Calcium and Sodium Disorders

Question 1

What is the principle ion in intracellular fluid?

Answer 1

K+

Question 2

What is the principle ion in extracellular fluid?

Answer 2

Na+

Question 3

What is plasma osmolality?

Answer 3

The ratio of plasma solutes (sodium, glucose and urea) and plasma water.

Question 4

What are the main mechanisms that regulate water status?

Answer 4

Thirst and ADH.

Question 5

What causes production of ADH?

Answer 5

• Decreased plasma volume (sensed by baroreceptors in atria, veins, carotids)
• Increased plasma osmolality (sensed by osmoreceptors in the hypothalamus).

Question 6

What receptor does ADH act on and where is this found? What does the binding of ADH to this receptor cause?

Answer 6

AVPR2 receptor.

Basolateral membrane of kidney collecting duct and inserts AQP channels onto apical membrane to increase renal water reabsorption.

Question 7

What is the homeostatic blood osmolality?

Answer 7

300 mOsm/L

Question 8

What structure senses reduced volume in the kidneys and what is its response?

Answer 8

Juxtaglomerular apparatus - secretes renin.

Question 9

What are the functions of angiotensin II?

Answer 9

Vasoconstriction

Aldosterone release

Question 10

What is the function of aldosterone in maintaining osmolality?

Answer 10

Increase Na reabsorption and potassium excretion in the distal nephron.

Question 11

What is the function of ANP in maintaining osmolality?

Answer 11

Create a diuresis - increase Na excretion

Question 12

What 3 mechanisms regulate effective arterial volume?

Answer 12

RAAS system.

Carotid/aortic baroreceptors.

Cardiac receptors.

Question 13

How does aldosterone affect plasma volume and blood pressure?

Answer 13

Increases both.

Question 14

What is the normal levels of serum sodium?

Answer 14

135-145 mmol/l.

Question 15

What level must sodium fall below before a person is said to have hyponatraemia?

Answer 15

<135 mmol/l.

Question 16

What are the causes of hyponatraemia due to both Na and water deficits?

Answer 16

Extrarenal

• vomiting
• diarrhoea
• pancreatitis

Renal

• diuretic excess
• mineralocorticoid deficiency
• renal tubular acidosis
• osmotic diuresis
• ketonuria

Question 17

What are the causes of hyponatraemia due to water excess?

Answer 17

Glucocorticoid deficiency

Drugs (PPIs etc)

Syndrome of inappropriate ADH secretion (SIADH - most common)

Pain

Hypothyrodism

Question 18

What are the causes of hyponatraemia due to Na and water excess?

Answer 18

Nephrotic syndrome

Cardiac failure

Cirrhosis

Acute and chronic renal failure

Question 19

What is SIADH?

Answer 19

Syndrome of inappropriate ADH - excess or inappropriate ADH secretion.

Question 20

What causes SIADH?

Answer 20

Drugs (opiates, PPIs, anti-depressants)

Cancer (lung/lymphoma/leukaemia)

Chest disease (pneumonia)

CNS disorders (infections, injury)

Question 21

What 5 criteria must be satisfied to diagnose SIADH?

Answer 21

• Hyponatraemia with inappropriate low plasma osmolality
• Urine osmolality > plasma osmolality
• Urine sodium > 20mmol/l
• Absence of adrenal, thyroid, pituitary or renal insufficiency
• No recent use of diuretic agents

Question 22

What can a rapid increase in serum Na concentrations cause?

Answer 22

Osmotic demyelination

Question 23

What can a rapid decrease in serum Na concentrations cause?

Answer 23

Cerebral oedema

Question 24

What are the clinical features of hyponatraemia?

Answer 24

Asymptomatic - mild confusion - gait instability - marked confusion - drowsiness - seizures.

Question 25

How can severe and acute hyponatraemia be treated?

Answer 25

Give infusion of 3% saline.

Question 26

How can less severe +/- chronic hyponatraemia be treated?

Answer 26

Try to establish cause. First line is fluid restriction. Second line is AVPR2 receptor antagonists. This must be corrected SLOWLY.

Question 27

What are the main causes of hypernatraemia?

Answer 27

Dehydration and inability to access water. - Insensible/sweat losses (severe burns/sepsis) - GI losses - Diabetes insipidus - Osmotic diuresis due to hyperglycaemia.

Question 28

How can hypernatraemia be managed?

Answer 28

- Treat underlying cause. - Estimate total body water deficit if possible to guide fluid regimen. - Use IV 5% dextrose and aim for less than 10mmol/l in 24 hours.

Question 29

What are 3 sources of calcium in the body?

Answer 29

GI - 10% of dietary calcium absorbed in small intestine. Bone - via action of osteoclasts and osteoblasts. Kidney - freely filtered at the glomerulus and 97-99% is reabsorbed.

Question 30

What is active vit D?

Answer 30

1,25 dihydroxy-vit D

Question 31

What are the effects of vit D?

Answer 31

Increases GI absorption, bone resorption and renal reabsorption.

Question 32

What are the effects of PTH?

Answer 32

Bone: Increased release of calcium and phosphate from bone. Kidney: Increased phosphate excretion, calcium reabsorption and calcitriol production. Calcitriol: Increased CaHPO4 absorption in the gut. Net effect = increase in plasma calcium with no change in plasma phosphate.

Question 33

What are the clinical features of hypercalcaemia?

Answer 33

``` Polyuria, polydipsia Anorexia, n&v Constipation Osteopenia/osteoporosis Depression Confusion Fatigue ```

Question 34

What will an ECG of someone with hypercalcaemia potentially look like?

Answer 34

Shortened QT interval | Bradycardia

Question 35

What percentage of Ca is free/ionised in plasma?

Answer 35

45%

Question 36

What can cause hypercalcaemia?

Answer 36

Primary hyperparathyroidism - usually single parathyroid adenoma Malignancy - PTH-related peptide

Question 37

How can hypercalcaemia be diagnosed?

Answer 37

Measure PTH levels - if high - primary hyperparathyroidism - if low - likely malignancy

Question 38

Classify severity of hypercalcaemia using PTH levels.

Answer 38

Mild <3 mmol/l Moderate 3-3.5 mmol/l Severe >3.5 mmol/l

Question 39

How can hypercalcaemia be treated?

Answer 39

Rehydration to correct hypovolaemia - using isotonic saline Biphosphonate Therapy Calcitonin Glucocorticoids Parathyroidectomy

Question 40

How can hypocalcaemia present?

Answer 40

Tetany - muscle cramps, peri-oral numbness, tingling of hands and feet - more severe involves carpopedal spasm, laryngospasm and seizures. Cardiac - dysrhythmias - hypotension

Question 41

What causes hypocalcaemia?

Answer 41

If low PTH - after parathyroid surgery - autoimmune parathyroidsim If high PTH - vit D deficiency - chronic renal failure - loss of Ca Drugs - PPIs Hypomagnesaemia