Question

	Sample 1	Drink	Sample 2	Sample 3	Sample 4	Sample 5	Sample 6
Time of day	2.10pm		2.40pm	3.10pm	3.40pm	4.10pm	4.40pm
Time interval (min)	76		30	30	30	30	30
Urination duration (s)	5		5	6	7	6	5
Urine volume (ml)	72		35	95	156	135	76
Urine flow rate (ml/sec)	14.4		7.0	15.8	22.3	22.5	15.2
Urine Production rate (ml/min)
Na+ conc’n (mmol/litre)	120		43	12	11	16	17
Na+ excretion rate (mmol/min)
Urine osmolality (mOsm/kg H2O)	743		453	169	94	109	188
Osmolar excretion rate (mOsm/min)

1. Calculate and show example of the

(a) Urine production rate (ml/min)

(b) Na⁺ excretion rate (mmol/min)

(c) Osmolar excretion rate (mOsm/min)

2. What are the possible reason that could lead to one of the subjects have high urine production rate but low urine flow rate? Provide and explain using two examples

Answer 1

• Urine flow rate: Urine volume divided by the time duration between the previous urine void and the urine sample collection.

  Urine flow rate = 72ml.

  Time = 76 mins.

  Urine flow rate: 72/76 = 0.947 ml/m.

  Urine production rate:

  Total urine output in mL / (Weight in kg x Hours)

  Na+ excretion rate:

  Na+ concentration = 120mMol/L

  = [(V x c) ÷ 1000] mmol/day

  = (72*120)/1000= 8.6mMol/L 8.6*10^3M/l

  Osmolar exccretion rate:

  Urine osmolarity = 743

  =number of excreted osmoles divided by the urine volume.

  743/72 = 10.32*10^3osmol/min.

2. Increased urine production occurs in association with bladder infection, diabetes, psychogenic polydipsia which is a mental disorder leads to excessive thirst. The urine flow rate is determined by the rate of osmoles excretion and the effective osmolality of the interstitial compartment of the renal medulla. Slow flow rate arises when there is an obstruction at the bladder neck or in the urethra, or due to an enlarged prostate in eldery men, or a weak bladder.