Lecture 2: Changes in Outflow

Question 1

During the 1st phase of unilateral ureteral obstruction, there is urine backflow, and how is GFR maintained?

Activation of what leads to the 2nd phase?

Answer 1

• Simultaneous increase in glomerular capillary pressure induced by afferent arteriolar vasodilation which maintains GFR
• Activation of RAAS leads to the 2nd phase

Question 2

During the 2nd phase of unilateral ureteral obstruction what occurs?

Answer 2

Decreased glomerular blood flow due to afferent arteriole vasoconstriction

Question 3

During the 3rd phase of unilateral ureteral obstruction there is a decrease in what 2 things?

Answer 3

• Decreased luminal hydrostatic pressure
• Decreased renal blood blow

*BOTH below baseline

Question 4

Persistent unilateral ureteral obstruction >24 hours cause what % decrease in GFR?

Answer 4

50% decrease in GFR

Question 5

In BUO how is the GFR maintained during the 2nd phase?

i.e., the major difference between BUO and UUO

Answer 5

Persistent efferent and (partial) afferent arteriole vasconstriction

Question 6

What occurs to sodium reabsorption in a unilateral ureteral obstruction?

Due to what?

Answer 6

Inability to reabsorb Na+ throughout the nephron (salt wasting) due to downregulation of receptor and enzyme activity

Question 7

In both bilateral and unilateral ureteral obstruction what occurs to glomerular blood flow and how?

Answer 7

Decreased glomerular blood flow due to afferent vasoconstriction

Question 8

In bilateral ureteral obstruction what is the effect of ANP and the net result of this action?

Answer 8

ANP blocks effects of renin –> decreased AT II = diuresis and natriuresis

Question 9

Na⁺ reabsorption in BUO differs from UUO due to presence of what?

Answer 9

Presence of volume expansion

Question 10

During ureteral obstruction which segments of the nephron are disrupted and how does this lead to increased excretion of solutes?

Answer 10

• Inability to absorb Na⁺ in ascending limb

AND

• Inability to dilute filtrate in DCT

Question 11

What is the effect on urea cycling during a ureteral obstruction?

Answer 11

• Defective urea recycling
• Transporter defect ↓ concentrating effect and allows urea to be excreted

Question 12

What happens to K⁺ concentrations in the collecting duct during the low-flow luminal state associated w/ ureteral obstruction?

Leads to what?

Answer 12

• High urinary [K⁺] in collecting duct = loss of gradient between cell and lumen
• Results in hyperkalemia

Question 13

Urinary obstruction leads to what type of RTA?

Answer 13

Form of RTA type 1 (distal), but w/ hyperkalemia

Question 14

Children presenting w/ frequent UTI or pyelonephritis should be evaluated for?

Answer 14

Vesicoureteral reflux

Question 15

With BPH, eventually the pressure in the bladder will increase so much that urine is forced backwards causing what?

Answer 15

Hydronephrosis

Question 16

What is the most common cause of bilateral hydronephrosis in boys?

Answer 16

Posterior urethral valves

Question 17

Overflow incontinence is due to loss of function in what?

Answer 17

Loss of detrusor m. function causing emptying phase abnormality = bladder empties when capacity exceeded

Question 18

What can be done at patients bedside to assess bladder emptying capability?

Which value of urine is indicative of incomplete empyting?

Answer 18

• Ultrasound evaluation for post-void residual
• After pt voids >100 mL left indicates incomplete emptying

Question 19

Neurogenic bladder is due to a disruption in the coordination of what during bladder contraction?

Answer 19

Coordination of relaxation of sphincter during bladder contraction

Question 20

Neurogenic bladder requires regular monitoring why?

Answer 20

Hydronephrosis may occur before irreversible injury occurs

Question 21

What is the typical pain pattern/radiation for Renal Lithiasis?

Answer 21

Back/flank pain that radiates to the groin

Question 22

Which imaging technique is preferred for diagnosis of renal lithiasis?

Answer 22

CT

Question 23

Transitional cell carcinoma may causes obstruction of the ureter at which 2 locations?

Answer 23

UPJ or UVJ

Question 24

What is a normal physiological event seen following bilateral ureteral obstruction?

Answer 24

Postobstructive diuresis

Question 25

Postobstructive diuresis following a BUO results from what 2 physiological events occuring during the obstruction?

Answer 25

• Downregulation of Na⁺ transporters during obstruction
• ANP released in response to cardiac preload during obstruction

Question 26

What is the treatment for postobstructive diuresis following BUO?

Answer 26

Fluid replacement in response to diuresis - 75% of urine volume w/ careful monitoring of urine and serum osmolality + electrolytes