer 41

TFTF
Guyton 7th ed. Ch.35 P.421-423. Ganong 13th ed.Ch.77 P.911,916 26 P.409.

Question 42

14636 – In the renal nephron, Na+ is actively absorbed from
1: proximal tubule
2: distal tubule and collecting duct
3: ascending portion of the loop of Henle
4: descending portion of loop of Henle

Answer 42

TTTF
Refer to Ganong, 19th Ed, Ch 38, page 677

Question 43

23594 – With regard to the renal tubular lumen
1: hydrogen ions are secreted into the lumen in exchange for sodium
2: carbon dioxide diffuses from the lumen into the tubular cells
3: secreted hydrogen is excreted predominantly as free hydrogen ions
4: filtered bicarbonate is directly resorbed into the tubular cells

Answer 43

TTFF
Guyton 9th ed.Page: 394 Ganong, 19th Ed, Ch 38 page 686-689
3 - bound to hydrogen phosphate/ammonia
4 - INdirect

Question 44

10058 – The renal changes associated with severe haemorrhage include
1: afferent and efferent arteriole constriction
2: increased filtration fraction
3: enhanced sodium retention by the renal tubules
4: potassium retention in association with sodium by the renal tubules

Answer 44

TTTF
Ganong, 19th ed, Ch 33
1, 2: Catecholamines (norepinephrine and epinephrine) increase filtration fraction by vasoconstriction of afferent and efferent arterioles, possibly through activation of alpha-1 adrenergic receptors. Severe haemorrhage will also result in an increased filtration fraction.

Question 45

13640 – Blood urea may rise with
1: hypovolaemic shock
2: severe infection
3: steroid therapy
4: liver failure

Answer 45

TTTF
Urea is synthesised in the liver, from ammonia formed by the deamination of amino acids. Thus, in liver failure, urea levels in blood will be low (D false). Urea is excreted by filtration through the renal glomerular membrane. In conditions of reduced blood flow, as in hypovolaemia, much water is reabsorbed in the proximal tubules, causing urea to become highly concentrated within the tubule. The diffusion of urea back into the renal interstitium is thereby facilitated (A true). Both infection and
steroid therapy produce a catabolic state, with increased turnover of protein and a resultant increased synthesis of urea (B and C true).

Question 46

10053, 12889 – Rise in blood urea in a previously normal man deprived of water is the consequence of
1: active reabsorption of urea in the distal tubule
2: increased diffusion of filtered urea from tubular lumen to medullary interstitium
3: increased production rate
4: reduced tubular flow rate of urine

Answer 46

FTFT
Ganong, 19th ed, Ch 17 and 38. Production rate of urea is primarily dependent upon diet and liver function and is independent of hydration state (C false). During dehydration, there is reduced glomerular filtration and most water is resorbed proximally. This causes an increased urea concentration in proximal tubular fluid and as a result there is increased diffusion of filtered urea into the interstitium (B and D true). Urea is not actively reabsorbed (A false).

Question 47

12620 – S: Urea clearance is increased at high rates of urine flow because R: reabsorption of urea across the tubular system of the nephron
is largely a passive phenomenon

Answer 47

S is true, R is true and a valid explanation of S.
Urea of the glomerular filtrate leaves the tubules by simple diffusion (R true) according to the countercurrent exchange of the vasa recta and, as water is reabsorbed in the tubules, so too is urea. At high glomerular filtration with consequent high urine flow the excretion of urea rises (S true R is a valid explanation of S).

Question 48

20667 – S. After a meal the urine maybe alkaline (postprandial alkaline tide) BECAUSE R. the stomach venous blood has a higher PCO2 than stomach arterial blood after a meal

Answer 48

S is true and Ris false.
Ganong 13th ed. CHAPTER: 26 PAGE: 410

Question 49

12803 – Creatinuria occurs in
1: normal children
2: pregnant women
3: thyrotoxicosis
4: starvation

Answer 49

TTTT
Creatine is synthesised in the liver from methionine, glycine and arginine and is phosphorylated in muscle to phosphocreatine which is an immediate energy source of ATP. Creatinine found in urine is derived from phosphocreatine not creatine, and its daily rate of excretion is relatively constant. Creatinuria occurs normally in children and in women during and after pregnancy (A and B true). There is very little creatine in the urine of men. Creatinuria is exacerbated in any condition associated with muscle breakdown, particularly starvation and thyrotoxicosis (C and D true).

Question 50

12914 – Changes after four hours of complete ureteric obstruction include
1: a rise in renal blood flow
2: a fall in glomerular filtration rate
3: a rise in renal tissue fluid volume
4: a fall in glomerular blood flow

Answer 50

FTFT
The ureters have a rich innervation by autonomic nerve fibres. When a ureter becomes obstructed a ureterorenal reflex produces constriction of renal arterioles, with a resultant fall in renal blood flow (A false), glomerular blood flow (D true) and glomerular filtration rate (B true), but no change in renal tissue fluid volume (C false).

