Control and abnormlities of salt and body water

Question 1

Changes in plasma [Na] suggest what?

Answer 1

Suggest excess or deficit of body water

Question 2

What is osmolality?

Answer 2

The number of particles per unit volume of fluid

Question 3

Osmolality

Answer 3

Per kg water

Question 4

Osmolarity

Answer 4

per litre solution

Question 5

Sodium

Answer 5

The principal cation in the ECFV : 135-145 mmol L-1 (mM)

Question 6

Plasma osmolarity equation

Answer 6

2[Na] + 2[K] + [glucose] + [urea]

Question 7

Normal plasma osmolality

Answer 7

275-295 mOsm Kg-1

Question 8

Plasma [Na]

Answer 8

135-145 mmol/L

Question 9

Hypernatremia

Answer 9

Means hyperosmolality

Question 10

Hyponatremia

Answer 10

Means hypo-osmolality

Question 11

How is the osmolality of ECFV adjusted?

Answer 11

Osmoreceptors: sensory receptors located in hypothalamus sense changes in osmolality of ECFV
Increase in osmolality stimulates
- thirst
- Secretion of vasopressin (ADH)

Question 12

What is ADH?

Answer 12

Osmoregulation hormone

Question 13

How does ADH work?

Answer 13

Regulates plasma osmolality primarily by controlling water excretion and reabsorption
Excretion of water is normally regulated independently of excretion of solute

Question 14

How is ADH secretion regulated?

Answer 14

Two major physiological mechanisms
Under normal conditions the function of ADH is osmoregulation
A large drop in arterial pressure is also a powerful stimulus for the release

Question 15

Volume depletion

Answer 15

Hemorrhage, loss of BP sufficient to stimulate ADH

Question 16

Thirst and water intake

Answer 16

First and highly effective line of defense against dehydration

Question 17

What are the 2 types of thirst

Answer 17

Hyperosmotic thirst

Hypovolemic thirst

Question 18

What happens in normal circumstances for the vasopressin system?

Answer 18

Maintain plasma osmolarity at 285 mOsmol L-1 in the face of variable water intake

Question 19

Solute load

Answer 19

Estimated at 10 x BW in kg (mOsmol L-1)

Question 20

Solute load in detail

Answer 20

If max urine concentration is 1200 mOsmol L-1 then 0.5 L is required to excrete this load
If min urine concentration is 50 then 12L would be required to urine to excrete water, within these limits

Question 21

Abnormalities of water balance

Answer 21

Water excess

Water depletion

Question 22

Water excess

Answer 22

Excessive water intake, impairment in renal water excretion

Question 23

Water depletion

Answer 23

Insufficient water intake, impairment in renal water reabsorption

Question 24

Continued water intake with failure to suppress ADH can lead to water overload and hyponatremia examples

Answer 24

Vomiting
Diarrhoea
Certain drugs (MDMA,’ecstacy’ promotes ADH secretion)
Ectopic secretion of ADH (syndrome of inappropriate ADH secretion, SIADH)
Hypocortisolism
Primary adrenal insufficiency (Addison’s disease)

Question 25

Description of Syndrome of inappropriate ADH secretion

Answer 25

Excessive ADH reduces urinary excretion of water 
Results in a state of water excess and:
- Low plasma sodium  
- Low plasma osmolality 
- High urine osmolality

Question 26

Cuases of inappropriate ADH secretion

Answer 26

Tumor
CNS disturbance
Drugs

Question 27

Water depletion from decreased intake of water can occur in

Answer 27

Infants
Elderly
Individuals in coma
Individual with no access to water

Question 28

Water depletion from the increased loss of water through the kidney can occur in

Answer 28

Diabetes mellitus

Impairment in ADH release and/or

Question 29

Central Diabetes Insipidus

Answer 29

Genetic mutations
Head trauma
The disease of the hypothalamus/pituitary region

Question 30

Nephrogenic DI

Answer 30

Impaired response to ADH 
Mutation of ADH receptor 
Mutation of ADH - dependent H2O channels 
Renal Disease 
Drugs