L27 Regulation of Water Balance

Question 1

What are the ‘inputs’ involved in water balance?

Answer 1

Drinking

Eating

Metabolism

Question 2

What are the ‘outputs’ involved in water balance?

Answer 2

Urine

Respiration

Skin

Faeces

Question 3

What is normal plasma osmolality?

Answer 3

280-290mOsmol (+/- 3)

Question 4

The fluid reaching the collecting ducts is:

A) Isotonic
B) Hypotonic
C) Hypertonic

Answer 4

B) Hypotonic

Question 5

Where is ADH synthesised?

Answer 5

Supraoptic and paraventricular nuclei of hypothalamus. Stored and released from neurohypophysis (posterior pituitary)

Question 6

What is the half-life of ADH?

Answer 6

15 minutes - it is degraded in the liver and kidney

Question 7

True or false: ADH is a molecule made of 166 amino acids

Answer 7

False

Its precursor is 166 aa, while ADH is a nonapeptide

Precursor is cleaved progressively as it moves through axons of hypothalamohypophyseal tract

Question 8

What is the primary signal for release of ADH?

Answer 8

Increase in plasma osmolality - above 280mOsmol

Question 9

True or false: The relationship between increasing plasma osmolality and ADH concentration is linear

Answer 9

True, after plasma osmolality reaches 280. Prior to that, no ADH released

Question 10

True or false: The relationship between plasma ADH concentration and urine osmolality is linear

Answer 10

True

Question 11

Why can BP medication affect the ADH system?

Answer 11

One of the stimuli for ADH release is low BP. By interfering with BP, you have a knock on effect within the ADH system.

Question 12

What stimuli can trigger ADH release?

Answer 12

1. ↑ plasma osmolality
2. ↓ decrease blood pressure
3. Nausea
4. Hypoglycaemia
5. Hypoxia (↓ O2 or ↑CO2)
6. Angiotensin

Question 13

True or false: ADH mechanism involves it binding to V2 receptors on the apical surface of principal cells

Answer 13

False

V2 receptors are located on the basal membrane of principal cells

Question 14

Binding of ADH to a V2 receptor triggers what cascade?

Answer 14

Activates adenylate cyclase (via G protein) to produce cAMP

cAMP activates protein kinase A

PKA phosphorylates and activate non-functional aquaporin-2 channels

Active aquaporin-2 channels insert into apical (luminal) membrane

Question 15

What is the maximal osmolality that can be achieved in urine concentration?

Answer 15

1400mOsmol

Question 16

True or false: The minimum amount of urine that can be excreted in one day is around 500-600ml

Answer 16

True

Question 17

What encourages urine flow through the ureters?

Answer 17

Peristalsis initiated by pacemaker cells in the renal pelvis

Question 18

Which nerves control voluntary micturition? Which structure is being controlled by this nerve?

Answer 18

Pudendal nerves control tone of the external sphincter.

Tonically active, keeping sphincter closed until voluntary release.

Question 19

Which nerve relaxes the internal urethral sphincter?

Answer 19

Efferent pelvic nerve

Question 20

The nerves innervating the urinary bladder and its associated sphincters originate from which vertebral levels?

Answer 20

L1-3 separate semen from wee

S2-4 keep the pee off the floor

Question 21

What is the role of the hypogastric nerves in relation to the urinary bladder? From where do they originate?

Answer 21

Prevent entry of semen into bladder during ejaculation

Originate from L1-3 (separate semen from wee)

Question 22

The pelvic nerves carry __1__ (afferent) fibres and __2__ (efferent) fibres.

Answer 22

1. sensory
2. parasympathetic

Pelvic nerve controls internal sphincter

Question 23

Which nerve controls the external sphincter of the bladder? is this control voluntary or autonomic?

Answer 23

Pudendal, voluntary

Question 24

Which of the following occurs as a result of excessive ADH:

A) Peripheral oedema
B) Hypernatremia
C) Diabetes insipidus
D) Diabetes mellitus

Answer 24

A) Peripheral oedema

Other conditions associated with excessive ADH include:

• Hyponatremia
• Secretion of Inappropriate ADH syndrome (SIADH)

Question 25

True or false: Inappropriately low levels of ADH can cause diabetes insipidus

Answer 25

True