Disorders of Ca2+ and Na+ regulation

Question 1

What is the main ion of ICF?

Answer 1

K+

Question 2

What is the main ion of ECF?

Answer 2

Na+

Question 3

What are the compartments of ECF?

Answer 3

Interstitial fluid
Intravascular fluid
Cellular space

Question 4

What are the different water compartments in the body and their %s?

Answer 4

1. ICF = 67%
2. ECF
   - IT 26%
   - IV 7%
   - CS <1%

Question 5

Define plasma osmolality

Answer 5

Ratio of plasma solutes (sodium, glucose, and urea) and plasma water

Plasma solutes:plasma water

Question 6

What are the mechanisms for regulating water status?

Answer 6

Thirst

Anti-diuretic hormone (Vasopressin)

Question 7

What determines [Na+]serum osmolality?

Answer 7

EC Water

Regulated by changing intake or output of water

Question 8

When is ADH produced?

Answer 8

In response to

• decrease plasma volume (sensed by baroreceptors in atria/veins/carotids)
• increase plasma osmolality (sensed by osmoreceptors in hypothalamus)

Question 9

What detects plasma osmolality?

Answer 9

osmoreceptors in hypothalamus

Question 10

What detects plasma volume?

Answer 10

baroreceptors in atria/veins/carotids

Question 11

Which hormone is released with increased plasma osmolality?

Answer 11

ADH

Question 12

Where does ADH act?

Answer 12

ACRP2 receptors

• basolateral membrane of kidney collecting duct
• inserts aquaporins to increase renal h2o reabsorption

Question 13

What is the systemic effects of AngII?

Answer 13

• cardiac and vascular hypertrophy
• systemic vasoconstriction
• thirst
• ADH secretion
• aldosterone secretion
• vasoconstrictor and promotes aldosterone release

Question 14

What is the regulatory response to a decrease in blood pressure and blood volume?

Answer 14

RAAS + SNS = increase BP

Question 15

What is the regulatory response to a increase in blood pressure and blood volume?

Answer 15

Heart receptors release atrial natriuretic peptic (ANP)

ANP/BNP = decrease renin = natriuretic diuresis = decrease blood volume = decrease BP

Question 16

What is hyponatremia?

Answer 16

Serum sodium <135mmol/L

Question 17

What is the normal blood serum sodium?

Answer 17

135-145mmol/L

Question 18

What is the commonest disorder of electrolyte balance?

Answer 18

hyponatremia

Question 19

What causes hyponatremia?

Answer 19

1. inability to suppress ADH release so inappropriate retention of water

• syndrome of inappropriate ADH secretion (SIADHS)
  lack of negative feedback
  ADH continually produced regardless of osmolality

2. renal impairment
3. diuretic effect (especially with thiazides)

Question 20

What is syndrome of inappropriate ADH secretion

Causes?

Answer 20

excess or inappropriate ADH for plasma osmolality
- commonest cause of low Na+ due to increase H2O

causes:

• cancer
• pneumonia
• infections injury of CNS
• drugs: opiates, thiazides, PPIs

Question 21

What brain condition is caused from hyponatremia?

Answer 21

Cerebral oedema

- water moves into cells to increase osmolality

Question 22

What is the consequence of rapid correction of hyponatremia ?

Answer 22

Osmotic demyelination (de-mylin-ation)
- sudden increase in Na+ causes water to move out of the brain

Question 23

What is the appropriate Tx for hyponatremia

Answer 23

Slow and gradual correction of hypotonic state

IV 3% saline

2nd line: AVPR2 antagonist

Question 24

List the symptoms of hyponatremia from least to worst

Answer 24

• often asymptomatic
• mild confusion
• gait instability
• marked confusion
• drowsiness
• seizures

Question 25

Causes of hypernatremia

Answer 25

deydration 
insensible/swear loss
burns
sepsis
GI loss
Diabetes insipidus 
osmotic diuresis (DM)

Question 26

Tx hypernatremia

Answer 26

estimate H2O deficit
avoid rapid correction - concern is cerebral oedema
IV 5% dextrose

Question 27

List the sources of Ca2+

Answer 27

GI: absorption through SI - VitD dependent
Bones: calcium reservoir
Kidneys: free Ca2+ filtered by glomerulus -97-99% reabsorbed

Question 28

Where first the first hydroxylation of vit d take place?

Answer 28

Liver

Question 29

Where first the second hydroxylation of vit d take place?

Answer 29

kidneys

Question 30

What is the main source of vitd?

Answer 30

Sunlight

UV radiation

Question 31

whats the effects of PTH on Ca2+

Answer 31

PTH increase Ca2+ with no change to plasma phosphate

1. bone
   - resorption
2. kidney
   - phosphate excretion
   - calcium reabsorption
   - calcitrol formation (vit D)

Question 32

What is the physiologically relevant form of calcium?

Answer 32

Free or ionised

Question 33

How much calcium is free and how much is bound (and to what)

Answer 33

55% is bound to albumin or other proteins

45% is free in ionised form

Question 34

What are the ECG changes in hypercalcaemia?

Answer 34

shortened QT, bradycardia

Question 35

Causes of hypercalcaemia

Differential Dx

Answer 35

1. primary hyperparathyroidism
   - parathyroid adenoma
2. Malignancy
   - secretion to PTH-related peptide e.g. breast/lung/etc.

• measure PTH
  if PTH is low then malignancy is likely
  if PTH is normal or increased than primary hyperparathyroidism

Question 36

what is normal calcium serum levels?

Answer 36

2.2 to 2.7 mmol/L

Question 37

What are the symptoms of acute hypocalcaemia ?

Answer 37

1. Tetany
   - neuromuscular excitability
   - numbness, cramps, tingling
   - in servere: seizures
2. Cardiac complications
   - dysrhymia
   - hypotension
   - ECG: QT/ST prolongation

Question 38

aetiology of hypocalcaemia

Answer 38

1. if low PTH
   - post-op
   - autoimmune
   - hypoparathyroidism
2. if high PTH
   - vit D deficiency
   - CKD
   - loss of Ca2+
   - drugs
   - hypomagnesaemia - Leads to PTH resistance (impairs secretion by inhibiting transport of PTH across membrane)

Question 39

Tx hypocalcaemia

Answer 39

Ca2+

Mg2+