Kidney Function III, Production of dilute urine

Question 1

Definition of oligouria

Answer 1

Urine output below obligatory water loss of 0.428l/day

Question 2

Definition of polyuria

Answer 2

Excessive output of urine over 1-2l/day

Question 3

Definition of polydipsia

Answer 3

Excessive thirst

Question 4

Definition of nocturia

Answer 4

Having to pass urine at night

Question 5

What are the 2 ways of maintaining a constant plasma osmolarity

Answer 5

Urine formation

Thirst

Question 6

What is the equation for osmolar clearance
What is osmolar clearance
What is the fasting osmolar clearance

Answer 6

Cosm = Uosm x urine flow rate / Post

Volume of plasma cleared of osmotically active molecules

2-3ml/min

Question 7

What is the obligatory osmolar clearance

What is the range of urine osmolarity

Answer 7

600mosmol/l
0.428l/day

50-1400mosmol/l

Question 8

What is the equation for free water clearance
What is free water clearance

How would you interpret the free water clearance
0<
0=
0>

Answer 8

CH2O = V - (Uosm x V/Posm)

Kidney’s ability to excrete dilute/conc urine

0< dilute
0= isotonic
0> conc

Question 9

Describe the pathway of action of ADH when dehydrated

Answer 9

Dehydration => increased Posm

Increased signalling from osmoreeptors in OVLT, MPN, SO => paraventricular, supraoptic

Neurohypophysis releases more ADH

Increased water absorption

Question 10

Describe the pathway of action of ADH when overhydrated

Answer 10

Overhydration => decreased Posm

Decreased signalling from osmoreceptors in OVLT, MPN, SO => paraventricular, supraoptic

Neurohypophysis releases less ADH

Decreased water absorption

Question 11

What promotes ADH release

Answer 11

Increased Posm
Ang2/decreased BV, BP
Nicotine, nausea, stress, pain

Question 12

What inhibits ADH release

Answer 12

ANP

Alcohol

Question 13

What is osmotic diuresis

Answer 13

Small molecules can’t be reabsorbed => increased osmolarity and water retention

Results in polyuria, polydipsia

Question 14

What is diabetes insidious
What are the 2 types
What are the 2 main symptoms

Answer 14

Neurogenic (no ADH released)
Nephrogenic (faulty V2 rec/AQP2)

Excess thirst
Polyuria
Polydipsia
Nocturia

Question 15

Describe the importance of potassium 
How is it reabsorbed/secreted in the
-PT
-Thick asc LOH
-Intercalated cells 
-Principle cells

Answer 15

Dictates cell resting membrane potential

PT

• Passive reabsorption/FD
• Some secretion via FD, driven by NaKATPase

Thick asc LOH

• NaKCl triporter/passive => cell, driven by NaKATPase
• KCl exchange/FD => medulla

Intercalated cells
-HK exchange => FD => medulla

Principle cells
-ROMK, BK, KCl secretion due to NaKATPase

Question 16

What are the 4 ways of regulating K secretion in principle cells

Answer 16

Increased Na reabsorption

Aldosterone
-acts on NaKATPase, ENac

Tubular flow rate
-increased flow => more secretion, less reabsorption

pH

• acidosis inhibits (KH intercalated cell activity inhibited)
• alkalosis enhances (NaH stimulated => NaK activated)

Question 17

What is hypokalaemia

What are the 3 causes

Answer 17

Plasma K < [3.5]

Increased external losses

• increased tubular flow rate
• hyperaldosteronism

Redistribution into cells

• metabolic alkalosis (NaH => NaK)
• excess insulin

Inadequate intake in diet

Question 18

What are the symptoms of hypokalaemia

Answer 18

Increased K in cell => hyperpolarisation
Larger stimulus needed to reach AP
Longer repolarisation
Affects muscle function

Question 19

What are the 4 methods of treating hypokalaemia

Answer 19

KCl admin
Consume K rich food
K sparing diuretics (Diuretics inhibit NaK)
Alkalosis correction

Question 20

What is hyperkalaemia

What are the 2 main causes

Answer 20

plasma K > 5.5

Decreased external losses

• renal failure
• hypoaldosteronism

Redistribution into cells

• metabolic acidosis/lack of insulin/ketoacidosis (NaH inhibited, NaK inhibited)
• Tissue death, released K

Question 21

What are the symptoms of hyperkalaemia

Why is hyperkalaemia more dangerous than hypokalaemia

Answer 21

Low cell K => depolarisation
Weaker stimuli needed to reach AP

Affect cardiac function => arrhythmias

Question 22

How would you treat hyperkalaemia

Answer 22

ADRESS THE HEART FIRST

Short term
-Ca admin => keep heart beating

Medium term
-Insulin and glucose admin => K moves into cells

Long term
-K secretion via diuretic