Question 51

12506 – A patient suffers from a metabolic acidosis due to excessive production of keto-acids. In this state all of the following exist EXCEPT
A. increased urinary NH excretion
B. decreased PCO2 of the arterial blood
C. increased renal excretion of titratable acid
D. decreased intracellular H+ concentration
E. an increased rate of production of bicarbonate

Answer 51

D
Little free hydrogen can be excreted in the urine; so in acidosis excess quantities of urinary hydrogen ion secreted are buffered with ammonia and phosphate buffers (A and C false). Free hydrogen ion is buffered by bicarbonate derived from CO2 and H2O to form carbonic anhydrase with dissociation to HCO and H+. The latter is excreted in the tubules in exchange for Na. This process is driven by increased H+ ions (D true) which cause increased rate and depth of respiration to blow off CO2 and decrease the blood pCO2 (E and B false).

Question 52

12899 – Regarding the acidification of urine
1: H+ is secreted into the urine by the cells lining the distal tubules
2: K+ is normally reabsorbed from the tubular fluid as part of the acidification process of urine
3: when there is a large load of H+ to be excreted, most of it appears in the urine in the form of ammonium salts
4: H2CO3 is present in the urine in very high concentration compared with plasma

Answer 52

TFTF
Hydrogen ions are secreted by tubular epithelial cells throughout the tubular system (A true). Carbon dioxide which diffuses into cells with water is rapidly converted by carbonic anhydrase into carbonic acid which in turn rapidly dissociates into H+ and HCO3- (D false). Potassium is reabsorbed in the proximal tubule but is predominantly secreted at other sites (B false). In the distal tubule potassium or hydrogen ions are secreted in exchange for sodium in an aldosterone dependent process. Hydrogen ions can only be secreted into urine until urine pH reaches approximately 4.5. To excrete the required acid load, secreted hydrogen ions combine with buffers, thereby enabling a great increase in capacity for H+ excretion. Ammonia produced by the tubular epithelial cells combines readily with H+ to form ammonium. Ammonium secretion may rise 10-fold to 15-fold in chronic acidosis and under these conditions is the major urinary buffer (C true).

Question 53

15082 – Regarding potassium excretion and the kidney
1: approximately 600 mmol of potassium are filtered each day in a normal person
2: secretion of potassium occurs in the distal tubule and the collecting duct
3: approximately 90% of filtered potassium is resorbed in the proximal tubule and loop of Henle
4: the rate of K+ secretion is proportionate to the rate of flow of the tubular fluid

Answer 53

TTTT
Refer to Ganong, 19th Ed, Ch 38, page 677, 690

Question 54

12823 – Extra-renal losses of potassium are usually small but may be markedly increased with
1: villous tumours of the rectum
2: fulminating ulcerative colitis
3: profuse sweating
4: small bowel fistulae

Answer 54

TTFT
Extra-renal losses of potassium are markedly increased in conditions involving excessive loss of mucus, which has a high protein content, from the large bowel. Potassium losses are excessive with villous tumours of the rectum and in fulminating ulcerative colitis, because of large amounts of diarrhoea (A and B true). The K+ loss in diarrhoea is appreciable because the potential difference across the mucosa is greater in the colon than in the ileum and the steady state K+ concentration of colonic contents is relatively high. Even though there will be some loss of K+ in small bowel fistulae, it
will be less than in colonic conditions (D true). The content of K+ in sweat is low (C false).

Question 55

22389 – The major consequences of untreated renal failure include
1: anaemia due to decreased production of erythropoietin
2: toxicity due predominantly to very high concentration of urea
3: coma due to the development of a profound acidosis
4: hypocalcaemia due to decreased secretion of parathyroid hormone

Answer 55

TFTF
Guyton Page: 347. Question updated 2 Dec 2002

Question 56

15463 – The osmolarity of the medullary interstitial fluid would become less hypertonic and eventually approach the osmolarity of plasma when
1: aldosterone secretion is reduced sufficiently
2: the fluid flow through the Loop of Henle increases sufficiently
3: an osmotic diuresis is pronounced
4: the blood flow through the vasa recta increases sufficiently

Answer 56

FTTT
Refer to Guyton, 7th Ed, Ch 35, page 416-422

Question 57

23964 – Urine pH less than 5.0
1: is within normal limits
2: contains HCO3- in greater than normal concentration
3: contains more H2PO4- than HPO4-
4: contains less than normal NH4+

Answer 57

TFTF
Burnett - C. S. S. CHAPTER: 13 PAGE: 204

Question 58

13433 – S: Bilateral nephrectomy in a patient suffering from renal failure is followed by osteomalacia because R: renal tissue is essential for the formation of 1,25 dihydroxycholecalciferol

Answer 58

S is true, R is true and a valid explanation of S
1,25 dihydroxycholecalciferol is the main metabolite of Vitamin D, and is responsible for most of the actions of the vitamin. It is produced in the renal cortical cells (R true and is a valid explanation). Chronic renal disease is often associated with osteomalacia (S true) and rickets late in the disease.